Optimizing near-adiabatic compressed air energy storage (NA-CAES) systems: Sizing and design considerations

This paper studies the challenges of designing and operating adiabatic compressed air energy storage (A-CAES) systems, identifies core causes for the reported discrepancies between round-trip efficiencies from current literature models versus experiments, and presents a near-adiabatic CAES (NA-CAES) system design that addresses these issues. The core causes are overly simplified heat management modeling, neglect of heat losses in the thermal energy reservoir, single-cycle modeling, replacing a diabatic CAES combustor with a TES without other major design changes, using a mirrored compression-expansion design, and/or efficiency definition limitations. To demonstrate an approach to designing an NA-CAES system that addresses the core causes of modeling vs. experiment efficiency discrepancies, a case study is presented for Ontario, Canada. This full system view approach yielded NA-CAES systems with maximum round-trip efficiencies of 60.5, 61.1, and 61.5% for a constant reservoir volume throttled system, a constant reservoir volume variable pressure system, and a constant pressure reservoir system, respectively. A sensitivity analysis was conducted to identify primary with a strong influence on efficiency (such as reservoir pressure limits and the expanders’ pressure ratio), and secondary parameters that more strongly affect TES size (including TES charging and discharging mass flow rates, inlet temperatures to the expanders, and TES tank temperatures). Multi-objective hierarchical optimization was employed to improve efficiency while reducing TES capacity. In brief, the results reveal that through design configuration selection it should still be possible to achieve in practice high NA-CAES efficiencies in excess of 60%.