Isothermal Compressed Air Energy Storage (i-CAES) System

In an Isothermal Compressed Air Energy Storage (i-CAES) system, energy is stored by compressing air from the atmosphere to a high pressure, and subsequently regenerated by expanding the compressed air back to atmospheric pressure. Both processes are to occur at nearly constant temperature. This provides the best efficiency and energy density. As a grid scale long duration storage approach, i-CAES can be configured so that it does not have a carbon footprint, and can be sited everywhere, The advantages of i-CAES is that it is cost effect, reliable, and does not require any special materials. This chapter explains the energy density of i-CAES, and approaches to make a liquid piston air compressor/expander more efficient and power-dense. Specifically, energy density can be increased by operating at higher pressure and using an open-accumulator configuration. Also, the trade-off between efficiency and power density can be improved by deploying porous media inserts to enhance heat transfer, and with the optimization of the compression/expansion profile and of the air compressor/expander geometry through co-design. Overall, two orders of magnitude increase in power density while maintaining high efficiency has been demonstrated.