US20090107489A1

US20090107489A1 - Solar thermal energy collector

Info

Publication number: US20090107489A1
Application number: US11/970,137
Authority: US
Inventors: Randy C. Gee; Roland Winston
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-10-29
Filing date: 2008-01-07
Publication date: 2009-04-30
Also published as: WO2009058713A1

Abstract

A solar thermal energy collector includes a receptacle and a tube. The tube is adapted to fit within the receptacle and defines a first region within the tube and a second region between the tube and an internal surface of the receptacle. A fluid is circulated between the first region and the second region for transferring of the solar thermal energy.

Description

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application claims priority under 35 U.S.C. §119(e) from U.S. Provisional Application Ser. Nos. 61/007,896, filed Oct. 29, 2007, and 60/989,772, filed Nov. 21, 2007, incorporated herein by reference in their entirety.

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, which is circulated 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 to the heat-transfer fluid.

SUMMARY OF THE INVENTION

In one aspect, the invention includes a solar thermal energy collector comprising a receptacle and a tube. The tube is adapted to fit within the receptacle and defines a first region within an internal surface of the tube and a second region between an external surface of the tube and an internal surface of the receptacle. A fluid is circulated through the first region and the second region for transferring of the solar thermal energy.
In one embodiment, the fluid for transfer of solar thermal energy is mineral oil.
In one embodiment, the tube is coupled to a manifold, and the manifold is coupled to a pump that circulates the fluid through the manifold, the first region and the second region. The manifold may be coupled to the receptacle with a seal. The manifold may include a tube-in-tube configuration. The manifold may be coupled to additional tubes.
In one embodiment, the tube is an integral part of a manifold.
In one embodiment, the fluid circulates first through the first region and then through the second region.
In one embodiment, the receptacle is a dewar, the dewar having an outer wall and an inner wall, the dewar having a vacuum drawn between the outer wall and the inner wall, and wherein the dewar is all glass. The dewar may have a solar-radiation absorption coating on an outer surface of the inner wall. The coating may be aluminum nitride cermets.
In one embodiment, absent a solar tracker component and in combination with an external reflector component, the fluid has a temperature above 280 degrees Fahrenheit when the fluid exits the receptacle.
In one embodiment, the collector further comprises an external reflector for reflecting sun rays onto the receptacle. The external reflector may be a compound parabolic concentrator (CPC).
In another aspect of the invention, a method for collecting solar thermal energy includes positioning one or more reflectors external to one or more receptacles, the reflectors being adapted to direct solar thermal energy to the one or more receptacles; positioning a manifold having one or more tubes adapted to fit within the one or more receptacles, each tube defining a first region within the tube and a second region between the tube and an internal surface of the receptacle; and circulating a fluid between the first region and the second region for transferring of the solar thermal energy.
In another aspect, the invention includes a solar collector for heating a thermal transfer fluid. The collector comprises a dewar having an inner wall with an inner surface and an outer surface, the dewar having an outer wall with an inner surface and an outer surface, the dewar having a vacuum drawn between the outer wall inner surface and the inner wall outer surface, and the dewar having an absorbing material coating the inner wall outer surface; a fluid tube disposed inside the dewar, the fluid tube having an inner surface and an outer surface defining a first region; and a second region disposed in substantially the complete area between the fluid tube outside surface and the dewar inner surface of the inner wall. The thermal transfer fluid flows through both the first region and the second region.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a solar thermal energy collector 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 collectors according to embodiments of the present invention; and

