Stored-Energy-Based Operation Rules for Cascaded Hydropower to Support High-Renewable Integration

Abstract

High wind and photovoltaic (PV) penetration reshapes intra-annual residual energy demand and changes hydropower generation space and operating patterns. Conventional medium- to long-term scheduling methods struggle to coordinate renewable-energy integration, supply reliability, and seasonal hydropower utilization. This study proposes a medium- to long-term cascade stored-energy dispatch-chart method under high-renewable penetration and derives the corresponding dispatch charts. A generation-space quantification model is developed for cascade hydropower, considering renewable-energy integration and thermal minimum-output constraints. The model describes how renewable expansion compresses hydropower generation space across planning years. Four key control points are then identified, including the end of drawdown, flood-season end, impoundment completion, and year-end. Stagewise recursion and closed-loop iteration are used to determine suitable stored-energy ranges at these points. Upper and lower envelopes of multi-scenario stored-energy trajectories are further used to construct a zoned dispatch chart. Generation-adjustment rules are then formulated according to the identified stored-energy zone. The method is validated using nine cascade hydropower stations in the Wujiang River Basin under a 2035 high-renewable scenario. Results show that hydropower generation-space contraction occurs mainly from the pre-flood period to the flood season. In April and May 2035, the upper bound of Wujiang cascade generation space falls to 19% to 24% of installed capacity. The end-of-drawdown control point should therefore be advanced from late April to late March. With the proposed dispatch chart, total cascade generation under the 2035 normal inflow increases from 27.80 to 28.45 TWh. Renewable-energy curtailment decreases from 2.43 to 1.22 TWh, a reduction of 49.8%. The proposed method converts complex operating boundaries into practical zonal stored-energy control rules. It supports medium- to long-term cascade hydropower operation under high-renewable penetration.