Modelling and Cost Analysis of a Hybrid Wind Turbine and Water Tower System as a Means of Energy Storage
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Date
26/11/2017Author
Roca, William Bellinazo
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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.
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