FIG. 3 illustrates a cross-sectional view taken along III-III of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention provide devices, methods and systems 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 collector according to an embodiment of the present invention is illustrated. In the illustrated embodiment, a collector 100 includes one or more receptacles 120 coupled to a manifold 110. The manifold 110 includes an inlet pipe 112 and an outlet pipe 114 for circulating fluid through the manifold 110 and the collector 100. A pump 116 is optionally provided to circulate the fluid 110. 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 manifold 110 is coupled to one or more receptacles 120. The number of receptacles 120 may be selected from any practical number dependant on the size of the collector system desired. Further, the manifold may be coupled to a plurality of receptacles in a serial manner, a parallel manner or any combination thereof. A seal 118 is provided to prevent leakage of the fluid from the manifold 110. In one embodiment, the seal 118 includes O-ring compression seals. In other embodiments, other types of seals may be used. Preferably, the seals allow simple and efficient assembly of the manifold 110 and the receptacle 120 while ensuring prevention of leakage.
Each receptacle 120 is preferably an all-glass dewar having a double-wall configuration, as most clearly illustrated in FIGS. 2A and 2B. Of course, in other embodiments, various other types of receptacles may be used. In one embodiment, the receptacles are cylindrical borosilicate glass bottles with a closed end, as exemplarily illustrated in FIG. 1. Each dewar 120 is provided with an inner wall 122 and an outer wall 124. The region between the inner wall 122 and the outer wall 124 is evacuated. The vacuum region results in low heat loss. The level of evacuation of the region between the inner wall 122 and the outer wall 124 may be varied to either increase efficiency (e.g., reduce heat loss) or improve cost-effectiveness.
In one embodiment, an outer surface of the inner wall (i.e., the surface facing the vacuum region) is coated with a solar-radiation absorption coating 126, such as aluminum nitride cermets. In other embodiments, other commercially available coatings may be used. The solar-radiation absorption coating 126 facilitates absorption of solar thermal energy by the receptacle 120.
Each receptacle 120 is provided with a tube 130 adapted to fit within the receptacle 120. In one embodiment, on one end, the tube 130 is inserted into the receptacle 120 and has an open end. As illustrated in FIG. 1, the open end of the tube 130 is spaced apart from the end of the receptacle 120. The amount of space between the open end and the end of the receptacle 120 is sufficient to allow fluid to flow freely around the open end of the tube 130. On the other end, the tube 130 is coupled to the manifold 110, which is coupled to a tube corresponding to each of the other receptacles of the collector 100. The tube 130 may be coupled to the manifold 110 in a variety of manners including, but not limited to, welding. In one embodiment, the coupling of the manifold 110 and the tube 130 includes used of screw-type threads formed on manifold 110 and the tube 130, similar to those found on conventional plumbing joints, that may use a thread seal. In a particular embodiment, as illustrated in FIGS. 1, 2A and 2B, the tube 130 is an integral part of the manifold 110. In this regard, the tube 130 may be formed as an integral part of the manifold and does not include any joints, connections or seals. Thus, once created, the tube 130 may not easily be removed from the manifold 110. The integral configuration of the tube 130 and the manifold 110 reduces the number of parts required, thereby reducing the time and effort required for installation and assembly of the collector 100 in the field. Thus, during assembly, the receptacle 120 only needs to be positioned around the tube 130 and secured with, for example, the seal 118. Further, the integral configuration eliminates a potential leakage point for fluid flowing through the receptacle, as described below.
In accordance with embodiments of the present invention, assembly and maintenance of the collection 100 is simplified. With the tube 130 integrally formed (or otherwise pre-assembled) with the manifold 110, only the receptacle 120 needs to be connected. Thus, for maintenance purposes, individual receptacles that may become damaged can be replaced without replacing the entire collector 100. Further, use of appropriate seals 118 between the receptacle 120 and the manifold 110 can make such replacement of receptacles simple, time-efficient and effective. A worker in the field can accomplish such maintenance without expending substantial time and effort.
The receptacle 120 and the manifold 110 are 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.
Thus, the shape of the reflector 140 directs substantially all sunlight incident on the reflector 140 within a predetermined angle of incidence onto the receptacle 120 and, more specifically, onto the thermal absorption coating 126 on the outer surface of the inner wall 122 of the dewar 120. In this regard, sunlight is concentrated efficiently onto the receptacle 120 while minimizing heat loss. Further, the evacuated, double-wall configuration of the dewar 120 facilitates minimizing of the heat loss. Thus, sufficient efficiency of the collector 100 can be achieved in the absence of a solar tracking component, thereby resulting in significant cost reduction. The combination of the reflector 140 and the receptacle 120 is preferably configured to have a large acceptance angle. For example, in one embodiment, an acceptance angle of at least ±35 degrees. Thus, sunlight within at least a 70-degree range is captured, and the associated solar thermal energy is collected.
