 Compressed air energy storage, CES, has gained attention in recent years due to its potential to store energy from intermittent renewable sources and provide reliable electricity supply. However, existing CES systems suffer from several drawbacks, including energy losses due to compression, the use of fossil fuels, and dependence on geologic formations. Innovative concepts of CES, such as adiabatic CES, isothermal CES, micro-CES combined with air cycle heating and cooling, and constant pressure CES combined with pumped hydro storage have been proposed to address these issues. By analyzing the energy and exergy of each concept, we can better understand the characteristics of each CES system and compare them. This article was authored by Youngmin Kim, Jang Hee Lee, Seok Joon Kim, and others.