Type and capacity configuration of hydropower retrofitted energy storage facilities in the regional hybrid energy system

With the increasing penetration of large-scale new energy into power grids, multi-time-scale energy storage and flexible regulation are increasingly required to ensure safe and stable operation. Hydropower retrofitted energy storage facilities, built on existing cascade reservoirs, offer extended-duration energy storage and flexible regulation by enabling cascade hydropower recycling. This study proposes a framework for determining the necessity, type, and capacity of the hydropower retrofitted energy storage facilities through a power system extension model aimed at minimizing lifecycle installation and operation costs. A multi-time-scale scheduling model and time-series simulation method are developed to support the technical–economic evaluation of expansion schemes. A case study on the Longyangxia-Laxiwa cascade reservoirs located on the upper Yellow River, China, is conducted for three regional power grids with varying demand characteristics. Results indicate that the type and capacity selection of the hydropower retrofitted energy storage facilities depend on system demand and operational economy. They can transformed excess new energy power into potential hydropower, utilized the seasonal spilled water for power generation and reduced the peak-shaving operation of thermal power. The hydropower retrofitted energy storage facilities are shown to increase new energy utilization by 0.1–2.18 % and reduce carbon emissions by 0.84–1.67 million tons. Continuous energy storage and regulation capacity of 12–14 h per day can be provided under extreme new energy generation conditions. The selected type and capacity configuration remain unchanged under a ±20 % variation in unit capacity investment, fuel and carbon emission cost.