WO2014090330A1

WO2014090330A1 - A solar thermal vacuum tube collector

Info

Publication number: WO2014090330A1
Application number: PCT/EP2012/075546
Authority: WO
Inventors: Viktor ÖLÉN
Original assignee: Heliocaminus Ab
Priority date: 2012-12-14
Filing date: 2012-12-14
Publication date: 2014-06-19

Abstract

A solar thermal vacuum tube collector (1) comprising a number of Single Walled Elongated Glass Tubes (SWEGTs) (2) designed to be placed side by side in contact with each other so as to form a row of SWEGTs. A circulation assembly (10a, 10b) is connected to each row of SWEGTs and a insulating hood (11) covers the circulation assembly. Each SWEGT has a topside (3'), which is arced, and is hermetically sealed and evacuated. Each SWEGT contains an absorber (8) and a pipe such as an U-pipe or a heat pipe (6) connected to the absorber to transfer the collected heat to a circulation assembly (10a, 0b), wherein the heat pipe protrudes out from the glass tube through a hermetic tight lid (4)formed at an end part (5) of the SWEGT. A tangent (H) at a midpoint of an arc (3a; 3c) of the topside of the SWEGT (2) is horizontal and the midpoint 1 forms the highest point of the SWEGT (2), and a tangent (V) of the two lowest points of the arc (3a) or a side circle arc (3d) of the topside (3') is vertical and forms the widest points of the profile, and that the width of the arc is more than twice the height of the arc.

Description

A SOLAR THERMAL VACUUM TUBE COLLECTOR

Field of the Invention

The invention relates to a solar thermal vacuum tube collector of the type described in the preamble of patent claim 1. Background of the Invention

Solar thermal vacuum tube collectors are used in solar thermal systems to convert incident solar radiation preferably into heat or electricity. This application describes a solar vacuum tube collector with the intended use of converting incident solar radiation into heat.

Incident solar radiation that reaches the Earth' s surface comprises of two components. The first component is the direct solar radiation that passes through the Earth' s atmosphere without refraction, and the second component is the diffuse solar radiation that is refracted by the atmosphere.

Diffuse solar radiation reaches an observer from an angle different than the direct line formed between the observer and the sun. The portion of direct and diffuse incident solar radiation varies depending on the observer' s location on the Earth, time of the year and level of humidity in the

atmosphere etc. The diffuse portion of the radiation reaching the earth surface can often be more than 50%.

There are mainly three factors that affect a solar thermal collector' s power output efficiency per module area (module area is defined as the outer dimensions of the entire solar collector module) :

a) The portion of the incident solar radiation that reaches the heat converting absorber in relation the total incident solar radiation on the module area. Radiation is lost in the transparent layer that surrounds the absorber, in mirrors (if used) where the radiation is reflected, and the part of the radiation that reaches the module area, however does not reach the absorber (i.e. between tubes or on a heat exchanger) .

b) How much of the solar radiation that reaches the absorber that then is converted into usable heat, which is determined by the absorber coating.

c) How significant the heat losses are from the solar

collector to the surrounding environment. This is among other things decided by the surface area of the hot absorber (and other heated parts) , the radiant emission of the surface coating of the hot parts, and the insulation that is used between the heated parts of the solar vacuum tube collector and the surrounding environment.

To summarize, the larger the portion of solar radiation that hits the absorber (either directly or after reflection) in comparison to the radiation that hits the entire module area, the higher the total amount of absorbed radiation in the collector. The lower the heat losses from the heated parts of the solar thermal vacuum tube collector area, the higher total power output of the collector will be.

Known solar thermal vacuum tube solutions for absorbing incident solar radiation include Sydney Vacuum Tubes and Super Conduction Vacuum Tubes. These solutions comprise of

cylindrical tubes, preferably made of glass, with an absorber coated with absorbent material inside the glass. Sydney Tubes consist of a double walled cylindrical glass tubes, with an empty space (preferably vacuum) between each wall. Inside the second wall, a cylindrical absorber sheet is placed, which is then heated by the incident solar radiation. See patent US4834066.

