Efficiency of Solar Electricity Production With Long-Term Storage

Solar electric production systems with energy storage were simulated and compared, including an ammonia thermochemical cycle, compressed air energy storage (CAES), pumped hydroelectric energy storage (PHES), vanadium flow battery, and thermal energy storage (TES). All systems used the same parabolic concentrator to collect solar energy and Stirling engine to produce electricity. Efficiency and storage losses were modeled after existing experiments. At receiver and ammonia synthesis temperatures of 800 K, efficiencies of all systems except TES were initially similar at 17-19%, while TES provided similar to 23%. Further, TES was most efficient for diurnal-scale storage. However, lower time-dependent storage losses caused the ammonia system to have the highest efficiency after one month of storage and to be increasingly favored as time of storage increased. Solar electric production with full capacity factor may be most efficient with a combination of systems including direct solar-electric production and systems with both diurnal and long-term storage.