US20090107488A1

US20090107488A1 - Apparatus and Method for Solar Thermal Energy Collection

Info

Publication number: US20090107488A1
Application number: US11/929,682
Authority: US
Inventors: Randy C. Gee; Roland Winston
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-10-30
Filing date: 2007-10-30
Publication date: 2009-04-30

Abstract

An apparatus for collecting solar energy includes a receptacle adapted for receiving solar thermal energy, an insert adapted for counter-flow located within the receptacle, and an absorption device positioned proximate to and substantially conforming to at least a portion of an internal surface of the receptacle and thermally coupled to the insert.

Description

BACKGROUND OF THE INVENTION

The present invention relates generally to the field of solar thermal energy. In particular, the present invention relates to solar thermal energy collectors.
Solar thermal collectors have been utilized for over 20 years. The designs have varied from flat plate, box, air, integral, unglazed more commonly to parabolic troughs and dishes and full power towers. Though they have been commercially available for over 20 years, recent designs of evacuated tubes have become more efficient and less costly, allowing them to be both commercially and domestically available as well as more widely utilized. Some devices contain heat removal inserts that are placed within the tubes that serve the purpose of transferring the collected energy to a heat-transfer fluid and are used to transfer heat to a manifold located at the end of the tubes or in connection with the inserts.
Conventional designs are limited in their ability to transfer heat from the collector. It is desirable to improve the efficiency with which such heat is transferred.

SUMMARY OF THE INVENTION

In one aspect, the invention includes an apparatus for collecting solar energy. The apparatus comprises a receptacle adapted for receiving solar thermal energy, an insert adapted for counter-flow located within the receptacle, and an absorption device positioned proximate to and substantially conforming to at least a portion of an internal surface of the receptacle and thermally coupled to the insert.
In one embodiment, the receptacle has a vacuum drawn interior that is sealed with a glass to metal seal.
In one embodiment, the apparatus further comprises a non-imaging optic reflector located external to the receptacle and adapted to direct solar thermal energy to the receptacle. The reflector may be a compound parabolic concentrator (CPC).
In one embodiment, a substantial portion of one side of the insert is adjacent the absorption device. The insert may enter the receptacle substantially at a cross-sectional center of the receptacle and, further inside the receptacle, the insert is shifted closer to the absorption device and closer to a non-imaging optical reflector.
In one embodiment, the insert is a metal selected from the group consisting of brass, copper and aluminum.
In one embodiment, the absorption device is a metal selected from the group consisting of brass, copper and aluminum.
In one embodiment, the apparatus further comprises a manifold adapted for circulating a fluid and coupled to the receptacle and a pump utilized for the circulating. The manifold may be coupled to multiple receptacles.
In one embodiment, the absorption device is coated with a coating. The coating may be aluminum nitride.
In one embodiment, the absorption device may have a corrugated shape.
In one embodiment, the insert is a counter-flow tube. The counter-flow tube may be disposed inside the receptacles and may be adapted to flow a thermal transfer fluid therein. The counter-flow tube may include an inner tube and an outer tube, and the thermal transfer fluid may flow between the inner tube and the outer tube.
In one embodiment, the apparatus further comprises a seal connecting the receptacle to the insert. The seal may be a metallic disk, and the insert may extend through a center of the metallic disk.
In another aspect of the invention, a method for collecting solar thermal energy includes positioning a reflector exterior to a receptacle, the receptacle containing an absorption device positioned proximate to and substantially conforming to at least a portion of an internal surface of the receptacle, wherein the reflector is adapted to direct sunlight onto the absorption device; positioning an insert inside the receptacle, the insert being coupled to the absorption device, and the insert being adapted for counter-flow; and circulating a fluid within the insert.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a solar thermal energy collecting apparatus according to an embodiment of the present invention;

FIGS. 2A and 2B illustrate cross-sectional views taken along II-II of FIG. 1 of solar thermal energy collecting apparatus according to embodiments of the present invention;

FIG. 3 illustrates a cross-sectional view of a receptacle with another embodiment of an absorption device; and

