is 0.4, the land area reduces to 1.5 km3 (0.6 mi3 ). A 1000 MWe plant could cover 6 mi (2.45 mi x 2.45 mi). For an overall system efficiency of 22.5%, the unused direct sunlight waste heat) is 344 MWt for each 100 MWe produced based on the area intercepted by the dish collector. The use of the term waste heat is something of a misnomer when applied to solar plants. A more useful term would be the plant excess waste heat. That is, the heat released by the plant subtracted from the heat that would be released over the plant land area if there were no solar plant on the land. The arid desert type land that would most probably be used has a certain absorptivity and reflectance to incoming solar radiation. Assuming that the albedo of the land is 0.30 (Ref. 11), 30% of the incoming solar energy would "bounce" off the surface and 70% would be absorbed. This would heat up the land surface and be re-radiated to the sky and heat the air convectively. The heat absorbed by the land should be compared to the heat left behind by the solar plant to see if there is a net positive or negative heat balance. The dish col lector-Brayton engine power plant does not require water for cooling. Only ambient air is used for cooling and it is heated from approximately 20°C to 110°C as it passes through the heat rejection heat exchanger. At the optimum design point of 815°C collector temperature, the collector efficiency is 70%. The Brayton engine efficiency was 36% at this point. The dish collector uses only direct sunlight. Typically,about 12% of solar insolation is diffuse on a clear day in the Southwest. Therefore, when operating at the rated conditions of 100 MWe, 444 MWt of direct solar energy is required for this cycle. The total insolation on the dishes is 498 MWt of which 54 MWt is diffuse. About 12% of the diffuse sunlight (6 MW) will be absorbed in the dish surface and subsequently rejected at the plant site. The rest
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