Most of the current research and development of CO2 cycles for power to heat - heat to power (P2H2P) energy storage systems are focused on applications of supercritical CO2 cycles. However, this work is focused on alternative application of CO2 power cycle with standard (i.e., non-supercritical) cycle and modified industrial turboexpanders as main working machines. Thermal Cycle for power storage system with thermal energy accumulator for energy storage and non-supercritical CO2 power cycle for backward production of electricity is described in this paper. The CO2 cycle is compared with Nitrogen cycle with same parameters as well. Initially, the thermal accumulator design, option of accumulation media (molten salts or liquid metals), and its parameters are described. The main part of the paper is focused on non-supercritical CO2 power cycles. Possible configurations of cycle, design aspects of main parts of cycle, possibilities of efficiency improvement are discussed; such as regeneration or intercooling. Finally, advantages and disadvantages of this CO2 and N2 cycle are discussed and compared. The concluding result of this paper is a very similar efficiency of the two working fluids at the selected parameters.

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