SPS is the Next Goal of Commercial Solar Cells AKIO SUZUKI, TAIZO HIRANO, AKIO USHIROKAWA & MAKOYO NAGATOMO Summary SPS solar cells are required to be the same low cost as that of mass-produced terrestrial ones. First, we describe the development situation of terrestrial solar cells, and second, the development trends and cost prospects of future terrestrial ones. The SEG single crystal cell is approaching the limit of cost reduction, and the SOG semicrystalline cell will take its place soon. The amorphous Si cell which is now expanding its market for consumer use rather than for terrestrial use has the advantage in cost reduction. Therefore, it will be the most useful product, if its low efficiency and poor reliability - still unsolved problems-are improved. The cost of the SPS solar cell will be rather higher than that of a terrestrial one because of its high performance. Here, we discuss the factors of high price and the cost prospects of the SPS cell. Introduction One of the main problems of a solar power satellite (SPS) which converts solar energy into electrical power with solar cells is the high cost of solar cells for present satellite systems. It is expected that mass production of them would reduce the cost, but the reduction of the cost of space-use solar cells is not given a high priority of research effort compared to increasing conversion efficiency and life. The high cost of space-use solar cells is accepted because the electrical power system is a subsystem of an expensive space system carried by expensive space transportation. Considering that the SPS is possible only when a much cheaper transportation cost is realized and solar cells are the dominant cost in a total SPS system, cost reduction should be the central issue for technical research and development for solar cells. The annual production of terrrestrial-use solar cells is growing as high as 10 MW in Japan, and the cost of solar cells is becoming as low as ¥1000 in round numbers per watt of direct output of electrical power of solar cells. The cost is doubled for electrical power system made of solar cells. The current cost target is as low as ¥100 per watt, which is a similar order of magnitude as the requirement for SPS. The reduction in cost would increase the need, and eventually mass production will reduce the cost again. Thus the terrestrial-use solar cells are expected to be competitive with other electrical sources in this century. The high quantity of solar cells will be pursued even after that. For example, current research and development of amorphous Akio Suzuki & Taizo Hirano, SHARP Corporation, Tokyo, Japan, and Akio Ushirokawa & Makoto Nagatomo, Institute of Space and Astronautical Sciences, Megoro-ku, Komaba 4-6-1, Tokyo 153, Japan.
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