Super Conduction Vacuum Tubes have only one cylindrical wall. Super Conduction Vacuum tubes preferably use a flat absorber plate, see EP2149017 (Al) .

The cylindrical tubes are in both cases preferably installed with a gap in between each tube, in order to prevent shading from neighboring tubes when incident radiation (both direct and diffuse) reaches the tubes from a low angle. This has the drawback that a portion of the incident solar radiation is lost in between the cylindrical tubes, and therefore the amount of radiation absorbed on a given module area is not maximized.

The use of cylindrical absorber sheets in Sydney tubes means that the total area of the absorber is larger than Super Conduction Vacuum Tubes and therefore radiation losses are greater. Absorber plates in Super Conduction Vacuum Tubes are preferably coated only on the side which faces the incident solar radiation, which has the drawback that the opposite side of the absorber plate is not used for absorbing solar

radiation, and therefore only contributes to heat radiation losses.

It would therefore be preferable to have a solar thermal vacuum tube system that uses non-cylindrical tubes, which can be placed next to each other, and where shading from

neighboring tubes has been reduced compared to cylindrical tubes . It would also be preferable if the absorber area could be minimized in order to decrease the radiation heat losses that arise from the absorber plate itself. Summary of the Invention

The purpose of this invention is to create a solar thermal vacuum tube collector that will harvest more energy on a given area than existing solar vacuum tube collectors.

This is achieved according to the invention with a solar thermal vacuum tube collector comprising a number of Single Walled Elongated Glass Tubes (SWEGTs) designed to be placed side by side in contact with each other so as to form a row of SWEGTs, a circulation assembly that is connected to each row of SWEGTs and a insulating hood that covers the circulation assembly characterized in that each SWEGT has a topside, which is arced, and is hermetically sealed and evacuated, that each SWEGT contains an absorber and a pipe such as an U-pipe or a heat pipe connected to the absorber to transfer the collected heat to a circulation assembly, wherein the heat pipe

protrudes out from the glass tube through a hermetic tight lid formed at an end part of the SWEGT, that a tangent at a midpoint of an arc of the topside of the SWEGT is horizontal and the midpoint forms the highest point of the SWEGT, that a tangent of the two lowest points of the arc or a side circle arc of the topside is vertical and forms the widest points of the profile, and that the width of the arc is more than twice the height of the arc.

Preferred embodiments are given in the dependent patent claims. Description of the Figures

The invention is described in more detail below with

references to the attached drawings, in which

- Fig. 1 is a perspective view of one Singe Walled Elongated Glass Tube (SWEGT) ,

- Fig. 2 is a cross sectional view of the SWEGT in Fig 1,

- Fig. 3 is an additional cross sectional view of SWEGT in Fig. 1 with a different preferred shape,

- Fig. 4 is an additional cross sectional view of SWEGT in Fig. 1 with a different preferred shape,

- Fig. 5 is a separate view of five SWEGTs placed next to each other, who's pipes are connected to a circulation assembly, with a hood in three separate components above the said SWEGTs and circulation assembly, - Fig. 6 is a separate view of five SWEGTS with a insulating hood, and

- Fig. 7 shows the solar thermal vacuum tube collector

integrated in a roof that consists of roof tiles, with a magnified portion. Description of preferred embodiments

Figure 1 shows an elongated Single Walled Elongated Glass Tube (SWEGT) 2 comprising of a housing 3, preferably a glass housing. An end part 5 comprises a lid 4, through which a tube 6 is connected to an absorber. The lid 4 is hermetically sealed to the tube 6 and to the housing 3.

