US20150247653A1

US20150247653A1 - Heat transfer device

Info

Publication number: US20150247653A1
Application number: US14/430,362
Authority: US
Inventors: Richard Boyle; Christophe Williams; Norman Cottington
Original assignee: Naked Energy Ltd
Current assignee: Naked Energy Ltd
Priority date: 2012-09-21
Filing date: 2013-09-20
Publication date: 2015-09-03
Also published as: WO2014045054A1; GB2507255A; GB201216942D0; EP2898270A1

Abstract

A heat transfer assembly comprising: an elongate envelope; an elongate heat transfer device located within the envelope, the heat transfer device having an elongate heat transfer chamber; and an elongate heat exchanger passing longitudinally through at least a portion of the elongate heat transfer chamber.

Description

FIELD OF THE INVENTION

This invention relates to heat transfer devices and in particular heat transfer devices for use in solar energy converter devices which convert incident solar energy into heat and electricity.
Devices converting solar energy into electricity are known. One means of converting solar energy into electricity is the use of photovoltaic arrays. Photovoltaic arrays generally consist of semi-conductor materials appropriately encapsulated, and arranged to generate electricity when exposed to solar radiation.
Separately, devices converting solar energy into useable heat are known. A variety of thermal collection devices are known which absorb heat energy when exposed to solar radiation. These thermal solar collectors heat up as they absorb heat energy from solar radiation and this heat energy may then be extracted for use, for example by pumping a liquid flow, such as water, through the thermal collector in order to heat the liquid.
It has been proposed to combine these two technologies to provide a hybrid solar energy collector converting solar energy simultaneously into both electricity and heat. Such hybrid devices have been found to suffer from the problem that the elements of the photovoltaic array become hot when the device is operating. In general, the efficiency of photovoltaic elements drops as their temperature increases. Also, in general, photovoltaic elements subject to high temperatures may suffer degradation resulting in a permanent decrease in efficiency. As a result, in use, the electricity generating efficiency of the photovoltaic arrays of such hybrid devices tends to be low, and tends to reduce over time.
Accordingly, a heat transfer device suitable to transfer heat away from a solar collector is desirable.

SUMMARY OF THE INVENTION

A first aspect provides a heat transfer assembly comprising:
an elongate envelope;
an elongate heat transfer device located within the envelope, the heat transfer device having an elongate heat transfer chamber; and
an elongate heat exchanger passing longitudinally through at least a portion of the elongate heat transfer chamber.
Preferably, the elongate envelope is transparent or translucent.
Preferably, the elongate envelope is glass.
Preferably, the elongate heat transfer chamber extends along substantially the whole length of the elongate heat transfer device.
Preferably, the elongate heat exchanger extends along substantially the whole length of the elongate heat transfer chamber.
Preferably, the elongate heat exchanger comprises a tube which passes through a first end of the elongate heat transfer chamber, extends along substantially the whole length of the elongate heat transfer chamber, and turns back to pass for a second time through the first end of the elongate heat transfer chamber.
Preferably, the elongate heat exchanger comprises a tube which passes twice through a first end of the elongate envelope.
Preferably, the elongate heat exchanger comprises a tube which passes through a first end of the elongate heat transfer chamber, extends along substantially the whole length of the elongate heat transfer chamber, and passes through a second end of the elongate heat transfer chamber opposite the first end.
Preferably, the tube and/or the elongate heat transfer device comprise means to accommodate differential thermal expansion between the tube and elongate heat transfer device.
Preferably, the means to accommodate differential thermal expansion comprise a bellows structure of the tube.
Preferably, the elongate heat exchanger comprises a tube which passes through a first end of the elongate envelope, extends along substantially the whole length of the elongate envelope, and passes through a second end of the elongate envelope opposite the first end.
Preferably, the tube and/or the elongate envelope comprise means to accommodate differential thermal expansion between the tube and elongate heat transfer device, and the elongate envelope.
Preferably, the means to accommodate differential thermal expansion comprise bends in the tube.
Preferably, the elongate heat exchanger comprises a tube which passes through a first end of the elongate envelope, passes through the elongate heat transfer chamber, and turns back to pass for a second time through the first end of the elongate envelope.
Preferably, the elongate heat exchanger comprises inner and outer concentric tubes which pass through a first end of the elongate heat transfer chamber and extend along substantially the whole length of the elongate heat transfer chamber, wherein the outer concentric tube is closed at an end remote from the first end of the elongate heat transfer chamber.
Preferably, the elongate envelope is at least partially evacuated.
Preferably, the heat transfer assembly further comprises at least one photovoltaic element mounted on the elongate heat transfer device.
Preferably, the elongate heat transfer chamber is a vapor chamber.
Preferably, the vapor chamber is at least partially evacuated.
Preferably, the heat transfer assembly is arranged for rotation about a rotation axis.
Preferably, the elongate envelope is cylindrical and has an axis of symmetry, and the axis of rotation is parallel to the axis of symmetry.
Preferably, the axis of rotation and the axis of symmetry are coaxial.
Preferably, the axis of rotation coincides with the location of a tube passing through an end of the elongate envelope.
Preferably, the tube passes twice through the first end of the elongate envelope and the axis of rotation passes between the locations at which the tubes passing through the end of the elongate envelope.
Preferably, the axis of rotation passes centrally between the locations at which the tubes passing through the end of the elongate envelope.
A second aspect provides a solar collector array comprising a plurality of heat transfer assemblies according to the first aspect mounted in parallel on a common supporting structure.
Preferably, the solar collector array further comprises means for synchronously rotating all of the plurality of heat transfer assemblies relative to the supporting structure about their respective axes of rotation.
Preferably, the solar collector array further comprises means for rotating the supporting structure about an axis perpendicular to the axes of rotation of the heat transfer assemblies.
A third aspect provides a heat transfer device comprising:
a plurality of fluid flow chambers;
a common heat transfer chamber serving all of the fluid flow chambers;
a heat exchanger passing through at least a portion of the heat transfer chamber.
Preferably, the heat transfer device comprises more than two fluid flow chambers.
A third aspect provides a heat transfer device comprising:
a working fluid pathway;
a heat transfer chamber located on the working fluid pathway;
a heat exchanger passing through at least a portion of the heat transfer chamber.
Preferably, the heat transfer device comprises a plurality of working fluid pathways.
Preferably, the heat transfer chamber extends along substantially the whole length of the heat transfer device.
Preferably, the heat exchanger extends along substantially the whole length of the heat transfer chamber.
Preferably, the heat exchanger comprises a tube which passes through a first end of the heat transfer chamber, extends along substantially the whole length of the heat transfer chamber, and turns back to pass for a second time through the first end of the heat transfer chamber.
Preferably, the heat exchanger comprises a tube which passes through a first end of the heat transfer chamber, extends along substantially the whole length of the heat transfer chamber, and passes through a second end of the heat transfer chamber opposite the first end.
Preferably, the tube and/or the heat transfer device comprise means to accommodate differential thermal expansion between the tube and heat transfer device.
Preferably, the means to accommodate differential thermal expansion comprise a bellows structure of the tube.
Preferably, the heat exchanger comprises inner and outer concentric tubes which pass through a first end of the heat transfer chamber and extend along substantially the whole length of the heat transfer chamber, wherein the outer concentric tube is closed at an end remote from the first end of the heat transfer chamber.
Preferably, the heat transfer device further comprises at least one photovoltaic element mounted on the heat transfer device.
Preferably, the heat transfer chamber is a vapor chamber.
Preferably, the vapor chamber is at least partially evacuated.
Preferably, the heat transfer assembly further comprises an envelope, the heat transfer device being located within the envelope.
Preferably, the envelope is transparent or translucent.
Preferably, the envelope is glass.
Preferably, the heat exchanger comprises a tube which passes through a first end of the heat transfer chamber, extends along substantially the whole length of the heat transfer chamber, and turns back to pass for a second time through the first end of the heat transfer chamber, and further comprises a tube which passes twice through a first end of the envelope.
Preferably, the heat exchanger comprises a tube which passes through a first end of the heat transfer chamber, extends along substantially the whole length of the heat transfer chamber, and passes through a second end of the heat transfer chamber opposite the first end, and further comprises a tube which passes through a first end of the envelope, extends along substantially the whole length of the envelope, and passes through a second end of the envelope opposite the first end.
Preferably, the tube and/or the envelope comprise means to accommodate differential thermal expansion between the tube and heat transfer device, and the envelope.
Preferably, the means to accommodate differential thermal expansion comprise bends in the tube.
Preferably, the heat exchanger comprises a tube which passes through a first end of the heat transfer chamber, extends along substantially the whole length of the heat transfer chamber, and passes through a second end of the heat transfer chamber opposite the first end, and further comprises a tube which passes through a first end of the envelope, passes through the heat transfer chamber, and turns back to pass for a second time through the first end of the envelope.
Preferably, the heat transfer assembly is arranged for rotation about a rotation axis.
Preferably, the elongate envelope is cylindrical and has an axis of symmetry, and the axis of rotation is parallel to the axis of symmetry.
Preferably, the axis of rotation and the axis of symmetry are coaxial.
Preferably, the axis of rotation coincides with the location of a tube passing through an end of the envelope.
Preferably, the tube passes twice through the first end of the envelope and the axis of rotation passes between the locations at which the tubes pass through the first end of the envelope.
Preferably, the axis of rotation passes centrally between the locations at which the tubes pass through the first end of the elongate envelope.
A fourth aspect provides a solar collector array comprising a plurality of heat transfer assemblies according to any the second or third aspects mounted in parallel on a common supporting structure.
Preferably, the solar collector array further comprises means for synchronously rotating all of the plurality of heat transfer assemblies relative to the supporting structure about their respective axes of rotation.
Preferably, the solar collector array further comprises means for rotating the supporting structure about an axis perpendicular to the axes of rotation of the heat transfer assemblies.
A fifth aspect provides a heat transfer assembly comprising a plurality of connected heat transfer devices each according to the second or third aspects, wherein each heat transfer device has a separate heat transfer chamber; and
an envelope;
the plurality of heat transfer devices being located within the envelope.
Preferably, the heat transfer assembly further comprises a heat exchange network, the heat exchange network connecting the respective heat exchangers of the plurality of heat transfer devices.
Preferably, the envelope is an elongate envelope.
Preferably, the envelope is transparent or translucent.
Preferably, the envelope is glass.
Preferably, the heat exchange network comprises a plurality of tubes which pass through an end of the envelope.
Preferably, the envelope is at least partially evacuated.
Preferably, the heat transfer assembly is arranged for rotation about a rotation axis.
Preferably, the envelope is cylindrical and has an axis of symmetry, and the axis of rotation is parallel to the axis of symmetry.
Preferably, the axis of rotation and the axis of symmetry are coaxial.
Preferably, the axis of rotation coincides with the location of a tube passing through an end of the envelope.
A sixth aspect provides a solar collector array comprising a plurality of heat transfer assemblies according to the fifth aspect mounted in parallel on a common supporting structure.
Preferably, the solar collector array further comprises means for synchronously rotating all of the plurality of heat transfer assemblies relative to the supporting structure about their respective axes of rotation.
Preferably, the solar collector array further comprises means for rotating the supporting structure about an axis perpendicular to the axes of rotation of the heat transfer assemblies.
A seventh aspect provides a heat transfer device comprising:
a fluid flow means partially filled with a liquid and arranged so that a first surface is in thermal contact with the liquid in a part of the fluid flow means inclined to the horizontal and containing the liquid;

- the first part of the fluid flow means being divided into a plurality of first fluid flow channels each having an upper end and a lower end and at least one second fluid flow channel having an upper end and a lower end arranged so that the liquid in the first fluid flow channels is in better thermal contact with the first surface than the liquid in the second fluid flow channel; and
- the upper ends of the first and second fluid flow channels being connected together by a vapor manifold, and a second surface being located in the vapor manifold;
- wherein the vapor manifold is at least partially evacuated;
- whereby, when the first surface is hotter than the second surface, heat energy from the first surface causes the liquid in the first fluid flow channel to vaporize, and the vapor travels through the liquid in the first fluid flow channel to the surface of the liquid, such that the liquid circulates around the first fluid flow channel and the second fluid flow channel;
- vapor travels from the surface of the liquid through the vapor manifold to the second surface and condenses at the second surface; and
- condensed liquid returns from the second surface to the first part of the fluid flow means;
- whereby heat energy is transported from the first surface to the second surface.

Preferably, the second surface is a surface of a heat exchanger containing a fluid, whereby, when the first surface is hotter than the fluid, heat energy is transported from the first surface to the fluid.
Preferably, the second surface is an external surface of a tube containing the fluid.
Preferably, the fluid is arranged to flow through the tube.
Preferably, the vapor manifold extends between first and second opposed surfaces, and the tube passes through the first surface, extends through the vapor manifold between the first and second surfaces, and passes through the second surface.
Preferably, the vapor manifold comprises a surface, and the tube passes through the surface, extends within the vapor manifold, and passes through the surface for a second time.
Preferably, the vapor manifold comprises a surface, the tube passes through the first surface and extends within the vapor manifold; and
an inner tube is arranged within the tube, whereby the fluid is arranged to flow through the inner tube, and to flow between the tube and the inner tube.
Preferably, the first part of the fluid flow means is divided into a plurality of first fluid flow channels and a plurality of second fluid flow channels.
Preferably, the number of first fluid flow channels is the same as the number of second fluid flow channels.
Preferably, the first and second fluid flow channels are located side by side with first fluid flow channels and second fluid flow channels interleaved.
Preferably, the cross sectional area of the first fluid flow channel and the cross sectional area of the second fluid flow channel are equal.
Preferably, the first fluid flow channel is in thermal contact with the first surface across a greater area than the second fluid flow channel.
Preferably, the lower ends of the first and second fluid flow channels are connected together.
Preferably, the first part of the fluid flow means is inclined to the horizontal by an angle of up to 90°.
Preferably, the liquid comprises water.
Preferably, the liquid comprises ethanol.
Preferably, the liquid comprises a mixture of water and ethanol.
Preferably, the mixture comprises up to 25% ethanol.
Preferably, the fluid comprises water.
Preferably, the part of the fluid flow means above the surface of the liquid is at a pressure of 40 mbar or less.
Preferably, the part of the fluid flow means above the surface of the liquid is at a pressure of 2 mbar or less.
Preferably, the part of the fluid flow means above the surface of the liquid is at a pressure of 1 mbar or less.
Preferably, the part of the fluid flow means above the surface of the liquid is at a pressure of 10⁻²mbar or less.
Preferably, the part of the fluid flow means above the surface of the liquid is at a pressure of 10⁻³mbar or less.
Preferably, the part of the fluid flow means above the surface of the liquid is at a pressure of 10⁻⁶mbar or less.
Preferably, the first fluid flow channels are closer to the first surface than the second fluid flow channels.
Preferably, at least a part of each first fluid flow channel is located between the first surface and a second fluid flow channel.
Preferably, the first fluid flow channels lie between the first surface and the second fluid flow channels.
Preferably, each of the first and second fluid flow channels has a section bounded by a perimeter, and a proportion of the perimeter of the first fluid flow channel which is in thermal contact with the first surface is greater than a proportion of the perimeter of the second fluid flow channel which is in thermal contact with the first surface.
Preferably, at least a portion of at least one surface of each first fluid flow channel in thermal contact with the first surface comprises features arranged to promote vapor bubble nucleation.
Preferably, at least a portion of at least one surface of each first fluid flow channel in thermal contact with the first surface has a surface texture adapted to promote vapor bubble nucleation.
Preferably, said portion of at least one surface has a roughened surface texture.
Preferably, the roughened surface texture is provided by a solder layer.
Preferably, vapor traveling from the surface of the liquid to the second surface passes through the manifold.
Preferably, condensed liquid returning from the second surface to the first part of the fluid flow means passes through the manifold.
Preferably, the second surface is located above the first surface such that the condensed liquid returns from the second surface to the first part of the fluid flow means by gravity.
Preferably, at least a portion of a surface of each first fluid flow channel in thermal contact with the first surface has a dimpled surface profile.
Preferably, the dimpled surface profile comprises a regular array of dimples.
Preferably, the regular array of dimples comprises dimples arranged in rows separated by flat strips without dimples.
Preferably, the first and second fluid flow channels are located between first and second spaced apart plates.
Preferably, the first plate is in thermal contact with the first surface and forms a surface of the or each first fluid flow channel.
Preferably, there are a plurality of first fluid flow channels and a plurality of second fluid flow channels located side by side with first fluid flow channels and second fluid flow channels arranged alternately, and each first fluid flow channel is separated from an adjacent second fluid flow channel by a partition extending between and attached to the first plate and the second plate.
Preferably, the first plate has a dimpled surface profile comprising a regular array of dimples arranged in rows separated by flat strips without dimples, and each partition is attached to the first plate at a position located in one of the flat strips.
Preferably, the part of each partition extending between the first plate and the second plate is substantially flat.
Preferably, a plurality of the partitions are formed by a third plate.
Preferably, all of the partitions are formed by a single third plate.
Preferably, the third plate is corrugated.
Preferably, each of the plates comprises a metal or a metal alloy material.
Preferably, each of the plates comprises mild steel.
Preferably, each of the plates comprises tin coated mild steel.
Preferably, the plates are bonded together by a bonding technique including at least one of: soldering; spot welding; roller welding; and an adhesive.
Preferably, the plates are bonded together by solder joints and at least a part of the first plate forming a surface of each first fluid flow channel is coated with solder.
Preferably, the heat transfer device comprises a substantially rigid heat conducting structure.
An eighth aspect provides a heat transfer device comprising:
a plurality of first fluid flow channels each having an upper and a lower end, inclined to the horizontal, and containing a liquid;
a second fluid flow channel having an upper and a lower end, connected to the first fluid flow channels and containing the liquid;
a vapor manifold connecting the upper ends of the first and second fluid flow channels;
a first surface in thermal contact with the liquid in the first fluid flow channel; and
a second surface in the vapor manifold;
whereby when the first surface is hotter than the second surface, heat energy from the first surface causes liquid in the first fluid flow channels to vaporize;
the vapor travels upwardly along the first fluid flow channels;
the vapor drives a flow of liquid from the second fluid flow channel to the first fluid flow channels and upwardly along the first fluid flow channels; and
the vapor travels from a surface of the liquid to the second surface and condenses at the second surface;
whereby heat energy is transported away from the first surface to the second surface.
A ninth aspect provides a heat transfer device comprising:
a first surface;
a second surface;
a liquid reservoir in thermal contact with the first surface and containing a liquid;
wherein the liquid reservoir comprises a plurality of first fluid flow channels inclined to the horizontal and containing the liquid and a second fluid flow channel connected to the first fluid flow channel and containing the liquid;
the device further comprising a vapor manifold connecting upper ends of the first and second fluid flow channels;
the first surface is in thermal contact with the liquid in the first fluid flow channel, the second surface is in the vapor manifold; and
the vapor manifold is at least partially evacuated;
whereby when the first surface is hotter than the second surface, heat energy from the first surface causes liquid in the first fluid flow channel to vaporize;
the vapor travels upwardly along the first fluid flow channel, into the vapor manifold, and condenses at the second surface;
the vapor drives a flow of liquid from the second fluid flow channel to the first fluid flow channel and upwardly along the first fluid flow channel; and
condensed liquid returns from the second surface to the liquid reservoir;
whereby heat energy is transported away from the first surface to the second surface.
A tenth aspect provides a heat transfer device comprising:
a first surface;
a second surface;
a liquid reservoir in thermal contact with the first surface and containing a liquid; and
a vapor manifold containing the second surface;
wherein at least a part of the vapor manifold is at least partially evacuated;
whereby when the first surface is hotter than the second surface, heat energy from the first surface causes liquid in the liquid reservoir to vaporize;
the vapor travels to the vapor manifold and condenses at the second surface; and
condensed liquid returns from the second surface to the liquid reservoir;
whereby heat energy is transported from the first surface to the second surface.
Preferably, at least a part of the heat transfer device is located in an envelope under at least a partial vacuum.
Preferably, the envelope is one of: a cylindrical tube; an elliptical tube.
Preferably, the envelope is formed, at least in part, of glass.
Preferably, a plurality of tubes are mounted in a solar energy collecting array.
Preferably, at least one of the plurality of tubes is rotatable to track light incident on the solar energy collecting array.
Preferably, the plurality of tubes are rotatable to track light incident on the solar energy collecting array.
Preferably, the heat transfer device comprises a substantially rigid heat conducting structure.
A sixth aspect provides an energy generator comprising a heat transfer device according to any preceding claim, and at least one photovoltaic element, the energy generator having an electrical output and a heated fluid output.
The invention further provides systems, devices and articles of manufacture for implementing any of the aforementioned aspects of the invention.

DESCRIPTION OF FIGURES

The invention will now be described in detail with reference to the following figures in which:

FIG. 1 is a diagram of a first embodiment of a hybrid solar energy converter according to the invention;

FIG. 2 is a diagram of a tube useable in the hybrid solar energy converter of FIG. 1;

FIG. 3 is a cut away diagram of a solar energy collector assembly useable in the hybrid solar energy converter of FIG. 1;

FIG. 4 is a transverse cross-section along the line A-A of the solar energy collector assembly of FIG. 3;

FIG. 5 is a longitudinal cross-sectional diagram along the line B-B of the solar energy collector assembly of FIG. 3;

FIG. 6 is a cut away view of the solar collector assembly of FIG. 3;

FIG. 7 is a diagram of a central sheet useable in the solar energy collector assembly of FIG. 3;

FIG. 8 is an explanatory diagram illustrating the operation of the solar energy collector assembly of FIG. 3;

FIG. 9 is a transverse cross section along the line C-C of the solar energy collector assembly of FIG. 3;

FIG. 10A is an explanatory diagram of the solar energy collector assembly of FIG. 3;

FIG. 10B is an explanatory diagram of the solar energy collector assembly of FIG. 3;

FIG. 11A is a detailed plan view of a part of the solar energy collector assembly of FIG. 3;

FIG. 11B is a cross section along the line D-D of a the part of the solar energy collector assembly of FIG. 3;

FIG. 12 is a diagram showing a part of the solar energy collector assembly of FIG. 3 with the photovoltaic elements removed;

FIG. 13 is a diagram of a part of a solar energy collector assembly according to a second embodiment according to the invention;

FIG. 14 is a diagram of a part of a solar energy collector assembly according to a third embodiment according to the invention;

FIG. 15 is a diagram of a part of a solar energy collector assembly according to a third embodiment according to the invention;

FIG. 16 is a diagram of a fourth embodiment of a hybrid solar energy converter according to the invention;

FIG. 17 is a cut away diagram of a part of a solar energy collector assembly useable in the hybrid solar energy converter of FIG. 16;

FIG. 18 is a diagram of a solar energy collector arranged for rotation about a single axis;

FIG. 19 is a diagram of a solar energy collector array arranged for rotation about two axes;

FIG. 20 is a diagram of a solar energy collector arranged for rotation about a single axis; and

FIG. 21 is a diagram of a solar energy collector array arranged for rotation about two axes.