FIG. 4 illustrates a detailed view of a section of the counter-flow tube in the apparatus of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention provide method and apparatus for collection and/or transferring of solar thermal energy. In this regard, embodiments of the present invention may provide inexpensive and efficient manners for collection of solar thermal energy.
Referring to FIGS. 1, 2A and 2B, a solar thermal energy collection apparatus 100 according to an embodiment of the present invention is illustrated. In the illustrated embodiment, the apparatus 100 includes one or more receptacles 120, each receptacle 120 having an insert 130 located therein. In the illustrated embodiment, the receptacle 120 is a single-layer cylindrical glass tubing that is closed at one end. The single-layer glass configuration allows for operation of the apparatus at higher temperatures and results in increased heat removal, as described below. Of course, in other embodiments, various other types of receptacles may be used. For example, in one embodiment, the receptacle 120 may be a double-walled dewar with an inner wall and an outer wall. The region between the inner wall and the outer wall may be evacuated to reduce heat loss. The level of evacuation of the region between the inner wall and the outer wall may be varied to either increase efficiency (e.g., reduce heat loss) or improve cost-effectiveness.
The other end of the receptacle 120 may be sealed with, for example, a metallic disk 118 by way of a glass-to-metal seal. In other embodiments, the metallic disk 118 may be replaced with another type of closure that is sealed with the receptacle 120. Preferably, the closure allows simple and efficient assembly of the receptacle 120 to the apparatus 100 while ensuring integrity in the sealing of the receptacle. In other embodiments the metallic device may be replaced with a glass device used as a seal. In other embodiments, the metallic disk may be replaced with a device having a non-disk configuration. Any device may be used instead of metal disk 118 as long as a reliable seal is a provided between the receptacle 120 and a manifold 110.
In one embodiment, the inside of the receptacle 120 is evacuated. The vacuum inside the receptacle 120 facilitates reduction of thermal loss, thereby improving efficiency of the apparatus, as described below. In this regard, the metallic disk 118 or other such closure provides sufficient sealing to maintain the vacuum within the receptacle 120. The level of evacuation of the receptacle 120 may be varied to either increase efficiency (e.g., reduce heat loss) or improve cost-effectiveness.
The receptacle 120 is positioned such that an external reflector 140 concentrates solar thermal energy (or solar irradiance) onto the receptacle 120. The shape of the reflector 140 may be selected from a variety of shapes. In some embodiments, the reflector 140 may operate in conjunction with a solar tracking component. Preferably, the reflector 140 is adapted to operate in the absence of such a tracking component. In one embodiment, the external reflector 140 is a compound parabolic concentrator (CPC). Such reflectors are well known to those skilled in the art.
FIGS. 2A and 2B illustrate two embodiments of an external reflector 140 a, 140 b for use with embodiments of the present invention. Referring first to FIG. 2A, the external reflector 140 a has two concave, parabolic components joined by a central convex, v-shaped component. Each concave component forms substantially half of a parabola.
Referring now to FIG. 2B, the external reflector 140 b includes two concave, parabolic segments joined to each other. In this embodiment, each concave component forms substantially more than half of a parabola. In this regard, the two concave segments join to form an inverted “v” shape. Other reflector configurations may also be used.
Thus, the shape of the reflector 140 directs all sunlight incident on the reflector 140 within a predetermined angle of incidence onto the receptacle 120. In this regard, sunlight is concentrated efficiently onto the receptacle 120 while minimizing heat loss. Further, the evacuated configuration of the receptacle 120 facilitates minimizing of the heat loss. Thus, sufficient efficiency of the apparatus 100 can be achieved in the absence of a solar tracking component, thereby resulting in significant cost reduction.
Each receptacle 120 is provided with an insert 130 adapted to fit within the receptacle 120. The insert 130 may be formed of a variety of materials. In one embodiment, the insert 130 is formed of a metal from the group of brass, copper and aluminum. The insert 130 enters the receptacle substantially at the cross-sectional center of the receptacle through the sealed area (e.g., the metal disk 118). In this example, a seal may be formed between the insert 130 and the metal disk 118 to maintain a vacuum within the receptacle 120. Further inside the receptacle 120, the insert 130 includes a shifting portion 132 which shifts the insert to become closer to a wall of the receptacle 120. In one embodiment, the shifting portion 132 shifts insert 130 toward the cross-sectional bottom of the tube, as shown in FIG. 2B, so that it is close to the apex of the reflector. In another embodiment, the shift may be further from the reflector and to one side as shown in FIG. 2A.
The insert 130 is coupled to a manifold 10, which is also coupled to an insert corresponding to each of the other receptacles of the apparatus 100. The number of receptacles 120 and corresponding inserts 130 coupled to the manifold 110 may be selected from any practical number dependant on the size of the apparatus 100 desired.
In one embodiment, as illustrated in FIGS. 1, 2A and 2B, the insert 130 may be coupled to the receptacle 120 in a variety of manners including, but not limited to, welding. In one embodiment, the coupling of the receptacle 120 and the insert 130 includes use of screw-type threads formed on the manifold 110 and the tube 130, similar to those found on conventional plumbing joints, that may use a thread seal. In this embodiment, the vacuum area in the receptacle 120 and the seal maintaining the vacuum are provided with the receptacle 120 and insert 130 together. This provides ease of on-site assembly and ease of maintenance and repair.
In one embodiment, the insert 130 is an integral part of the manifold 110. In this regard, the insert 130 may be formed as an integral part of the manifold 110 and does not include any joints, connections or seals. The integral configuration of the insert 130 and the manifold 110 reduces the number of parts required, thereby reducing the time and effort required for installation and assembly of the apparatus 100 in the field. Thus, during assembly, the receptacle 120 only needs to be positioned around the insert 130, a vacuum area pulled and secured with, for example, the metallic disk 118. Further, the integral configuration eliminates a potential leakage point for fluid flowing through the receptacle, as described below.