As seen in Figure 2 the SWEGT 2 comprises a reflector 7 and an absorber 8. The reflector combined with the absorber is so designed that almost all incident solar radiation, which does not reach the absorber directly, is projected up onto the absorber's opposite (lower) side, irrespective of the incident angle of the solar radiation. In a first embodiment, the glass housing's 3 topside 3', which is the part facing the sun and formed by a top arc 3a (Figure 2) or a top circle arc 3c and two side circle arcs 3d (Figure 4) , is arced and thereby decreasing shadowing from neighboring SWEGTs when placed side by side next to each other compared to circular tubes. A bottom part 3h is flat, and a transition between the topside 3' of the glass and the bottom part is preferably circularly arced .

Absorber 8 converts the incident solar radiation into heat, and is therefore covered with a layer that acts as "a black body" in wavelengths below the infrared spectrum. The absorber will therefore convert these wavelengths into heat. In order to prevent the heat from radiating out as long wave radiation from the absorber, the absorber layer approaches a "white body" in longer wavelengths. This maximizes the energy

conversion from the sun's shortwave radiation into heat, without the large heat losses that can occur from long wave radiation from the absorber.

In order to further decrease the energy losses that arise from long wave infrared radiation, the absorber surface area is minimized. This is accomplished without reducing the solar thermal vacuum tube collector's active absorption area, i.e. the surface that absorbs the incident solar radiation, in comparison to the module area.

Absorber 8 comprises preferably a pipe 6 with two thin wings 9a, 9b. The pipe is preferably constructed either as a heat pipe or a U-pipe. As shown in Figure 3 the top arc 3a and bottom arc 3b of the single walled elongated glass tube can in a second embodiment have the profile of an ellipse. This will decrease the

shadowing effects of neighboring tubes compared to circular tubes when several tubes are placed side by side and in contact with each other.

When producing a non-circular vacuum tube, the pressure difference on the tubes inner and outer side will create tensile stresses in the glass. These stresses can be harmful to the integrity of the glass.

One way of reducing these stresses is to design the single walled elongated glass tube as seen in Figure 4 from circle arcs with two different radiuses where the radius of the circle arcs 3d and 3e comprise the sides of the profile is smaller than the radius of the top 3c and bottom 3f circle arcs connecting the two side circle arcs 3d and 3e . The top 3c, the part facing the sun, and bottom circle arc 3f

coincides with the two side circle arcs 3d and 3e so that the tangents in these points are equal. The two circle arcs radiuses is chosen in such a way that the connection point between the circle arcs coincide with the area where the internal stress of the glass wall is low. This design will decrease the shadowing effects of neighboring tubes compared to circular tubes when several tubes are placed side by side and in contact with each other.

As seen in Figures 2 and 4, a tangent H at a midpoint of the SWEGT 2 profile arc 3a, 3c is horizontal and forms the highest point of the SWEGT 2, and a tangent V of the two lowest points of the arc 3a, or the top circle arc 3c in combination with the side circle arc 3d is vertical and forms the widest points of the profile. The width of the arc 3a, and the arc made up from 3c and 3d, respectively, is preferably more than twice the height of the arc.

In one embodiment the profile of the lower part of the SWEGT is preferably shaped so that the bottom part 3h is flat with the width of two r and the connecting parts between the flat bottom part 3h and the topside 3a is shaped like quarter circles 3g with radius r, and the lower part of the SWEGT contains a reflector 7 shaped as two half circles with radius R and the absorber 8 with the width of two R centered in the profile .

From Figure 5 it is apparent that the pipe 6 for each

respective absorber 8 is connected to a circulation assembly 10a, 10b. The circulation pipes are preferably U-shaped and can comprise of an incoming circulation pipe 10b and an outgoing circulation pipe 10a. An insulating hood 11 is placed over the circulation assembly 10a, 10b. In the preferred arrangement, the hood has three parts 11a, lib, 11c, and in more detail an end piece 11a, a middle piece lib, and a closing piece 11c. The hood 11 is preferably placed over the parts of the collector where heat exchange occurs.