DETAILED DESCRIPTION OF THE INVENTION

First Embodiment

Apparatus according to a first embodiment of the present invention is illustrated in FIG. 1. FIG. 1 shows a general exterior view of a first embodiment of a hybrid solar energy converter 101 according to the present invention.

Overview

In the first embodiment, the hybrid solar energy converter 101 includes a solar energy collector assembly 102 housed within a sealed transparent tube 103. The solar energy collector assembly 102 includes an elongate heat transport element 104 and an array of photovoltaic elements 105 mounted on an upper surface of the elongate heat transport element 104. The hybrid solar energy converter 101 also includes a support assembly 106 at one end of the transparent tube 103. One end of the solar energy collector assembly 102 is connected to the support assembly 106. In one example the photovoltaic elements 105 may be formed of silicon. In another example the photovoltaic elements 105 may be formed of gallium arsenide. In other examples, photovoltaic elements of other suitable semiconductor materials may be used. In other examples organic photovoltaic elements may be used. In other examples hybrid photovoltaic elements may be used.
Photovoltaic elements may also be referred to as photovoltaic cells, solar cells or photoelectric cells. For the avoidance of doubt, in the present application the term photovoltaic element is used to refer to any element which converts incident electromagnetic radiation into electrical energy.
In the first embodiment, the heat transport element 104 includes a heat exchanger 107 arranged to transfer heat energy from the heat transport element 104 to a first fluid. The heat exchanger 107 is located within the heat transport element 104 in the first embodiment, and accordingly is not visible in FIG. 1.
In one possible example, in use the hybrid solar energy converter 101 may be mounted on a roof. Accordingly, mounting brackets may be provided.
An overview of the operation of the hybrid solar energy converter 101 of the first embodiment is that solar energy, in other words sunlight, incident on the hybrid solar energy converter 101 passes through the sealed transparent tube 103 and is incident on the photovoltaic elements 105 of the solar energy collector assembly 102. The photovoltaic elements 105 convert a part of the energy of the incident solar energy into electrical energy, and convert a part of the energy of the incident solar energy into heat energy. A further part of the incident solar energy may be incident on any parts of the solar energy collector assembly 102 which are not covered by the photovoltaic elements 105, and this further part of the incident solar energy may also be converted into heat energy. In general, it is desirable to maximize the proportion of the surface of the solar energy collector assembly 102 exposed to incident solar energy which is covered by the photovoltaic elements 105, and to minimize the proportion which is not so covered. However, in some circumstances it may be preferred to leave some parts of this exposed surface uncovered, for example to simplify manufacture and/or assembly of the solar energy collector assembly 102 and attachment of the photovoltaic elements 105 to the solar energy collector assembly 102. Usually, in the first embodiment the surface of the solar energy collector assembly exposed to incident solar energy will be the upper surface.
The electrical energy produced by the photovoltaic elements 105 is carried along the heat transport element 104 by electrical conductors and away from the solar energy converter 101 for use. The heat energy absorbed by the photovoltaic elements 105 is transferred into the heat transport element 104, cooling the photovoltaic elements 105, and is then transferred in the heat exchanger 107 to the first fluid. The first fluid is supplied to the heat transport element 104 and the heat exchanger 107 through the support assembly 106, and the heated first fluid travels out of the heat transport element 104 and through the support assembly 106, so that the heat energy in the heated first fluid can be removed from the solar energy converter 101 and is available for use.
In one typical arrangement, the hybrid solar energy converter 101 may be used in a domestic situation, such as on a household roof, to generate electricity for household use and/or for export, and to generate hot water for a domestic hot water and/or heating system. In this arrangement the heat energy transferred to the first fluid in the heat exchanger 107 is used by a domestic or industrial hot water system, and the electrical energy produced by the photovoltaic elements 105 is supplied to an electrical supply system. In some arrangements the first fluid may be water.
Accordingly, the heat transport element 104 cools the photovoltaic elements 105. The efficiency of semiconductor photovoltaic elements generally drops as the temperature of the semiconductor material rises. The temperature above which efficiency drops with increasing temperature and the rate at which efficiency drops with increasing temperature will vary for different semiconductor materials and different designs of photovoltaic element. For silicon photovoltaic elements the efficiency of electrical energy generation generally drops by about 0.35% to 0.5% for each degree centigrade of temperature increase above 25° C.

Transparent Tube

In the first embodiment illustrated in FIG. 1 the sealed transparent tube 103 is formed by a cylindrical glass tube having one open end 103 a and one closed domed end 103 b. The sealed transparent tube 103 is illustrated in more detail in FIG. 2. The open end 103 a of the cylindrical glass tube is sealed by a metal end cap 120 which is bonded to the glass tube with adhesive to form an air tight seal. The interior of the tube 103 is at least partially evacuated. That is, the interior of the tube is at a pressure below normal atmospheric pressure. The pressure of the vacuum within the tube 103 may be 10⁻³mbar.
The open end 103 a of the cylindrical glass tube sealed by the cap 120 is attached to the support assembly 106 and the closed domed end 103 b is remote from the support assembly 106.
Insulated electrical conductors (not shown) pass through the metal cap 120 to carry the electrical energy generated by the photovoltaic elements 105 away from the solar energy collector assembly 102.
As discussed above, the solar energy collector assembly 102 housed within the transparent tube 103 includes photovoltaic elements 105. Typically, photovoltaic devices are made from semiconductor materials which may suffer from oxidation and other environmental effects adversely affecting their performance and lifetime when exposed to the atmosphere. The use of an evacuated tube 103 may protect the semi-conductor materials of the photovoltaic elements 105 from such environmental damage. This may allow the cost of encapsulating the photovoltaic elements to be avoided.
The use of an evacuated tube may also increase the efficiency with which heat can be collected from incident solar energy by the solar energy collector assembly 102. Having the solar energy collector assembly 102 surrounded by an evacuated tube 103 may reduce or effectively prevent convective heat loss from the solar energy collector assembly 102 into the material of the transparent tube 103 and the air around the hybrid solar energy converter 101.
Other vacuum pressures may be used. In some examples the vacuum pressure may be in the range 10⁻²mbar to 10⁻⁶mbar. In general, it is expected that lower vacuum pressure, or in other words a harder vacuum, will provide greater insulating benefits. Further, it is expected that lower vacuum pressure, or in other words a harder vacuum, will provide greater protection from environmental damage in examples where the photovoltaic elements are not encapsulated. In practice the benefits of using a lower vacuum pressure may need to be balanced against the increased cost of achieving a lower vacuum pressure. In some examples a vacuum pressure of 10⁻²mbar, or lower, may be used.
In an alternative example the sealed transparent tube 103 may be filled with an inert gas instead of being evacuated. In particular, the inert gas may be nitrogen.
In another alternative example the sealed transparent tube 103 may be filled with an inert gas at a reduced pressure. In some examples this may be achieved by filling the tube 103 with the inert gas and then evacuating the tube 103. In particular, the inert gas may be nitrogen.
In the illustrated first embodiment the tube 103 is cylindrical having a circular cross section. In alternative examples the tube 103 may have other shapes. In some examples the cross sectional size and/or shape of the tube 103 may vary at different positions along its length. In an alternative example the tube 103 may have an elliptical cross section. In particular, the tube 103 may have an elliptical cross section with the long axis of the ellipse aligned with the plane of the solar energy collector assembly 102. The use of a tube 103 having an elliptical cross-section with the long axis of the ellipse aligned with the plane of the solar energy collector assembly may reduce the amount of glass required by the tube 103 and may reduce reflection losses due to the reflection of incident solar energy from the tube 103.
In the illustrated first embodiment the tube 103 is formed of glass. The use of glass may allow the vacuum within the tube 103 to be maintained longer because the rate of migration of gas molecules from the atmosphere through glass is, in practice, effectively zero. In alternative examples suitable transparent plastics materials or laminated structures may be used to form the tube 103.
In the illustrated first embodiment the tube 103 is transparent. In alternative examples the tube may be only partially transparent.
In the illustrated first embodiment the metal end cap 120 may be bonded to the glass tube 103 by adhesive. In other embodiments alternative glass to metal bonding techniques may be used, for example welding, brazing or soldering.
In the illustrated first embodiment the tube 103 has a metal end cap 120 at one end 103 a. In alternative examples the end cap 120 may be made of other materials. In some examples the end cap 120 may be made of glass. This may reduce conductive heat losses from the collector assembly 102.
In the illustrated first embodiment the tube 103 has an end cap 120 at one end 103 a and one domed end 103 b. In alternative examples the tube 103 may have an open end sealed by an end cap at both ends.

Collector Assembly

In the first embodiment, the solar energy collector assembly 102 includes a heat transport element 104 and an array of photovoltaic elements 105 mounted on a surface of the heat transport element 104. In order to allow radiant solar energy to be incident on the photovoltaic elements 105 the array of photovoltaic elements 105 are mounted on the surface of the heat transport element 104 which is exposed to the incident radiant solar energy in operation of the hybrid solar energy converter 101. This will usually be the upper surface of the heat transport element 104.
In some arrangements the surface of the heat transport element 104 exposed to the incident radiant solar energy may not be the upper surface. In particular, this would be the case if the solar energy collector assembly 102 was located in a vertical, or substantially vertical, plane, or if the incident solar radiant energy was incident horizontally or from below, for example after redirection by an optical system, such as a mirror. Accordingly, references to upper and lower surfaces, and similar directional terminology in this description, should be understood as referring to the situation illustrated in the figures where the solar energy collector assembly is in a plane at an angle to the horizontal and radiant solar energy is incident from above.
In the illustrated example of the first embodiment, the solar energy collector assembly 102 is supported by a cylindrical tube 119 of the heat transport element 104. The cylindrical tube 119 passes through the end cap 120 and extends between the heat transport element 104 and the support assembly 106. Although two sections of cylindrical tube 119 can be seen extending between the heat transport element 104 and the support section 106 in FIG. 1, these are both sections of the same cylindrical tube 119, as will be explained in more detail below.
Where the cylindrical tube 119 passes through the end cap 120 the cylindrical tube 119 is soldered to the end cap 120 to retain the cylindrical tube 119 in place and support the solar energy collector assembly 102. In alternative examples the cylindrical tube 119 may be secured to the end cap 120 in other ways. In one example the cylindrical tube 119 may be welded to the end cap 120.
The supporting of the solar energy collector assembly 102 by a physical connection through the cylindrical tube 119 may increase the efficiency with which heat can be collected from incident solar energy by the solar energy collector assembly 102. Having the solar energy collector assembly 102 supported by a single physical connection through the cylindrical tube 119 may reduce conductive heat loss from the solar energy collector assembly 102 into the supporting structure outside the transparent tube.
In the first embodiment the heat transport element 104 has a substantially flat upper surface 104 a. Each of the photovoltaic elements 105 is square, and the width of the heat transport element 104 is the same as the width of each square photovoltaic element 105. Five square photovoltaic elements 105 are mounted side by side to one another along the length of the heat transport element 104. Substantially the entire upper face of the heat transport element 104 is covered by the photovoltaic elements 105. Covering a large proportion of the upper surface 104 a of the heat transport element 104 with photovoltaic elements 105 may increase the efficiency of the hybrid solar energy converter 101.
In one example the square photovoltaic elements 105 may each be a 125 mm by 125 mm square and 0.2 mm thick. In another example the square photovoltaic elements may each be a 156 mm by 156 mm square. In other examples, photovoltaic elements having other sizes or shapes may be used.
The photovoltaic elements 105 are bonded to the substantially flat upper surface 104 a of the heat transport element 104 using a layer 149 of heat conducting adhesive in a similar manner to the first embodiment. This thermally conductive adhesive bonding layer 149 is shown in FIG. 3. The adhesive bonding layer 149 is electrically insulating. The adhesive bonding layer 149 between the photovoltaic elements 105 and the heat transport element 104 is arranged to be thin. This may improve the degree of thermal conduction between the photovoltaic elements 105 and the heat transport element 104. This may increase the rate of heat transfer laterally across the photovoltaic elements 105. An adhesive material loaded with solid spheres of a predetermined size may be used to form the adhesive bonding layer 149. This may allow a thin adhesive layer 149 to be consistently and reliably formed. The adhesive bonding layer 149 is formed of a flexible or “forgiving” adhesive material. This may relieve stresses in the assembled solar energy collector assembly 102 and reduce any stress applied to the photovoltaic elements 105.
The photovoltaic elements 105 are semiconductor photovoltaic elements formed of silicon. In one example the photovoltaic elements are formed of single-crystal silicon. In one example the photovoltaic elements are formed of amorphous silicon. In one example the photovoltaic elements are formed of polycrystalline silicon, or polysilicon. In other examples alternative types of semiconductor photovoltaic elements may be used.
As discussed above, in operation of the hybrid solar energy converter 101 the photovoltaic elements 105 are cooled by the heat transport element 104. This cooling may allow the temperature of the photovoltaic elements 5 to be maintained at a desired value.
This cooling may provide the advantage that the appearance of hot spots or regions in the photovoltaic elements 105 can be reduced or eliminated, and the temperature of the photovoltaic elements 105 maintained at a uniform desired value. Such hot spots or regions may for example be produced by heating by incident solar radiation, by inhomogeneities or faults in the photovoltaic elements 105, or by a combination of, or interaction between, these causes.
Such hot spots or regions can reduce the efficiency of the photovoltaic elements 105. It is believed that hot spots in the photovoltaic elements 105 may reduce the efficiency of the photovoltaic elements 105 in the short term, and may also degrade the performance of the photovoltaic elements 105 in the longer term. As discussed above, the efficiency of photovoltaic elements reduces as the temperature increases. In the short term a hot spot in a photovoltaic element may reduce the output of the photovoltaic element because the material forming the hot spot is at a higher temperature than the rest of the photovoltaic element, and so has a reduced efficiency compared to the rest of the photovoltaic element. Further, in the longer term the degrading of the performance of the photovoltaic element may also take place more rapidly at a hot spot because the material forming the hot spot is at a higher temperature than the rest of the photovoltaic element.
Accordingly, maintaining the photovoltaic elements 105 at a more uniform temperature value and reducing, or eliminating, hot spots or regions may improve the efficiency of the photovoltaic elements 105 at a specific temperature, and may reduce the amount of degradation of the photovoltaic elements 105 caused by higher temperatures.
This may allow the photovoltaic elements 105 to operate at a higher overall temperature than would otherwise be the case. This may be understood by considering that where hot spots exist in the photovoltaic elements 105 it may be the temperature induced reduction in efficiency and temperature induced degradation in these hot spots that limits the maximum operating temperature of the photovoltaic element 105 as a whole. As a result, reducing, or eliminating, these hotspots may allow the maximum operating temperature of the photovoltaic element 105 as a whole to be raised.
The illustrated example of the first embodiment has a solar energy collector assembly 102 supported by a physical connection through the cylindrical tube 119. In other examples alternative supporting arrangements may be used. In some examples the solar energy collector assembly 102 may be supported by physical connections at each end of the solar energy collector assembly 102. In some examples, the physical connection at one end of the solar energy collector assembly may be the through the cylindrical tube. In general, it is advantageous to minimize the number of physical supports in order to minimize the escape of heat from the solar energy collector assembly by conduction through the physical supports.
In other examples the number of photovoltaic elements 105 mounted on the heat transport element 104 may be different. In other examples the relative sizes of the photovoltaic elements 105 and the heat transport element 104 may be different.
In some examples the adhesive layer 149 may comprise an epoxy resin which remains non-brittle after curing.
In other examples the adhesive layer 149 may be formed by a double sided adhesive tape.

