Development of a Radial-Axial Pump-Turbine for Decentralized Small Pumped Storage Power Plants

The increasing number of installations of wind and solar power plants in Germany need more storage power capacity to balance the uctuations of the electrical grid load. The most e cient and mature technology is represented by Pumped Storage Power Plants (PSP) reach ing overall e ciencies more than 80%. However, the realization of big PSP becomes more and more di cult due to environmental and economic aspects. To overcome this energy storage problem decentralized small but highly e cient PSP could be developed in combination with a farm of wind turbines and solar power plants. A case study of a 5.3 MW PSP delivering a storage capacity of 30 MWh per day is shown. Di†erent con‡gurations of hydraulic machinery and a new two-stage concept consisting of an axial plus a radial runner are discussed.