Investigation on Different Types of Electric Storage Batteries Used in Off-grid Solar Power Plants and Procedures for Their Performance Improvement

Abstract

Electric storage batteries are the vital part of off-grid photovoltaic power plants which are widely used in most developing and underdeveloped nations of the world. Batteries are also needed for load leveling and frequency voltage stabilization in grid connected solar and wind farms. More than 10,000 numbers are the estimated number of off-grid battery-based large and small community solar power plants in India. Almost all of these power plants and their batteries suffer from major capacity degradation within five years of installation although the design life of batteries with minimum 80% capacity retention is 8–10 years. This paper studies the capacity loss due to cycling in batteries used for solar power plant application through solar simulated laboratory tests. Through the tests, capacity degradation process could be simulated in laboratory conditions. It was found therefrom that the degradation pattern is different in different types of batteries. Further, the said degradation in capacity can be reversed through a servicing process termed as equalizing charge. The periodicity of equalizing charge has been determined for two major battery types used in solar power plants. The said equalizing charge process if done periodically can reverse the degradation due to cycling, thus extending the battery life to its design value of 8–10 years.