Heat Transport Element

The heat transport element 104 according to the first embodiment is shown in more detail in a cut away view in FIG. 3, and in transverse and longitudinal cross-sectional views in FIGS. 4, and 5 respectively. The transverse cross section of FIG. 4 is taken along the line A-A in FIG. 3. The longitudinal cross section of FIG. 5 is taken along the line B-B in FIG. 3.
In the second embodiment, the elongate heat transport element 104 is generally rectangular. The heat transport element 104 has a flat upper surface 104 a and a lower surface 104 b which is flat across most of its area, and has an outwardly projecting section 110 along one edge 104 c of the heat transport element 104. The outwardly projecting section 110 contains and defines an elongate heat transfer chamber or vapor manifold 111 extending along substantially the entire length of the elongate heat transport element 104. In operation the heat transport element 104 is arranged to be transversely sloping, so that the side edge 104 c of the heat transport element 104 bearing the outwardly projecting section 110 is higher than the opposite side edge 104 d of the heat transport element 104, for reasons which will be explained in detail below. The inclination angle of the heat transport element 104 to the horizontal may be small. An inclination of about 5° is sufficient. Larger angles of inclination may be used if desired. An angle of inclination up to and including 90° may be used, i.e. the heat transport element 104 may be arranged transversely vertically.
FIG. 6 shows a cut away plan view from below of the heat transport element 104 of FIG. 3 with the outwardly projecting section 110 removed, so that the heat exchanger 107 is visible.
As can be best seen in FIG. 6, the heat exchanger 107 is comprises a cylindrical tube 119 which extends within the elongate heat transfer chamber or vapor manifold 111 along substantially the entire length of the elongate heat transfer chamber or vapor manifold 111. The cylindrical tube 119 comprises first and second parallel straight sections 119 a and 119 b, each parallel to the sides of the vapor manifold 111, such as the upper surface 104 a and the projecting section 110, and extending along substantially the entire length of the vapor manifold 111. The two straight sections 119 a and 119 b are connected together by a curved section 119 c.
In use, the first fluid passes along the cylindrical tube 119 as indicated by the arrows in FIG. 6, so that the first fluid passes through the first straight section 119 a, the curved section 119 c and the second straight section 119 b, so that the first fluid passes through the cylindrical tube 119, and travels along substantially the entire length of the vapor manifold twice.
In the illustrated example the first and second sections 119 a and 119 b of the cylindrical tube 119 are arranged one above the other and the first fluid enters through the first section 119 aa and leaves through the second section 119 b. In other examples the direction of flow of the first fluid may be reversed. In other examples the first and second sections 119 a and 119 b may be differently arranged.
The heat transport element 104 has an upper surface 104 a formed by an upper sheet 114 and a lower surface 104 b formed by a lower sheet 115. A central sheet 116 is located between the upper sheet 114 and the lower sheet 115, so that fluid flow passages 117 and 118 running transversely across the heat transport element 104 are defined between the central sheet 116 and each of the upper sheet 114 and the lower sheet 115. The fluid flow passages 117 and 118 are sloped along their lengths. In the illustrated example the heat transport element 104 is transversely sloping, and as a result the fluid flow passages 117 and 118 running transversely across the heat transport element 104 will be sloped along their lengths.
FIG. 5 shows the profile of the central sheet 116 in more detail. FIG. 5 shows a longitudinal cross section along the line B-B in FIG. 3. The central sheet 116 is formed with a corrugated profile having ridges and troughs which run transversely across the heat transport element 104. The cross-sectional profile of the corrugated central sheet 116 can be understood as a zig-zag profile with the points of the zig-zag forming the peaks and troughs being flattened. Accordingly, the upper and lower fluid flow passages 117 and 118 are interleaved. The upper and lower fluid flow passages 117 and 118 are arranged side by side in a planar array with upper fluid flow passages 117 and lower fluid flow passages 118 arranged alternately.
To be more specific, in the illustrated example of the first embodiment the central sheet 116 comprises a plurality of flat surfaces connected by folds running transversely across the heat transport element 104. As shown in FIG. 7, the central sheet 116 comprises a first series of first coplanar surfaces 116 a spaced apart equidistantly in a first plane C and a second series of second coplanar surfaces 116 b spaced apart equidistantly in a second plane D, each of the first and second coplanar surfaces 116 a and 116 b having the same width, and the separation between successive coplanar surfaces 116 a or 116 b of each of the first and second series of first and second coplanar surfaces 116 a and 116 b being larger than the width of the coplanar surfaces 116 a and 116 b. The first and second planes C and D are parallel and spaced apart. The first and second series of coplanar surfaces are arranged so that in plan view, i.e. when viewed perpendicularly to the first and second planes C and D, each of the first coplanar surfaces 116 a is located equidistantly between two of the second coplanar surfaces 116 b, and vice-versa. The first and second coplanar surfaces 116 a and 116 b are interconnected by a first series of first parallel linking surfaces 116 c and a second series of second parallel linking surfaces 116 d.
As is shown particularly in FIG. 5, the central sheet 116 is arranged with the first surfaces 116 a contacting an inner face of the upper sheet 114 and the second surfaces 116 b contacting an inner face of the lower sheet 115. The first surfaces 116 a of the central sheet are bonded to the upper sheet 114 and the second surfaces 116 b of the central sheet 116 are bonded to the lower sheet 115. Accordingly, the upper lower, and central sheets 114, 115, 116 define a plurality of trapezoid cross-section upper fluid flow channels 117 and lower fluid flow channels 118 between them. The upper fluid flow channels 117 are defined between the upper sheet 114 and the central sheet 116. The lower fluid flow channels 118 are defined between the lower sheet 115 and the central sheet 116. The trapezoid upper fluid flow channels are arranged so that the larger one of the two parallel faces of the trapezoid channel is formed by the upper sheet 114.
The edges of the heat transport element 104 are formed by upwardly bent parts of the lower sheet 115, which are bonded to the upper sheet 114. The photovoltaic elements 105 are bonded to the upper sheet 114. At the edges of the heat transport element 104, the upper sheet 114 is bonded directly to the lower sheet 115, the central sheet 116 is not located between the upper and lower sheets 114 and 115 at their edges.
In some examples the central sheet 116 may extend at least partially between the upper and lower sheets 114 and 115 at the end edges of the heat transport element 104 so that the upper and lower sheets 114 and 115 are both bonded to the central sheet 116. This may assist in locating and securing the central sheet 116 relative to the upper and lower sheets 114 and 115.
As discussed above, the heat transport element 104 has an outwardly projecting section 110 along the upper side edge 104 c of the heat transport element 104. The outwardly projecting section 110 is substantially semi-cylindrical and is formed by an outwardly projecting part of the lower sheet 115. The outwardly projecting section 110 defines a vapor manifold 111. The fluid flow channels 117 and 118 connect to the vapor manifold 111. It should be noted that the central sheet 116 extends across most of the width of the vapor manifold 111. Accordingly, the upper fluid flow channels 117 defined between the upper sheet 114 and the central sheet 116 connect to the vapor manifold 111 towards the top of the vapor manifold 111, while the lower fluid flow channels 118 defined between the lower sheet 115 and the central sheet 116 connect to the vapor manifold 111 towards the bottom of the vapor manifold 111. All of the upper and lower fluid flow channels 117 and 118 are interconnected by the vapor manifold 111.
At the lower side edge 104 d of the heat transport element 104 opposite the outwardly projecting section 110, there is a gap 123 between the edge of the central sheet 116 and the side edge 104 c of the heat transport element 104 formed by an upwardly bent part of the lower sheet 115. This gap 123 allows water to flow between different ones of the fluid flow channels 117 and 118. The gap 123 extends along the side edge 104 d of the heat transport element 104, and forms a fluid manifold 124 interconnecting all of the upper and lower fluid flow channels 117 and 118.
At each end of the heat transport element 104 the substantially semi-cylindrical outwardly projecting section 110 extending most of the length of the heat transport element 104 is closed by an end wall 108. The upper and lower sheets 114 and 115 are sealed by the end walls 108 so that the interior of the heat transport element 104 is sealed. The cylindrical tube 119 passes through the end wall 108 adjacent the open end of the glass tube 103 and the end cap 120, through the end cap 120 and into the support assembly 106. The cylindrical tube 119 within the heat transfer chamber or vapor manifold 111 forms the heat exchanger 107 and acts to carry heat energy from the heat transport element 104 away from the hybrid solar energy converter 101, as will be explained below.
The cylindrical tube 119 physically supports the solar energy collector assembly 102 within the sealed transparent tube 103. There is no other physical support of the solar energy collector assembly 102. This may reduce conductive heat losses from the solar energy collector assembly 102, which may increase the amount of useful heat energy produced by the hybrid solar energy converter 101.
The fluid flow channels 117 and 118 are at least partially filled with degassed distilled water 121 as a working fluid and the interior of the heat transport element 104 including the fluid flow channels 117 and 118, and the vapor manifold 111 are at least partially evacuated. That is, the interior of the heat transport element 104 is at a pressure below normal atmospheric pressure. The interior of the heat transport element 104 may be under a vacuum at a pressure of 10⁻³mbar. The heat transport element 104 is arranged to be laterally inclined to the horizontal with the side 104 a of the heat transport element 104 where the vapor manifold 111 is located being arranged to be higher than the opposite side 104 b of the heat transport element 104.
In the illustrated first embodiment the amount of water 121 in the fluid flow channels 117 and 118 is such that an upper surface 132 of the water 121 in the lower fluid flow channels 118 is level with the ends of the lower fluid flow channels 118 where the lower fluid flow channels 118 connect to the vapor manifold 111. In the illustrated second embodiment the level of the surface 132 of the water 121 in the upper fluid flow channels 117 and lower fluid flow channels 118 is substantially the same. Accordingly, in the illustrated second embodiment the lower fluid flow channels are filled with liquid water, while the upper fluid flow channels 117 are only partially filled with liquid water.
In other examples the level of the water 121 may be different. In some examples the upper surface 132 of the water 121 in the lower fluid flow channels 118 may be below the vapor manifold 111. In some examples the upper surface 132 of the water 121 in the lower fluid flow channels 118 may be above the bottom of the vapor manifold 111, with some water being present in the bottom of the vapor manifold 111.
It is expected that in practice the heat transport element 104 will operate most efficiently with the upper surface 122 of the water being at, or close to, the point where the lower fluid flow channels 118 contact the vapor manifold 111. If the level of the water in the heat transport element 104 is too high, so that the upper surface 122 of the water is too high within the vapor manifold 111, the efficiency of operation of the heat transport element 104 may be reduced, as will be discussed in more detail below.
The upper surface 132 of the water 121 in the upper fluid flow channels 117 may be higher than in the lower fluid flow channels 118 as a result of capillary action. The extent of this capillary effect in any specific example will depend upon the dimensions of the upper fluid flow channels 117. In the illustrated first embodiment some of the inner surface of the upper sheet 114, that is, the surface forming a part of the upper fluid flow channels 117, is above the surface of the water 121. In some examples the upper fluid flow channels 117 may have a small enough cross-sectional area that the upper surface 123 of the water 121 in the upper fluid flow channels 117 is at the ends of the upper fluid flow channels 117 due to capillary action.
It should be noted that it is not necessary that the inner surface of the upper sheet 114, that is, the surface forming a part of the upper fluid flow channels 117, is below the upper surface 132 of the water 121 at a position corresponding to the location of the uppermost parts of the photovoltaic elements 105. However, in some examples this may be the case.
In operation of the first embodiment, when the solar energy collector assembly 102 is exposed to incident solar radiative energy, the photovoltaic elements 105 absorb some of this energy, converting a part of the absorbed energy into electrical energy. The remainder of the absorbed energy is converted into heat energy, raising the temperature of the photovoltaic elements 105. The absorbed heat energy flows from the photovoltaic elements 105 into the heat transport element 104, being transmitted through the upper sheet 114 and into the water 121 inside the upper fluid flow channels 117, which water is in contact with the inner surface of the upper metal sheet 114 across the larger parallel faces of the trapezoid upper fluid flow channels 117.
The liquid water 121 inside the upper fluid flow channels 117 absorbs the heat energy from the photovoltaic elements 105 passing through the upper sheet 114 and vaporizes, producing bubbles 122 of steam or water vapor, as shown in FIG. 8. The liquid water may vaporize and produce bubbles as a result of either or both of convection boiling and nucleation. At the vacuum pressure of 10⁻³mbar inside the upper fluid flow channels 117 water boils from around 0° C., so that the water 121 vaporizes readily at the normal operating temperatures of the hybrid solar energy converter 101.
The bubbles 122 of water vapor are less dense than the liquid water 121. Further, as explained above the upper fluid flow channels 117 are sloping along their lengths. Accordingly, as a result of this density difference the water vapor bubbles 122 travel upwards along the upper fluid flow channels 117 towards the upper side edge 104 c of the heat transport element 104 and the surface of the water 121. When a bubble 122 of water vapor reaches the surface of the water 121 the vapor is released into the vacuum above the water 121 in the vapor manifold 111. Further, as a bubble 122 travels upwards along a fluid flow channel 117 the bubble 122 will act as a piston to drive the liquid water, and any other bubbles 122 above it, upwardly along the upper fluid flow channel 117. This pistonic driving may tend to accelerate the speed with which the vapor bubbles 122 move upward along the upper fluid flow channels 117. This pistonic driving may act to pump liquid water upwards along the upper fluid flow channels 117 to the ends of the upper fluid flow channels 117, where the liquid water will be ejected from the upper fluid flow channels 117 into the vapor manifold 111. In the illustrated first embodiment, where some of the inner surface of the upper sheet 114 is above the surface of the water 121, this pumping of liquid water upwards along the upper flow channels 117 ensures that the part of the inner surface of the upper sheet 114 above the surface of the water 121 is in contact with a flow of water so that it can be cooled.
The amount of the pistonic driving produced by the bubbles 122 will depend upon the relative sizes of the bubbles 122 compared to the cross-sectional areas of the upper fluid flow channels 117. The amount of pistonic driving produced by the bubbles 122 may be increased where the size of the bubbles is relatively large compared to the cross-sectional areas of the upper fluid flow channels 117. The pistonic driving produced by the bubbles 122 may be particularly effective in examples where the size of the bubbles 122 of water vapor is equal to, or only a little smaller than, the cross sectional areas of the upper fluid flow channels 117.
In practice the sizes of individual water vapor bubbles will vary. However, the likely average sizes of the bubbles and the likely variability in their sizes can be determined in any specific case, based on the operating parameters to be used in the hybrid solar energy converter.
The bursting of the bubbles of water vapor at the water surface and any pistonic pumping of liquid water out of the ends of the upper fluid flow channels 117 may generate droplets of liquid water, and may project at least some of these water droplets into the vacuum within the vapor manifold 111 above the water surface. As a result, the heat transfer mechanism may be a multi-phase system comprising liquid water, water vapor and droplets of liquid water, and not just a two-phase system comprising liquid water and water vapor only. The presence of such droplets of water in the vacuum, and any pumping of liquid water out of the ends of the upper fluid flow channels 117, may enhance the rate of vaporization by increasing the surface area of the water exposed to the vacuum.
The water vapor in the vacuum within the vapor manifold 111 travels at a very high speed through the vacuum within the vapor manifold 111 into contact with the exterior surface of the tube 119 forming the heat exchanger 107. The travel speed of the hot water vapor in the vacuum is very fast, approximating to the thermal speed of the water vapor molecules. The water vapor condenses on the external surface of the tube 119, which acts as a heat exchange surface. The condensed water falls off the tube 119 to the bottom of the vapor manifold 111, and is returned back into the water 121 within the lower fluid flow channels 118. This generating of hot water vapor within the upper fluid flow channels 117 and the vapor manifold 111, and the condensing of the hot water vapor on the tube 119, followed by return of the condensed water into the fluid flow channels 117 and 118, transfers heat energy from the heat transfer element 104 to the first fluid within the tube 119.
Thus, the working fluid is caused to circulate on a working fluid pathway inside the heat transfer device such that the heat of the working fluid is transferred to the heat exchanger in the heat transfer chamber. In the illustrated example the working fluid pathway is formed by the fluid flow channels 117 and 118 and the heat of the working fluid is absorbed from the cooled surface 104 a of the heat transport element 104.
The first fluid flows from the support element 106, through the heat transfer element 104, where it absorbs heat, and the heated fluid then returns to the support element 106. In the illustrated first embodiment the first fluid is water and a pumped water supply passes through the support element 106 and the cylindrical tube 119.
Any liquid water ejected from the upper fluid flow channels 117 into the vapor manifold 111 which does not vaporize will also fall to the bottom of the vapor manifold 111, and is returned back into the water 121 within the lower fluid flow channels 118.
The description indicates that water droplets and condensed water falls into the bottom of the vapor manifold 111. In some examples, depending upon the orientation of the collector assembly 102, some or all of this water may fall into the lower fluid flow channels 118 without necessarily contacting the surface of the vapor manifold 111.
The location of the heat exchanger 107 within the heat transfer chamber or vapor manifold 111 may improve the efficiency of the heat transfer element 104 by providing a short path for water vapor to travel between the upper surface of the working fluid and the heat exchanger 107.
As is explained above, all of the upper and lower fluid flow channels 117 and 118 are interconnected by the fluid manifold 124 formed by the gap 123. Accordingly, it is not important which of the lower fluid flow channels 118 is entered by any liquid water returning from the vapor manifold 111.
As is clear from the description above, the heat transfer chamber or vapor manifold 111 generally includes liquid water in addition to water vapor when the hybrid solar energy converter 101 is operating. However, as is also discussed above, if the level of the water in the heat transport element 104 is too high, so that the upper surface 122 of the water is too high within the vapor manifold 111, the efficiency of operation of the heat transport element 104 may be reduced. This reduction in efficiency of operation may occur because there is insufficient space within the vapor manifold 111 above the surface of the water for the movement and evaporation of the droplets of liquid water. This reduction in efficiency of operation may occur because the droplets of liquid water and waves and splashing upwardly of the liquid water surface may reduce the open, or water free, cross sectional area of the vapor manifold 111 at some locations to a relatively small amount, or even to zero, momentarily closing the vapor manifold 111. This reduction in the open, or water free, cross sectional area of the vapor manifold 111 may interfere with the movement of the water vapor in the vacuum within the vapor manifold 111.
The bubbles 122 of water vapor will tend to move upwardly through the liquid water in the upper fluid flow channel 117 because of the lower density of the water vapor compared to the liquid water 121, which will result in an upward buoyancy force on each bubble 122. Further, the movement of the bubbles 122 of water vapor will tend to drive the liquid water 121 in the upper fluid flow channel 117 upwardly, particularly in examples where pistonic driving takes place. As a result, the bubbles 122 of water vapor cause the water 121 in the upper and lower fluid flow channels 117 and 118 to circulate, with relatively hot liquid water and bubbles 122 of water vapor flowing upwards along the upper fluid flow channels 117, and relatively cool liquid water flowing downwards along the lower fluid flow channels 118. The upper and lower fluid flow channels 117 and 118 are interconnected by the vapor manifold 111 and the fluid manifold 124, as explained above. Accordingly, the relatively hot liquid water flowing upwards along the upper fluid flow channels is continuously replaced by relatively cool liquid water from the lower fluid flow channels 118. This circulation is driven primarily by the difference in density between the water vapor and the liquid water. However, this circulation may also be driven by convection as a result of the difference in density between the relatively hot liquid water in the upper fluid flow channels 117 and the relatively cool liquid water in the lower fluid flow channels 118, in a similar manner to a thermosiphon. Accordingly, the upper fluid flow channels 117 may be regarded as riser channels, while the lower fluid flow channels 118 may be regarded as sinker channels or return channels.
As the bubbles 122 of water vapor travel upwardly along the upper fluid flow channels 117 the pressure head acting on the bubbles 122 decreases, so that the bubbles 122 tend to expand. As a result, the tendency of the vapor bubbles 122 to collapse and implode is reduced by the effects of the expansion and decreasing pressure as the bubbles 122 move upwardly. When considering this point, it should be remembered that when the heat transport element 104 is operating the bubbles 122 will be forming within an established density driven circulation fluid flow and will move upwardly carried by this flow in addition to the bubbles movement due to their own buoyancy relative to the liquid water. Further, it is believed that expansion of the bubbles 122 as they move upwardly will further increase the speed of the density driven circulation flow by increasing the buoyancy of the expanding bubbles 122. In some examples expansion of the bubbles as they move upwardly may also increase the degree of pistonic driving.
This density driven circulation may form a highly effective heat transport mechanism because water has a relatively high enthalpy of vaporization, so that the movement of the bubbles 122 of water vapor may carry a large amount of heat energy, in addition to the heat energy carried by the movement of relatively hot water out of the upper fluid flow channels 117, and its replacement by cooler water. In arrangements where pistonic driving of the flow of the liquid water by the water vapor bubbles takes place the effectiveness of the heat transport mechanism may be further increased by the increase in the flow rate of the liquid water caused by the pistonic driving. This pistonic driving is a component of the overall density driving producing the density driven circulation. The pistonic driving is caused by the density difference between the liquid water and the bubbles of water vapor.
In general, the speed of the density driven circulation increases and the effectiveness of the heat transport mechanism increases as the temperature of the upper sheet 114 of the heat transport element 104 increases.
The density driven circulation of the water 121 within the fluid flow channels 117 and 118 is a vapor driven circulating or rolling flow.
The density driven circulation of the water 121 within the fluid flow channels 117 and 118 becomes particularly vigorous, and becomes particularly effective as a heat transport mechanism, when the temperature of the upper sheet 114 of the heat transport element 104 becomes sufficiently high that the water 121 within the fluid flow channels 117 and 118 enters a rolling boil state. The effectiveness of the heat transport mechanism significantly increases when rolling boiling of the water 121 commences. In general, when other parameters of the system remain constant, entry into the rolling boil state will take place when the temperature of the upper sheet 114 of the heat transport element 104 reaches a specific temperature.
In the illustrated example using water, the water 121 within fluid flow channels 117 and 118 may enter a rolling boil state at a temperature of about 40° C.
The arrangement of fluid flow channels 117 extending laterally across the heat transport element 104 may allow the vertical height of the liquid water in the heat transport element 104 to be reduced compared to arrangements in which the density driven flow extends along the length of a heat transport element, and so reduce the pressure head acting on the liquid water at the bottom of the heat transport element 104. In general, increased pressure reduces the tendency of liquids to vaporize and so increases the boiling point of liquids. Accordingly, reducing the pressure head acting on the liquid water at the bottom of the heat transport element 104 may increase the tendency of the liquid water 121 towards the lower ends of the upper fluid flow channels 117 to vaporize and produce bubbles 122, and so may improve the efficiency and effectiveness of the heat transport element 104.
In particular, the reduction of the pressure head acting on the liquid water at the bottom of the upper fluid flow channels 117 may reduce any temperature differential along the lengths of the upper fluid flow channels between their the top and bottom ends by reducing any difference in the tendency of the liquid water to vaporize due to differences in pressure. This may reduce temperature differentials between the different points on the heat transport element 104 and may assist in reducing or avoiding the formation of hot spots in the photovoltaic elements 105.
In general the forming of hot spots in the photovoltaic elements 105 is undesirable because these may lead to a reduction in the efficiency of electrical energy generation in the photovoltaic elements 105, which reduction in efficiency may be permanent.
The arrangement of the upper fluid flow channels 117 extending laterally across the heat transport element 104 and interconnected by a heat transfer chamber or vapor manifold 111 containing a heat exchanger 107 extending longitudinally along the heat transport element 104 may allow a very rapid flow of heat energy along the heat transport element 104 away from any upper fluid flow channel 117 having a higher temperature. This may reduce temperature differentials between the different points on the heat transport element 104 and may reduce, or avoid, the formation of hot spots in the photovoltaic elements 105.
The provision of the two separate heat transport mechanisms of the movement of water vapor along the heat transfer chamber or vapor manifold 111 and the density driven flow of liquid water and water vapor along each of the upper fluid flow channels 117, respectively acting longitudinally and transverse the length of the heat transport element 104, may tend to equalize the temperature across the entire upper surface of the heat transport element, and thus tend to equalize the temperature across the photovoltaic elements 105 and reduce, or avoid, the formation of hot spots.
The movement of water vapor along the heat transfer chamber or vapor manifold 111 provides a very rapid heat transport mechanism that tends, by the vaporization and condensation of water, to move heat energy from relatively hot locations to relatively cold locations. As a result, the movement of water vapor along the heat transfer chamber or vapor manifold 111 may tend to equalize the temperature of the liquid water surface at different positions along the heat transfer element 104, in addition to transporting heat energy from the heat transport element 104, and specifically from the upper surface 104 a of the heat transport element 104, to the heat exchanger 107 formed by the tube 119. This temperature equalization may have the effect of removing more heat energy from hotter parts of the upper surface 104 a of the heat transport element 104, and so tending to equalize the temperature across the upper surface 104 a. It is clear that such isothermal cooling will tend to reduce, or avoid, the formation of hot spots, for example in any photovoltaic element attached to the upper surface 104 a.
The lower sheet 115 of the heat transport element 104 has a plurality of hollow ridges 125 extending between the flat part of the lower surface 104 b and the semi-cylindrical surface of the outwardly projecting section 110. Each hollow ridge 125 has a ‘V’ profile, and the hollow ridges 125 are located spaced apart at regular intervals along the length of the heat transport element 104. FIG. 9 shows a transverse cross section of the heat transport element 104 taken along the line C-C in FIG. 3. The line C-C of FIG. 9 is parallel to the line A-A of FIG. 4, but passes through one of the hollow ridges 125. The hollow ridges 125 act as supports for the outwardly projecting section 110, acting as buttresses and helping to keep the curved part of the lower sheet 115 forming the outwardly projecting section 110 fixed relative to the flat part of the lower metal sheet 115 and the other parts of the heat transport element 104.
The hollow ridges 125 also act as drains to return liquid water from the vapor manifold 111 into the lower fluid flow channels 118, as will be explained in more detail below.
As explained above, the vapor manifold 111 is semi-cylindrical, being defined by the semi-cylindrical outwardly projecting section 110 formed by a curved part of the lower sheet 115. Further, as explained above, the heat transport element 104 is transversely sloping so that the side edge 104 c of the heat transport element 104 bearing the outwardly projecting section 110 is higher than the other side edge 104 d of the heat transport element 104. As a result, depending upon the transverse inclination angle of the heat transport element 104 there may, or may not, be parts of the vapor manifold 111 which are located below the ends of the lower fluid flow channels 118 where the lower fluid flow channels 118 connect to the vapor manifold 111.