The manifold 110 includes an inlet pipe 112 and an outlet pipe 114 for circulating a fluid through the manifold 110 and the insert 130. A pump 116 is provided to circulate the fluid 110. The pump 116 may be located in the main portion of the manifold (as shown) or away from the receptacles 120. The dimensions of the inlet pipe 112, the outlet pipe 114 and the pump 116 may be selected according to the requirements of the specific implementation of the collector 100.
The inlet pipe 112 and the outlet pipe 114 are coupled to the insert 130. The insert 130 is adapted for counter-flow of fluid. One embodiment of such an insert is illustrated more clearly in FIG. 4. In the illustrated embodiment, the insert 130 includes an outer tube 134 and an inner tube 136. As illustrated in FIG. 4, the bottom end of the inner tube 136 is spaced apart from the end of the outer tube 134. The amount of space between the bottom end of the inner tube 136 and the end of the outer tube 134 is sufficient to allow fluid to flow freely around the open end of the tube 130. As illustrated by the arrows in FIG. 4, fluid may flow in through the inner tube 136 and may flow out through a region between the outer tube 134 and the inner tube 136. In this regard, the inner tube 136 and the outer tube 134 may be concentrically positioned. Those skilled in the art will understand that the direction of flow within the insert 130 may be reversed in other embodiments, which are also contemplated within the scope of the present invention.
An absorption device, such as absorption fin 150, is positioned within the receptacle 120. The absorption fin 150 may be formed of a variety of materials and may take a shape other than that generally categorized as a fin. In one embodiment, the absorption fin 150 is formed of a metal from the group of brass, copper and aluminum. In one embodiment, the absorption fin 150 is positioned proximate to the internal surface of the receptacle 120. Further, the absorption fin 150 is configured to substantially conform to the internal surface of the receptacle 120. Although the embodiment illustrated in FIGS. 1, 2A and 2B includes an absorption fin 150 which conforms to the entire circular cross section of the receptacle 120, other embodiments may include fins which conform to a portion of the receptacle 120.
In one embodiment, the outer surface of at least a portion of the absorption fin 150 is covered with a selective coating. The coating facilitates thermal absorption of solar thermal energy by the absorption fin 150 to increase efficiency of the apparatus 100. The coating may be aluminum nitride cermets or other types of materials that facilitate thermal absorption.
In one embodiment, the absorption fin 150 is thermally coupled to the insert 130 in order to facilitate transfer of thermal energy to the manifold 110. In this embodiment, a substantial portion of one side of the insert is adjacent the absorption fin 150. The insert 130 may also be adjacent the absorption fin 150 so as to be thermally coupled to it, but not be physically coupled. In another embodiments the absorption fin 150 is integrally formed with the insert 130. In other embodiments the absorption fin 150 is thermally coupled to the insert 130 by mechanical means, such as welding, for example. The length of the absorption fin 150 and the insert 130 within the receptacle 120 may be as long as the receptacle 120 in which it is located or the devices 130, 150 may be shorter than the receptacle 120.
As illustrated most clearly in FIG. 2, the absorption fin 150 may have a circular cross section to conform to the circular cross section of the receptacle 120. In the embodiment illustrated in FIG. 2, the absorption fin 150 is provided with a substantially smooth, continuous surface. In other embodiments, as exemplarily illustrated in FIG. 3, an absorption fin 152 may be provided with a corrugated surface. The corrugations provide an increased surface area for the absorption fin 152 while still conforming to the internal surface of the receptacle 120.
In operation, a fluid is circulated through the manifold 110 via the pump 116. The flowrate of the fluid through the manifold 110 may be adjusted for particular conditions and particular implementations. The fluid circulates through the inlet pipe 112 and into the counter-flow insert 130 within the receptacle 120. In embodiments in which the insert 130 is integral with the manifold 110 (and the inlet pipe 112), no leakage issues are present. The flow of the fluid through the insert, as exemplarily described above with reference to FIG. 4, forms a circulation path within the receptacle 120 (through the insert 130) and the manifold 110. The fluid then exits the insert 130 and the receptacle 120 to the outlet pipe 114. Thus, in this embodiment, substantially all of the insert 130 contains circulating fluid. Again, the integral configuration of the insert 130 and the manifold 110 prevents leakage of the fluid as it exits the receptacle 120. Those skilled in the art will understand that the circulation path (inlet pipe to insert to outlet pipe) may be reversed in other embodiments, which are also contemplated within the scope of the present invention.
Thus, solar thermal energy is directed by the reflector 140 onto the receptacle 120. The solar thermal energy is absorbed by the receptacle 120 and, more specifically, the absorption coating on the outer surface of the absorption fin 150. The vacuum created within the receptacle 120 reduces thermal heat loss by eliminating the conduction and convection from the absorption fin 150 and the insert 130.
While circulating through the insert 130, the fluid is heated by the thermal energy transferred through the absorption fin 150, thereby facilitating transfer of solar thermal energy from the apparatus 100. The fluid circulated through the apparatus 100 may be selected from a variety of fluids. In one embodiment, the fluid is mineral oil.
Embodiments of the present invention are capable of heating the fluid to temperatures of above 280 degrees Fahrenheit without the use of a solar tracker component. Certain embodiments are capable of heating the fluid to temperatures of above 300 degrees Fahrenheit as the fluid exits the receptacle 120. Thus, embodiments of the present invention can provide efficient collection of solar thermal energy in a cost-effective manner.
While particular embodiments of the present invention have been disclosed, it is to be understood that various different modifications and combinations are possible and are contemplated within the true spirit and scope of the appended claims. There is no intention, therefore, of limitations to the exact abstract and disclosure herein presented.

