Sharing hydropower flexibility in interconnected power systems: A case study for the China Southern power grid

Abstract In 2020, China pledged to become carbon neutral before 2060, which implies the acceleration of China’s low-carbon energy transition and development of new energy (wind and solar). As a result, the demand for flexibility in China’s power system has never been so urgent. Because China has the greatest installed hydropower capacity in the world, sharing hydropower flexibility in its interconnected power systems is of great practical significance to China. This paper reports the necessity and feasibility of sharing the hydropower flexibility of Yunnan’s large hydropower bases in the China Southern Power Grid (CSG) through direct-current (DC) tie-lines. In addition, an effective solution to this problem is presented. First, several quantitative methods of flexibility are proposed. Second, a decentralized and coordinated scheduling model that taps and shares the power flexibility of large hydropower bases in interconnected power systems is constructed. The model considers the complex nonlinear constraints of hydropower and DC tie-lines. Third, new linearization modeling methods are proposed to transform the model to a mixed integer linear programming (MILP) model, reducing the computational complexity. The MILP model is applied to the CSG to determine the hourly generation schedules for power plants in Yunnan’s large hydropower bases and the power transmission plans for DC tie-lines. The cases studies demonstrate that the proposed model can fully tap hydropower flexibility and ensure that large hydropower bases simultaneously respond to the flexibility demands of sending-end and receiving-end power grids. The study provides a valuable technical approach for alleviating the lack of power flexibility in other countries with large hydropower bases.