Stability and efficiency performance of pumped hydro energy storage system for higher flexibility

The pumped hydro energy storage station flexibility is perceived as a promising way for integrating more intermittent wind and solar energy into the power grid. However, this flexible operation mode challenges the stable and highly-efficient operation of the pump-turbine units. Therefore, this paper focuses on stability and efficiency performance of pumped hydro energy storage system (PHESS) under the various flexibility scenarios. First, a nonlinear model of PHESS coupling the hydraulic loss, mechanical loss and electrical loss of pumpturbine is established to study its stability and efficiency characteristics. Second, six flexibility scenarios including four transient processes and two steady processes are extracted based on the historical power output of a pump-turbine unit. Parameter responses indicate that the stability performance of PHESS got worse when the range of load-variation increased. Parameters response in the first 10s is steeper than that in the later 30s. Rotation speed and water head in part-load fluctuates periodically in a range of from -0.0024 to 0.01. In other words, 10 times more compared to the range response under the rated-load. Efficiency analysis suggests that the friction loss in scroll case is the dominated loss type in the transient processes, except for the FL condition. The responses of friction loss in straight pipe, impact loss in scroll case and volume loss are characterized by the corresponding discharge laws. The response curve of winding loss is similar with the response feature of rotation speed. This paper provides the stability and efficiency perspective when the operator exploits the flexibility potential of pumped hydro energy storage station.