Geothermal energy-assisted pumped thermal energy storage: Configuration mapping

Abstract

Unstable renewable energy sources, including wind and photovoltaic power generation with the inherent characteristics of intermittency and randomness, pose an extremely significant challenges to the safety and stability of electrical grids. Considered a viable solution, energy storage technology increases the flexibility and regulatory capacity of power grids by storing and releasing excess electricity at different times. Pump thermal energy storage technology offers an efficient large-scale electricity storage solution that is completely free from geographical location limitations. Skillfully integrating pumped thermal energy storage technology with low-grade heat can effectively improve its thermodynamic and economic performance. To significantly enhance the utilization rate of geothermal energy and effectively achieve a more optimal performance of pumped thermal energy storage systems, the in-depth and comprehensive study conducted a thermo-economic evaluation of 15 types of geothermal-assisted transcritical pumped thermal energy storage systems. This study provides configuration selection maps for the round trip efficiency and the levelized cost of storage, thereby enabling an extremely effective and swift evaluation of the performance of these various configuration systems. When the geothermal temperature changes within the range from 50 °C to 90 °C, the efficiency of the systems that are considered to be the most suitable under these conditions varies from 66.2 % to 105.6 %. This variation in efficiency occurs when the compressor outlet pressure is optimized within the range from 5 MPa to 8 MPa. The system levelized cost of storage declines as geothermal temperature rises and its minimum value is 0.472 CNY/kWh when the geothermal temperature is 90 °C.