Optimum battery size selection in standalone renewable energy systems

This paper presents the optimum calculation of battery size when used as energy storage in standalone systems with renewable energy resources. The focus in this analysis is on the effect of battery charging/discharging characteristics on system reliability and cost. Renewable resources such as wind and PV cannot be the only source of energy in standalone system due to their fluctuating nature. Therefore, additional means of energy is required to achieve a reliable and continuous energy system. Battery energy storage systems are widely used in such applications. In this regard, the size of batteries plays an important role in the overall system reliability and cost. This paper uses the Loss of Load Expectation (LOLE) index to evaluate the reliability of a standalone system consisting of wind turbines and battery storage system. The analysis is carried out based on time series simulation, i.e. different system parameters are arranged in sampled time series format. The main contribution of the work is in modeling the complete charging/discharging characteristics of battery. It is shown that by taking the charging efficiency and discharge rate into consideration, the resulted LOLE is lower than what is expected. Simulation results for a case study are presented in the paper.