To facilitate collection of solar thermal energy, the reflector 140 may be configured specifically to capture energy within the solar spectrum. In this regard, the reflector 140 may be formed of a material optimized for the solar spectrum of energy. In some embodiments, the reflector 140 may be coated with a material for such optimization.
In one embodiment, a protective cover 150 is positioned above the receptacles 120. The protective cover 150 may be sized to cover multiple receptacles 120. Alternatively, a single protective cover 150 may be positioned above each receptacle 120. The receptacle is preferably formed of a transparent glazing, such as soda lime glass, which does not interfere with the transmission of sunlight to the reflectors 140.
To further prevent such interference, the protective cover 150 may be provided with an anti-reflective coating. Such anti-reflective coating ensures that sunlight is transmitted to the reflectors 140 without substantial reflecting of the sunlight away from the collector 100. The anti-reflective coating may be applied to either the inner surface of the protective cover 150 (i.e., the surface facing the reflector 140 and the receptacle 120) or the outer surface of the protective cover 150. In one embodiment, a similar anti-reflective coating may also be applied to a surface of the receptacle 120. The anti-reflective coating may be formed of any of a variety of materials. In one embodiment, the anti-reflective coating includes multi-layer, solgel texturing. Thus, collection of solar thermal energy is permitted while providing protection of the collector 100 from debris, for example.
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 tube 130 within the receptacle 120. In embodiments in which the tube is integral with the manifold 110 (and the inlet pipe 112), no leakage issues are present. The positioning of the tube 130 within the receptacle 120 forms a circulation path within the receptacle 120. The circulation path includes a first region 132 within an internal surface of the tube 130 and a second region 134 between an outer surface of the tube 130 and an inner surface of the inner wall 122 of the receptacle 120. Thus, in one embodiment, the fluid is circulated first from the inlet pipe 112 through the first region and then through the second region. In this regard, while the fluid is flowing, it occupies substantially the entire volume within the receptacle 120 with one direction of flow occupying the volume in the first region and the opposite direction of flow occupying the second region. The fluid then exits the receptacle 120 to the outlet pipe 114. The seal 118 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 first region to second region 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 external reflector 140 onto the receptacle 120. The solar thermal energy is absorbed by the receptacle 120 and, more specifically, the absorption coating 126 on the outer surface of the inner wall 122 of the receptacle 120. As noted above, the evacuated region between the inner wall 122 and the outer wall 124 facilitates reduction in heat loss, thereby improving efficiency of the collector 100. While circulating through the first region 132 and the second region 134, the fluid is heated, thereby facilitating transfer of solar thermal energy from the collector 100. Since the fluid flows through the second region and adjacent the inner wall 122, the thermal energy is more directly transferred from the absorption coating 126 to the fluid flowing through the receptacle 120. The fluid then carries the thermal energy out of the receptacle in the form of heat, whereby the fluid is heated by the thermal energy as it flows through the receptacle. The fluid circulated through the collector 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.
In one embodiment, the fluid is selected such that the boiling point of the fluid is higher than the maximum temperature reached by the fluid within the receptacle 120, typically at the point at which the fluid exits the receptacle 120. In this regard, the fluid does not boil while circulating within the receptacle 120 and, therefore, does not exert additional pressure on the walls of the receptacle 120. Accordingly, the receptacle 120 may be formed of a greater variety of materials. In a particular embodiment, the avoidance of additional pressure on the walls allows the receptacle 120 to be formed of glass.
In various embodiments, the fluid is selected such that the flash point of the fluid is higher than the maximum temperature reached by the fluid. In this regard, in the event of a leakage of fluid in the system (e.g., from the manifold in the region of the seal 118), the fluid does not ignite, thereby presenting a fire hazard. Accordingly, the system is made inherently fire-safe.
In one embodiment, the manifold 110 has a tube-in-tube configuration, as exemplarily illustrated in FIG. 3. In this regard, the inlet pipe 112 is positioned within the outlet pipe 114. In one embodiment, the inlet pipe 112 and the outlet pipe 114 are concentrically positioned. Such tube-in-tube configuration may facilitate assembly of the manifold with the receptacles 120. In alternate embodiments, the inlet pipe 112 and the outlet pipe 114 are separated tubes.
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. A solar thermal energy collector, comprising:

