US20090050133A1

US20090050133A1 - Reflector and a receiver for a solar energy collection system

Info

Publication number: US20090050133A1
Application number: US11/720,072
Authority: US
Inventors: Yongbai YIN
Original assignee: University of Sydney
Current assignee: University of Sydney
Priority date: 2004-11-26
Filing date: 2005-11-28
Publication date: 2009-02-26
Also published as: EP1851488A1; CN101111729B; WO2006056025A1; CN101111729A

Abstract

The present invention provides a reflector (24) for a solar energy collection system (20). The reflector (24) is arranged for diverting light received from solar energy collectors (22). The solar energy collectors (22) are arranged for focusing the collected light to an elongate focal region of the reflector (24) wherein, the light is further diverted away.

Description

FIELD OF THE INVENTION

The present invention broadly relates to a reflector and to a receiver for a solar energy collection system. The present invention relates particularly, though not exclusively, to a reflector and to a receiver for reflecting and absorbing solar energy from an array of solar energy collectors.

BACKGROUND OF THE INVENTION

In many countries the demand for environmentally friendly energy sources is increasing. For example, radiation from the sun may be converted into heat or electricity. A solar energy collection system typically includes an array of solar energy collectors, such as an array of reflectors, which collect the sunlight and direct the collected sunlight to a receiver positioned over the array.
Typically the collected sunlight is focussed onto an absorber in the receiver and heats the absorber locally to a temperature of approximately 350° C. However, it is known that the conversion efficiency of the energy from the collected sunlight to electricity is better at higher temperatures such as temperatures of 500° to 600°. Using technology presently available, such high temperatures cause a number of problems. In order to reach such high temperatures the collected sunlight needs to be concentrated onto a very small area of the absorber. However, especially for large solar collection arrays, radiation from collectors typically reaches the absorber with a very small angle of incidence which results in beam broadening and consequently in loss of concentration. This may be avoided by positioning the receiver very high over the array of collectors. However, the receiver typically is a heavy and complex device and the positioning of the absorber at a position that is sufficiently high is a challenge for construction and is expensive.
Further, typical receivers comprise an absorbing body positioned in an evacuated glass housing and typically cannot withstand temperatures higher than approximately 350° C. Consequently, there is a need for an alternative technological solution.

