Exergoeconomic optimization and working fluid comparison of low-temperature Carnot battery systems for energy storage

The increasing share of renewable energy in energy constituent requires the development of large-scale energy storage technologies to tackle with the grid connection problem, Carnot Battery is a possible candidate. In this study, the theoretical models of two Carnot Battery systems with four different working fluid pairs were established, analyzed and compared. Genetic algorithm was introduced in the optimization. The results show that working fluid pairs R245fa-HFO-1336mzz(Z) (the former for ORC, the latter for heat pump) presents the best economic performance, reaching the lowest levelized cost of storage (LCOS) of 0.2631 $·kWh⁻¹ when the thermal storage temperature is 130 °C. The power-to-power efficiency (P2P) competes with LCOS, with the increase of P2P the LCOS decreases. The working fluid pairs R245fa-HFO-1336mzz(Z) and HFO-1336mzz(Z)-HFO-1336mzz(Z) show better exergoeconomic performance, the obtained optimum value of P2P is 42.63%. The variation of exergy efficiency (η_ex) with thermal storage temperature is non-monotonic. The working fluid pairs with the highest η_ex is HFO-1336mzz(Z)-R245fa, and the maximum value is 19.88%. In each configuration, the most costing components are turbine and compressor. In addition, the throttling valve, compressor and heat exchanger takes large proportions in the total exergy destruction.