The balance between supply and demand for electricity is mainly disrupted by the growing contribution of renewable energy sources to the electrical grid since these sources are intermittent by nature. Therefore, the energy storage systems, mainly those of considerable size, become essential to restore the electricity balance. The compressed air energy storage (CAES) system is one of the mature technologies used to store electricity on a large scale. Therefore, this article discusses the energy and exergy analysis of different configurations of a constant-pressure CAES system to improve its overall efficiency and energy density. The exergy efficiency of our basic adiabatic configuration using water as thermal storage medium is 56.4% and the energy density is 12.17 kWh/m3. The results show that the CAES system using a packed bed of quartzite rock as thermal storage medium has the best efficiency (67.2%) and energy density (17 kWh/m3) among adiabatic systems. The diabatic CAES systems could have a net efficiency up to 70.1% and an energy density up to 31.95 kWh/m3 by using combustion chambers. Finally, the waste heat recovery from other installations such as a gas turbine power plant has the potential to improve the energy density to 20.53 kWh/m3 without using fossil fuel sources.