Comprehensive comparison on the ecological performance and environmental sustainability of three energy storage systems employed for a wind farm by using an emergy analysis

Due to the environmental and economic circumstances, the use of renewable-energy increases every year. The uncertainty, volatility, and difficulty of storing energy in the large scales are obstacles to the more penetration of renewable energies in the market. Energy storage systems can be used as a solution to store energy at a time when energy consumption is lower than the generated energy or at a time when more energy is generated compared to what is demanded. In this paper, a comparison study has been conducted on the three energy storage systems that proportionated for a typical wind power plant with the capacity of 109 MW. The energy storage systems which are investigated in the current study, include a compressed air energy storage, a liquid air energy storage, and a hydrogen energy storage. For this purpose, the power generated from the wind farm, for eight hours (at peak-off times) is considered as an input for the energy storage systems. To explore various factors such as the environmental impact, economic efficiency, sustainability and renewability, a new method based on emergy analysis is employed. The results showed that the transformity of electricity from hydrogen energy storage was much inferior to that of electricity from the compressed air energy storage and liquid air energy storage. This means that the above-mentioned system utilized the lowest emergy to produce a unit of electricity. Emergy yield ratio of hydrogen energy storage power was 1.98. In fact, it was lower than the emergy yield ratio of compressed air energy storage (2.62) and liquid air energy storage (2.92). This finding proved that liquid air energy storage was more efficient at utilizing local resources. Environmental load ratio of hydrogen energy storage (1.02) was much higher than those of compressed air energy storage (0.62) and liquid air energy storage (0.52). Liquid air energy storage had an emergy sustainability index of 5.6, which was preferable compared to two other cases. It also had better ecological performance and environmental sustainability.