a receptacle; and

a tube adapted to fit within the receptacle, the tube defining a first region within an internal surface of the tube and a second region between an external surface of the tube and an internal surface of the receptacle,

wherein a fluid is circulated through the first region and the second region for transferring of the solar thermal energy.

2. The collector of claim 1, wherein the fluid for transfer of solar thermal energy is mineral oil.

3. The collector of claim 1, wherein the tube is coupled to a manifold and the manifold is coupled to a pump that circulates the fluid through the manifold, the first region and the second region.

4. The collector of claim 3, wherein the manifold is coupled to the receptacle with a seal.

5. The collector of claim 3, wherein the manifold includes a tube-in-tube configuration.

6. The collector of claim 3, wherein the manifold is coupled to additional tubes.

7. The collector of claim 1, wherein the tube is an integral part of a manifold.

8. The collector of claim 1, wherein the fluid circulates first through the first region and then through the second region.

9. The collector of claim 1, wherein the receptacle is a dewar, the dewar having an outer wall and an inner wall, the dewar having a vacuum drawn between the outer wall and the inner wall, and wherein the dewar is all glass.

10. The collector of claim 9, wherein the dewar has a thermal absorption coating on an outer surface of the inner wall.

11. The collector of claim 10 wherein the coating is aluminum nitride cermets.

12. The collector of claim 1, wherein absent a solar tracker component and in combination with an external reflector component, the fluid has a temperature above 280 degrees Fahrenheit when the fluid exits the receptacle.

13. The collector of claim 1, further comprising an external reflector for reflecting sun rays onto the receptacle.

14. The solar collector of claim 13, wherein the external reflector is a compound parabolic concentrator (CPC).

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

positioning one or more reflectors external to one or more receptacles, the reflectors being adapted to direct solar thermal energy to the one or more receptacles;

positioning a manifold having one or more tubes adapted to fit within the one or more receptacles, each tube defining a first region within the tube and a second region between the tube and an internal surface of the receptacle; and

circulating a fluid between the first region and the second region for transferring of the solar thermal energy.

16. The method for collecting solar thermal energy of claim 15, wherein the fluid is mineral oil.

17. The method for collecting solar thermal energy of claim 15, wherein the receptacle is a dewar, the dewar has an outer wall and an inner wall, the dewar has a vacuum drawn between the outer wall and the inner wall, and the dewar is all glass.

18. The collector of claim 17, wherein the dewar has a thermal absorption coating on an outer surface of the inner wall.

19. A solar collector for heating a thermal transfer fluid, comprising:

a dewar having an inner wall with an inner surface and an outer surface, the dewar having an outer wall with an inner surface and an outer surface, the dewar having a vacuum drawn between the outer wall inner surface and the inner wall outer surface, and the dewar having an absorbing material coating the inner wall outer surface;

a fluid tube disposed inside the dewar, the fluid tube having an inner surface and an outer surface defining a first region; and

a second region disposed in substantially the complete area between the fluid tube outside surface and the dewar inner surface of the inner wall;

wherein the thermal transfer fluid flows through both the first region and the second region.

20. The solar collector of claim 19 further comprising an external reflector for reflecting sun rays onto the absorbing material inside the dewar.

21. The solar collector of claim 19, wherein the fluid is mineral oil.

22. The collector of claim 19, further comprising a manifold coupled to the receptacle with a seal.

23. The collector of claim 19, wherein the tube is coupled to a manifold and the manifold is coupled to a pump that circulates the fluid through the manifold and the first region and the second region.

24. The collector of claim 19, wherein the tube is an integral part of a manifold.

25. The collector of claim 19, wherein the manifold is coupled to multiple tubes.