A Comparative Study on VRLA and Li-ion Battery for Use in Frequency Modulation (FM) Station

Recently, importance of energy storage system is growing rapidly due to its high energy density, low discharge rate and zero memory effect. Among various type of storage system, Li-ion and VRLA batteries are widely used in renewable energy sector. Specially, battery is used in Solar PV System in which, battery is charged at day time and used as per our requirement. In this paper, we studied these two types of energy storage system used in one of the FM station which is operated in the remote part of Nepal. It is standalone system in which solar PV system is used to generate the electricity and li-ion battery is used as an energy storage device. So, our study was focused to find the characteristic differences between VRLA and li-ion battery used in FM backup storage system. Mainly, we studied about operational cost, temperature effect, energy density, cycle-life and internal resistance of these batteries. Experimentally it was found that, Li-ion battery has smaller size and weight with high energy density, low internal resistance, long cycle life and less temperature effect as compared to VRLA battery system. Also it was found that initial installation cost of li-ion battery is slightly expensive but due to high energy density and long life, li-ion battery is more preferable than VRLA battery system. Moreover, by using experimental and simulation results, we tried to optimize the performance of FM station.