Performance assessment of compressed air energy storage systems with and without phase change materials

In this study, two integrated hybrid solar energy-based systems with thermal energy storage options for power production are proposed, thermodynamically analyzed and comparatively evaluated. The first system uses an underground cavern to store compressed air energy. When electricity production is high during the day, a compressor set pressurizes the air and directs it to the storage unit. A heat transfer model is developed to determine temperature variations and heat losses through the cavern walls. During the insufficient solar radiation period, the compressed air inside the cavern is discharged to meet the energy needs. The second energy storage system employs a cascade latent heat storage approach to reduce heat dissipation within the cavern. The temperature of the compressed hot air gradually decreases as it passes through three-stage phase change material (PCM) units. The cascaded PCMs help reduce the temperature differences between the storage media and minimize the exergy destruction rates. Similar to the first energy storage option, the pressurized air is stored in an underground cavern. The compressed air is then discharged and passes through the latent heat storage medium in the energy recovery mode, eventually reaching the turbine inlet temperature. Finally, the high-pressure and high-temperature air drives the gas turbine and hence generator to generate electricity. The thermodynamic quantities, including energy and exergy efficiencies and exergy destruction rates, are determined for all system elements and comparatively assessed. Furthermore, a comprehensive evaluation of the thermodynamic performance criteria of these energy storage options is carried out.