Chemical energy storage for solar thermal conversion

ABSTRACT:
The technical and economic aspects of using reversible chemical reactions to store energy in Solar Thermal Electric Conversion (STEC) facilities have been studied. The study included identification of nine promising chemical reactions from a list of over 550 candidates, preliminary process

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designs of energy storage subsystems based on these nine reactions, and extensive systems studies of autonomous (100% solar) and hybrid (requiring alternate energy backup) STEC plants with energy storage subsystems based on the reversible oxidation of S02. Storage round-trip thermal efficiencies . for the reactions studied ranged from 20 to 50 percent; power-related unit co~ts varied between 0.5 x 105 and 10 x' 105 S/MWt maximum storage charging rate; and energy-related unit costs varied between 0.5 x 103 and 24 x 103 S/MWt-hr storage capacity. Process designs based on the two reactions, S02 + 1/2 02 = S03, and CaO + H20 = Ca(OH)2, are discussed in detail. The systems studies used a detailed simulation, based on a year-long, hour-by-hour energy balance, of a central-receiver STEC facility. Over a range of alternate energy cost and geographic location, the optimum busbar energy costs from autonomous STEC plants were 15 to 90 percent higher than those from hybrid plants. Optimum storage requirements of autonomous STEC plants were in the range of 200 to 400 hours, while those for hybrid plants were in the range of 15 to 30 hours.

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