A reliable operation strategy on the compressed-air-regulates-pressure underground pumped storage system and its thermo-economic investigation

Abstract

Reducing fossil fuel consumption and developing renewable energy sources are essential ways to reduce carbon emissions. Restricting coal consumption produces a large number of abandoned coal mines, while the rapid development of renewable energy raises the demand for energy storage in power grids. Transforming abandoned coal mines into energy storage systems not only reuses the abandoned mines, but also promotes the development of renewable energy. Traditional underground pumped storage hydropower (UPSH) systems have a limit on the range of cavern heights. The compressed-air-regulates-pressure underground pumped storage (CARPUPS) system proposed in this study improves the adaptability of the storage system to underground caverns through different operating modes, and obtains the best economic benefits under different regulated pressures. Based on a specific coal mine within China, regulation methods of compressed air are explored when the head of compressed air varies in the range of 0-350 m. The new system can help to increase space utilization by 14 % and the energy storage density by 51 % when the regulated pressure is 1.0 MPa. Based on the optimized operation mode, the system economics analysis is carried out for different market energy prices (Be). The results show that, when Be = 0.1 ¥/kWh, the levelized cost of energy (LCOE) for the system is not sensitive to the regulated pressure. However, the energy storage capacity of the CARPUPS would be 292 MWh, which is 3 times that of the conventional UPSH system, with an efficiency of 52 % when the regulated pressure is 3.5 MPa.