According to the invention the hood 11 is built up from at least two parts, namely part 11a and end part 11c. It is apparent for the man skilled in the art that if the solar thermal vacuum tube collector module contains several SWEGTs 2, then the middle part lib can comprise of several additional identical parts .

As is apparent in Figure 6 the solar vacuum tube collector 1 in the shape of a module, in this case five SWEGTs 2, and with mounted circulation assembly 10a, 10b and the hood 11,

intended to be placed in an appropriate matter on e.g. a roof. Figure 7 shows a solar vacuum tube collector 1 according to the invention placed in a roof 12 that is covered with roof tiles, and two rows of several SWEGTs 2 placed side by side in contact with each other. It is obvious to the man skilled in the art that the number of SWEGTs and the number of rows can be varied according to the appropriate need.

In the magnified portion of Figure 7 it is apparent that the lower part of the upper row of SWEGTs 2 is placed in parallel with the roof tiles and on top of the insulating hood that corresponds to the underlying lower row of SWEGTs 2. This has the benefit that more of the incident solar radiation of the module area is being converted into heat and the solar thermal vacuum tube collector will harvest more energy on a given area than existing solar thermal vacuum tube collectors.

Claims

Patent claims

1. A solar thermal vacuum tube collector (1) comprising a number of Single Walled Elongated Glass Tubes (SWEGTs) (2) designed to be placed side by side in contact with each other so as to form a row of SWEGTs, a circulation assembly (10a,

10b) that is connected to each row of SWEGTs and a insulating hood (11) that covers the circulation assembly characterized in that each SWEGT has a topside (3' ) , which is arced, and is hermetically sealed and evacuated, that each SWEGT contains an absorber (8) and a pipe such as an U-pipe or a heat pipe (6) connected to the absorber to transfer the collected heat to a circulation assembly (10a, 10b), wherein the heat pipe

protrudes out from the glass tube through a hermetic tight lid (4) formed at an end part (5) of the SWEGT, that a tangent (H) at a midpoint of an arc (3a; 3c) of the topside of the SWEGT (2) is horizontal and the midpoint forms the highest point of the SWEGT (2), that a tangent (V) of the two lowest points of the arc (3a) or a side circle arc (3d) of the topside (3' ) is vertical and forms the widest points of the profile, and that the width of the arc is more than twice the height of the arc.

2. The solar thermal vacuum tube collector (1) according to claim 1, characterized in that the topside (3' ) is in the form of a half ellipse when the height of the ellipse is smaller than the width of the ellipse.

3. The solar thermal vacuum tube collector (1) according to claim 1, characterized in that the topside (3' ) is made up from one top circle arc (3c) and two side circle arcs (3d) , where the radius of the circle arcs making up the sides of the arc (3d) is smaller than the radius of the top circle arc (3c) connecting the two side circle arcs (3d) , the top circle arc (3c) coinciding with the two side circle arcs (3d) so that the tangents in these points are equal, and that the radiuses of the two circle arcs are chosen in such a way that the

connection point between the circle arcs coincide with the area where the internal stress of the glass wall is low.

4. The solar thermal vacuum tube collector (1) according to any one of claims 1-3, characterized in that lower part of the SWEGT' s (2) profile is in the form of a half ellipse (3b) where the height of the ellipse is smaller or equal than the width.

5. The solar thermal vacuum tube collector according to any one of claims 1-3, characterized in that the profile of a lower part of the SWEGT is shaped so that the bottom part (3h) is flat with the width of two r and the connecting parts between the flat bottom part (3h) and the topside (3a) is shaped like quarter circles (3g) with radius r, and that the lower part of the SWEGT contains a reflector (7) shaped as two half circles with radius R and the absorber (8) with the width of two R centered in the profile.

6. The solar thermal vacuum tube collector (1) according to any one of claims 1-5, characterized in that when mounting several rows of SWEGTs the lower part of the upper row is placed on top of the insulating hood (11) of the lower row.