WO1995006330A1

WO1995006330A1 - Non-tracking solar concentrator heat sink and housing system

Info

Publication number: WO1995006330A1
Application number: PCT/US1994/009401
Authority: WO
Inventors: Christopher P. Kinkaid
Original assignee: Kinkaid Christopher P
Priority date: 1993-08-20
Filing date: 1994-08-18
Publication date: 1995-03-02
Also published as: AU7600494A; TW252183B

Abstract

The invention discloses a system (10) for solar concentration which achieves uniform concentration onto interchangeable receivers (16) at wide angles of acceptance. The preferably single element (11) operates as a non-tracking concentrator while simultaneously functioning as a heat sink. The shaping provides strength and mantains even optical spacing and also serves as the housing (21) for the solar receiver (16). Operating as a heat sink, the concentrator conducts heat from the receivers (16) to the reflectors (13) which functions as a radiator cooling the receiver. This device provides optically wide angles of solar incidence and functions as an isotropic concentrator through these hours. The static concentrator is a standardized solar optical deployment system which provides for receivers which are interchangeable for photovoltaic, photochemical, and photothermal applications.

Description

NON-TRACKING SOLAR CONCENTRATOR HEAT SINK AND HOUSING SYSTEM

Field of the nvention

The present invention relates to solar cell concentrator assemblies and, more particularly, to improved structures for the capture of solar radiation in such assemblies. Background of the Invention

Various types of solar collectors are known. A number of these collectors incorporate V-shaped troughs as the collection device including U.S. Patent Nos. 4,789,408 to Fitzsimmons; 3,350,234 to Ule; 4,217,881 to Brent; and 4,295,463 to Citron. However, existing V- shaped trough solar collectors present a number of problems. First, most of these solar collectors require tracking devices to track the solar radiation in order to ensure operation of the solar collectors over a longer time period during the day thereby generating a sufficient amount of energy to make the solar collectors energy efficient. Such tracking devices are required because these solar concentrators have an angle of acceptance which is quite narrow. Those solar concentrators that have achieved a wider angle of acceptance have usually done so at the expense of isotropic or even irradiation of the solar receiver. Additionally, existing V-shaped solar concentrators in order to incorporate a heat sink function require additional hardware and materials which are both bulky and expensive to operate since the material of the concentrator itself is not suitable for heat sink functions.

Yet another problem with these concentrators is the number of parts required to make the concentrator operational, all of which are subject to wear and require periodic replacement. These concentrators can require a large amount of time and mechanical hardware to position and keep the solar receivers in place. A V-shaped solar concentrator not exhibiting the drawbacks of existing V- shaped trough concentrators is therefore desirable. Biitntnx-ry of the Invention

It is an object of the present invention to provide for an improved V-shaped trough solar concentrator.

It is yet another object of the present invention to provide for a V-shaped trough concentrator having a wide acceptance angle and not requiring tracking hardware.

It still another object of the present invention to provide for a V-shaped trough solar concentrator providing isotropic irradiation of the solar receiver.

Yet another object of the present invention is to provide a V-shaped trough solar concentrator fabricated in such a way as to not require additional hardware or materials for its heat sink.

Still another object of the present invention is to provide for a V-shaped trough solar concentrator which can incorporate the functions of a solar reflector, heat sink, and receiver housing in a single element structure.

Yet another object of the present invention is to provide for- a single element V-shaped trough solar concentrator. Still another object of the present invention is to provide for a V-shaped trough solar concentrator in which irradiated receivers can accomplish different functions such as photothermal and photochemical operations interchangeably. These and other objects of the present invention are accomplished by a single element non-tracking solar concentrator heat sink and housing for holding solar receivers comprising at least one sheet of solar reflective material structured so as to form at least one V-shaped trough, each of the at least one V-shaped troughs having two walls and a base, the base having two sides, each wall having an upper edge and a lower edge. Each trough has a base positioned between the lower edges of the two walls of the at least one trough. A solar receiver housing area is located on one side of the base. The at least two walls and the base may be formed of a heat conducting material which allows the concentrator to act as a heat sink. At least a portion of the joined at least two walls and base may be in contact with a structural member. Preferably, the heat conducting material is aluminum. Preferably, each of the at least one V-shaped trough's base and walls are joined at an angle of 120°. Preferably, the concentrator is formed of only one sheet of solar reflective material so that the concentrator can be formed with a single element. Brief Description of the Drawings Figure 1 is a perspective view of a non-tracking solar concentrator of the present invention;

Figure 2 is a partially exploded side view of the non-tracking solar concentrator of the present invention;

