Contents lists available at ScienceDirect Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman Comprehensive comparison on the ecological performance and environmental sustainability of three energy storage systems employed for a wind farm by using an emergy analysis Shima Yazdani a , Mahdi Deymi-Dashtebayaz a, ⁎ , Erfan Salimipour b a Department of Mechanical Engineering, Hakim Sabzevari University, Sabzevar, Iran b Department of Mechanical Engineering, Quchan University of Technology, Quchan, Iran ARTICLE INFO Keywords: Emergy analysis Wind farm Compressed air energy storage Liquid air energy storage Hydrogen energy storage ABSTRACT 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. 1. Introduction In recent years, the share of the total installed capacity covered by intermittent renewable-energy sources (RESs), in particular of wind power for electricity generation has considerably increased due to en- vironmental conditions (when there is a need to reduce greenhouse-gas emissions) as well as economic circumstances. Wind power is presented as a very clean and sustainable energy source because of its reliance on the wind resource for a portion of the input, does not require any fuel, and consequently does not cause environmental pollution [1]. Besides the benefits of RESs, there are some problems such as the unpredict- ability and instability of RESs productions, which make the energy storage systems (ESSs) be the essential systems. Based on the energy conversion mode the ESSs can be classified as several types including mechanical, electrical, electrochemical systems, and hydrogen storage [2]. Some of the mechanical types such as pumped hydroelectric and compressed air energy systems have geographical limitations [3]. Many challenges have been presented in the traditional ESSs with regard to the increase in renewable electricity utilizations [4]. In CAES system, by consuming the electricity, the air is compressed. The compressed air is stored in a steel pressure vessel for above-ground storage [5], or in a salt cavern (large scale) for below-ground storage [6]. Then, the air is heated up by burning the conventional fuel before deriving a turbine/generator unit. For adiabatic CAES, the heat gen- erated during the air compression stage is stored in a thermal energy storage unit in order to heat up the air in the discharge process [7].A much higher efficiency is achieved in stored adiabatic CAES compared to diabatic CAES. In fact, in adiabatic CAES the efficiency of the overall https://doi.org/10.1016/j.enconman.2019.04.021 Received 29 November 2018; Received in revised form 21 March 2019; Accepted 5 April 2019 ⁎ Corresponding author. E-mail address: m.deimi@hsu.ac.ir (M. Deymi-Dashtebayaz). Energy Conversion and Management 191 (2019) 1–11 0196-8904/ © 2019 Published by Elsevier Ltd. T