Numerical study on the influence of hybrid pumped-storage power station on outflow water temperature

【Background and Objective】 As renewable energy is expanding, complementary energy storage solutions such as pumped-storage power stations have been developed. By the end of 2020, the total installed capacity of pumped-storage power stations in China had surpassed 30 million kW. Differing from conventional hydropower stations, pumped-storage power stations operate under distinct thermal and dynamic conditions, which can affect the environment as the temperature of water discharged from these reservoirs is closely linked to river ecosystems. Low-temperature discharges not only delay or prevent fish spawning, but also adversely affect crop growth, leading to crop yield reduction. Despite these concerns, research on the change in outflow water temperature of hybrid pumped-storage power stations is limited. This paper is to bridge this knowledge gap. 【Method】 Taking the Jinshuitan Reservoir as an example, we simulate outflow water temperature under different inlet-outlet elevations and pumping rates using used the MIKE3 water temperature model. This allowed us to assess the impact of hybrid pumped-storage hydropower stations on outflow water temperature. 【Result】 Compared to the outflow water temperature without pumping and storage, pumping-storage reduced the outflow water temperature from May to September and increased it during the other month; the maximum decrease and increase in temperature were less than 0.7 ℃ and 0.8 ℃, respectively. Specifically, at a pumping rate of 110 m3/s, raising the outlet elevation from 130 m to 150 m led to the reduction in the outflow water temperature to decrease from 0.4 ℃ to 0.1 ℃ between May and October, and the rise in temperature to decrease from 0.5 ℃ to 0.02 ℃ during the remaining months, compared to conditions without pumping-storage. When the outlet elevation was maintained at 139 m, increasing the pumping rate from 50 m3/s to 70 m3/s only affected decrease in the outflow water temperature between May and September, with the decrease increasing from 0.1 ℃ to 0.2 ℃. Further increases in the pumping rate, while keeping the outlet elevation at 139 m, had no significant impact on the outflow water temperature. 【Conclusion】 The elevation of the inlet and outlet significantly affects the outflow water temperature; a lower elevation results in a greater temperature difference. While the pumping rate does influence the temperature difference, the effect is less pronounced, though the temperature difference does increase with pumping rates. To minimize the adverse impacts of pumped-storage operation on downstream ecosystems, it is advisable to position the inlet and outlet at the highest feasible elevations.