FIGS. 10A and 10B are explanatory diagrams, each showing a transverse cross sectional view of the heat transport element 104 corresponding to the view shown in FIG. 4. FIG. 10A shows the heat transport element 104 inclined at a relatively large angle to the horizontal, while FIG. 10B shows the heat transport element 104 inclined at a relatively small angle to the horizontal.
When the heat transport element is inclined at a relatively small angle to the horizontal, as shown in FIG. 10A, the lower fluid flow channels 118 connect to the vapor manifold 111 at the lowest point of the semi-cylindrical outwardly projecting section 110 of the lower sheet 115 defining the vapor manifold 111. In this position all liquid water within the vapor manifold 111 will drain directly into the lower fluid flow channels 118. In contrast, when the heat transport element 104 is inclined at a relatively large angle to the horizontal, as shown in FIG. 10B, the part of the semi-cylindrical outwardly projecting section 110 of the lower sheet 115 defining the vapor manifold 111 is located below the point at which the lower fluid flow channels 118 connect to the vapor manifold. In this position, in the absence of the hollow ridges 125, some liquid water within the vapor manifold 111, specifically liquid water below the horizontal line 126, could be retained within the vapor manifold 111 and not drain into the lower fluid flow channels 118.
The hollow ridges 125 form a drain path for liquid water in the vapor manifold 111 to return to the lower fluid flow channels 118 and so prevent the retention of a reservoir of liquid water within the vapor manifold 111 which might otherwise occur.
As discussed above, the heat transport assembly 104 can operate with liquid water within the vapor manifold 111. However, in the absence of the hollow ridges 125 the existence and size of any reservoir of liquid water retained in the vapor manifold 111 will vary depending on the angle of inclination to the horizontal of the heat transport element 104, and the resulting changes in the liquid water level in the fluid flow channels 117 and 118 at different angles of inclination may adversely affect the operation of the heat transport element 104 at some angles of inclination and so limit the range of angles of inclination at which the heat transport element 104 can be used.
Accordingly, the hollow ridges 125 may extend the range of angles of inclination at which the heat transport element 104 can be used.
Depending upon the geometry of the different parts of the heat transport element 104 in any specific design, even when the hollow ridges 125 are used there may still be a minimum angle of inclination at which the heat transport element 104 can operate without the retention of liquid water in the vapor manifold 111 having adverse effects on operation of the heat transport element 104.
In the illustrated example of the first embodiment the hollow ridges 125 act as supports for the outwardly projecting section 110 and also act as drains to return liquid water from the vapor manifold 111 into the lower fluid flow channels 118. In some examples these functions may be carried out by separate dedicated structures.
The corrugated profile of the central sheet 116 and the bonding of the first and second surfaces 116 a and 116 b of the central sheet 116 to the upper sheet 114 and the lower sheet 115 so that the linking surfaces 116 c and 116 d of the central sheet 116 interconnect the upper and lower sheets 114 and 115 increases the strength and rigidity of the heat transport element 104. This may make the heat transport element 104 a more rigid structure. This may tend to reduce the amount of flexing of the heat transport element 104 in use. This may prevent damage to the photovoltaic elements 105 by reducing the amount of mechanical stress applied to the photovoltaic elements 105. This may allow the upper, lower, and/or central metal sheets 114, 115, 116, to be thinner, which may reduce weight and costs. This may allow the upper metal sheet 114 to be thinner, which may improve the transfer of heat from the photovoltaic elements 105 into the liquid water within the upper fluid flow channels 117.
The heat transport element 104 is a substantially rigid structure. This may minimize changes in the level of the upper surface 132 of the water 121 due to flexing of the components of the heat transport element 104, such as the upper and lower sheets 114 and 115. Such changes in the level of the upper surface 132 of the water 121 may affect the efficiency of the cooling of the photovoltaic elements 105.
As is explained above, the interior of the heat transport element 104 is evacuated, and the heat transport element 104 is located within an evacuated tube 103. Usually the heat transport element 104 and the evacuated tube 103 are evacuated to the same pressure. In the illustrated example of the second embodiment described above this pressure may be 10⁻³mbar.
When the water within the heat transport element 104 is heated the proportion of the water in a vapor phase will increase and the proportion in a liquid phase will decrease. As a result the pressure within the heat transport element 104 will increase, producing a pressure differential between the interior and exterior of the heat transport element 104. This pressure differential may cause the upper and lower metal sheets 114 and 115 to ‘balloon’, or bend outwards. The interconnection of the upper and lower metal sheets 114 and 115 by the linking surfaces 116 c and 116 d of the central metal sheet 116 may resist such ballooning of the upper and lower metal sheets 114 and 115 and reduce or prevent ballooning. Arranging for the linking surfaces 116 c and 116 d of the central metal sheet 116 to be straight may increase the resistance to ballooning. Reducing or preventing ballooning may prevent damage to the photovoltaic elements 105 by reducing the amount of mechanical stress applied to the photovoltaic elements 105. This may allow the upper metal sheet 114 to be thinner, which may reduce weight and costs and/or may improve the transfer of heat from the photovoltaic elements 105 into the liquid water within the upper fluid flow channels 117.
The above description of the operation of the heat transfer element 104 according to the second embodiment describes the transfer of heat energy from the photovoltaic elements 105 through the upper metal sheet 114 and into the water within the upper fluid flow channels 117. In addition, in the regions of the upper metal sheet 114 bonded to the first surfaces 116 a, some heat energy will pass through the upper metal sheet 114 and the central metal sheet 116 into the water within the lower fluid flow channels 118. Although this transfer of heat energy will cool the photovoltaic elements 105, the heating of the water in the lower fluid flow channels 118 is generally undesirable because it will tend to counteract and slow the density driven circulation of water produced by the heating of the water in the upper fluid flow channels 117 described above. Accordingly, it is preferred for the sizes of the first surfaces 116 a of the central metal sheet 116 in contact with the upper metal sheet 114 to be as small as possible, subject to the contact area between the first surfaces 116 a and the upper metal sheet 114 being sufficiently large to form a reliable bond of the required strength.
It is not necessary for the heat transport element 104 according to the first embodiment to be inclined to the horizontal along its longitudinal axis. In other words, it is not necessary for the end of the heat transport element 104 adjacent the support assembly 106 to be higher than the end of the heat transport element 104 remote from the support assembly 106.
In the illustrated first embodiment the heat transport element 104 is arranged to be horizontal along its longitudinal axis. That is, the end of the heat transport element 104 adjacent the support assembly 106 should be at the same height as the end of the heat transport element 104 remote from the support assembly 106. However, in practice some deviation from the horizontal may be tolerated without significant impact on the operation of the heat transport element 104. Such deviation from the horizontal will result in differences in the level of the liquid water surface relative to the structure of the heat transport element 104 at different positions along the length of the heat transport element 104. As is explained above, the level of the liquid water surface may be varied. Accordingly, the minor differences in level caused by small deviations from the horizontal may be accommodated.
In the illustrated example of the first embodiment, each of the upper and lower sheets 114 and 115 has a dimpled profile. This dimpled profile is shown in more detail in FIGS. 11A and 11B. FIG. 11A shows a plan view from above of a part of the upper sheet 114. FIG. 11B shows a cross section through the upper sheet 114 along the line D-D in FIG. 11A.
As is shown in FIG. 11A, a plurality of dimples 127 are formed in the flat upper surface 104 a of the heat transport element 104 in the upper sheet 114. The dimples 127 are formed in straight rows and columns to form a regular two dimensional square array, and are spaced apart leaving a flat strip 128 between each row of dimples 127.
Each dimple 127 comprises a looped recess 127 a having a circular inner perimeter 127 b and a square outer perimeter 127 c. The square outer perimeter 127 c has rounded off corners 127 d. Within the circular inner perimeter 127 b a circular region 127 e is raised relative to the looped recess 127. The circular region 127 e is at the same level as the surface 104 a of the flat strips of the upper sheet 115 outside the dimple 127.
The flat strips 128 run transversely across the upper sheet 114 and have the same width as the width of the first coplanar surfaces 116 a of the central sheet 116. The flat strips 128 provide flat areas for bonding with the first surfaces 116 a of the central sheet 116. The flat strips 128 may allow reliable and strong bonds to be made between the first surfaces 116 a and the upper sheet 114. The flat strips 128 may allow a good seal to be formed between adjacent upper fluid flow passages 117.
A plurality of dimples 129 are formed in the lower sheet 115. The dimples 129 are formed in straight rows and columns to form a regular two dimensional square array, and are spaced apart leaving a flat strip 130 between each row of dimples 129. The dimples 129 in the lower sheet 115 are the same as the dimples 127 in the upper sheet 114. The flat strips 128 run transversely across the upper metal sheet 114 and have the same width as the width of the first and second coplanar surfaces 116 a and 116 b. The flat strips 130 provide flat areas for bonding with the second surfaces 116 b of the central sheet 116. The flat strips 130 may allow reliable and strong bonds to be made between the second surfaces 116 b and the lower sheet 115.
In the illustrated example of the first embodiment of the invention both the dimples 127 in the upper sheet 114 and the dimples 130 in the lower sheet 115 are formed by downward recesses. Accordingly, the dimples 127 in the upper sheet 114 have recesses extending into the heat transport element 104, while the dimples 130 in the lower sheet 115 have recesses extending out of the heat transport element 104. In other examples the dimples 127 and 130 may be formed by recesses extending upwardly, or by recesses extending in opposite directions.
The array of dimples 130 on the lower metal sheet 115 extends across the flat part of the lower sheet 115, but does not extend into the semi-cylindrical surface of the outwardly projecting section 110. Further, the array of dimples 130 on the lower sheet 115 has dimples omitted from the array at the locations of the hollow ridges 125.
The dimples 127 and 130 may increase the rigidity of the upper and lower sheets 114 and 115. This may tend to reduce the amount of flexing of the heat transport element 104 in use. This may prevent damage to the photovoltaic elements 105 by reducing the amount of mechanical stress applied to the photovoltaic elements 105. This may allow the upper, lower, and/or central sheets 114, 115, 116, to be thinner, which may reduce weight and costs. This may allow the upper sheet 114 to be thinner, which may improve the transfer of heat from the photovoltaic elements 105 into the liquid water within the upper fluid flow channels 117.
The surfaces of the dimples 127 may provide additional nucleation sites for the formation of water vapor bubbles 122, which may improve efficiency.
In examples where adhesive is used to attach the photovoltaic elements 105 to the heat transport element 104 the dimples 127 on the flat upper surface 104 a of the heat transport element 104 may provide reservoirs for the adhesive. This may allow more secure attachment of the photovoltaic elements 105. This may allow a thinner layer of adhesive to be used, which may improve the transfer of heat from the photovoltaic elements 105 into the liquid water within the upper fluid flow channels 117.
As discussed above the heat transport element 104 has a flat upper surface 104 a formed by an upper sheet 114 with a dimpled profile. In addition the upper sheet 114 is has two longitudinal recesses 129 running across in its upper surface 104 a which form two parallel troughs running along the upper surface 104 a of the heat transport element 104. FIG. 12 shows one of these recesses 129. Electrically conductive ribbons or wires 130 run along the longitudinal recesses 129 between the heat transport element 104 and the photovoltaic elements 105. The wires 130 are electrically connected to the photovoltaic elements 105 and to the conductors 21 which pass through the cap 12 to provide a conductive path to carry the electrical power generated by the photovoltaic elements 105 out of the sealed transparent tube 103. This electrical power may be supplied to an inverter for voltage conversion and/or for conversion to alternating current for supply to a domestic or mains electrical system.
In examples where adhesive is used to attach the photovoltaic elements 105 to the heat transport element 104, an electrically insulating adhesive can be used to electrically insulate the electrically conductive ribbons or wires 130 from the photovoltaic elements 105 and from the upper surface 104 a of the heat transport element 104. The electrically insulating adhesive can also be used to electrically insulate the photovoltaic elements 105 from the upper surface 104 a of the heat transport element 104.
In the first embodiment the longitudinal recesses 129 run perpendicularly to the fluid flow channels 117 and 118. Accordingly, each of the first surfaces 116 a of the central metal sheet 116 has two recesses to receive the longitudinal recesses 129.
In the illustrated example of the first embodiment each dimple 127 comprises a looped recess with a circular inner perimeter 127 b and a square outer perimeter 127 c, with the circular region 127 e at the same level as the surface 104 a of the flat strips of the upper metal sheet 115 outside the dimple 127. In some examples the circular region 127 e may not be at the same level as the surface 104 a of the flat strips of the upper metal sheet 115 outside the dimple 127. In other examples different dimple shapes and/or profiles may be used. In some examples the perimeters may have different shapes. In some examples the circular region 127 e may not be at the same level as the surface 104 a of the flat strips of the upper metal sheet 115 outside the dimple 127. In some examples the dimples may simply comprise a recessed region, rather than a recessed outer region surrounding a relatively raised inner region.
In the illustrated example of the first embodiment 0.2 mm thick tin coated mild steel sheets are used to form the different sheets of the heat transport element. In alternative examples other thicknesses may be used, in particular 0.1 mm thick tin coated mild steel sheets may be used. The use of a thinner upper metal sheet may improve the rate of heat energy transfer from the photovoltaic elements to the water inside the upper fluid flow channels. In other examples the different sheets may have different thicknesses.
In the illustrated example of the first embodiment the spacing between the upper sheet 114 and the parallel lower sheet 115 is 1.8 mm at the locations of the longitudinal recesses 129. Accordingly, the thickness of the fluid flow channels 117 and 118 at the locations of the longitudinal recesses 129 is 1.6 mm, since the thickness of the central sheet is 0.2 mm.
The use of mild steel may avoid or reduce problems produced by differential thermal expansion of the silicon semiconductor photovoltaic elements 105 and the heat transport element 104 because the coefficients of thermal expansion of silicon and mild steel are similar.
The sheets used to form the heat transport element may be shaped by pressing.
In other examples different materials may be used, in particular sheets of other metals or metal alloys, such as copper or brass may be used. In other examples the upper, lower and/or partition sheets may be formed from materials which are not metals. In other examples there may be openings in the upper sheet allowing the water inside the upper fluid flow channels to directly contact the back surfaces of the photovoltaic elements to maximize heat transfer. In such examples the thickness or material used to form the upper sheet could be selected without having to take thermal conductivity into account.
In the illustrated example of the first embodiment the tube 119 is cylindrical. In other examples different tube shapes may be used. In some examples a tube 119 having an elliptical cross section may be used. The use of an elliptical tube may increase the heat exchange area formed by the exterior of the tube 119 where the water vapor condenses, which may improve the heat transfer rate between the water vapor and the fluid within the tube 119.
In different examples the size of the tube 119 may be varied. However, the tube 119 should not entirely fill the vapor manifold 111. If there is insufficient free space within the vapor manifold 111 to allow the water vapor and liquid water to freely circulate this may adversely affect the operation of the heat transport element 104.
In the illustrated example of the first embodiment the tube 119 is made from copper. In other examples different materials may be used. The tube 119 is connected at only one end to the heat transport element 104, with the other end, the curved section 119 c, being free to move relative to the heat transport element 104. Accordingly, differential thermal expansion of the tube 119 and the heat transport element 104 is not generally a problem and will generally not need to be taken into account when selecting materials.
In the first embodiment of the invention the roughening of the surfaces of the upper sheet 114 produced by the tin coating may provide nucleation sites, increasing the tendency of the liquid water 121 to vaporize and form bubbles 122 of water vapor. In the first embodiment of the invention the roughening of the surfaces of the central sheet 116 produced by the tin coating may provide nucleation sites, increasing the tendency of the liquid water 121 to vaporize and form bubbles 122 of water vapor.
In some examples other coatings may be added to the surfaces of the upper sheet 114 in order to promote or increase nucleation and formation of bubbles of water vapor. In some examples these coatings may be of metals, or plastics. In some examples these coatings may be of PTFE.
In the illustrated example of the first embodiment the different sheets are soldered together. In alternative embodiments different bonding techniques may be used. In some examples the different sheets may be bonded by techniques including spot welding, roller welding or adhesive.
In the illustrated example of the first embodiment inner faces of the upper and lower sheets 114 and 115, and both faces of the central metal sheet 116, are coated with a solder layer. In the illustrated example the solder layers are 2 to 6 microns thick. Other examples may have different thicknesses.
The edges of the upper and lower sheets 114 and 115 are then soldered together to form a gas tight seal between them, and to form a gas tight seal between the upper and lower sheets 114 and 115 and the tube 119. As is explained above, the central metal sheet 116 is not located between the upper and lower metal sheets 114 and 115 at their edges.
The heat transport element 104 is then heated in an oven to a sufficiently high temperature to reflow the solder layers on the upper, lower and central sheets 114, 115, 116, and is simultaneously evacuated.
This manufacturing procedure may ensure good solder bonding between the central sheet 116 and the upper and lower sheets 114 and 115. This manufacturing procedure may allow a better level of vacuum to be achieved within the heat transport element 104 by evacuating the heat transport element 104 at a high temperature when out-gassing by the metal sheets and solder is taking place.
The solder may microscopically roughen the surfaces of the upper and central sheets 114 and 116. This may provide nucleation sites, increasing the tendency of the liquid water 121 to vaporize and form bubbles 122 of water vapor.
In other examples, a solder layer is formed on the central sheet 116 only on the parts of the central metal sheet which contact the upper or lower sheets 114 and 115. As can be understood from a comparison of FIGS. 13 and 14 this will be the contact faces of the first and second surfaces 116 a and 116 b. Similarly, in some examples a solder layer is formed on the surfaces of the upper sheet 114 and the lower sheet 115 only on the parts of the surfaces which will contact one of the other sheets. Reducing the amount of solder used may reduce costs.
In one example the upper sheet 114 only is coated in solder across its entire surface, while the central sheet and lower sheet 116 and 115 are coated in solder only on the parts of the surfaces which will contact one of the other sheets. This may allow the solder layer to provide nucleation sites on the surface of the upper sheet 114 forming parts of the upper fluid flow channels, while reducing the total amount of solder used.
As explained above, in the illustrated example of the first embodiment the flow of water vapor and liquid water through the heat transport element 104 tends to keep the cooled upper surface of the heat transport element 104 at a uniform operating temperature during operation. That is, the cooled upper surface of the heat transport element 104 tends to be kept isothermal. The isothermal nature of the cooled upper surface of the heat transport element 104 tends to give rise to isothermal cooling of the photovoltaic elements 105, where hotter parts of the photovoltaic elements 105 tend to be preferentially cooled so that the photovoltaic elements 105 themselves tend to become isothermal.
Such isothermal cooling provides further advantages in addition to those provided by cooling.
Isothermal cooling may provide the advantage that the appearance of hot spots or regions in the photovoltaic elements 105 produced by heating by incident solar radiation can be reduced or eliminated. Such hot spots or regions can reduce the efficiency of the photovoltaic elements 105.
Isothermal cooling may simplify the control and wiring arrangements of the photovoltaic elements 105 by reducing or eliminating any requirement for compensation for differences in the performance of the different parts of the photovoltaic elements 105 that are at different temperatures.
Isothermal cooling tends to reduce, or prevent, the formation of hot spots or regions in the photovoltaic elements 105. As is explained above, this may allow the efficiency of the photovoltaic elements 105 to be improved at a specific temperature. Further, this may reduce the amount of degradation of the photovoltaic elements 105 caused by higher temperatures.
Still further, this may allow the photovoltaic elements 105 to operate with a given degree of efficiency at a higher temperature than would otherwise be the case. This may allow the solar energy collector assembly 102 including the photovoltaic elements 105 to be operated at a higher temperature without reducing the efficiency with which the photovoltaic elements 105 produce electrical energy.
One example of this effect of isothermal cooling is that the general figure quoted above for silicon photovoltaic elements that the efficiency of electrical energy generation generally drops by about 0.35% to 0.5% for each degree centigrade of temperature increase above 25° C. may not apply to silicon photovoltaic elements that are isothermally cooled. Such isothermally cooled silicon photovoltaic elements having hotspots eliminated or reduced may have a higher threshold temperature at which the efficiency of electrical energy generation begins to drop and/or may have a reduced rate of reduction in efficiency for each degree centigrade of temperature increase above the threshold temperature. Further, the temperature at which there is a risk of permanent degradation of the silicon photovoltaic elements may also be increased for isothermally cooled silicon photovoltaic elements. Similar effects may be found in photovoltaic elements formed of other semiconductor materials.
In some examples, one or more layers of heat conductive material may be located between the upper sheet 114 and the photovoltaic elements 105. Such layers of heat conductive material may increase the rate of heat transfer between the photovoltaic elements 105 and the upper sheet 114, and thus the rate of heat transfer between the photovoltaic elements 105 and the liquid within the upper fluid flow channels 117. Such layers of heat conductive material may also increase the rate of heat transfer laterally across the photovoltaic elements 105.
Accordingly, providing a layer of heat conductive material may increase the degree of isothermal cooling and further tend to reduce, or eliminate, the formation of hot spots or regions in the photovoltaic elements 105.
The heat transport element may be used in other applications separately from the rest of the solar energy converter.
In some examples control methods can be used to control the temperature of the solar energy collector assembly 102. In some examples the temperature of the solar energy collector assembly 102 may be controlled by changing the rate of removal of heat energy from the solar energy collector assembly 102.
In some examples the rate of removal of heat energy from the solar energy collector assembly 102 can be controlled by altering the flow rate of the first operating fluid passing through the tube 119 forming the heat exchanger 107.
In some examples the rate of removal of heat energy from the solar energy collector assembly 102 can be controlled by altering the vacuum pressure within the tube 103. This may change the rate of convective heat loss from the solar energy collector assembly 102 to the tube 103. In general, heat transferred to the tube 103 will be rapidly lost to the outside environment by convection and/or conduction.
In some examples the rate of removal of heat energy from the solar energy collector assembly 102 can be controlled by altering the vacuum pressure within the heat transport element 104. In general, the tendency of the liquid water within the upper fluid flow channel 117 to vaporize and form bubbles of vapor 122 will increase as the vacuum pressure is reduced, and the tendency of the liquid water within the upper fluid flow channel 117 to vaporize and form bubbles of vapor 122 will decrease as the vacuum pressure is increased. As is explained above, the density driven circulation of water around the upper and lower fluid flow channels 117 and 118 and the transport of heat energy along the vapor manifold 111 and the tube 119 are both driven by water vapor. Accordingly, altering the tendency of the liquid water to vaporize by altering the vacuum pressure may allow the rate of removal of heat energy from the solar energy collector assembly 102, and the rate of removal of heat energy from the photovoltaic elements 105 to be controlled, and so allow the temperature of the solar energy collector assembly 102 and photovoltaic elements 105 to be controlled.
Further, the temperature at which rolling boiling of the water 121 within the upper fluid flow channel 117 commences will tend to increase as the vacuum pressure is increased, and will tend to decrease as the vacuum pressure is decreased. Accordingly, in examples where the vacuum pressure within the heat transport element 104 is altered the temperature at which the water 121 within the upper fluid flow channel 117 commences rolling boiling can be changed.
As is explained above, the density driven circulation of water around the upper and lower fluid flow channels 117 and 118 becomes particularly vigorous, and becomes particularly effective as a heat transport mechanism, when the water 121 within the upper fluid flow channel 117 enters a rolling boil state. Accordingly, altering the temperature at which the water 121 within the upper fluid flow channel 117 commences rolling boiling by altering the vacuum pressure may allow the rate of removal of heat energy from the solar energy collector assembly 102 and photovoltaic elements 105 to be controlled, and so allow the temperature of the solar energy collector assembly 102 and photovoltaic elements 105 to be controlled.
In some examples the temperature of the solar energy collector assembly 102 may be controlled by changing the amount of solar energy incident on the solar energy collector assembly 102, and so changing the rate of absorption of heat energy by the solar energy collector assembly 102.
In some examples the amount of incident solar energy may be controlled by changing the orientation of the solar energy collector assembly relative to the direction of the incident solar energy. This can be carried out using a drive mechanism able to rotate the solar energy collector assembly about one or more axes.
In some examples the amount of incident solar energy may be controlled using adjustable light intercepting or blocking mechanisms in the path of the incident solar energy. In some examples variable filters, shutters, stops, or the like may be used. In some examples these adjustable light intercepting or blocking mechanisms may comprise physical devices. In some examples these adjustable light intercepting or blocking mechanisms may comprise devices having electronically controlled optical characteristics, such as liquid crystals.
In examples where the temperature of the solar energy collector assembly and/or the photovoltaic elements are to be controlled, a temperature sensor and a temperature controller may be provided, together with a temperature control mechanism arranged to carry out one, some, or all, of the methods of controlling temperature described above.
The temperature sensor is arranged to measure the temperature of the solar energy collector assembly and provide this temperature value to the temperature controller. The temperature controller can then operate the temperature control mechanism in a suitable manner to control the temperature of the solar energy collector assembly to the desired value.
Examples where the temperature of the photovoltaic elements is to be controlled a temperature sensor arranged to measure the temperature of a photovoltaic element or elements and provide this temperature value to the temperature controller may be provided. This may be additional to, or instead of, the temperature sensor arranged to measure the temperature of the solar energy collector assembly. The temperature controller can then operate the temperature control mechanism in a suitable manner to control the temperature of the photovoltaic element or elements to the desired value.
In some examples the temperature sensor can be provided on the upper surface of the solar energy collector assembly. In some examples the temperature sensor can be formed on the same semiconductor wafer as a photovoltaic element.
Conveniently, the temperature controller may be a suitably programmed general purpose computer.
The illustrated first embodiment is a hybrid solar energy converter comprising photovoltaic elements and arranged to convert incident solar radiation into outputs of both electrical energy and hot water. In other examples the photovoltaic elements may be omitted to provide a solar energy converter arranged to convert incident solar radiation into an output of hot water.

