Integrating deep offshore wind with pumped hydro storage in a central Mediterranean archipelago’s electricity generation system

Abstract

This investigation starts off with a hypothetical deep sea offshore wind turbine array consisting of twenty 5 MW NREL reference wind turbines for offshore deployment. Measure-correlate-predict techniques are utilised to transpose long-term measured wind data from a reference site located at an elevation of just under 220 m above mean sea level to a short-term 80 m wind-monitoring station close to sea level at a coastal location. The extrapolated long-term 80 m level wind speed and direction time series are then used as climatological inputs to a computational fluid dynamics software program that is used to generate wind resources over the extents of the hypothetical 100 MW offshore wind farm zone. Time series of wind speed, wind direction and power production are generated for the array covering a number of years, with the period being analysed here covering the years 2007-2011. Meanwhile, electrical load data on an hourly basis are also assessed in order to enable a wind power/pumped hydroelectric storage to electrical load interfacing exercise. The implications of combining a pumped hydroelectric storage system into the electrical system are assessed. The studies have shown that if the output from the wind farm is set to meet a fixed load threshold on a monthly basis, the surplus wind power can be used to pump water into the storage system. The stored potential energy can then be converted back to electricity by means of a water turbine in instances when wind power falls short of the set threshold. Such a system will decouple the renewable energy (RE) supply from the load and, with careful balancing of the stored hydraulic energy against the energy required to reach the threshold, supply a steady contribution to the load over a predetermined period of time. Such a steady contribution is highly desirable in an electrical system as a variable input coming from large-scale wind farms could cause grid imbalance, induce fluctuations and possibly compromise stability. The work has shown that the contribution of a wind farm coupled to a pumped hydroelectric system could contribute primarily to the base load whilst also allowing for green energy generation, facilitate the integration of RE technologies and help achieve part of Malta’s RE targets.