Comparative analysis and optimization of pumped thermal energy storage systems based on different power cycles

As the proportion of renewable energy in the world’s energy mix gradually increasing, energy storage technologies are gaining more and more attention. Pumped thermal energy storage (PTES) technology is one of the most promising electrical energy storage technologies. In many power cycles that can be adopted as discharge subsystems of PTES, organic Rankine cycle (ORC) is widely used because of its advantages of efficiently utilizing low-temperature waste heat and converting it into electrical energy. In addition, organic flash cycle (OFC) is considered as a promising candidate for the thermal power conversion subsystem of PTES due to its higher potential performance. In the present work, by taking four different forms of OFC and one basic ORC as power cycles, five PTES systems are established, optimized and analyzed. The results show that the turbine and compressor occupy the largest percentage of the total investment cost, while the throttle valve has the largest exergy destruction. The optimized results illustrate that the PTES system combining basic vapor compression heat pump cycle with basic organic Rankine cycle (BORC-BVCHP) shows the best economic performance with the Levelized cost of storage (LCOS) value as low as 0.4413 $/kWh at the storage temperature of 403.15 K. BORC-BVCHP system also shows the optimal round-trip efficiency (31.15%) and maximum exergy efficiency (23.40%), respectively. This indicates that ORC-based PTES system has obvious advantages over the OFC-based PTES systems in terms of economic performance and thermodynamic performances, and ORC is more suitable to be applied in the study of PTES system.