Second Embodiment

In a second embodiment a different arrangement of the tube forming the first heat exchanger is used. Otherwise, the second embodiment is substantially similar to the first embodiment.
FIG. 13 shows a cut away plan view from below of a heat transport element 104 according to the second embodiment with the outwardly projecting section 110 removed, so that the heat exchanger 107 is visible.
As shown in FIG. 13, in the second embodiment the heat exchanger 107 comprises a cylindrical tube 133 which extends within the vapor manifold 111 along the entire length of the vapor manifold 111. The cylindrical tube 133 comprises a first straight section 133 a forming the heat exchanger 107 which extends parallel to the sides of the vapor manifold 111, such as the upper surface 104 a and the projecting section 110, and extends through one end 108 of the vapor manifold 111, along the entire length of the vapor manifold 111, and through the other end 108 of the vapor manifold 111. A straight return section 133 b extends behind the rear face of the heat transport element 104 through the end cap 120 to the support element 106.
The first and second sections 133 a and 133 b are connected together by a curved section 133 c.
In use, the first fluid passes along the cylindrical tube 133 as indicated by the arrows in FIG. 13, so that the first fluid passes through the first straight section 133 a, the curved section 133 c and the second straight section 133 b, so that the first fluid passes through the cylindrical tube 119, and travels along substantially the entire length of the vapor manifold 111.
In the illustrated example the first and second sections 133 a and 133 b of the cylindrical tube 133 are arranged one above the other and the first fluid enters through the first section 133 a and leaves through the second section 133 b. In other examples the direction of flow of the first fluid may be reversed. In other examples the first and second sections 133 a and 133 b may be differently arranged.
Similarly to the first embodiment, in other examples the tube 133 may be shapes other than cylindrical. In some examples the tube 133 may have an elliptical cross section. In some examples the cylindrical tube 133 may have a different cross sectional shape at different positions. For example, the first straight section 133 a may have an elliptical cross section, while the second straight section 133 b and the curved section 133 c may have a circular cross section.
In different examples the size of the tube 133 may be varied. However, the tube section 133 a should not entirely fill the vapor manifold 111. If there is insufficient free space within the vapor manifold 111 to allow the water vapor and liquid water to freely circulate this may adversely affect the operation of the heat transport element 104.
In the illustrated example the tube 133 is made from mild steel. In some examples the tube 133 and the heat transport element 104 may be formed of other materials.
In some examples, different materials may be used for the tube 133 and the heat transport element 104. In such examples, since the tube section 133 a is connected at both ends to the heat transport element 104, it may be necessary to take differential thermal expansion of the tube 133 and the heat transport element 104 into account when selecting materials. In such examples where different materials are used, the tube 133 and/or one or both of the end faces 108 of the vapor manifold 111 could be formed with flexible elements to allow relative movement of the tube 133 and the heat transport element 104 in order to accommodate differential thermal expansion. Such flexible elements could be formed from the material of the tube 133 and/or the end faces 108, or could be separate components. This may allow a wider range of materials to be used. Such flexible elements could be formed at one or both ends of the heat transport element 104. In one example the flexible element could be provided by forming a bellows arrangement in the wall of the tube 133.

Third Embodiment

In a third embodiment a different arrangement of the tube forming the first heat exchanger is used. Otherwise, the third embodiment is substantially similar to the first embodiment.
FIG. 14 shows a cut away plan view from below of a heat transport element 104 according to the third embodiment with the outwardly projecting section 110 removed, so that the heat exchanger 107 is visible.
As can be best seen in FIG. 14, the heat exchanger 107 is comprises a cylindrical tube assembly 134 which extends within the vapor manifold 111 along substantially the entire length of the vapor manifold 111. The cylindrical tube assembly 134 comprises an inner concentric tube 134 a and an outer concentric tube 134 b. The tube assembly 134 is shown in cross section in FIG. 14, to allow the both of the concentric tubes 134 a and 134 b to be seen. The inner and outer concentric tubes 134 a and 134 b run parallel to the sides of the vapor manifold 111, such as the upper surface 104 a and the projecting section 110, and extend along substantially the entire length of the vapor manifold 111. The outer concentric tube 134 b extends slightly further than the inner concentric tube 134 a, the outer concentric tube 134 b is sealed by an end cap 134 c, and the inner concentric tube 134 a is open ended, so that the inner and outer concentric tubes 134 a and 134 b form a single fluid flow path.
In use, the first fluid passes through the cylindrical tube assembly 134 as indicated by the arrows in FIG. 14, so that the first fluid passes through the inner concentric tube 134 a along substantially the entire length of the vapor manifold 111, then moves outwardly into the outer concentric tube 134 b, and travels through an annular channel 134 d defined between the inner concentric tube 134 a and the outer concentric tube 134 b back along substantially the entire length of the vapor manifold 111.
The water vapor in the vacuum within the vapor manifold 111 condenses on the outer surface of the outer concentric tube 134 b and transfers heat energy from the heat transfer element 104 to the first fluid within the tube assembly 134.
In the illustrated example the first fluid enters through the inner concentric tube 134 a and leaves through the annular channel 134 d. In other examples the direction of flow of the first fluid may be reversed.
In the illustrated example of the first embodiment the tube 119 is cylindrical. In other examples different tube shapes may be used. In some examples a tube 119 having an elliptical cross section may be used. The use of an elliptical tube may increase the heat exchange area formed by the exterior of the tube 119 where the water vapor condenses, which may improve the heat transfer rate between the water vapor and the fluid within the tube 119.
In different examples the size of the tube assembly 134 may be varied. However, the tube assembly 134 should not entirely fill the vapor manifold 111.
In the illustrated example of the third embodiment the tube assembly 134 is made from copper. In other examples different materials may be used. The tube assembly 134 is connected at only one end to the heat transport element 104, with the other end being free to move relative to the heat transport element 104. Accordingly, differential thermal expansion of the tube assembly 134 and the heat transport element 104 is not generally a problem and will generally not need to be considered when selecting materials.

Fourth Embodiment

In a fourth embodiment a different arrangement of the tube forming the first heat exchanger is used. Otherwise, the fourth embodiment is substantially similar to the first embodiment. The fourth embodiment may be used in examples where the tube 103 has an end cap 120 at each end.
FIG. 15 shows a cut away plan view from below of a heat transport element 104 according to the fourth embodiment with the outwardly projecting section 110 removed, so that the heat exchanger 107 is visible.
As shown in FIG. 15, in the fourth embodiment the heat exchanger 107 comprises a cylindrical tube 135 which extends within the vapor manifold 111 along the entire length of the vapor manifold 111. The cylindrical tube 135 comprises a straight section 135 a forming the heat exchanger 107 which extends parallel to the sides of the vapor manifold 111, such as the upper surface 104 a and the projecting section 110, and extends through one end 108 of the vapor manifold 111, along the entire length of the vapor manifold 111, and through the other end 108 of the vapor manifold 111.
At each end of the straight section 135 a a respective connecting section 135 b of the tube 135 extends through the end cap 120 at each end of the tube 103 to a support structure, such as the support element 106.
In use, the first fluid passes along the cylindrical tube 135 as indicated by the arrows in FIG. 14, so that the first fluid passes through the first straight section 135 a and travels along substantially the entire length of the vapor manifold 111.
Similarly to the first embodiment, in other examples the tube 135 may be shapes other than cylindrical. In some examples the tube 135 may have an elliptical cross section. In some examples the cylindrical tube 135 may have a different cross sectional shape at different positions. For example, the first straight section 135 a may have an elliptical cross section, while the connecting sections 135 b of the tube 135 have a circular cross section.
In different examples the size of the tube 135 may be varied. However, the tube section 135 a should not entirely fill the vapor manifold 111. If there is insufficient free space within the vapor manifold 111 to allow the water vapor and liquid water to freely circulate this may adversely affect the operation of the heat transport element 104.
In the illustrated example the tube 135 is made from mild steel. In some examples the tube 135 and the heat transport element 104 may be formed of other materials.
In some examples, different materials may be used for the tube 135 and the heat transport element 104. In such examples, since the tube section 135 a is connected at both ends to the heat transport element 104, it may be necessary to take differential thermal expansion of the tube 135 and the heat transport element 104 into account when selecting materials. In such examples where different materials are used, the tube 135 and/or one or both of the end faces 108 of the vapor manifold 111 could be formed with flexible elements to allow relative movement of the tube 135 and the heat transport element 104 in order to accommodate differential thermal expansion. Such flexible elements could be formed from the material of the tube 135 and/or the end faces 108, or could be separate components. This may allow a wider range of materials to be used. Such flexible elements could be formed at one or both ends of the heat transport element 104. In one example the flexible element could be provided by forming a bellows arrangement in the wall of the tube 135.
As shown in FIG. 15, the connecting sections 135 b of the tube 135 are bent through bends or elbows. These bends may provide flexibility or “give” in order to accommodate differential thermal expansion of the heat transport element 104 and tube 135 and the tube 103. In other examples different means to accommodate differential thermal expansion may be provided.

Fifth Embodiment

Apparatus according to a fifth embodiment of the present invention is illustrated in FIG. 16. FIG. 16 shows a general exterior view of a fifth embodiment of a hybrid solar energy converter 201 according to the present invention.

Overview

In the fifth embodiment, the hybrid solar energy converter 201 includes a solar energy collector assembly 202 housed within a sealed transparent tube 203. The solar energy collector assembly 202 includes a heat transport element 204 and an array of photovoltaic elements 205 mounted on a front surface of the heat transport element 204, the front surface being the surface exposed to incident solar radiation in use. The hybrid solar energy converter 201 also includes a support assembly 206 at one end of the transparent tube 203. One end of the solar energy collector assembly 202 is connected to the support assembly 206. Similarly to the first embodiment, in different examples the photovoltaic elements 205 may be formed of silicon, or gallium arsenide, or other suitable semiconductor materials. In other examples organic photovoltaic elements may be used. In other examples hybrid photovoltaic elements may be used.
In the fifth embodiment, the support assembly 206 supplies a first fluid to a heat exchanger 207 arranged to transfer heat energy from the heat transport element 204 to the first fluid.
In one possible example, in use the hybrid solar energy converter 201 may be mounted on a wall. Accordingly, suitable mounting brackets may be provided.
In overview, the operation of the hybrid solar energy converter 201 of the fifth embodiment is similar to operation of the hybrid solar energy converter 101 of the first embodiment. Solar energy incident on the hybrid solar energy converter 201 passes through the sealed transparent tube 203 and is incident on the photovoltaic elements 205 of the solar energy collector assembly 202. The photovoltaic elements 205 convert a part of the energy of the incident solar energy into electrical energy, and convert a part of the energy of the incident solar energy into heat energy. A further part of the incident solar energy may be incident on any parts of the solar energy collector assembly 202 which are not covered by the photovoltaic elements 205, and this further part of the incident solar energy may also be converted into heat energy.
In general, it is desirable to maximize the proportion of the surface of the solar energy collector assembly 202 exposed to incident solar energy which is covered by the photovoltaic elements 205, and to minimize the proportion which is not so covered. However, in some circumstances it may be preferred to leave some parts of this exposed surface uncovered, for example to simplify manufacture and/or assembly of the solar energy collector assembly 202 and attachment of the photovoltaic elements 205 to the solar energy collector assembly 202.
The electrical energy produced by the photovoltaic elements 205 is carried along the heat transport element 204 by electrical conductors and away from the solar energy converter 201 for use. The heat energy absorbed by the photovoltaic elements 205 is transferred into the heat transport element 204, cooling the photovoltaic elements 205, and then transferred into the first fluid by the heat exchanger 207.
In one typical arrangement, the hybrid solar energy converter 201 may be used to generate electricity, and to generate hot water. Similarly to the first embodiment, in this arrangement the first fluid is water and the heat energy transferred to the heat exchanger 207 is transferred into a pumped water supply flowing through the heat exchanger 207 to heat the water. This heated water is then used by a domestic or industrial hot water system, and the electrical energy produced by the photovoltaic elements 205 is supplied to an electrical supply system.

Transparent Tube

In the fifth embodiment illustrated in FIG. 16 the sealed transparent tube 203 is similar to the sealed transparent tube 103 of the first embodiment, having one closed domed end and one open end sealed by an end cap 220. The interior of the tube 203 is at least partially evacuated. That is, the interior of the tube 203 is below normal atmospheric pressure.
The pressure of the vacuum within the tube 203 may be 10⁻³mbar. Other pressures may be used, as discussed regarding the first embodiment. In some examples the vacuum pressure may be in the range 10⁻²mbar to 10⁻⁶mbar. In general, it is expected that lower vacuum pressure, or in other words a harder vacuum, will provide greater insulating benefits. Further, it is expected that lower vacuum pressure, or in other words a harder vacuum, will provide greater protection from environmental damage in examples where the photovoltaic elements are not encapsulated. In practice the benefits of using a lower vacuum pressure may need to be balanced against the increased cost of achieving a lower vacuum pressure. In some examples a vacuum pressure of 10⁻²mbar, or lower, may be used.
In an alternative example the sealed transparent tube 203 may be filled with an inert gas instead of being evacuated. In particular, the inert gas may be nitrogen.
In another alternative example the sealed transparent tube 203 may be filled with an inert gas at a reduced pressure. In some examples this may be achieved by filling the tube 203 with the inert gas and then evacuating the tube 203. In particular, the inert gas may be nitrogen.
In the illustrated fifth embodiment the tube 203 is cylindrical having a circular cross section. Similarly to the first and second embodiments, in alternative examples the tube 203 may have other shapes. In some examples the cross sectional size and/or shape of the tube 203 may vary at different positions along its length. In an alternative example the tube 203 may have an elliptical cross section. In particular, the tube 203 may have an elliptical cross section with the long axis of the ellipse aligned with the plane of the solar energy collector assembly 202.
In the illustrated fifth embodiment the tube 203 is formed of glass. In alternative examples suitable transparent plastics materials or laminated structures may be used to form the tube 203.
In the illustrated fifth embodiment the tube 203 is transparent. In alternative examples the tube may be only partially transparent.
In the illustrated fifth embodiment the metal end cap 220 may be bonded to the glass tube 203 by adhesive. In other embodiments alternative glass to metal bonding techniques may be used, for example welding, brazing or soldering.
Similarly to the first embodiment the tube 203 has a metal end cap 220 at one end. In alternative examples the end cap 220 may be made of other materials. In some examples the end cap 220 may be made of glass. This may reduce conductive heat losses from the collector assembly 202.

Collector Assembly

In the fifth embodiment, the solar energy collector assembly 202 includes a heat transport element 204 and an array of photovoltaic elements 205 mounted on one surface of the heat transport element 204. In order to allow radiant solar energy to be incident on the photovoltaic elements 205 the array of photovoltaic elements 205 are mounted on the surface of the heat transport element 204 which is exposed to the incident radiant solar energy in operation of the hybrid solar energy converter 201. In the fifth embodiment the heat transport element 204 may be mounted vertically. In examples where the heat transport element 204 is not mounted vertically the surface which is exposed to the incident radiant solar energy in operation will usually be the upper surface of the heat transport element 204.
In some arrangements the surface of the heat transport element 204 exposed to the incident radiant solar energy may not be the upper surface. In particular, this would be the case if the incident solar radiant energy was incident horizontally or from below, for example after redirection by an optical system such as a mirror.
In the illustrated example of the fifth embodiment, the solar energy collector assembly 202 is supported by cylindrical tubes 234 of the heat transport element 204. The cylindrical tubes 234 pass through the end cap 220 and into the support assembly 206, as will be explained in more detail below. Where the cylindrical tube 234 passes through the end cap 220 the cylindrical tube 234 is soldered to the end cap 220 to retain the cylindrical tube 234 in place and support the solar energy collector assembly 102.
The cylindrical tubes 234 are assemblies comprising inner and outer concentric tubes 234 a and 234 b, similarly to the heat exchanger arrangement according to the third embodiment. In alternative examples the heat exchanger arrangements according to the first, second or fourth embodiments may be used instead.
In alternative examples the cylindrical tubes 234 may be secured to the end cap 220 in other ways. In one example the cylindrical tubes 234 may be welded to the end cap 220.
The supporting of the solar energy collector assembly 202 by physical connections through the cylindrical tubes 234 may increase the efficiency with which heat can be collected from incident solar energy by the solar energy collector assembly 202. Having the solar energy collector assembly 202 supported by physical connections only through the cylindrical tubes 234 may reduce conductive heat loss from the solar energy collector assembly 202 into the supporting structure outside the transparent tube.
In the illustrated example of the fifth embodiment the heat transport element 204 has a substantially flat front surface 204 a. Each of the photovoltaic elements 205 is square, and the width of the heat transport element 204 is the same as the width of each square photovoltaic element 205. Six square photovoltaic elements 105 are mounted side by side to one another along the length of the heat transport element 204. Substantially the entire front face of the heat transport element 204 is covered by the photovoltaic elements 205. Covering a large proportion of the upper surface 204 a of the heat transport element 204 with photovoltaic elements 205 may increase the efficiency of the hybrid solar energy converter 201.
In one example the square photovoltaic elements 205 may each be a 125 mm by 125 mm square and 0.2 mm thick. In another example the square photovoltaic elements may each be a 156 mm by 156 mm square. In other examples, photovoltaic elements having other sizes or shapes may be used.
The photovoltaic elements 205 are bonded to the substantially flat upper surface 204 a of the heat transport element 204 using a layer of heat conducting adhesive in a similar manner to the first embodiment. The adhesive bonding layer is electrically insulating. The adhesive bonding layer between the photovoltaic elements 205 and the heat transport element 204 is arranged to be thin. This may improve the degree of thermal conduction between the photovoltaic elements 205 and the heat transport element 204. This may increase the rate of heat transfer laterally across the photovoltaic elements 205. An adhesive material loaded with solid spheres of a predetermined size may be used to form the adhesive bonding layer. This may allow a thin adhesive layer to be consistently and reliably formed. The adhesive bonding layer is formed of a flexible or “forgiving” adhesive material. This may relieve stresses in the assembled solar energy collector assembly 202 and reduce any stress applied to the photovoltaic elements 205.
The photovoltaic elements 205 are semiconductor photovoltaic elements formed of silicon. In one embodiment the photovoltaic elements are formed of single-crystal silicon. In one embodiment the photovoltaic elements are formed of amorphous silicon. In one embodiment the photovoltaic elements are formed of polycrystalline silicon, or polysilicon. In other embodiments alternative types of semiconductor photovoltaic elements may be used.
Similarly to the first embodiments, in operation of the hybrid solar energy converter 201 the photovoltaic elements 205 are cooled by the heat transport element 204, which may provide similar advantages to those discussed above. This cooling may allow the temperature of the photovoltaic elements 205 to be maintained at a desired value.
This cooling may provide the advantage that the appearance of hot spots or regions in the photovoltaic elements 205 can be reduced or eliminated, and the temperature of the photovoltaic elements 205 maintained at a uniform desired value. Such hot spots or regions may for example be produced by heating by incident solar radiation, by inhomogeneities or faults in the photovoltaic elements 205, or by a combination of, or interaction between, these causes.
As discussed above regarding the first embodiment, such hot spots or regions can reduce the efficiency of the photovoltaic elements 205 in the short term, and may also degrade the performance of the photovoltaic elements 205 in the longer term.
Accordingly, maintaining the photovoltaic elements 205 at a more uniform temperature value and reducing, or eliminating, hot spots or regions may improve the efficiency of the photovoltaic elements 205 at a specific temperature, and may reduce the amount of degradation of the photovoltaic elements 205 caused by higher temperatures.
This may allow the photovoltaic elements 205 to operate at a higher overall temperature than would otherwise be the case, for the same reasons as discussed regarding the first embodiment.
The illustrated example of the fifth embodiment has a solar energy collector assembly 202 supported only by physical connections through the cylindrical tubes 234. In other examples alternative supporting arrangements may be used. In some examples the solar energy collector assembly 202 may be supported by a physical connections both ends of the solar energy collector assembly 202. In some examples, the physical connections at one end of the solar energy collector assembly may be the through the cylindrical tubes 234. In general, it is advantageous to minimize the number of physical supports in order to minimize the escape of heat from the solar energy collector assembly by conduction through the physical supports.
In other examples the number of photovoltaic elements 205 mounted on the heat transport element 204 may be different. In other examples the relative sizes of the photovoltaic elements 205 and the heat transport element 204 may be different.
In some examples the adhesive layer may comprise an epoxy resin which remains non-brittle after curing.
In other examples the adhesive layer may be formed by a double sided adhesive tape.

