The hydropower station supporting energy storage system is a key supporting facility for optimizing hydropower operation efficiency, improving grid stability and promoting the integration of renewable energy. Hydropower is a clean and renewable energy source with stable power generation capacity, but it is also affected by seasonal changes in water flow, rainfall and other natural factors, resulting in fluctuations in power output—during the rainy season, water flow is abundant, and hydropower stations may have excess power generation that cannot be fully utilized; during the dry season, water flow decreases, leading to insufficient power supply, which is difficult to match the dynamic changes of grid load. The supporting energy storage system solves this contradiction by storing surplus power and releasing it when needed, realizing the peak shaving and valley filling of the power grid and improving the comprehensive utilization efficiency of hydropower.

At present, the most widely used form of hydropower station supporting energy storage is pumped-storage hydroelectricity (PSH), which accounts for about 95% of all active energy storage installations worldwide. A typical PSH system consists of two reservoirs at different elevations connected by pressure tunnels and pump-turbines. During periods of low grid demand (valley periods), when hydropower stations have surplus power, the system uses the surplus power to drive pumps to pump water from the lower reservoir to the upper reservoir, converting electrical energy into gravitational potential energy for storage. When the grid demand peaks, the stored water is released from the upper reservoir, flows through the pump-turbines to generate electricity, and the potential energy is converted back into electrical energy to be fed into the grid, making up for the power gap. In addition to PSH, battery energy storage systems (BESS) are also increasingly used as auxiliary storage facilities, especially in small and medium-sized hydropower stations, to quickly respond to grid load changes and improve the flexibility of power output.

The application of hydropower station supporting energy storage systems has multiple practical values. For hydropower stations, it can stabilize power output, avoid waste of surplus power, and increase revenue by selling electricity during peak demand periods when electricity prices are higher. The round-trip efficiency of PSH is between 70% and 80%, and although there is a certain energy loss in the pumping process, the overall economic benefit is significant. For the power grid, the system can balance the grid load, reduce the impact of hydropower output fluctuations on the grid, improve the stability and reliability of the grid, and create conditions for the integration of intermittent renewable energy sources such as wind and solar power. Taking Portugal’s Tâmega hydroelectric complex as an example, its integrated pumped-storage system not only provides large-scale renewable power generation but also has strong grid balancing capabilities, setting a benchmark for the integration of hydropower and energy storage. With the continuous development of energy storage technology, the hydropower station supporting energy storage system will play a more important role in the global energy transition, helping to build a more stable, efficient and clean power system.