Modelling and Cost Analysis of a Hybrid Wind Turbine and Water Tower System as a Means of Energy Storage

Abstract

This study presents the software modelling of a hybrid power plant, integrating wind energy and pumped hydroelectric energy storage and compromising the wind turbine tower as the upper reservoir of the pumped storage scheme, along with a brief cost analysis of the technology. The model is created using Simulink, being constituted by four 2 MW wind turbines, a 4 MW hydroelectric scheme and 4 MW pumps. The upper reservoir holds 24,630 m3 of water and 11 MWh of energy storage. Statistical analysis from real wind data from North Harris, UK, allows the pumped storage scheme to be designed to balance the wind generation output fluctuations, targeting to provide a constant design power output of 4 MW to the grid, equivalent to 50% of the wind capacity installed. Three cases are analysed and compared on the simulations with wind data from North Harris and the cost analysis: wind farm without energy storage, with energy storage inside the turbine tower and with an artificial external reservoir. Results indicate that the storage inside the tower is more expensive than excavating an artificial reservoir of similar storage capacity, as the increased penstock length and tower costs make the alternative more expensive. The total costs for the tower storage and artificial reservoir are 1.83 and 1.60 times higher than the costs for the wind farm without energy storage. The simulation results show that it is possible for the pumped storage scheme to balance the wind output. However, even though a power output within 0.8-1.2 pu of the design power is achieved during 98% of the time in the first 10 hours of simulation, the governor has difficulties balancing the short-term wind variations and variable speed technology would provide a better dynamic response for the system. Furthermore, the reservoir is completely emptied towards the end of the 12-hour simulation, due to a prolonged period of low wind speeds. Therefore, the studied storage capacity is insufficient for providing more than an hourly balance to the power output. Additionally, increasing the tower diameter is suggested as a better alternative for increasing the storage, rather than higher inside the tower due to water pressure issues.