Heat Transport Element

The heat transport element 204 according to the fifth embodiment is shown in more detail in a cut away view in FIG. 17.
In the fifth embodiment, the heat transport element 204 is generally rectangular. The heat transport element 204 has a flat front surface 204 a and a rear surface 204 b which is flat across most of its area, and has three outwardly projecting sections 210 spaced out along its length, with a first outwardly projecting section 210 at an upper end of the heat transport element 204, a second outwardly projecting section 210 located one third of the way along the length of the heat transport element 204, and a third outwardly projecting section 210 located two thirds of the way along the length of the heat transport element 204.
The heat transport element 204 is divided into three sections, an upper section 204 c, a central section 204 d, and a lower section 204 e. Each section 204 c to 204 e is cooled by a separate density driven circulation acting as a heat transport mechanism similar to the mechanism of the second embodiment and comprising a respective one of the three outwardly projecting sections 210. Each of the three sections 204 c to 204 e supports and cools two of the six photovoltaic elements 205.
Each outwardly projecting section 210 contains and defines an elongate heat transfer chamber or vapor manifold 211 extending substantially from one side to the other of the heat transport element 204. In operation the heat transport element 204 is arranged to be longitudinally sloping, so that the heat transport element 204 has an upper end and a lower end. The heat transport element 204 may be arranged longitudinally vertically, or at an angle to the vertical.
The heat transport element 204 has a front surface 204 a formed by a front sheet 214 and a rear surface 204 b formed by a rear sheet 215. Three central sheets 216 are located between the front sheet 214 and the rear sheet 215, with one of the central sheets 216 in each of the sections 204 a to 204 c, so that fluid flow passages 217 and 218 running longitudinally along the heat transport element 204 are defined between each central sheet 216 and each of the front sheet 214 and the rear sheet 215. Since the heat transport element 204 is longitudinally sloping the fluid flow passages 217 and 218 running longitudinally along the heat transport element 204 will be sloped along their lengths.
Each central sheet 216 has a similar profile to the central sheet 116 of the first embodiment, except that, compared to the second embodiment, the profile of the central sheets 216 of the third embodiment is rotated through 90° to define flow channels running longitudinally along the heat transport element 204. The cross-sectional profile of the corrugated central sheets 216 can be understood as a zig-zag profile with the points of the zig-zag forming the peaks and troughs being flattened.
To be more specific, in the illustrated example of the fifth embodiment the central sheets 216 each comprise a plurality of flat surfaces connected by folds running longitudinally along the heat transport element 204. Accordingly, the front, rear, and central sheets 214, 215, 216 define a plurality of trapezoid cross-section front fluid flow channels 217 and rear fluid flow channels 218 between them. The front fluid flow channels 217 are defined between the front sheet 214 and the central sheets 216. The rear fluid flow channels 218 are defined between the rear sheet 215 and the central sheets 216. The trapezoid front fluid flow channels 271 are arranged so that the larger one of the two parallel faces of each trapezoid channel 217 is formed by the upper sheet 214.
The front and rear fluid flow channels 217 and 218 of the fifth embodiment respectively correspond in function to the upper and lower fluid flow channels 117 and 118 of the second embodiment.
The edges of the heat transport element 204 are formed by bent parts of the rear sheet 215, which are bonded to the front sheet 214. The photovoltaic elements 205 are bonded to the front sheet 214. At the edges of the heat transport element 204, the front sheet 214 is bonded directly to the rear sheet 215, the central sheets 216 are not located between the front and rear sheets 214 and 215 at their edges.
In some examples the central sheets 216 may extend at least partially between the front and rear sheets 214 and 215 at the side edges of the heat transport element 204 so that the front and rear sheets 214 and 215 are both bonded to the central sheets 216. This may assist in locating and securing the central sheets 216 relative to the front and rear sheets 214 and 215.
As discussed above, the heat transport element 204 has three outwardly projecting sections 210 each running transversely across the rear surface 204 b of the heat transport element 204. Each outwardly projecting section 210 is substantially semi-cylindrical and is formed by an outwardly projecting part of the rear sheet 215. Each outwardly projecting section 210 defines a vapor manifold 211. The fluid flow channels 217 and 218 connect to the vapor manifolds 211. It should be noted that the central sheets 216 extend across most of the width of the vapor manifolds 211. Accordingly, the front fluid flow channels 217 defined between the front sheet 214 and the central sheets 216 connect to the vapor manifolds 211 towards the top of each vapor manifold 211, while the rear fluid flow channels 218 defined between the rear sheet 215 and the central sheets 216 connect to the vapor manifolds 211 towards the bottom of each vapor manifold 211.
The front and rear fluid flow channels 217 and 218 are formed into three groups with the front and rear fluid flow channels 217 and 218 of each group interconnected by one of the vapor manifolds 211. Each group of fluid flow channels 217 and 218 extends along one of the sections 204 c to 204 e of the heat transport element 204 and, together with the vapor manifold with which they are connected, forms a separate heat transport mechanism cooling the respective section 204 c to 204 e of the heat transport element 204.
FIG. 17 is an explanatory diagram showing a longitudinal cross section of a part of the heat transport element 204 along the line D-D in FIG. 16. FIG. 17 shows the section of the heat transport element 204 around the boundary between the central section 204 d and the lower section 204 e. The boundary between the central section 204 d and the upper section 204 c is identical.
At the top of the lower section 204 e of the heat transport element 204, at the top of the outwardly projecting section 110, there is a wall 231 extending transversely across the interior of the heat transport element 204. The wall 231 contacts and is bonded to the front and rear sheets 214 and 215 and forms a fluid tight seal between the fluid flow channels 217 and 218 of the central section 204 d of the heat transport element 204 and the vapor manifold 211 of the lower section 204 e of the heat transport element 204. The walls 131 divide the interior of the heat transport element 204 into three separate fluid circulation regions corresponding to the sections 204 c to 204 e of the heat transport element 204.
There is a gap 223 between the edge of the central sheet 216 of the central section 204 d of the heat transport element 204 and the wall 231. This gap 223 allows water to flow between different ones of the fluid flow channels 217 and 218. The gap 223 extends along the side wall 231, and forms a fluid manifold 224 interconnecting all of the front and rear fluid flow channels 217 and 218 of the central section 204 d.
In the fourth embodiment the heat exchanger 207 comprises a cylindrical tube assembly 234 which extends within the elongate heat transfer chamber or vapor manifold 211 along substantially the entire length of the elongate heat transfer chamber or vapor manifold 211. The cylindrical tube assembly 234 comprises an inner concentric tube 234 a and an outer concentric tube 234 b. The inner and outer concentric tubes 234 a and 234 b run parallel to the sides of the vapor manifold 211, such as the upper surface 204 a and the projecting section 210, and extend along substantially the entire length of the vapor manifold 211. The outer concentric tube 234 b extends slightly further than the inner concentric tube 234 a, the outer concentric tube 234 b is sealed by an end cap, and the inner concentric tube 234 a is open ended, so that the inner and outer concentric tubes 234 a and 234 b form a single fluid flow path.
In use, the first fluid passes through the cylindrical tube assembly 234, so that the first fluid passes through the inner concentric tube 234 a along substantially the entire length of the vapor manifold 211, then moves outwardly into the outer concentric tube 234 b, and travels through an annular channel 234 d defined between the inner concentric tube 234 a and the outer concentric tube 234 b back along substantially the entire length of the vapor manifold 211.
At each edge of the heat transport element 204 the substantially semi-cylindrical outwardly projecting section 210 extending most of the width of the heat transport element 204 is closed by an end wall 208. The upper and lower sheets 214 and 215 are sealed by the end walls 208 so that the interior of the heat transport element 204 is sealed. The cylindrical tube 234 passes through the end wall 208 and the end cap 220 and into the support assembly 206. Each cylindrical tube 234 within the vapor manifold 211 forms a heat exchanger 207 and acts to carry heat energy from part of the heat transport element 204 away from the hybrid solar energy converter 201, as will be explained below.
The cylindrical tubes 234 physically support the solar energy collector assembly 202 within the sealed transparent tube 203. There is no other physical support of the solar energy collector assembly 202. As in the previous embodiments this may reduce conductive heat losses from the solar energy collector assembly 202, which may increase the amount of useful heat energy produced by the hybrid solar energy converter 201.
The fluid flow channels 217 and 218 are at least partially filled with degassed distilled water 221 as a working fluid and the interior of the heat transport element 204 including the fluid flow channels 217 and 218 and the vapor manifolds 211 are at least partially evacuated. That is the interior of the heat transport element 204 is below normal atmospheric pressure. The interior of the heat transport element 104 may be under a vacuum at a pressure of 10⁻³mbar.
In the fifth embodiment the amount of water 221 in the fluid flow channels 217 and 218 is similar to the first embodiment except that the interior of each of the sections 204 c to 204 e is sealed off from the others so that the level of the water 221 is independent in each of the sections 204 c to 204 e of the heat transfer element 204.
In each of the three sections 204 c to 204 e the level of the water 221 in the fluid flow channels 217 and 218 is such that the upper surface of the water 221 in the rear fluid flow channels 218 is level with the ends of the rear fluid flow channels 218 where they connect to the vapor manifold 211. In the illustrated fifth embodiment the level of the surface of the water 221 in the front fluid flow channels 217 and rear fluid flow channels 218 is the same. Accordingly, in the illustrated fifth embodiment the rear fluid flow channels 218 are filled with liquid water, while the front fluid flow channels 217 are only partially filled with liquid water.
Similarly to the first embodiment, in other examples the level of the water 221 may be different. In some examples the upper surface of the water 221 in the rear fluid flow channels 218 may be below the vapor manifold 211. In some examples the upper surface of the water 221 in the rear fluid flow channels 218 may be above the bottom of the vapor manifold 211, with some water being present in the bottom of the vapor manifold 211.
It is expected that in practice the heat transport element 204 will operate most efficiently with the upper surface of the water being at, or close to, the point where the lower fluid flow channels 218 contact the vapor manifold 211. If the level of the water in the heat transport element 204 is too high, so that the upper surface of the water is too high within the vapor manifold 211, the efficiency of operation of the heat transport element 204 may be reduced, for the same reasons as are discussed regarding the first embodiment.
The upper surface of the water 221 in the front fluid flow channels 217 may be higher than in the rear fluid flow channels 218 as a result of capillary action. The extent of this capillary effect in any specific example will depend upon the dimensions of the front fluid flow channels 217. In the illustrated fifth embodiment some of the inner surface of the upper sheet 214, that is, the surface forming a part of the upper fluid flow channels 217, is above the surface of the water 221. In some examples the front fluid flow channels 217 may have a small enough cross-sectional area that the upper surface of the water 221 in the front fluid flow channels 217 is at the ends of the front fluid flow channels 217 due to capillary action.
Similarly to the first embodiment, it is not necessary that the inner surface of the front sheet 214, that is, the surface forming a part of the front fluid flow channels 217, is below the surface of the water 221 at a position corresponding to the location of the uppermost parts of the photovoltaic elements 205 for each of the sections 204 c to 204 e of the heat transport element 204. However, in some embodiments this may be the case.
In operation of the fifth embodiment, when the solar energy collector assembly 202 is exposed to incident solar radiative energy, the photovoltaic elements 205 absorb some of this energy, converting a part of the absorbed energy into electrical energy. The remainder of the absorbed energy is converted into heat energy, raising the temperature of the photovoltaic elements 205. The absorbed heat energy flows from the photovoltaic elements 205 into the heat transport element 204, being transmitted through the front sheet 214 and into the water 221 inside the front fluid flow channels 217, which water is in contact with the inner surface of the front metal sheet 214 across the larger parallel faces of the trapezoid front fluid flow channels 217.
The liquid water 221 inside the front fluid flow channels 217 absorbs the heat energy from the photovoltaic elements 205 passing through the front sheet 214 and vaporizes, producing bubbles 222 of steam or water vapor. At the vacuum pressure of 10⁻³mbar inside the front fluid flow channels 217 water boils from around 0° C., so that the water 221 vaporizes readily at the normal operating temperatures of the hybrid solar energy converter 201.
As discussed above regarding the first embodiment, the bubbles 222 of water vapor are less dense than the liquid water 221. Further, as explained above the front fluid flow channels 117 are sloping along their lengths. Accordingly, as a result of this density difference the water vapor bubbles 222 travel upwards along the front fluid flow channels 217 towards the top of the heat transport element 204 and the surface of the water 221. When a bubble of water vapor 222 reaches the surface of the water 221 the vapor is released into the vacuum above the water 221 in the respective vapor manifold 211. Further, the bubbles 222 will give rise to pistonic driving in a similar manner to the first embodiment. In the illustrated fifth embodiment, where some of the inner surface of the upper sheet 214 is above the surface of the water 221, this pumping of liquid water upwards along the upper flow channels 217 ensures that the part of the inner surface of the upper sheet 214 above the surface of the water 221 is in contact with a flow of water so that it can be cooled.
The bursting of the bubbles of water vapor at the water surface and any pistonic pumping of liquid water out of the ends of the front fluid flow channels 217 may generate droplets of liquid water, and may project at least some of these water droplets into the vacuum within the respective vapor manifold 211 above the water surface. As a result, the heat transfer mechanism may be a multi-phase system comprising liquid water, water vapor and droplets of liquid water, and not just a two-phase system comprising liquid water and water vapor only. The presence of such droplets of water in the vacuum, and any pumping of liquid water out of the ends of the front fluid flow channels 217, may enhance the rate of vaporization by increasing the surface area of the water exposed to the vacuum.
Similarly to the first embodiment, the water vapor in the vacuum within the heat transfer chamber or vapor manifold 211 travels at a very high speed through the vacuum within the vapor manifold 211 into contact with the exterior surface of the outer tube 234 b forming the heat exchanger 207. The travel speed of the hot water vapor in the vacuum is very fast, approximating to the thermal speed of the water vapor molecules. The water vapor condenses on the external surface of the outer tube 234 b, which acts as a heat exchange surface. The condensed water falls off the outer tube 234 b to the bottom of the vapor manifold 211, and is returned back into the water 221 within the lower fluid flow channels 218. This generating of hot water vapor within the upper fluid flow channels 217 and the vapor manifold 211, and the condensing of the hot water vapor on the outer tube 234 b, followed by return of the condensed water into the fluid flow channels 217 and 218, transfers heat energy from the heat transfer element 204 to the first fluid within the tube 234.
Thus, the working fluid is caused to circulate on a working fluid pathway inside the heat transfer device such that the heat of the working fluid is transferred to the heat exchanger in the heat transfer chamber. In the illustrated example the working fluid pathway is formed by the fluid flow channels 217 and 218 and the heat of the working fluid is absorbed from the cooled surface 204 a of the heat transport element 204.
The first fluid flows from the support element 206, through the heat transfer element 204, where it absorbs heat, and the heated fluid then returns to the support element 206. In the illustrated second embodiment the first fluid is water and a pumped water supply passes through the support element 206 and the cylindrical tube 234.
Any liquid water ejected from the front fluid flow channels 217 into a vapor manifold 211 which does not vaporize will also fall to the bottom of the respective vapor manifold 211, and is returned back into the water 221 within the rear fluid flow channels 218 associated with that vapor manifold 211.
The description indicates that water droplets and condensed water falls into the bottom of the vapor manifold 211. In some examples, depending upon the orientation of the collector assembly 202, some or all of this water may fall into the lower fluid flow channels 218 without necessarily contacting the surface of the vapor manifold 211.
The location of the heat exchangers 207 within the heat transfer chambers or vapor manifolds 211 may improve the efficiency of the heat transfer element 204 by providing a short path for water vapor to travel between the upper surface of the working fluid and the heat exchanger 207.
As is explained above all of the front and rear fluid flow channels 217 and 218 in each section 204 c to 204 e of the heat transfer element 204 are interconnected by the respective fluid manifold 224 formed by the respective gap 223. Accordingly, within each section 204 c to 204 e of the heat transfer element 204, it is not important which of the rear fluid flow channels 218 is entered by any liquid water returning from the respective vapor manifold 211.
As is clear from the description above, each heat transfer chamber or vapor manifold 211 generally includes liquid water in addition to water vapor when the hybrid solar energy converter 201 is operating. However, as is also discussed above, if the level of the water in a section 204 c to 204 e of the heat transport element 204 is too high, so that the upper surface of the water is too high within the respective vapor manifold 211, the efficiency of operation of the heat transport element 204 may be reduced. This reduction in efficiency of operation may occur because there is insufficient space within the vapor manifold 211 above the surface of the water for the movement and evaporation of the droplets of liquid water. This reduction in efficiency of operation may occur because the droplets of liquid water and waves and splashing upwardly of the liquid water surface may reduce the open, or water free, cross sectional area of the vapor manifold at some locations to a relatively small amount, or even to zero, momentarily closing the vapor manifold. This reduction in the open, or water free, cross sectional area of the vapor manifold may interfere with the movement of the water vapor in the vacuum within the vapor manifold 211.
In a similar manner to the first embodiment the bubbles 222 of water vapor will tend to move upwardly through the liquid water in the front fluid flow channel 217 because of the lower density of the water vapor compared to the liquid water 221, which will result in an upward buoyancy force on each bubble 222. Further, the movement of the bubbles 222 of water vapor will tend to drive the liquid water 221 in the front fluid flow channel 217 upwardly, particularly in examples where pistonic driving takes place. As a result, the bubbles 222 of water vapor cause the water 221 in the front and rear fluid flow channels 217 and 218 in each section 204 c to 204 e to circulate, with relatively hot liquid water and bubbles 222 of water vapor flowing upwards along the front fluid flow channels 217, and relatively cool liquid water flowing downwards along the rear fluid flow channels 218. The front and rear fluid flow channels 217 and 218 are interconnected by the vapor manifold 211 and the fluid manifold 224, as explained above. Accordingly, the relatively hot liquid water flowing upwards along the front fluid flow channels is continuously replaced by relatively cool liquid water from the rear fluid flow channels 218. This circulation is driven primarily by the difference in density between the water vapor and the liquid water. However, this circulation may also be driven by convection as a result of the difference in density between the relatively hot liquid water in the front fluid flow channels 217 and the relatively cool liquid water in the rear fluid flow channels 218, in a similar manner to a thermosiphon. Accordingly, the front fluid flow channels 217 may be regarded as riser channels, while the rear fluid flow channels 218 may be regarded as sinker channels or return channels.
As the bubbles 222 of water vapor travel upwardly along the front fluid flow channels 217 the pressure head acting on the bubbles 222 decreases, so that the bubbles 222 tend to expand. As a result, the tendency of the vapor bubbles 222 to collapse and implode is reduced by the effects of the expansion and decreasing pressure as the bubbles 222 move upwardly. When considering this point, it should be remembered that when the heat transport element 204 is operating the bubbles 222 will be forming within established density driven circulation fluid flows and will move upwardly carried by these flows in addition to the bubbles movement due to their own buoyancy relative to the liquid water. Further, it is believed that expansion of the bubbles 222 as they move upwardly will further increase the speed of the density driven circulation flow by increasing the buoyancy of the expanding bubbles 222. In some examples expansion of the bubbles as they move upwardly may also increase the degree of pistonic driving.
This density driven circulation may form a highly effective heat transport mechanism because water has a relatively high enthalpy of vaporization, so that the movement of the bubbles 222 of water vapor may carry a large amount of heat energy, in addition to the heat energy carried by the movement of relatively hot water out of the front fluid flow channels 217, and its replacement by cooler water. In arrangements where pistonic driving of the flow of the liquid water by the water vapor bubbles takes place the effectiveness of the heat transport mechanism may be further increased by the increase in the flow rate of the liquid water caused by the pistonic driving. This pistonic driving is a component of the overall density driving producing the density driven circulation. The pistonic driving is caused by the density difference between the liquid water and the bubbles of water vapor.
In general, the speed of the density driven circulation increases and the effectiveness of the heat transport mechanism increases as the temperature of the upper sheet 214 of the heat transport element 204 increases.
The density driven circulation of the water 221 within the fluid flow channels 217 and 218 is a vapor driven circulating or rolling flow.
The density driven circulation of the water 221 within the fluid flow channels 217 and 218 becomes particularly vigorous, and becomes particularly effective as a heat transport mechanism, when the temperature of the upper sheet 214 of the heat transport element 204 becomes sufficiently high that the water 221 within the fluid flow channels 217 and 218 enters a rolling boil state. The effectiveness of the heat transport mechanism significantly increases when rolling boiling of the water 221 commences. In general, when other parameters of the system remain constant, entry into the rolling boil state will take place when the temperature of the front sheet 214 of the heat transport element 204 reaches a specific temperature.
In the illustrated examples using water, the water 221 within fluid flow channels 217 and 218 may enter a rolling boil state at a temperature of about 40° C.
The arrangement of the heat transfer element 204 into sections 204 c to 204 e with separate fluid flow channels 217 extending along the heat transport element 104 may allow the vertical height of the liquid water in each section 204 c to 204 e of the heat transport element 204 to be reduced compared to embodiments in which the density driven flow extends along the length of a heat transport element, and so reduce the pressure head acting on the liquid water at the bottom of the heat transport element 204. In general, increased pressure reduces the tendency of liquids to vaporize and so increases the boiling point of liquids. Accordingly, reducing the pressure head acting on the liquid water at the bottom of the heat transport element 204 may increase the tendency of the liquid water 221 in the front fluid flow channels 217 to vaporize and produce bubbles 222, and so may improve the efficiency and effectiveness of the heat transport element 204.
In particular, the reduction of the pressure head acting on the liquid water at the bottom of the front fluid flow channels 217 may reduce any temperature differential along the lengths of the front fluid flow channels between their the top and bottom ends by reducing any difference in the tendency of the liquid water to vaporize due to differences in pressure. This may reduce temperature differentials between the different points on the heat transport element 204 and may avoid the formation of hot spots in the photovoltaic elements 205. Accordingly, reducing the pressure head acting on the liquid water at the bottom of the heat transport element 204 may make the temperature of the front sheet 214 of the heat transport element 204 more isothermal.
The arrangement of fluid flow channels 217 extending longitudinally along the heat transport element 204 and interconnected by vapor manifolds 211 extending laterally across the heat transport element 204 may allow a very rapid flow of heat energy along the heat transport element 204 away from any fluid flow channel 217 having a higher temperature. This may reduce temperature differentials between the different points on the heat transport element 204 and may reduce, or avoid, the formation of hot spots in the photovoltaic elements 205.
The provision of the two separate heat transport mechanisms of the movement of water vapor along the vapor manifold 211 and the density driven flow of liquid water and water vapor along each of the front fluid flow channels 217, respectively acting longitudinally and transverse the length of the heat transport element 204 may tend to equalize the temperature across the entire upper surface of the heat transport element, and thus tend to equalize the temperature across the photovoltaic elements 205 and reduce, or avoid, the formation of hot spots.
The movement of water vapor along the vapor manifold 211 provides a very rapid heat transport mechanism that tends, by the vaporization and condensation of water, to move heat energy from relatively hot locations to relatively cold locations. As a result, the movement of water vapor along the vapor manifold 211 may tend to equalize the temperature of the liquid water surface at different positions across the heat transfer element 204, in addition to transporting heat energy from the heat transport element 204 to the heat exchanger 107 formed by the tube 234. This temperature equalization may have the effect of removing more heat energy from hotter parts of the heat transport element 204, and so tending to equalize the temperature across the front surface of the heat transport element 204. It is clear that such isothermal cooling will tend to reduce, or avoid, the formation of hot spots, for example in any photovoltaic element attached to the front surface of the heat transport element 204.
Similarly to the first embodiment, the rear sheet 215 of the heat transport element 204 has a plurality of hollow ridges 225 extending between the flat part of the rear surface 204 b and the semi-cylindrical surface of each outwardly projecting section 210. Each hollow ridge 225 has a ‘V’ profile, and the hollow ridges 225 are located spaced apart at regular intervals along the length of each outwardly projecting section. The hollow ridges 225 act as supports for the outwardly projecting sections 210, and also act as drains to return liquid water from the vapor manifolds 211 into the rear fluid flow channels 218 in a similar manner to the hollow ridges 125 of the first embodiment.
The hollow ridges 225 may extend the range of angles of inclination at which the heat transport element 204 can be used, as explained above regarding the first embodiment.
Depending upon the geometry of the different parts of the heat transport element 204 in any specific design, even when the hollow ridges 225 are used there may still be a minimum angle of inclination at which the heat transport element 204 can operate without the retention of liquid water in the vapor manifolds 211 having adverse effects on operation of the heat transport element 204.
The corrugated profile of the central sheet 216 and the bonding of the central sheets 216 to the front sheet 214 and the rear sheet 215 increases the strength and rigidity of the heat transport element 204, and may reduce or prevent ballooning for the reasons discussed regarding the second embodiment. This may make the heat transport element 204 a more rigid structure. This may tend to reduce the amount of flexing of the heat transport element 204 in use. This may prevent damage to the photovoltaic elements 205 by reducing the amount of mechanical stress applied to the photovoltaic elements 105. This may allow the front, rear, and/or central sheets 214, 215, 216, to be thinner, which may reduce weight and costs. This may allow the front sheet 214 to be thinner, which may improve the transfer of heat from the photovoltaic elements 205 into the liquid water within the front fluid flow channels 217.
The heat transport element 204 is a substantially rigid structure. This may minimize changes in the level of the upper surface 232 of the water 221 due to flexing of the components of the heat transport element 204, such as the upper and lower sheets 214 and 215. Such changes in the level of the upper surface 232 of the water 221 may affect the efficiency of the cooling of the photovoltaic elements 205.
As is explained above, the interior of the heat transport element 204 is evacuated, and the heat transport element 104 is located within an evacuated tube 203. Usually the heat transport element 204 and the evacuated tube 203 are evacuated to the same pressure. In the illustrated example of the second embodiment described above this pressure may be 10⁻³mbar.
The interconnection of the front and rear sheets 214 and 215 by the linking surfaces of the central sheet 216 may resist ballooning of the front and rear sheets 214 and 215 and reduce or prevent ballooning. Arranging for the linking surfaces of the central sheet 216 to be straight may increase the resistance to ballooning. Reducing or preventing ballooning may prevent damage to the photovoltaic elements 205 by reducing the amount of mechanical stress applied to the photovoltaic elements 205. This may allow the front sheet 214 to be thinner, which may reduce weight and costs and/or may improve the transfer of heat from the photovoltaic elements 205 into the liquid water within the front fluid flow channels 217.
For the same reasons as explained with regard to the first embodiment it is preferred for the sizes of the surfaces of the central sheets 216 in contact with the front sheet 214 to be as small as possible, subject to the contact area between the central sheets 216 and the upper sheet 214 being sufficiently large to form a reliable bond of the required strength.
In the illustrated example of the fifth embodiment 0.2 mm thick tin coated mild steel sheets are used to form the different sheets of the heat transport element. In alternative examples other thicknesses may be used, in particular 0.1 mm thick tin coated mild steel sheets may be used.
In the illustrated example of the fifth embodiment the spacing between the front sheet 214 and the parallel parts of the rear sheet 215 is 1.8 mm at the locations of the recesses. Accordingly, the thickness of the fluid flow channels 217 and 218 at the locations of the recesses is 1.6 mm, since the thickness of the central sheet is 0.2 mm.
The sheets used to form the heat transport element may be shaped by pressing.
In the illustrated fifth embodiment the heat transport element 204 is arranged to be horizontal transversely to longitudinal axis. That is, the vapor manifolds 211 should be horizontal. However, in practice some deviation from the horizontal may be tolerated without significant impact on the operation of the heat transport element 204. Such deviation from the horizontal will result in differences in the level of the liquid water surface relative to the structure of the heat transport element 204 at different positions along the length of each vapor manifold 211. As is explained above, the level of the liquid water surface may be varied. Accordingly, the minor differences in level caused by small deviations from the horizontal may be accommodated.
The front and rear sheets 214 and 215 of the fifth embodiment have a dimpled profile similarly to the upper and lower metal sheets 114 and 115 of the second embodiment.
As discussed above the heat transport element 204 has a flat front surface 204 a formed by a front sheet 214 with a dimpled profile. In addition, the front sheet 214 is has two longitudinal recesses running across in its front surface 204 a which form two parallel troughs running along the upper surface 204 a of the heat transport element 204 behind the photovoltaic elements 205. Similarly to the first embodiment electrically conductive ribbons or wires run along the longitudinal recesses between the heat transport element 204 and the photovoltaic elements 205. The wires are electrically connected to the photovoltaic elements 205 and to the conductors 21 which pass through the cap 12 to provide a conductive path to carry the electrical power generated by the photovoltaic elements 205 out of the sealed transparent tube 203. This electrical power may be supplied to an inverter for voltage conversion and/or for conversion to alternating current for supply to a domestic or mains electrical system.
In examples where adhesive is used to attach the photovoltaic elements 205 to the heat transport element 204, an electrically insulating adhesive can be used in a similar manner to the second embodiment.
In the fifth embodiment the longitudinal recesses run parallel to the fluid flow channels 217 and 218. Accordingly, each of the longitudinal recesses can be accommodated by reducing the thickness of one of the front fluid flow channels 217 in each section 204 c to 204 e of the heat transfer element 204.
In the illustrated example of the fifth embodiment the spacing between the front sheet 214 and the parallel rear sheet 215 is 1.8 mm at the locations of the longitudinal recesses 129. Accordingly, the thickness of the front fluid flow channels 217 at the locations of the longitudinal recesses is 1.6 mm, since the thickness of the central sheet is 0.2 mm.
The heat transport element of the fifth embodiment may be formed using the same materials and bonding techniques as in the first embodiment.
In the illustrated example of the fifth embodiment the flow of water vapor and liquid water through the heat transport element 204 tends to keep the cooled front surface of the heat transport element 204 at a uniform operating temperature during operation. That is, the cooled upper surface of the heat transport element 104 tends to be kept isothermal. The isothermal nature of the cooled upper surface of the heat transport element 104 tends to give rise to isothermal cooling of the photovoltaic elements 105, where hotter parts of the photovoltaic elements 105 tend to be preferentially cooled so that the photovoltaic elements 105 themselves tend to become isothermal
Such isothermal cooling provides further advantages in addition to those provided by cooling.
Isothermal cooling may provide the advantage that the appearance of hot spots or regions in the photovoltaic elements 205 produced by heating by incident solar radiation can be reduced or eliminated. Such hot spots or regions can reduce the efficiency of the photovoltaic elements 205.
Isothermal cooling may simplify the control and wiring arrangements of the photovoltaic elements 205 by reducing or eliminating any requirement for compensation for differences in the performance of the different parts of the photovoltaic elements 205 that are at different temperatures.
Isothermal cooling tends to reduce, or prevent, the formation of hot spots or regions in the photovoltaic elements 205. As is explained above, this may allow the efficiency of the photovoltaic elements 205 to be improved at a specific temperature. Further, this may reduce the amount of degradation of the photovoltaic elements 205 caused by higher temperatures.
Still further, this may allow the photovoltaic elements 205 to operate with a given degree of efficiency at a higher temperature than would otherwise be the case. This may allow the solar energy collector assembly 202 including the photovoltaic elements 205 to be operated at a higher temperature without reducing the efficiency with which the photovoltaic elements 205 produce electrical energy.
One example of this effect of isothermal cooling is that the general figure quoted above for silicon photovoltaic elements that the efficiency of electrical energy generation generally drops by about 0.35% to 0.5% for each degree centigrade of temperature increase above 25° C. may not apply to silicon photovoltaic elements that are isothermally cooled. Such isothermally cooled silicon photovoltaic elements having hotspots eliminated or reduced may have a higher threshold temperature at which the efficiency of electrical energy generation begins to drop and/or may have a reduced rate of reduction in efficiency for each degree centigrade of temperature increase above the threshold temperature. Further, the temperature at which there is a risk of permanent degradation of the silicon photovoltaic elements may also be increased for isothermally cooled silicon photovoltaic elements. Similar effects may be found in photovoltaic elements formed of other semiconductor materials.
In some examples, one or more layers of heat conductive material may be located between the upper sheet 214 and the photovoltaic elements 205. Such layers of heat conductive material may increase the rate of heat transfer between the photovoltaic elements 205 and the front sheet 214, and thus the rate of heat transfer between the photovoltaic elements 205 and the liquid within the front fluid flow channels 217. Such layers of heat conductive material may also increase the rate of heat transfer laterally across the photovoltaic elements 205.
Accordingly, providing a layer of heat conductive material may increase the degree of isothermal cooling and further tend to reduce, or eliminate, the formation of hot spots or regions in the photovoltaic elements 205.
The heat transport element may be used in other applications separately from the rest of the solar energy converter.
In some examples control methods can be used to control the temperature of the solar energy collector assembly 202. In some examples the temperature of the solar energy collector assembly 202 may be controlled by changing the rate of removal of heat energy from the solar energy collector assembly 202.
In some examples the rate of removal of heat energy from the solar energy collector assembly 202 can be controlled by altering the flow rate of the first operating fluid passing through the tube 234 forming the heat exchanger 207.
In some examples the rate of removal of heat energy from the solar energy collector assembly 202 can be controlled by altering the vacuum pressure within the tube 203. This may change the rate of convective heat loss from the solar energy collector assembly 202 to the tube 203. In general, heat transferred to the tube 203 will be rapidly lost to the outside environment by convection and/or conduction.
In some examples the rate of removal of heat energy from the solar energy collector assembly 202 can be controlled by altering the vacuum pressure within sections 204 c to 204 e of the heat transport element 204. In general, the tendency of the liquid water within the front fluid flow channel 217 to vaporize and form bubbles of vapor 222 will increase as the vacuum pressure is reduced, and the tendency of the liquid water within the front fluid flow channel 217 to vaporize and form bubbles of vapor 222 will decrease as the vacuum pressure is increased. As is explained above, the density driven circulation of water around the front and rear fluid flow channels 217 and 218 and the transport of heat energy along the vapor manifolds 211 and the tubes 219 are both driven by water vapor. Accordingly, altering the tendency of the liquid water to vaporize by altering the vacuum pressure may allow the rate of removal of heat energy from the solar energy collector assembly 202, and the rate of removal of heat energy from the photovoltaic elements 205 to be controlled, and so allow the temperature of the solar energy collector assembly 202 and photovoltaic elements 205 to be controlled.
Further, the temperature at which rolling boiling of the water 221 within the front fluid flow channels 217 commences will tend to increase as the vacuum pressure is increased, and will tend to decrease as the vacuum pressure is decreased. Accordingly, in examples where the vacuum pressure within the heat transport element 204 is altered the temperature at which the water 221 within the front fluid flow channels 217 commences rolling boiling can be changed.
As is explained above, the density driven circulation of water around the front and rear fluid flow channels 217 and 218 becomes particularly vigorous, and becomes particularly effective as a heat transport mechanism, when the water 221 within the front fluid flow channels 217 enters a rolling boil state. Accordingly, altering the temperature at which the water 221 within the front fluid flow channels 217 commences rolling boiling by altering the vacuum pressure may allow the rate of removal of heat energy from the solar energy collector assembly 202 and photovoltaic elements 205 to be controlled, and so allow the temperature of the solar energy collector assembly 202 and photovoltaic elements 205 to be controlled.
In some examples the temperature of the solar energy collector assembly 202 may be controlled by changing the amount of solar energy incident on the solar energy collector assembly 202, and so changing the rate of absorption of heat energy by the solar energy collector assembly 202.
In some examples the amount of incident solar energy may be controlled by changing the orientation of the solar energy collector assembly relative to the direction of the incident solar energy. This can be carried out using a drive mechanism able to rotate the solar energy collector assembly about one or more axes.
In some examples the amount of incident solar energy may be controlled using adjustable light intercepting or blocking mechanisms in the path of the incident solar energy. In some examples variable filters, shutters, stops, or the like may be used. In some examples these adjustable light intercepting or blocking mechanisms may comprise physical devices. In some examples these adjustable light intercepting or blocking mechanisms may comprise devices having electronically controlled optical characteristics, such as liquid crystals.
In examples where the temperature of the solar energy collector assembly and/or the photovoltaic elements are to be controlled, a temperature sensor and a temperature controller may be provided, together with a temperature control mechanism arranged to carry out one, some, or all, of the methods of controlling temperature described above.
The temperature sensor is arranged to measure the temperature of the solar energy collector assembly and provide this temperature value to the temperature controller. The temperature controller can then operate the temperature control mechanism in a suitable manner to control the temperature of the solar energy collector assembly to the desired value.
Examples where the temperature of the photovoltaic elements is to be controlled a temperature sensor arranged to measure the temperature of a photovoltaic element or elements and provide this temperature value to the temperature controller may be provided. This may be additional to, or instead of, the temperature sensor arranged to measure the temperature of the solar energy collector assembly. The temperature controller can then operate the temperature control mechanism in a suitable manner to control the temperature of the photovoltaic element or elements to the desired value.
In some examples the temperature sensor can be provided on the upper surface of the solar energy collector assembly. In some examples the temperature sensor can be formed on the same semiconductor wafer as a photovoltaic element.
Conveniently, the temperature controller may be a suitably programmed general purpose computer.
In the illustrated fifth embodiment, the heat transport element 204 is divided into three sections 204 c to 204 e, each of which has a separate heat transfer system comprising a number of front and rear fluid flow channels 217 and 218, a vapor manifold 211, and a tube 234. Each of these separate heat transfer systems operates in a similar manner to the first embodiment described above. In other examples the heat transport element 204 may be divided into a different number of sections, each having a separate heat transfer system.
In the illustrated fifth embodiment the tubes 234 each extend outwardly from the side of the heat transport element 204, then turn through a right angle and extend parallel to the axis of the tube 203 to pass through the end cap 220 of the tube 203. In other examples, the tubes 234 may be arranged differently. In some examples the tubes 234 may be interconnected for mutual support. This may improve the support provided to the heat transport element 204. The tubes 234 connect the respective heat exchangers 207 to the support structure 206, and may be regarded as a heat exchange network.
In the illustrated fifth embodiment the tubes 234 each extend outwardly from the end of a respective vapor manifold 211. In some examples the tubes 234 may extend from a different part of the respective vapor manifolds 211. In some examples the tubes 234 may extend from different parts of the respective vapor manifolds 211 from one another.
In the illustrated fifth embodiment the different sections 204 c to 204 e of the heat transport element 204 are each divided by a wall 231 extending between the front and rear sheets 214 and 215 to form a fluid tight seal between the fluid flow channels of the different sections. In other examples a different sealing structure could be used. In some examples the front and rear sheets 214 and 215 could be brought into contact to form the fluid tight seal. In some examples the rear sheet 215 could be bent towards the flat front sheet 214 to contact the front sheet 214 and form the fluid tight seal. In some examples the rear sheet 215 may be shaped by pressing.
The illustrated fifth embodiment is a hybrid solar energy converter comprising photovoltaic elements and arranged to convert incident solar radiation into outputs of both electrical energy and hot water. In other examples the photovoltaic elements may be omitted to provide a solar energy converter arranged to convert incident solar radiation into an output of hot water.
The illustrated example of the fifth embodiment has a heat exchanger comprising concentric tubes according to the third embodiment. In other examples the fifth embodiment may have a heat exchanger comprising tubes according to those of the first, second or fourth embodiments.
In the illustrated embodiments the heat exchanger is formed by simple smooth tubes. In other examples the heat exchanger tube or tubes could be shaped or surface profiled to increase their surface area and/or to encourage and increase contact between the different fluids and the surfaces. In some examples the surfaces may be convoluted, threaded and/or spiraled. In some examples the tubes may contain flow controlling or modifying structures to increase or improve the contact between the first fluid and the walls of the tube or tubes forming the heat exchanger. In some examples the flow controlling or modifying structure may comprise a helical insert within the tube.

