Efficiency analysis of underground pumped storage hydropower plants

• Published in: Journal of energy storage Vol. 28; p. 101234
• Main Authors: Menéndez, Javier, Fernández-Oro, Jesús M., Galdo, Mónica, Loredo, Jorge
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.04.2020
• Subjects: Electricity storage; Energy efficiency; Underground pumped-storage; Underground reservoir; Variable renewable energies; Energy efficiency; Electricity storage; Underground reservoir; Underground pumped-storage; Variable renewable energies
• ISSN: 2352-152X; 2352-1538
• DOI: 10.1016/j.est.2020.101234

•The round trip efficiency is analyzed in underground pumped storage hydropower plants.•The energy efficiency depends on the operation pressure in the underground reservoir.•Analytical and numerical models have been developed to study the operation pressure.•The efficiency decreases from 77.3% to 73.8% when the pressure reaches −100 kPa.•An impact on the energy balance of 8.25 GWh year−1 could be produced at −100 kPa. Large-scale energy storage systems, such as underground pumped-storage hydropower (UPSH) plants, are required in the current energy transition to variable renewable energies to balance supply and demand of electricity. In this paper, a novel method to determinate the round trip energy efficiency in pumped storage hydropower plants with underground lower reservoir is presented. Two Francis pump-turbines with a power output of 124.9 and 214.7 MW (turbine) and a power input of 114.8 and 199.7 MW (pump), respectively, have been selected to investigate the overall operation of UPSH plants. Analytical models and two-phase 3D CFD numerical simulations have been carried out to evaluate the energy generated and consumed, considering a typical water mass of 450,000 t and a maximum gross pressure of 4.41 MPa. The results obtained in both analytical and numerical models show that unlike conventional pumped-storage hydropower plants, the round trip energy efficiency depends on the pressure inside the underground reservoir. The round trip energy efficiency could be reduced from 77.3% to 73.8% when the reservoir pressure reaches -100 kPa. In terms of energy balance, the energy generation decreases down to 3,639 MWh −1 and the energy consumption increases up to 4,606 MWh year−1 compared to optimal conditions.