SUMMARY OF THE INVENTION

The present invention provides in a first aspect a reflector for a solar energy collection system, the reflector being arranged for diverting radiation received from solar energy collectors, the solar energy collectors being arranged for focusing the collected light to an elongate focal region and the reflector comprising at least one elongate reflecting surface portion arranged to divert radiation received from a solar energy collectors.
For example, the reflector may in use be positioned at a level above the solar energy collectors, which may themselves be primary reflectors, and arranged to divert the radiation in a downward direction to a level below that of the reflector so that the elongate focal region is in use at a level below that of the reflector such as a position on or near a ground plane. This has the significant advantage that relatively high angles of incidence of the radiation may be achieved without the need to position a receiver, which may comprise a further reflector, high above the solar energy collectors.
The elongate reflecting surface may be substantially planar, but typically has a concave or convex cross-sectional shape in a plane perpendicular to the direction of elongation.
The elongate reflecting surface portion may have a cross-sectional shape that varies in the direction along the elongation. For example, the reflector may also have a first region having a concave cross-sectional shape and a second region having a convex cross-sectional shape. Typically, however, the reflector has a cross-sectional shape that is substantially constant in the direction of the elongation of the reflecting surface portion. In one specific embodiment the cross-sectional shape of the elongate reflecting surface portion is concave. For example, the concave reflecting surface portion may comprise a plurality of surface portions or segments which may be joined. In this case, the reflecting surface portion may comprise a plurality of substantially planar reflecting portions which are arranged in a concave shape. Alternatively the reflecting surface may comprise a concave layer which may be integrally formed.
The present invention provides in a second aspect a receiver for a solar energy collection system, the receiver comprising:
a housing having an interior space which can be evacuated and a light-transmissive window for transmission of light through the window into the interior space,
an absorbing body positioned in the interior space of the housing for absorbing the light,
wherein the receiver is arranged for evacuation of the interior space using a vacuum pump during use of the receiver.
The housing of the receiver may be arranged for connection to the vacuum pump. The vacuum pump may be an external pump, but may also be an internal pump that may be positioned in the housing (for example a getter pump).
The receiver has a number of advantages. Because the interior space can be evacuated by the vacuum pump during use of the receiver, heat conduction from the absorber body to the window, which may be a glass window, is reduced and consequently the window has in use typically a temperature that is much lower than that of the absorber body. Consequently, the receiver is suitable for higher temperatures than conventional receivers.
Direct contact between the absorber body and the window typically can be avoided. The housing typically comprises a material that is thermally insulating and is arranged to reduce heat conduction from the absorbing body to the window which further increases suitability for high temperatures. For example, the housing may comprise an inner portion which may be metallic and an outer portion which may comprise the thermally insulating material.
Further, supports, such as pilar-type supports, which support the absorber body in the housing may comprise the thermally insulating material. The thermally insulating material typically is a ceramics material.
The absorber body may have any suitable shape but typically is shaped so that at least a portion of the light that is reflected by a surface portion of the absorber body is reflected to another surface portion of the absorber body. For example, if the light is reflected three times and each time 80% of the light is absorbed, only less than 1% of the light may escape. In a specific embodiment of the present invention the absorber body has a substantially U-shaped or V-shaped cross-sectional shape. The substantially U- or V-shaped absorber body has the advantage of having a larger surface to volume ratio than a conventional absorber body which typically is a pipe having a round cross-sectional shape. Consequently, the substantially U- or V-shape of the absorber body increases the absorption efficiency.
The receiver may be arranged for heating of any suitable material such as a gas or a liquid. In one embodiment the absorber body comprises a conduit for a fluid that is in use directed through the absorber body. For example, the conduit may also have a substantially V- or U-shaped cross-sectional shape. If the fluid is a liquid that is in use directed through the absorber body and heated by the absorber body, this shape of the conduit has a particular advantage. Liquids may form bubbles when heated which would diffuse to areas near end portions of the legs of the substantially V- or U-cross-sectional shape of the conduit. However, other regions of the conduit would be largely bubble free and can efficiently absorb heat. If the conduit had a round cross-sectional shape, bubbles would be located in areas where typically the main amount of heat is received which would be of detriment for the absorption efficiency.
The absorber body may comprise any suitable material but typically comprises an absorptive surface coating such as a highly absorptive “black body” type surface coating. The absorber body may also have a solar selective coating such as a coating that absorbs sunlight but only emits a relatively small amount of infrared radiation. The housing typically has an interior surface portion that is reflective so that solar light that is directed to the interior surface is reflected to the absorber body and heat loss is reduced. For example, the housing interior surface may comprise a metallic material that is reflective.
The receiver may be arranged for receiving radiation collected by a plurality of collectors which focus the collected light to an elongated focal region such as a linear focal region. In this case, the absorber body typically is elongated so that the absorber body can receive the radiation associated with the elongated focal region.
The present invention provides in a third aspect a solar energy collection system comprising the reflector according to the second aspect of the present invention.
Because the reflector in use diverts radiation to the receiver, it is possible to avoid relatively small angles of incidence without the need to position the absorber at a very high level above the solar energy collectors. As relatively small angles of incidence can be avoided, loss of concentration due to broadening of the beam is reduced and it is possible to achieve higher absorber body temperatures.
The solar energy collection system according to the third aspect of the present invention typically comprises a receiver such as the receiver according to the first aspect of the invention. The reflector typically is positioned at a level above the solar energy collectors and arranged to divert the radiation in a downward direction. The receiver may be positioned on a ground plane. An elongate focal region of the solar energy collection system typically is in use directed into the receiver of the solar energy collection system.
Alternatively, the solar energy collection system may not comprise a receiver but may be arranged for direct heating of a material such as a solid material. For example, the solar energy collection system may be arranged for heating of a solid fuel such as brown coal. Australian brown coal has a relatively large concentration of moisture which is of disadvantage for combustion. The solar energy collection system may be arranged for heating of the brown coal and thereby reducing moisture concentration in the brown coal.
The reflector may comprise two or more concave reflecting surface portions. For example, the reflector may comprise two concave reflecting surface portions arranged so that the reflector has a cross-section that comprises two concave portions. In this case, the system typically is arranged so that the reflector is positioned over the receiver with collectors positioned on either side of the receiver and respective concave reflecting surface portions divert radiation received from solar energy collectors located at respective sides of the reflector.
The invention will be more fully understood from the following description of specific embodiments of the invention. The description is provided with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-sectional view of a receiver for a solar energy collection system according to a specific embodiment of the present invention,

FIG. 2 shows a cross-sectional view of a solar energy collection system according to a specific embodiment of the present invention,

FIG. 3 shows a top-view of the solar energy collection system shown in FIG. 2, and

