Multi-criteria/comparative analysis and multi-objective optimization of a hybrid solar/geothermal source system integrated with a carnot battery

Among the different electrical energy storage technologies, the Carnot batteries are promising options with low specific cost that do not suffer from geographical limitations and power-capacity coupling. In addition to power balancing, this approach can also be unique for multi-vector energy management. A comprehensive evaluation (thermodynamic design and exergoenvironmental and exergoeconomic evaluations), comparison, and multi-objective optimization of four Carnot battery configurations based on solar-electric energy and a geothermal source is presented. Geothermal energy can simultaneously improve the thermodynamic and environmental performances of the Carnot battery. The main structure of all configurations is based on electrical energy obtained from PV and captured thermal energy from a geothermal source. The four Brayton, heat pump, flash, and organic Rankine cycle (ORC) units are periodically integrated. The outcomes point out that the discharging process is based on an ORC unit and a flash-heat pump cycle (F-HPC)-based charging process makes more optimal heat-to-power efficiency. Moreover, the Carnot battery based on the regenerative-Brayton cycle (R-BC) unit has a higher investment cost rate compared to the ORC unit (in the discharging process). When integrating the geothermal, the third configuration (R-HPC/R-BC) experiences the greatest improvement (5.3-fold) due to the increase in thermal energy received from the geothermal source.