Claims

1. An apparatus for collecting solar energy, comprising:

a receptacle adapted for receiving solar thermal energy;

an insert adapted for counter-flow located within the receptacle; and

an absorption device positioned proximate to and substantially conforming to at least a portion of an internal surface of the receptacle and thermally coupled to the insert.

2. The apparatus of claim 1, wherein the receptacle has a vacuum drawn interior that is sealed with a glass to metal seal.

3. The apparatus of claim 1, further comprising a non-imaging optic reflector located external to the receptacle and adapted to direct solar thermal energy to the receptacle.

4. The apparatus of claim 3, wherein the reflector is a compound parabolic concentrator (CPC).

5. The apparatus of claim 1, wherein a substantial portion of one side of the insert is adjacent the absorption device.

6. The apparatus of claim 5, wherein the insert enters the receptacle substantially at a cross-sectional center of the receptacle and, further inside the receptacle, the insert shifts to become closer to the absorption device and closer to a non-imaging optical reflector.

7. The apparatus of claim 1, wherein the insert is a metal selected from the group consisting of brass, copper and aluminum.

8. The apparatus of claim 1, wherein the absorption device is a metal selected from the group consisting of brass, copper and aluminum.

9. The apparatus of claim 1, further comprising:

a manifold adapted for circulating a fluid and coupled to the receptacle; and

a pump utilized for the circulating.

10. The apparatus of claim 9, wherein the manifold is coupled to multiple receptacles.

11. The apparatus of claim 1, wherein the absorption device is coated with a coating.

12. The apparatus of claim 11, wherein the coating is aluminum nitride.

13. The apparatus of claim 1, wherein the absorption device has a corrugated shape.

14. The apparatus of claim 1, wherein the insert is a counter-flow tube.

15. The apparatus of claim 14, wherein the counter flow tube is disposed inside the receptacle and is adapted to flow a thermal transfer fluid therein.

16. The apparatus of claim 14, wherein the counter-flow tube includes an inner tube and an outer tube and wherein the thermal transfer fluid flows between the inner tube and the outer tube.

17. The apparatus of claim 1, further comprising a seal connecting the receptacle to the insert.

18. The apparatus of claim 17, wherein the seal is a metallic disk, and wherein the insert extends through a center of the metallic disk.

19. A method for collecting solar thermal energy, comprising:

positioning a reflector exterior to a receptacle, the receptacle containing an absorption device positioned proximate to and substantially conforming to at least a portion of an internal surface of the receptacle, wherein the reflector is adapted to direct sunlight onto the absorption device;

positioning an insert inside the receptacle, the insert being coupled to the absorption device, and the insert being adapted for counter-flow; and

circulating a fluid within the insert.

20. The method of claim 19, wherein a manifold is adapted to circulate the fluid, the receptacle being coupled to the manifold.

21. The method of claim 19, wherein the counter flow insert is an element of the manifold.

22. The method of claim 20, wherein the manifold is coupled to multiple receptacles.

23. The method of claim 19, wherein the absorption device is coated with a coating of aluminum nitride.

24. The method of claim 19, wherein the reflector is a compound parabolic concentrator (CPC).

25. The method of claim 19, wherein the insert and the absorption device are formed of a metal selected from the group consisting of brass, copper and aluminum.