Thermodynamic, Economic and Maturity Analysis of a Carnot Battery with a Two-Zone Water Thermal Energy Storage for Different Working Fluids

Abstract

The rising share of renewable energies leads to increased fluctuations in electrical power supply. One possibility to shift the surplus energy based on demand is a Carnot battery (CB). A CB uses a heat pump or resistance heater to convert and store thermal energy into electrical energy. Later, the stored thermal energy is converted back into electrical energy using a heat engine. This study investigates a CB with a two-zone tank for thermal energy storage. A transcritical process with CO2 is applied for charging, while discharging employs a transcritical process with CO2 and six refrigerants operating in a subcritical process. The transcritical process with CO2 and the four most promising subcritical processes are compared regarding round trip efficiency and levelized cost of electricity (LCOE) depending on the pinch points 5 K and 1 K in the heat exchangers. Additionally, the technology readiness level (TRL) is determined for these configurations. The results show round-trip efficiencies between 11.3% and 33.5% and LCOEs ranging from EUR 0.95 (kWh)−1 to EUR 2.09 (kWh)−1 for the considered concepts with TRLs of up to six.

Keywords

• Carnot battery
• CO₂ heat pump
• organic Rankine cycle
• water storage tank