Advanced isothermal compressed air energy storage and wind-farm siting

Abstract As the world’s electric grids include greater shares of wind energy, the intermittency of wind power is becoming more problematic. As such, low-cost, high-efficiency, long-duration energy storage will be increasingly critical for electric grids with high wind shares. One storage option is utility-scale (e.g., 500 MW) Advanced Adiabatic Compressed Air Energy Storage (AACAES). However, AACAES requires large reservoir volumes (e.g., 690,000 m 3 ), has low round-trip efficiency, and includes a complex thermal storage system to recover compression heat. This study introduces Advanced Isothermal Compressed Air Energy Storage (AICAES), which eliminates the need for dedicated thermal energy storage while improving efficiency through near-isothermal, spray-assisted reciprocating compression and expansion while also allowing elevated temperatures in the underground and surface reservoirs. To evaluate the proposed approach, reference AACAES and AICAES systems are defined, each rated at 500 MW with 8 h of storage duration. Results indicate that AICAES can increase round-trip efficiency by approximately 7% while reducing total system costs by about 10% relative to AACAES (based on a simple high-level cost model). Furthermore, replacing an underground reservoir based on a hardrock formation with one based on a rock salt formation or abandoned coal mine may reduce the system costs by an additional 18% or more. This study also considers such storage co-located at a wind farm and sized with a storage power that is 15% of the wind-farm power. This Wind-located Advanced Isothermal Compressed Air Energy Storage (WAICAES) leads to reservoirs that are about ten times smaller, which allows more site opportunities near wind energy resources via inexpensive bedded salt formations. WAICAES can also draw charging power directly from the wind farm (instead of the grid) to further reduce round-trip losses and can leverage the wind-farm electrical infrastructure (transformer, substation, transmission lines, etc.), to further reduce costs. However, economies of scale aspects must be considered (whereby a larger number of systems can increase cost savings, but smaller system sizes can reduce cost savings) to quantify the overall cost impact for WAICAES.