Study of hybrid wind-hydro power plants operation and performance in the autonomous electricity system of Crete Island

This work analyses the configuration and operation principles of hybrid wind-hydro power plants with pumped storage integrated into autonomous electric grid systems, in order to support high wind energy penetration. The plant consists of wind generation units, combined with a pumped-hydro storage system. It operates on a daily basis, storing the surplus wind production by pumping water in an elevated reservoir, and re-feeding this energy to the electric grid during high load demand periods through its hydroturbines. The new concept for the operation strategy of such plants is the provision of both guaranteed power and guaranteed energy to the grid, combining high wind energy integration and improved operation of the conventional generation system. A computer algorithm is developed to simulate in detail the hybrid plant operation during a reference year and it is applied to the case of Crete Island in Greece, where the penetration limit of the great wind potential available has almost reached. Two different configurations for the pumped storage system are investigated, using reversible pump-turbine machines or separate pumping station and double penstock. The possibility of installing very large hybrid plant power is investigated, as also the effect of some main design parameters on the plant energy results, like the reservoir capacity and the wind farm power. The results showed that a hybrid plant with the new operation strategy is able to effectively substitute a significant portion of both installed power and electricity production of the conventional fossil-fuel plants in the island. Key-Words: Hybrid wind-hydro power plant; Pumped storage; autonomous electricity grid.