Abstract
The present study introduces a novel combined energy storage system that integrates geothermal and modified adiabatic compressed air technologies. The system employs both dual-pressure and single-pressure organic Rankine cycles, upgraded by a zeotropic mixture, to recover waste heat. The introduced combination is analyzed through thermodynamic and economic approaches. A detailed sensitivity analysis is applied to the geothermal plant and adiabatic compressed air system. Additionally, a triple objective optimization of energy, exergy, and economics is carried out to achieve the optimum state of the geothermal plant. Consequently, the geothermal plant produces 5.54 MW of power, of which 2.41 MW is consumed in the adiabatic compressed air system by compressors and high-temperature energy storage during the charging phase. The system provides 7.14 MW of power for peak shaving during the discharging phase, resulting in a 63.15 % exergy efficiency for the geothermal system and a 66.22 % exergy round-trip efficiency for the adiabatic compressed air system. The performance of the geothermal plant is highly sensitive to the inlet pressure of the second separator, while the pressure ratio between the charging and discharging phases significantly affects the performance of the adiabatic compressed air system. The payback period and net profit of the system are estimated to be approximately 4.09 years and $13.55 million at the optimum state.
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