COMPARISON OF METHODS FOR LONG -TERM STORAGE OF SOLAR ENERGY FOR ELECTRIC PRODUCTION

摘要

An ammonia thermochemical energy storage cycle was simulated with TRNSYS and MATLAB. The collector was a parabolic dish with a receiver/dissociation reactor at the focal point. Major sources of loss in the receiver were due to convection and emitted radiation terms, both of which were directly related to the average receiver temperature. The product gases (nitrogen and hydrogen) were stored at ambient temperature. To produce electricity, a catalytic reactor was used to reform ammonia and release heat to drive a Stirling engine. Overall efficiency of the solar ammonia cycle system was found to be a strong function of synthesis reactor temperature, ranging from ～2% at 500 K to ～18% at 800 K. In contrast, the dissociation reactor temperature was found to have relatively little effect on efficiency. Performance was compared against compressed air energy storage (CAES), pumped hydroelectric energy storage (PHES), and vanadium flow batteries, with reported round-trip (electricity-storage-electricity) efficiencies of 82%, 75%, and 74%, respectively. For comparison with the ammonia system, these efficiencies were integrated with that of a dish Stirling system for producing the original electricity. The overall (solar-electric-storage-electric) efficiencies of the CAES, vanadium flow battery, and PHES systems ranged from ～10% to ～18% for solar receiver temperature of 500 K to 800 K. For dissociation and synthesis reactor temperatures of 800 K, efficiency of the ammonia system was 18%, comparable to the alternatives. However, the ammonia thermochemical energy storage system has the advantage that solar energy can be stored indefinitely, whereas the other storage mechanisms involve time-dependent losses.