Figure 3 is a top view of one embodiment of the solar concentrator of the present invention;

Figure 4 is a diagram of the present invention operating as a heat sink;

Figure 5 is a diagram illustrating the wider angle of acceptance achieved with the non-tracking solar concentrator of the present invention; and

Figure 6 is an alternative embodiment of the non- tracking solar concentrator of the present invention. Description of the Preferred τn-hrι<iim«»τ.t-

Referring now to Figure 1, an embodiment of the solar concentrator 10 of the present invention is shown. The solar concentrator is comprised of at least one sheet 11 of solar reflective material structured so as to form at least one V-shaped trough 12. Each of the at least one V-shaped troughs 12 has two walls 13 and a base 14. Referring now to Figure 2, another view of the solar concentrator 10 of the present invention is shown. The preferably single sheet 11 of reflective material is shown shaped into V-shaped troughs 12. Preferably, the at least one sheet 11 is formed of aluminum. The preferred material is the Everbrite™ material manufactured by Alcoa Aluminum Corporation. If aluminum is used, the single element solar concentrator can be fully recycled, thereby providing an additional benefit of the instant invention. Additionally, the solar concentrator 10 of the present invention is capable of inexpensive and easy manufacture. Moreover, the solar concentrator assembly also exhibits a structural rigidity and strength which is desirable for the stresses of the environment in which a solar concentrator must operate. These stresses include chemical degradation by ultra¬ violet light, wind loading, hail bombardment, and thermal cycling each day and night. The high structural rigidity results from the reverse angle formed when two side walls 13 are joined at a seam for multiple sets of walls and bases. When the two side wall sections are formed with a bend, the reverse angle creates an inverse "roman arch" which dissipates stress and is extremely strong.

As seen in Figure 2, the solar receiving cells 16 are placed on one side of the base 14 of the V-shaped trough 12. Preferably, the solar receivers 16 are placed on the side of the trough facing the incoming solar radiation 20. Preferably, the at least one sheet 11 is structured so as to create a fitted housing area 21 at the base of the V-shaped trough 12 to help position and secure the solar receiver 16. This can be accomplished by forming or bending the sheet to follow the dimensions of the solar receivers. A top view of one embodiment of the concentrator 10 and the receivers 16 is seen in Figure 3. The preferred method of securing the solar receiver 16 to the receiving trough 21 at the base of the V-shaped trough 12 is with a thermally conducting epoxy which is known in the art or with mechanical locks. Thus, because of the existence of the housing area 21, the receiver 16 can remain stable with respect to the reflecting walls 13 throughout operation thereby assuring more reliable operation of the solar concentrator. The preferred dimensions for the walls, base, and solar receivers are walls—5 1/2" x 48"; base—4 5/16" x 48"; and receivers—4 4/16" x 40". These, of course, can be varied and scaled.

To also achieve the function of the heat sink, the single element concentrator is preferably made of a heat conducting material such as aluminum. The concentrator 10 is then joined to a strut 18, which is preferably aluminum, which enhances the structural rigidity of the invention. The thin high surface area of the at least one sheet 11 operates at a very effective heat sink conducting heat away from the solar receivers through both convection and radiative cooling as seen in Figure 4.

In Figure 4, incident rays of solar radiation 20 contact the wall 13 of the concentrator 10 at points F. The major reflected rays 20' are reflected into housing area 21. The heat generated by the receiver(s) placed in area 21 is dissipated along a path of heat conduction G from the housing area 21 to the reflector walls 13 at a point or area H. At area or point H, heat is conducted away from the concentrator 10 and solar receiver(s) both orthagonally (I) and radially (J) in an efficient manner. Thus, heat is removed from the receivers by (1) conduction (heat transferring to reflecting walls of concentrator) ; (2) convection (ambient air or wind pulls heat off walls); and (3) radiation. The concentrator is an efficient heat sink due to its large surface area and high thermal conductivity.

The preferred angle of the walls 13 with respect to the base 14 is 120°. However, significant variations can be taken on this angle with a proportional reduction in the efficiency of the irradiation of the cells 16. The 120° angle occurs between the base 14 and the lower edge 24 of the walls 13. The upper edges 22 of the walls 13 serve as a transition between each V-shaped trough.

Typical available concentrators require one or two axis tracking hardware. However, the increased complexity, vulnerability to error, and cost of tracking makes it undesirable. Static concentrators (i.e., concentrators not using tracking hardware) typically have been unable to produce a concentrator which is isotropic in its irradiance characteristics and is also capable of receiving solar radiation from wide angles. However, in the instant invention, isotropic irradiance is achieved at wide angles without the need for tracking. Tracking hardware moves the concentrator and solar cells with respect to the normal angle of the solar radiation. The instant invention accomplishes this by using an east-west orientation with the concentrator preferably facing south. At this normal angle, the concentrator remains non-moving during daily operation. As the seasonal angle changes from summer solstice to winter solstice, the instant invention can be adjusted during night operation allowing for a static non-moving orientation during daily operation.

