This invention relates to solar energy collectors that track the sun throughout the year. More particularly, the present invention is concerned with concentrator type collectors that use mirror strips to reflect solar radiation to a focal zone.
It is now well established that the cost of solar electricity (photovoltaics) can be greatly reduced when an inexpensive optical material is used to concentrate a large area of sunlight upon the small area of a solar cell. In this manner a single photovoltaic cell will generate the same amount of direct current electricity as would many expensive cells.
Presently, parabolic reflectors and Fresnel refractors are used to concentrate sunlight on cells. Though effective, they are about three times too expensive to be cost-competitive with conventional power plants.
Another type of concentrator is the "slatted" mirror. These reflectors, as shown in U.S. Pats. Nos. 1,951,404 and 2,945,417 use narrow mirror strips, or slats, to perform work. The focal zone that these reflective slats produce is distinctly advantageous to concentrator photovoltaics. In operation, to bring sunlight to convergence, the slats are set at progressively different angles in a framework. The slats reflect many rectangular paths of light that combine, one on top of the other, upon the rectangular face of the solar cell. This "stacked" type focal zone uniformly illuminates the whole cell face which results in a superior electrical conversion efficiency. Furthermore, the evenly distributed character of concentrated sunlight insures that no extreme temperature excursions occur upon the cell. This prolongs the service life of expensive solar cells and their solder joints thus increasing module durability and reliability.
However, these unique advantages cannot overcome the high material cost and labor content involved with prior art slatted modules. Their parts are very complicated to produce and awkward to assemble. For example, each slat must be manufactured to include a fastener at both ends. Then both ends of each slat must be inserted into precisely drilled holes in an expensive frame. Mounted on a fixture and using ray tracing techniques, each slat must be inclined in a manner that assures accurate reflection geometry. Then each of the slats' fasteners must be carefully tightened without changing the inclinations. The result is a delicate and complex device that has highly desirable optical characteristics. In view of their potential impact as photovoltaic concentrators a real need exists to radicaly improve the cost-effectiveness of manufacturing slatted reflectors.
In U.S. Pat. No. 4,519,384 by the present inventor, there is shown an enclosed slatted mirror that begins to eliminate the multitude of parts associated with the prior art. In that patent I show, but do not claim, one-piece louvered sheet material as the optical element. Mounted in a framework, this panel uses stamped louvers to concentrate sunlight rather than individual mirror slats of the prior art. Louvered sheet material was developed for heating and ventilation purposes as a simple, yet sturdy, grill that can be found in most homes and offices today. As embodied in U.S. Pats. Nos. 2,366,224 and 3,403,615, these louvered and ribbed stampings are very inexpensive to mass-produce.
It is prudent to incorporate louvered sheet material and slatted solar concentrators as this combination of art produces an increased electrical efficiency and a lighter module that requires far fewer parts than had heretofore been used or thought necessary. Highly advanced modules are presented hereupon.