TABLE 9-2. ENERGY CONSUMPTION FOR PRODUCTION OF SPS At present, the United States imports 90 percent of its aluminum as alumina and bauxite. The remainder is produced from domestic bauxite of which 70 million tons are known to exist. However, aluminum is the third most abundant element in the Earth's crust (8 percent), being exceeded only by silicon (28 percent) and oxygen (47 percent). The enormous identified resources are contained in a variety of other aluminous materials that pose technological problems. The most promising of these are high alumina clays and dawsonite in the rich oil shale deposits of Colorado. United States reserves of tungsten are much less than the projected demand through the year 2000. Hence, the use of tungsten in the solar thermal and nuclear concepts was eliminated. Approximately half of the known world reserves would have been required for this application (most of which are in China). Molybdenum which is far more abundant was chosen as an alternate. For the photovoltaic baseline concept, the solar cells were assumed to be silicon. If galium arsenide is chosen as an alternate, the availability of both galium and arsenic must be considered.
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