Intermediate Photovoltaic Concentrator Systems

Abstract

A 53.5 sq m (576 sq ft) 3,000 Wp second generation intermediate concentrator system has been constructed using funds provided by the U.S. Department of Energy concentrates approximately 4.5x -suns on Motorola's lx-sun, 33.0 cm (13 in) wide panels. The panels are actively cooled by circulating water from the shallow pool on which the collector floats. Azimuth tracking, made possible by the water bearing, is used.The lightweight collector can float on as little as 2.5 to 5 cm (1 to 2 in) of water. The segmented parabolas are cut out of blocks of expanded polystyrene with a hot wire. The width of each mirror segment is selected so as to reflect a full beam of light across the receiver. By using a laser for mirror alignment, optimum concentration is achieved . The use of the laser alignment makes it possible to build larger parabolas with widths of 6m (20 feet) or more. Collector and /or photovoltaic panel widths can be varied to achieve any desired concentration up to about 20x -suns.For the lower latitudes the use of large floating modules tracked in an azimuth mode continues to look intriguing. For the high latitudes narrower collector widths can be used and tracked in the more conventional altitude tracking mode. In the 2 to 10x-sun range terrestrial (lx-sun) photovoltaic panels appear to be the most cost effective, particularly in the smaller system sizes. The use of 10 to 20x sun concentrator cells with low-cost methods of mounting, look promising for large photovoltaic systems. The above concentrator systems are actively cooled, which increases cell efficiency and /or rakes it possible to sell low temperature thermal energy, which further improves the economics of the system. The thermal energy can be stored in the water on which the collector floats.