Study of a Small Scale Combined Pumped Water and Compressed Air Storage
Abstract: The recent developments in renewable energy has led to an increasing demand for energy storage capability. This report aims to combine two of the most widely used methods: Pumped Hydro Energy Storage and Compressed Air Energy Storage. By using a closed pressure vessel of 200 m3, the system stores energy in the form of compressed air and gravitational potential energy of water.Two different charging and discharging methods were investigated to examine the behaviour of the proposed small-scale model, one “slow process” and one “fast process”. In the first one, water is pumped up and let out in increments and heat transfer is considered between each step. The other case assumes a constant flow of water with no heat transfer except when the tank is full.The best efficiency found was 70.7 % for the slow process. It was shown that the fast process could reach a higher efficiency if the storage time between charge and discharge was low. With a pump and turbine efficiency of 90 % each, an equivalent Pumped Hydro Energy Storage system would have 81 % efficiency. Although the energy density increases, the economic study concludes that the system is not worth investing as compared to other small scale energy storage systems like battery energy storage systems.
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