Temperature Control

The embodiments described above may further comprise, in addition to the described heat exchanger, an additional secondary heat exchanger and a heat transfer control valve. The secondary heat exchanger may be connected to the vapor manifold by a vapor passage or pipe with the heat transfer control valve arranged to selectively allow, or prevent, the transfer of heat energy from the heat transport element to the secondary heat exchanger.
The heat transfer control valve is able to selectively allow, or prevent, the transfer or transport of heat energy from the heat transport element to the secondary heat exchanger. Accordingly, the degree of cooling applied to the photovoltaic elements can be varied.
In some arrangements the heat energy transferred to the secondary heat exchanger is transferred into ambient air and allowed to escape and the secondary heat exchanger is used, under the selective control of the heat transfer control valve, to release heat energy in order to regulate the temperature of the solar energy collector assembly.
The trigger temperature of the heat transfer control valve at which the valve opens may be predetermined. In some examples the trigger temperature may be settable in use, or on installation or manufacture of the hybrid solar energy converter. In some examples the trigger temperature may be settable to different values depending on the intended maximum water temperature of the water to be heated. In particular, in some examples the trigger temperature may be settable to 65° C. when the hybrid solar energy converter is to be used to heat water for a domestic hot water system and may be settable to 135° C. when the hybrid solar energy converter is to be used to heat water for an industrial hot water system.
In some examples the trigger temperature of the heat transfer control valve may be selected to maximize the generation of electrical energy by the photovoltaic elements. In some examples the trigger temperature value may be selected to increase the amount of heat energy transferred to the first operating fluid. In some examples the trigger temperature may be selected to optimize the overall production of energy, taking into account both the amount of electrical energy produced by the photovoltaic elements and the amount of heat energy transferred to the first operating fluid. In some examples the optimizing may maximize the total production of energy. In some examples the optimum overall production of energy may take into account the relative demand for, or value of, the different types of energy, rather than simply maximizing the total amount of energy produced.
As explained above, the isothermal cooling tends to reduce, or prevent, the formation of hot spots or regions in the photovoltaic elements. This may allow the solar energy collector assembly including the photovoltaic elements to be operated at a higher temperature without reducing the efficiency with which the photovoltaic elements produce electrical energy. This may allow the temperature of the collector assembly to be increased to produce more useable heat energy without the increase in temperature reducing the efficiency with which the photovoltaic elements produce electrical energy. This may allow the trigger temperature to be increased.
In some examples the trigger temperature may be set to different temperatures during use of the hybrid solar energy converter. This may allow the temperature of the collector assembly to be controlled to produce different amounts of useable heat energy or electricity depending upon which type of energy is most in demand at a specific time.
For example, when hot water is more in demand than electricity the valve may be closed to pass hot water vapor from the heat transport element only to the heat exchanger to maximize the amount of heat applied to the water acting as the first operating fluid regardless of any temporary reduction in efficiency of the photovoltaic elements as a result of any resulting increase in temperature of the collector assembly. Further, when hot water is less in demand than electricity, the valve may be opened in order to pass hot water vapor from the heat transport element to both of the heat exchangers in order to cool the photovoltaic elements as much as possible and maximize the efficiency of electricity generation regardless of the effects on the temperature of the water acting as the first operating fluid.

Alternative Collector Arrangements

The illustrated embodiments all employ a single substantially flat collector assembly within a tube. Other arrangements may be used.
In some examples the collector assembly may be curved. The curved collector assembly may be arranged to have a curved outer surface concentric with a cylindrical tube within which the collector assembly is mounted. This may allow a collector assembly having a greater surface area to be fitted within a cylindrical tube of a particular size. The curved collector assembly may have curved photovoltaic elements mounted on it.
Some examples may mount multiple collector assemblies within a single tube.
Some examples may mount multiple collector assemblies at different angles within a single tube. In examples where the collector assemblies and the tube are fixed this may allow the efficiency of the collector to be increased by arranging the different collector assemblies at angles adapted to more efficiently collect energy at different times of day.
In some examples mirrors and/or lenses may be associated with the hybrid solar energy converter to direct or focus incident solar energy onto the collector assembly. Such mirrors may be flat or curved. Such mirrors and/or lenses may be fixed or moveable. In some examples moveable mirrors or lenses may be arranged to track the sun.
In some examples the transparent tube may incorporate a lens to direct or focus incident solar energy onto the collector assembly. In some examples the transparent tube may incorporate a Fresnel lens.
In the illustrated examples the first fluid is water. In other examples other fluids may be used, which may be liquids, vapors or gasses.