The need for tracking hardware is also removed because of the concentrator's ability to obtain a wide angle of acceptance via the structure of the solar concentrator 10. First, the concentrator 10 is constructed only with walls 13 and without any side walls which can block solar radiation and shade the solar receiver 10. The concentrator 10 of the instant invention further achieves this wide acceptance angle by preferably ensuring that base 14 of the concentrator extends beyond the dimensions of the solar receiver 16.

A schematic illustrating the benefit of this extension on the angle of acceptance can be seen in Figure 5. If the walls 13 of the solar concentrator 10 are extended a distance e beyond the distance b of the solar receiver 16 on either end of the solar receivers, the solar concentrator 10 can accept solar irradiance and irradiate the receivers isotropically between the hours of 9:00 a.m. and 3:00 p.m. If the distance e was not added to the walls 13 of the solar concentrator 10, the solar receiver 16 could accept solar irradiance only during a brief period of the day unless tracking hardware was included to move the concentrator with respect to the normal angle of the incoming solar radiation. Thus, with the instant invention, the east-west orientation previously mostly abandoned by those of skill in the art because of the inability to obtain even irradiance of solar cells can now be employed, thus avoiding the problem of the limited acceptance angle without the addition of tracking hardware.

As seen in Figure 6, the walls 13 of the solar concentrators 10 can also be parabolic in nature. Additionally, a number of solar concentrators 10 can operate together most efficiently with a slight overlap of the concentrators 10, thereby allowing tight stacking of the concentrators in defined areas.

In summary, a single element solar concentrator for photovoltaic, photochemical, and photother al applications is disclosed. A single element concentrator is positioned to receive direct and diffused solar radiation and then transmit dispersed and focused radiation toward solar receivers 20 with optical characteristics of static deployment, isotropic irradiation, and operation from wide angle of incidence. Additionally, the single element can operate as a waste- heat sink radiator and a housing structure for the photovoltaic, photochemical, or photothermal receivers.

It will therefore be readily understood by those persons skilled in the art that the present invention is susceptible of broad utility and application. Many embodiments and adaptations of the present invention other than those herein described, as well as many variations, modifications and equivalent arrangements will be apparent from or reasonably suggested by the present invention and the foregoing description thereof, without departing from the substance or scope of the present invention. Accordingly, while the present invention has been described herein in detail in relation to its preferred embodiment, it is to be understood that this disclosure is only illustrative and exemplary of the present invention and is made merely for purposes of providing a full and enabling disclosure of the invention. The foregoing disclosure is not intended or to be construed to limit the present invention or otherwise to exclude any such other embodiments, adaptations, variations, modifications and equivalent arrangements, the present invention being limited only by the claims appended hereto and the equivalents thereof.

Claims

I claim:

1. A non-tracking solar concentrator heat sink and housing for holding solar receivers comprising:

(a) at least one sheet of solar reflective material structured so as to form at least one V- shaped trough, each said at least one V-shaped trough having two walls and a base, said base having two sides, each wall having an upper edge and a lower edge, and each trough having said base positioned between said lower edges of said two walls of said at least one trough; and

(b) a solar receiver housing area located on one said side of said base.

2. A non-tracking solar concentrator according to claim 1 wherein said at least two walls and said base are formed of a heat conducting material.

3. A non-tracking solar concentrator according to claim 2 wherein at least a portion of said joined said at least two walls and said base is in contact with a structural member.

4. A non-tracking solar concentrator according to claim 2 wherein said heat conducting material is aluminum.

5. A non-tracking solar concentrator according to claim 1 wherein for each said at least one V-shaped trough said base and each said wall are joined at angle of 120°.

6. A non-tracking solar concentrator according to claim 1 wherein the dimensions of said V-shaped trough adjacent said solar receiver are larger than the dimensions of said solar receiver so as to allow for a wider angle of acceptance for the concentrator.

7. A non-tracking solar concentrator and housing for holding solar receivers comprising:

(a) a sheet of solar reflective material structured so as to form at least one V-shaped trough, each said at least one V-shaped trough having two walls and a base, said base having two sides, each wall having an upper edge and a lower edge, and each trough having said base positioned between said lower edges of said two walls of said at least one trough; and

(b) a solar receiver housing area located on one said side of said base.