Patent Application
20100012169
The present invention relates generally to the field of solar energy collection. In particular, the present invention relates to the field of concentrated photovoltaics (CPV). Solar energy collection has already proven to be a very effective energy option. A particular type of module utilized in a conventional solar system employs a photovoltaic (PV) cell. PV cells may be configured into modules and arrays that convert solar irradiation into usable electrical power for a wide variety of applications. As a power generation and distribution solution, PV modules can provide an alternative or supplement to traditional grid-supplied electricity or can serve as a stand-alone source of power in remote regions.
Concentrating solar collectors reduce the need for large semiconductor substrates by concentrating solar radiation (i.e., sun rays) using, e.g., a parabolic reflectors or lenses that focus the beams, creating a more intense beam of solar energy that is directed onto a small PV cell. Thus, concentrating solar collectors have an advantage over flat-panel collectors in that they utilize substantially smaller amounts of semiconductor. Another advantage that concentrating solar collectors have over flat-panel collectors is that they are more efficient at generating electrical energy. Two element CPV systems comprised of a primary mirror for collecting solar radiation and a secondary mirror for focusing the collected irradiation onto a non imaging optical concentrator or directly onto a PV cell are known in the art.
As the use of CPV systems becomes more widespread, there exists a need to optimize the efficiency of these systems. CPV and related solar energy systems are rendered less efficient by the loss of energy from irradiance striking the rear surface of the secondary mirror. The amount of energy loss caused by the obscuration by the secondary mirror is dependent on the size of the mirror. There exists a need in the art to make CPV systems more efficient and utilize more of the solar radiation striking the solar energy collection unit.
The present invention provides a solar energy system comprising a substantially planar surface capable of allowing solar radiation to pass through it. The solar energy system of this invention provides a first and second solar energy collection system. In one embodiment of this invention, the solar energy system provides a first and second photocell for receiving solar energy. The first photocell may receive a portion of solar radiation. The second photocell may receive a second portion of the solar radiation that is not collected by the first photocell. The first and second photocells then may convert a substantial amount of the received solar radiation into usable electricity.
The present invention may receive reflected or unreflected solar radiation. The second photocell may be a flat panel or a multi-junction cell or any other solar to electrical energy converting material known in the art. The second solar energy system may comprise an optical polymer coating on the outer surface of the second primary mirror. The optical polymer coating may be further treated to function as the secondary mirror of the first solar energy system for directing solar radiation to the first photocell.
The electricity generated by the first and second photocells may be conducted along parallel wiring systems or may be conducted along the same wiring system. A portion of the wiring may be imbedded in the optical polymer coating. The solar energy system of this invention may be made by providing a substantially planar surface capable of allowing solar radiation to pass through it, and a first concave mirror for reflecting a first portion of the solar radiation. The method of making this invention further comprises providing a first convex mirror for reflecting the first portion of the solar radiation reflected by the first concave mirror and providing a first photocell for receiving the first portion of the solar radiation reflected by both the first concave mirror and the first convex mirror. A second photocell for receiving a second portion of the solar radiation not reflected by the first mirror is then provided. This method results in generating a first electrical current from the major photocell and generating a second electrical current from the minor photocell.
In order to understand the invention and to see how it may be carried out in practice, a number of embodiments will now be described, by way of non-limiting examples only, with reference to the accompanying drawings in which:
Reference will now be made in detail to embodiments of the disclosed invention, one or more examples of which are illustrated in the accompanying drawings.
The present invention provides for electrical power to be generated locally using a solar energy system that is comprised of a major solar energy system and a minor solar energy system. In one embodiment of this invention, the minor solar energy system may be comprised of a photocell (260) interposed between the mechanical attachment surface of the secondary mirror (230) and the protective front panel (210) as shown in
An alternative embodiment of this invention shown in
In another embodiment of this invention, a two element optical system located above the secondary mirror of the primary solar energy system may be a solid optical element. The solid optical element may be a monolithic molded optic, made of glass or other transparent material. The optical system may be aplanatic and the primary and secondary reflectors may the first and second surface of the solid optical element respectively
The secondary mirror of the major solar energy system and the primary mirror of the minor solar energy system may be formed from a single substrate. In one embodiment of this invention the shape of the two mirrors may be independently optimized to function as required. The shape of the minor primary mirror (390) may be substantially parabolic to concentrate solar radiation onto the minor secondary mirror (360). The shape of the major secondary mirror (380) may be substantially hyperbolic in order to collect a maximum amount of radiation reflected from the major primary mirror (not shown) and direct it towards the major photocell (not shown). In one embodiment the substrate may be made by injection molding, resulting in deep meniscus lens. In this way the concave surface of the substrate may be made substantially parabolic and the convex surface may be made substantially hyperbolic. After injection molding, the convex front and concave back surfaces may each be coated to form a mirror surface.
One embodiment for the method for making a solar energy system comprises placing a liquid optical coating into a mold that conforms to the shape of the first secondary mirror and is substantially hyperboloid, then inserting a substrate into the mold that conforms to the shape of the second concave primary mirror and is substantially parabolic. The liquid optical coating may then be polymerized. A mirror surface may then be applied to the convex surface of the optical coating. The surface of the substrate may be may be optionally mirrored on the convex front side prior to insertion into the liquid optical coating or the concave back side at any time in the manufacturing process
In another embodiment, the two mirror layers may be formed from a single substrate by a polymerization process (
In one embodiment of this invention the optical system of the minor solar energy system may be housed in the area bounded by the secondary mirror of the major solar energy system and the protective front panel. This is seen in
In this embodiment of this invention, solar energy received by the minor solar energy system may be focused onto the photocell of the major solar energy system. In one embodiment the invention, a cut out in the secondary mirror of the major solar energy system would permit light received by a minor energy system to be directed to the photocell of the major solar energy system. This approach need not impact the performance of the major solar energy system as the projection onto the secondary mirror of the area cutout out of the primary mirror to house the major photocell defines an unused region of the secondary mirror. Under ideal tracking conditions, the unused central region may be about 6 mm in diameter. Allowing for tracking errors of up to about 1.75 degrees, the region always free of optical irradiance may reduced to about 3.0 mm for some embodiment of this invention.
In another embodiment of this invention shown in
In one embodiment electrical energy from the minor solar energy system may be brought to the electrical system of the major solar energy system by the use of additional wiring as shown in
Although embodiments of the invention have been discussed primarily with respect to specific embodiments thereof, other variations are possible. For example, while the invention has been described with respect to solar energy collectors, the invention may applied to the recovery of solar radiation for the purposes of illumination, solar thermal collection etc. . . . Steps can be added to, taken from or modified from the steps in this specification without deviating from the scope of the invention. In general, any flowcharts presented are only intended to indicate one possible sequence of basic operations to achieve a function, and many variations are possible.
While the specification has been described in detail with respect to specific embodiments of the invention, it will be appreciated that those skilled in the art, upon attaining an understanding of the foregoing, may readily conceive of alterations to, variations of, and equivalents to these embodiments. These and other modifications and variations to the present invention may be practiced by those of ordinary skill in the art, without departing from the spirit and scope of the present invention, which is more particularly set forth in the appended claims. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only, and is not intended to limit the invention. Thus, it is intended that the present subject matter covers such modifications and variations as come within the scope of the appended claims and their equivalents.