Sun Tracking

The embodiments described above are solar energy converters which convert incident solar radiation into useable electrical and/or heat energy.
In some examples the collector assemblies of the solar energy converters may be arranged to change their orientation to follow the apparent movement of the sun across the sky, or track the sun. This may increase the amount of solar radiation energy incident on the collector assemblies, for well-known geometric reasons, and so may increase the amount of useable electrical and/or heat energy produced.
FIG. 18 shows a general view of a sixth embodiment of a solar energy converter 300 arranged to be able to change orientation to track the sun.
The solar energy converter 300 comprises a sealed transparent tube 301 containing a solar energy collector assembly 302 and mounted to a heat exchange assembly 303. The solar energy converter 300 may be a solar energy converter according to any of the embodiments disclosed herein. Sun tracking arrangements may be added to any of the embodiments.
In the illustrated example of the sixth embodiment the sealed transparent tube 301 is cylindrical and has an axis 304. The sealed transparent tube 301 is mounted for rotation about the axis 304 together with the solar energy collector assembly 302 mounted within the tube 301. A drive motor 305 is arranged to rotationally drive the tube 301 through a transmission mechanism 306. In the illustrated example the transmission mechanism 306 is a cog and chain transmission mechanism.
By selectively operating the drive motor 305 based on the time and date, the sealed transparent tube 301 and solar energy collector assembly 302 can be rotated to follow the sun as the apparent position of the sun changes as a result of the rotation of the earth.
Adding such a solar tracking drive system may increase the amount of energy gathered by the solar energy collector assembly by about 20%.
FIG. 19 shows a general view of a seventh embodiment of an array 307 of solar energy converters 300, In FIG. 19 a plurality of solar energy converters 300 according to the sixth embodiment are mounted to form an array 307. Each of the solar energy converters 300 comprises a sealed transparent tube 301 containing a solar energy collector assembly 302 and mounted to a heat exchange assembly 303. Each sealed transparent tube 301 is mounted for rotation about an axis 304 together with the solar energy collector assembly 302 mounted within the tube 301. The transparent tubes 302 are mounted on the array 310 so that their respective axes of rotation 304 are parallel.
A drive motor 311 is arranged to rotationally drive the tubes 301 of the array 310 in synchrony through a transmission mechanism 312. In the illustrated example of the seventh embodiment the transmission mechanism 312 is a cog and chain transmission mechanism.
The array 310 is mounted on a turntable 313 for rotation about an axis 314 perpendicular to the axes 304. A drive motor 315 is arranged to rotationally drive the turntable 313 through a transmission mechanism 316. In the illustrated example the transmission mechanism 316 is a geared transmission mechanism.
By selectively operating the drive motors 305 and 315 based on the time and date, the sealed transparent tubes 301 and solar energy collector assemblies 302 of the array 310 can be rotated to follow the sun as the apparent position of the sun changes as a result of the rotation of the earth.
Adding such a dual axis solar tracking drive system may increase the amount of energy gathered by the solar energy collector assemblies 302 by up to about 48%.
In the examples of FIGS. 18 and 19, the operating of the drive motor or motors should take into account the location of the solar energy converter or converters 300.
FIG. 20 shows a general view of a eighth embodiment of a solar energy converter 400 arranged to be able to change orientation to track the sun.
The solar energy converter 400 comprises a sealed transparent tube 401 containing a solar energy collector assembly 402 and mounted to a heat exchange assembly 403. The solar energy converter 400 may be a solar energy converter comprising a heat transport device according to any of the first to sixth embodiments described above. Sun tracking arrangements may be added to any of the embodiments.
In the illustrated example of the eighth embodiment the sealed transparent tube 401 is cylindrical and has an axis 404. The sealed transparent tube 401 has two opposed open ends sealed by respective end caps 420. The solar energy collector assembly comprises a heat transport element 404 according to any of the first to sixth embodiments covered by photovoltaic elements. The heat transport element 404 is cooled by heat exchanger supplied with a first fluid through tube sections 405, which pass through the end cap 420 at one end of the transparent tube 401.
The heat transport element 404 is supported at one end by the tube sections 405 as discussed above. In order to support the other end of the heat transport element 404 inward projections 406 are provided on an inner face of the end cap 420. These inward projections 406 are arranged to allow sliding movement of the heat transport element 404 parallel to the axis of the transparent tube 401 in order to accommodate differential thermal expansion of the heat transport element 404 and the transparent tube 401.
The sealed transparent tube 401 is mounted for rotation about an axis 407 midway between the tube sections 405 together with the solar energy collector assembly 402 mounted within the tube 401.
In the illustrated example the heat transport element 404 is supplied with fluid through pipes 405 passing through an end cap 420 at one end only of the transparent tube 401. In other examples the heat transport element may be supplied by a single tube passing through an end cap 420 at one end only of the transparent tube 401, or by tubes passing through the end caps 420 at both ends of the transparent tube 401. In examples where a single tube passes through the end cap at each end of the transparent tube it is preferred that positions where these tubes pass through the respective end caps are aligned. In examples where only a single tube passes through the end cap at one or both ends of the transparent tube the transparent tube may be mounted for rotation about an axis coincident with the tube.
In other examples tube may be mounted for rotation about the axis of the tube.
In other examples the heat transport element 404 may be supported only at one end by the tube sections 405.
A solar tracking drive system may be arranged to selectively rotate the solar energy converter 400 so that the sealed transparent tube 401 and solar energy collector assembly 402 can be rotated to follow the sun as the apparent position of the sun changes as a result of the rotation of the earth. Carrying out such rotation may increase the amount of energy gathered by the solar energy collector assembly by about 20%.
FIG. 21 shows general view of a ninth embodiment of a solar energy converter array 500 arranged to be able to change orientation to track the sun.
In FIG. 21 a plurality of solar energy converters 400 according to the eighth embodiment are mounted to form an array 500. The solar energy converters 400 are mounted horizontally in a frame 501, and are arranged for rotation about their respective axes 407. The solar energy converters 400 are arranged with their respective axes of rotation 407 horizontal and parallel. The array 500 comprises suitable motors and drive mechanisms located within the frame 501 to carry out rotation of the solar energy converters 400, but these are not visible in the figures.
The array 500 is arranged to synchronously rotate the solar energy converters 400 about their respective axes 407. In other examples the array 500 may be arranged to allow separate rotation of the individual solar energy converters 400.
The frame 501 comprises fluid supply tubes 502 and a fluid supply network allowing the first fluid to be supplied to and from each of the heat transport elements 404 of the solar energy converters 400. In the illustrated example the first fluid is water.
The frame 501 is mounted for rotation about a vertical axis on a bearing section 503 to allow the array 500 to change orientation to track the sun. The vertical axis of rotation of the frame 501 is perpendicular to the axes of rotation of the individual solar energy converters 400. The array 500 comprises a suitable motor and drive mechanism located within the frame 501 to carry out rotation of the array 500, but these are not visible in the figures.
By selectively rotating the solar energy converters 400 and the array 500 based on the time and date, the sealed transparent tubes 401 and solar energy collector assemblies 402 can be rotated to follow the sun as the apparent position of the sun changes as a result of the rotation of the earth.
Adding such a solar tracking drive system may increase the amount of energy gathered by the solar energy collector assembly by about 48%.
In general, it is not necessary to rotate the solar energy converters 400 freely, but only through a limited angular range. Accordingly, it may not be necessary to use fully rotating joints to connect the tube sections 405 to the fluid supply tubes 502. In some examples coiled pipes allowing a limited range of angular movement by coiling or uncoiling as the solar energy converters 400 rotate may be used. Where there are two tube sections 405 connected to a solar energy converter 400 they may be coiled in opposite senses to reduce any change in the torsional forces they apply to the solar energy converter 400 as it rotates.
In the illustrated example there are six solar energy converters 400 in the array 500. In other examples a different number of converters 400 may be used.
In the illustrated example the solar energy converters are arranged horizontally. In other examples they may be arranged in other orientations. In one example they may be arranged vertically.
In the illustrated example the solar energy converters are arranged for rotation about respective horizontal axes. In other examples they may be arranged to rotate about axes with other orientations. In one example they may be arranged to rotate about respective vertical axes.
In the illustrated example the array is arranged for rotation about a vertical axis. In other examples the array may be arranged for rotation about an axis with a different orientation. In some examples the array may be arranged to rotate about an axes perpendicular to the axes of rotation of the solar energy converters.
In examples where the solar collectors can be rotated about one or two axes to follow the sun, rotation about a single axis may increase the amount of energy gathered by up to about 20%, while rotation about two axes may increase the amount of energy gathered by up to about 48%.
In some examples the solar energy collector assembly may be mounted within the tube for rotation relative to the tube and a drive motor arranged to rotationally drive the solar energy collector assembly only. In such examples a drive mechanism which will not allow air leakage, which would destroy the vacuum within the tube, should be used.
In some examples the solar energy collector assembly, or the solar energy collector assembly together with the tube, may be rotated about an axis other than the axis of the tube.

General

In the description above the level of water within the heat transport elements of the different embodiments is referred to. The references to the level of water refer to the level of water when the heat transport element is cold and the liquid water contains essentially no bubbles of water vapor. It will be understood from the above description that the level of the water will vary during operation of the heat transport elements as water vapor bubbles are formed in the liquid water and burst, and as the liquid water is vaporized and the water vapor condenses.
In the illustrated embodiments the heat transport elements may have an operating temperature range from just over 0° C. to about 270° C. In practice, the operating temperature range for domestic instillations may be limited to a maximum temperature of 95° C., or of 65° C., for safety, and to comply with legal requirements in some jurisdictions. Where silicon photovoltaic elements are used the optimum temperature range to maximize the generation of electricity may be in the range 20° C. to 65° C., or in the range 20° C. to 30° C., or in the range 25° C. to 30° C.
The heat transfer rate of the heat exchanger, that is the rate at which the heat exchanger can transfer heat energy from the heat transfer element to the first respective operating fluids, may be matched to the heat transfer rate of the heat transfer element, that is the rate at which the heat transfer element can transfer heat from the isothermally cooled face of the collector assembly to the heat exchanger assembly, at the expected operating temperature, or over the expected operating temperature range, of the system. This may improve efficiency.
In the illustrated embodiments the first operating fluid is water. In other examples the primary operating fluid may be air.
In other examples the first operating fluids may be fluids other than water and air.
In the illustrated embodiments a transparent tube or envelope is used. In other examples this may be replaced by a translucent or partially opaque tube or envelope.
In general, in all of the embodiments it may be preferred to have the photovoltaic elements as thin as possible to ensure effective cooling of the entire thickness of the photovoltaic elements by the heat transport element. This may assist in preventing localized hot spots of elevated temperature developing within the photovoltaic elements, which hot spots may degrade the performance and reliability of the photovoltaic elements. However, in practice there may be a minimum required thickness of the photovoltaic elements for other reasons, for example physical strength.
In the illustrated embodiments degassed distilled water is used. This may provide the advantage that the tendency to vaporize of the water is maximized, increasing the efficiency of the heat transfer by the thermo siphon. Impurities dissolved in the water, including dissolved gasses, will tend to suppress vaporization of the water.
In some examples the water may contain vaporization enhancing additives to increase the tendency of the water to vaporize. In some embodiments particles of hydrophobic materials may be used, in particular particles of zinc oxide may be used. The particles of hydrophobic molecules may act as nucleating sites, boosting the formation of bubbles of water vapor, without tending to suppress vaporization.
In all of the embodiments, nucleation enhancing structures may be added to the surfaces of the riser channels only, and not the return channels. This may encourage the liquid water to vaporize and form bubbles primarily, or only, in the riser channels even when the water in the riser and return channels are at similar, or the same, temperature. Suitable nucleation enhancing structures may include micropores and/or surface roughening.
In all of the embodiments, pores or apertures may be provided in the sheet separating the riser and return channels to allow water to pass from the return channel to the riser channel. This may improve the circulation of the liquid water and improve the efficiency of the heat transfer.
In the illustrated embodiments water is used as the working fluid within the heat transport element to provide the density driven circulation. In other embodiments other vaporizable liquids, solutions or mixtures may be used. In particular a mixture of water and glycol may be used, ethanol may be used, and a mixture of ethanol and water may be used. Mixtures of dissimilar fluids where one fluid acts as a nucleating agent for another fluid may be used.
In other examples a mixture of 75% water and 25% ethanol may be used as the working fluid within the heat transport element. When a mixture of 75% water and 25% ethanol is used the mixture may enter a rolling boil state at a temperature of about 22° C. In other embodiments the relative proportions of water and ethanol used as the working fluid may be varied in order to set the temperature at which a rolling boil commences to a desired temperature.
As discussed above, the effectiveness of the heat transport mechanism significantly increases when rolling boiling of the working fluid commences. Accordingly, it applications where it is desirable to keep the temperature of the cooled face of the collector assembly below a specific temperature, it may be preferred to select a working fluid, or mixture, which commences rolling boiling at a temperature at or below said specific temperature at the intended vacuum pressure conditions within the heat transfer device.
In the illustrated embodiments the tubes forming the heat exchanger are located inside the vapor manifold so that the entire circumference of outer surface of the tube is inside. In other examples the tubes may be arranged so that only a part of the tubes project inside the vapor manifold,
In examples where the solar energy collector assembly rotates relative to the evacuated tube a rotating vacuum seal must be provided between them. In some examples a rotating vacuum seal may be provided by a multi-stage seal. In particular a multi-stage O-ring seal may be used.
Where a multi-stage O-ring seal is used an advantageous method of manufacture may be to form the O-ring seals of the different stages in order from the interior of the evacuated tube to the exterior while evacuating the tube. This will provide a multi-stage O-ring seal with the regions between the seals initially having the same vacuum pressure as the interior of the tube. Such a multi-stage O-ring seal may support a long lasting vacuum within the tube even when the multi-stage O-ring seal is used as a rotating vacuum seal.
The above embodiments illustrate and describe a single solar energy converter. In practice an array made up of a plurality of such units may be used. In such an array each solar energy converter may have a dedicated electrical inverter. Alternatively, a group of a plurality of solar energy converters may share a common inverter.
In an array of solar energy converters it may be preferred to have a primary operating fluid channel running through the primary heat exchangers of all of the energy converters of the array as a common manifold.
In an array of solar energy converters it may be preferred for adjacent solar energy converters to have their respective inlet opening and outlet opening connected directly together. This may be done by providing a flange around each inlet opening and outlet opening and clamping together the flanges of the adjacent inlet opening and outlet opening of adjacent solar energy converters.
In an array of solar energy converters it may be desirable to be able to extract individual solar energy converters from the array for servicing, or to replace faulty converters, without having to drain all of the fluid from the common manifold. Accordingly, fluid cut off valves may be provided in the support element of each solar energy converter in order to seal the appropriate one of the inlet opening or outlet opening when an adjacent solar energy converter is removed from the array.
The embodiments described above comprise a collector assembly within an evacuated cylindrical tube. In some examples the collector assembly may be located within an enclosure which is not evacuated. In some examples enclosures which are not cylindrical tubes may be used.
The embodiments set out above are described in the context of a hybrid solar energy converter. The different parts of the described hybrid solar energy converter may be useable independently.
In particular, the solar energy collector assembly and the heat exchange assembly may be used in a flat panel device without a separate evacuated transparent tube for the solar energy collector assembly. Such a flat panel device may be evacuated, or alternatively may not be evacuated.
In particular, the collector assembly may be used as a thermal collector to gather heat energy from incident solar radiation without any photovoltaic elements being mounted on the collector assembly.
An array of solar energy converters may comprise both hybrid solar energy converters with photovoltaic elements mounted on the collector assembly and thermal solar energy converters without photovoltaic elements mounted on the collector assembly. Such an array may be used to heat water, with the hybrid solar energy converters heating the water to an intermediate temperature and the thermal solar energy converters heating the water from the intermediate temperature to a high temperature. The thermal solar energy converters without photovoltaic elements may operate at a higher temperature than the hybrid solar energy converters because they do not have any photovoltaic elements to suffer thermal degradation.
In some examples the collector assembly may be used as a thermal collector to heat air or water in industrial or domestic applications. In some examples the collector assembly may be used as a thermal collector to heat water in a desalination or water purifying application.
In particular, the heat exchange assembly may be used separately in solar energy heat collectors without the photovoltaic elements and/or without the heat transport element. This may allow the problem of stagnation to be solved.
In particular, the heat transport element may provide a density driven heat transport mechanism useable in other heat transport applications.
In particular, the heat transport element may provide an isothermal cooled surface useable in other applications.
In particular, the isothermal cooled surface may be curved. This may allow curved objects to be cooled more efficiently.
In one example the heat transport element may be used to cool electrical circuits, for example in a computer.
If the heat transport element is used in other applications, and not in conjunction with photovoltaic elements, the heat transport element may operate at a wider range of temperatures. In one example the heat transport element using water as the working fluid may operate at a temperature of up to 280° C. In other examples other fluids may be used as the working fluid. In one example of a high temperature application sodium may be used as the working fluid within the heat transport element.
In some examples the heat transport element may transport heat to one or more electro-thermal power generators in place of one or both heat exchangers. This may increase the amount of electrical energy generated. In particular the heat transport element may transport heat to a Stirling engine or engines.
In the illustrated embodiment vacuums are used within the heat transport element having a pressure of about 10⁻³mbar. Higher or lower pressures may be used. In general, it is expected that using lower vacuum pressures would improve the performance of the hybrid solar energy converter. In some examples a vacuum pressure of 10⁻²bar or lower may be used. In some examples vacuum pressures of 10⁻⁶mbar or 10⁻⁸mbar may be used.
A vacuum pressure of 10⁻³mbar is generally the lowest pressure that can be provided by simple vacuum pumps, so that the use of this vacuum pressure is convenient as the necessary vacuum pumps are readily available. The use of this vacuum pressure may be economically advantageous in commercial scale production of hybrid solar energy converters because of the cost of providing a lower vacuum pressure. In other embodiments higher or lower vacuum pressures may be used.
In the illustrated embodiments the hybrid solar energy converter has roof and/or wall mounting brackets. In other embodiments different mounting methods and components may be used.
The description above describes three embodiments. All of the embodiments are closely related and alternatives, explanations and advantages disclosed in relation to one of the embodiments can generally be applied in an analogous manner to the other embodiments. In particular, elements of one embodiment may be used in the other embodiments, and analogous elements can be exchanged between the embodiments.
The above description uses relative location terms such as upper and lower and front and rear. These are used for clarity to refer to the relative locations of the referenced parts in the illustrated figures, and should not be regarded as limiting regarding the orientation and/or location of parts of embodiments of the invention during manufacture or in use.
Those skilled in the art will appreciate that while the foregoing has described what are considered to be the best mode and, where appropriate, other modes of performing the invention, the invention should not be limited to specific apparatus configurations or method steps disclosed in this description of the preferred embodiment. It is understood that various modifications may be made therein and that the subject matter disclosed herein may be implemented in various forms and examples, and that the teachings may be applied in numerous applications, only some of which have been described herein. It is intended by the following claims to claim any and all applications, modifications and variations that fall within the true scope of the present teachings. Those skilled in the art will recognize that the invention has a broad range of applications, and that the embodiments may take a wide range of modifications without departing from the inventive concept as defined in the appended claims.

Claims

1. A heat transfer assembly comprising:

an elongate envelope;

an elongate heat transfer device located within the envelope, the heat transfer device having an elongate heat transfer chamber; and

an elongate heat exchanger passing longitudinally through at least a portion of the elongate heat transfer chamber.

2. A heat transfer assembly according to claim 1, wherein the elongate envelope is transparent or translucent.

3. A heat transfer assembly according to claim 2, wherein the elongate envelope is glass.

4. A heat transfer assembly according to claim 1, wherein the elongate heat transfer chamber extends along substantially the whole length of the elongate heat transfer device.

5. A heat transfer assembly according to claim 1, wherein the elongate heat exchanger extends along substantially the whole length of the elongate heat transfer chamber.

6. A heat transfer assembly according to claim 5, wherein the elongate heat exchanger comprises a tube which passes through a first end of the elongate heat transfer chamber, extends along substantially the whole length of the elongate heat transfer chamber, and turns back to pass for a second time through the first end of the elongate heat transfer chamber.

7. A heat transfer assembly according to claim 6, wherein the elongate heat exchanger comprises a tube which passes twice through a first end of the elongate envelope.

8. A heat transfer assembly according to claim 5, wherein the elongate heat exchanger comprises a tube which passes through a first end of the elongate heat transfer chamber, extends along substantially the whole length of the elongate heat transfer chamber, and passes through a second end of the elongate heat transfer chamber opposite the first end.

9. A heat transfer assembly according to claim 8, wherein the tube and/or the elongate heat transfer device comprise means to accommodate differential thermal expansion between the tube and elongate heat transfer device.

10. A heat transfer assembly according to claim 9, wherein the means to accommodate differential thermal expansion comprise a bellows structure of the tube.

11. A heat transfer assembly according to claim 8, wherein the elongate heat exchanger comprises a tube which passes through a first end of the elongate envelope, extends along substantially the whole length of the elongate envelope, and passes through a second end of the elongate envelope opposite the first end.

12. A heat transfer assembly according to claim 11, wherein the tube and/or the elongate envelope comprise means to accommodate differential thermal expansion between the tube and elongate heat transfer device, and the elongate envelope.

13. A heat transfer assembly according to claim 12, wherein the means to accommodate differential thermal expansion comprise bends in the tube.

14. A heat transfer assembly according to claim 8, wherein the elongate heat exchanger comprises a tube which passes through a first end of the elongate envelope, passes through the elongate heat transfer chamber, and turns back to pass for a second time through the first end of the elongate envelope.

15. A heat transfer assembly according to claim 5, wherein the elongate heat exchanger comprises inner and outer concentric tubes which pass through a first end of the elongate heat transfer chamber and extend along substantially the whole length of the elongate heat transfer chamber, wherein the outer concentric tube is closed at an end remote from the first end of the elongate heat transfer chamber.

16. A heat transfer assembly according to claim 1, wherein the elongate envelope is at least partially evacuated.

17. A heat transfer assembly according to claim 1, and further comprising at least one photovoltaic element mounted on the elongate heat transfer device.

18. A heat transfer assembly according to claim 1, wherein the elongate heat transfer chamber is a vapor chamber.

19. A heat transfer assembly according to claim 18, wherein the vapor chamber is at least partially evacuated.

20. A heat transfer assembly according to claim 1, wherein the heat transfer assembly is arranged for rotation about a rotation axis.

21. A heat transfer assembly according to claim 20, wherein the elongate envelope is cylindrical and has an axis of symmetry, and the axis of rotation is parallel to the axis of symmetry.

22. A heat transfer assembly according to claim 21, wherein the axis of rotation and the axis of symmetry are coaxial.

23. A heat transfer assembly according to claim 7, wherein the heat transfer assembly is arranged for rotation about a rotation axis, and the axis of rotation coincides with the location of a tube passing through an end of the elongate envelope.

24. A heat transfer assembly according to claim 7, wherein the heat transfer assembly is arranged for rotation about a rotation axis, and the tube passes twice through the first end of the elongate envelope and the axis of rotation passes between the locations at which the tubes passing through the end of the elongate envelope.

25. A heat transfer assembly according to claim 24, wherein the axis of rotation passes centrally between the locations at which the tubes passing through the end of the elongate envelope.

26. A solar collector array comprising a plurality of heat transfer assemblies according to claim 20 mounted in parallel on a common supporting structure.

27. A solar collector array according to claim 26, and further comprising means for synchronously rotating all of the plurality of heat transfer assemblies relative to the supporting structure about their respective axes of rotation.

28. A solar collector array according to claim 26, and further comprising means for rotating the supporting structure about an axis perpendicular to the axes of rotation of the heat transfer assemblies.

29-98. (canceled)