FIG. 4 shows a cross-sectional view of a reflector according to an embodiment of the present invention.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Referring initially to FIG. 1, a receiver 10 for a solar energy collection system according to a specific embodiment of the present invention is now described.
The receiver 10 comprises a housing 12 which has an interior space 13. An absorber body 14 is positioned in the interior space 13 and a window 16 closes the interior space. The window 16 is composed of a light transmissive material such as glass. The interior space 13 is in use evacuated using vacuum pump 17.
The receiver 10 is arranged to receive solar radiation through the window 16 and to absorb the solar radiation by the absorber body 14. In this embodiment the absorber body 14 has a shape that increases likelihood for multiple reflections of received solar light. In this example, the absorber body 14 has a U-shaped cross-sectional shape. The absorber body 14 in this example is composed of a metallic material which has a “black body” coating to increase the absorption of received sunlight. Due to the likelihood for multiple reflections of the received sunlight by the absorber body 14 the absorption efficiency is increased.
In a variation of this embodiment the absorber body 14 is coated with a solar reflective coating, such as a coating that has a relatively high absorption efficiency for solar light and a relatively low emission efficiency for infrared radiation. Such a layer may comprise a ceramic material having a graded metal concentration.
Supports 18 support the absorber body 14 in the housing 12. In this example the supports 18 are composed of a thermally insulating material, such as a ceramics material. Due to the thermally insulating material, heat conduction from the absorber body 14 through the housing 12 to the glass window 16 is reduced. Consequently, the receiver 10 is suitable for relatively high temperatures. In this embodiment the housing 12 comprises an inner portion that is metallic and an outer portion that is thermally insulating and in this example also is composed of the thermally insulating ceramics material.
It will be appreciated that in variations of this embodiment the housing 12 may be composed of any suitable material, such as a metallic material. Further, if the housing 12 comprises a thermally insulating material, the supports 18 may not necessarily be composed of a thermally insulating material.
The absorber body 14 may be arranged for heating a fluid that is transmitted through the absorber body 14. The absorber body 14 typically comprises suitable conduits (not shown) for transportation of the fluid or the solid material through the absorber body 14.
The receiver 10 may have any substantially square, rounded or rectangular cross-sectional shape in a section parallel to the window 16. In this embodiment, however, the absorber 10 and the absorber body 14 have a shape which is elongated in the plane of the window 16 and in a direction perpendicular to the plane of the drawing shown as FIG. 1. The receiver 10 therefore is arranged to receive collected solar radiation from a solar energy collection system having a linearly extended focal region.
It will be appreciated that in variations of this embodiment the absorber body 14 may have any suitable shape. For example, the absorber body 14 may be a pipe that conveys a fluid and that may have any cross-sectional shape, such as a round or rectangular shape.
FIGS. 2 and 3 show a solar energy collection system according to a specific embodiment of the present invention. The system 20 comprises an array of solar energy collectors 22 which direct collected sunlight via reflector 24 to receiver 26. For clarity, FIG. 3 does not show the reflector 24. In this embodiment each collector 22 is a reflector and the reflector 24 has a concave reflecting surface. Because of the reflector 24 it is possible to maintain relatively high angle of incidence for radiation received by the receiver 26 without the need to position the absorber high above the solar energy collectors.
In the embodiment shown in FIG. 2 the radiation collected by collectors 22 is directed to respective portions of the reflector 24.
For example, the reflecting surface may be a film deposited on a concave substrate. Alternatively, the reflector 24 may be composed of a reflecting material. Further, the reflector 24 may comprise a plurality of reflecting surface portions which may be connected. In this case, each of the surface portions may be planar and the plurality of the reflecting portions may be connected so that the reflector 24 has a concave reflecting surface.
In this embodiment the receiver 26 is positioned on a ground plane. For example, the receiver 26 may be the receiver 10 shown in FIG. 1 as discussed above. The reflector 24 typically comprises a metallic reflective surface coating but may alternatively comprise any other suitable reflective coatings or may be composed from a reflective material. In this embodiment the reflector 24 is elongated in a direction perpendicular to the plane of the drawing shown in FIG. 2 and the receiver 26 has a corresponding elongated shape which is also shown in FIG. 3.
Dashed line 30 is provided in order to illustrate a variation of this embodiment. The dashed line 30 represents a plane of symmetry for the reflector 24 and the receiver 26. In this case the reflector 24 comprises two concave reflecting portions which is further illustrated by the reflector 32 shown in FIG. 4. The solar energy collectors 22 are arranged on either side of the dashed line 30 and respective concave portions of the reflector 24 divert solar radiation received from respective sides of the system. FIG. 4 shows the reflector 32 having two concave reflecting portions 34 and 36 and supports 38.
In a further variation of the embodiment shown in FIGS. 2 and 3 the solar energy collection system may not comprise a receiver, but may be arranged for direct heating of a material, such as a fuel (eg. brown coal).
Although the invention has been described with reference to particular examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms. For example, it will be appreciated that collectors 22 may not necessarily be mirrors but may also be lenses, such as a Fresnel lenses. Further, the collectors 22 may not be arranged in an array. In the embodiments discussed above, the reflector 24 has a concave reflecting surface. It will be appreciated that in variations of this embodiment the reflector 24 may also have a convex reflecting surface. In this case the positions of the collectors 22 will be adjusted so that focussing of the collected sunlight onto the absorber is possible.
In addition, the person skilled in the art will appreciate that the reflector 24 may be replaced by a suitable mirror which may be combined with a lens such as a Fresnel lens to have similar optical properties as the concave or convex reflector 24.
Further, the focal region of the solar energy collection system may not necessarily be linear but may alternatively have any other shape including partially curved or angled shapes. The receiver may also be shaped to receive sunlight from a solar energy collection system having any shape for the focal region.

