An innovative high-temperature pumped thermal energy storage driven by transcritical CO2 heat pump and steam Rankine cycles

Pumped thermal energy storage (PTES) is an emerging scheme for low-cost, site-independent, and environmentally friendly electricity storage. However, it faces critical technical challenges of low round-trip efficiency (generally<60 %) and significant irreversible loss during heat transfer process. This paper proposes an innovative high-temperature PTES coupling a transcritical CO 2 (TCO 2 ) heat pump cycle with a transcritical steam Rankine cycle (TSRC). It originally employs dual-storage fluids of molten salts and water with a four-tank structure, covering a wide temperature range from about 33 °C to 560 °C. Water is both low-temperature storage fluid and TSRC working fluid, thereby eliminating a secondary water-water heat transfer. In the charging process, CO 2 at the compressor outlet releases heat to the molten salts and then splits into two streams. One stream increases water storage temperature, and the other preheats CO 2 from the evaporator. Fundamentals of the PTES are illustrated, and mathematical models are built. The results show that the cascade sensible storage configuration can tackle the challenge of large throttling irreversibility and a high round-trip efficiency of 60.21 % can be achieved.