Adiabatic Compressed Air Energy Storage: An analysis on the effect of thermal energy storage insulation thermal conductivity on round-trip efficiency

Compressed Air Energy Storage (CAES) has demonstrated promising potential for widescale use in the power distribution network, especially where renewables are concerned.Current plants are inefficient when compared to other technologies such as battery and pumped hydro. Presently, the greatest round-trip efficiency of any commercial CAES plant is 54% (McIntosh Plant), while the highest energy efficiency of any experimental plant is 66-70% (ADELE Project). So far, Adiabatic CAES systems have yielded promising results with round-trip efficiencies generally ranging between 65-75%, with some small-scale system models yielding round-trip efficiencies exceeding 90%. Thus far, minimal research has been devoted to analysing the thermodynamic effects of the thermal energy storage (TES) insulation. This metastudy identifies current industry and research trends pertaining to ACAES with a focus on the TES insulation supported by model simulations. Charged standby time and insulation of the TES on overall system efficiency was determined by performing a thermodynamic analysis of an ACAES system using packed bed heat exchangers (PBHE) for TES. The results provide insight into the effect various insulators, including concrete, glass wool and silica-aerogel, have on exergy loss in the TES and overall system efficiency. TES insulation should be carefully considered and selected according to the expected duration of fully charged standby time of the ACAES system. Keywords: Compressed air energy storage; adiabatic compressed air energy storage; thermal energy storage; thermodynamic efficiency; renewable energy storage, packed bed heat exchange