Claims

1. A reflector for a solar energy collection system, the reflector being arranged for diverting radiation received from solar energy collectors, the solar energy collectors together being arranged for focusing the collected light to an elongate focal region and the reflector comprising at least one elongate reflecting surface portion arranged to divert radiation received from the solar energy collectors.

2. The reflector as claimed in claim 1 wherein the elongate reflecting surface has a concave cross-sectional shape in a plane perpendicular to the direction of elongation.

3. The reflector as claimed in claim 1 wherein the elongate reflecting surface has a convex cross-sectional shape in a plane perpendicular to the direction of elongation.

4. The reflector as claimed in claim 1 comprising a first region having a concave cross-sectional shape and a second region having a convex cross-sectional shape.

5. The reflector as claimed in claim 1 wherein the elongate reflecting surface portion has a cross-sectional shape that is substantially constant in the direction of the elongation of the reflecting surface portion.

6. The reflector as claimed in claim 1 wherein the reflecting surface portion comprises a plurality of surface portions.

7. The reflector as claimed in claim 1 wherein the reflecting surface comprises a concave layer.

8. A receiver for a solar energy collection system, the receiver comprising:

a housing having an interior space which can be evacuated and a light-transmissive window for transmission of light through the window into the interior space,

an absorbing body positioned in the interior space of the housing for absorbing the light,

wherein the receiver is arranged for evacuation of the interior space using a vacuum pump during use of the receiver.

9. The receiver as claimed in claim 8 being arranged for connection to the vacuum pump.

10. The receiver as claimed in claim 8 wherein thermally insulating material is provided in the form of supports which support the absorber body in the housing.

11. The receiver as claimed in claim 8 wherein at least a portion of the housing comprises a thermally insulating material.

12. The receiver as claimed in claim 8 wherein the absorber body is shaped so that at least a portion of the light that is reflected by a surface portion of the absorber body is reflected to another surface portion of the absorber body.

13. The receiver as claimed in claim 8 wherein the absorber body has a substantially U-shaped cross-sectional shape.

14. The receiver as claimed in claim 8 wherein the absorber body has a substantially V-shaped cross-sectional shape.

15. The receiver as claimed in claim 8 being arranged for heating of a fluid.

16. The receiver as claimed in claim 8 wherein the absorber body comprises a conduit for a fluid that is in use conducted through the absorber body.

17. The receiver as claimed in claim 16 wherein the conduit has a substantially V-shaped cross-sectional shape.

18. The receiver as claimed in claim 16 wherein the conduit has a substantially U-shaped cross-sectional shape.

19. The receiver as claimed in claim 8 being arranged for receiving radiation collected by a plurality of collectors which focus the collected light to an elongated focal region.

20. A solar energy collection system comprising:

solar energy collectors, the solar energy collectors together being arranged for focusing collected light towards an elongate focal region and

the reflector as claimed in claim 1 for diverting collected light to a receiver.

21. A solar energy collection system as claimed in claim 20 wherein the reflector is positioned at a level above the solar energy collectors and arranged to divert the radiation in a downward direction.

22. The solar energy collection system as claimed in claim 20 wherein the receiver comprises:

23. The solar energy collection system as claimed in claim 22 wherein an elongate focal region of the solar energy collection system is directed into the receiver.

24. The solar energy collection system as claimed in claim 22 wherein the receiver is in use positioned below the reflector.

25. The solar energy collection system as claimed in claim 24 wherein the receiver is in use positioned on a ground plane.

26. The solar energy collection system as claimed in claim 20 wherein the receiver comprises:

wherein the receiver is arranged for evacuation of the interior space using a vacuum pump during use of the receiver;

and being arranged for direct heating of a material.

27. The solar energy collection system as claimed in claim 20 wherein the receiver comprises:

wherein the reflector has a concave cross-sectional shape in a plane perpendicular to the direction of elongation; and

wherein the reflector comprises two or more concave reflecting surface portions.

28. The solar energy collection system as claimed in claim 26 wherein the system is arranged so that the reflector is positioned over the receiver with collectors positioned on either side of the receiver and respective concave reflecting surface portions divert radiation received from solar energy collectors located at respective sides of the reflector.