Thermodynamic Analysis of a Compressed Air Energy Storage Facility Exporting Compression Heat to an External Heat Load

Fluctuations of electric load call for flexible generation technologies such as gas turbines. Alternatively, bulk energy storage (BES) facilities can store excess off-peak electricity to generate valuable peaking electricity. Interest in electricity storage has increased in the past decade in anticipation of higher penetration levels of intermittent renewable sources such as wind. Compressed Air Energy Storage (CAES) is one of the most promising BES technologies due to the large amount of energy (hundreds of MWh) that can be economically stored. CAES uses off-peak electricity to compress air into underground reservoirs. Air is combusted and expanded at a later time to regenerate electricity. One of the downsides of CAES is the large energy losses incurred in the form of waste compression heat. Distributed CAES (D-CAES) has been proposed in order to improve the roundtrip efficiency of CAES by utilizing the compression heat for space and water heating. The compressor of D-CAES is located near a heat load (e.g. a shopping mall) and the compression heat is recovered to meet this external load. D-CAES collects fuel credits equal to the negated heating fuel, leading to a higher overall efficiency compared to conventional CAES. We perform a thermodynamic analysis of conventional CAES and D-CAES to compare their heat rate, work ratio (electric energy stored per unit of electric energy regenerated), and exergy efficiency.