Optimization of autonomous hybrid energy storage system for photovoltaic applications

Autonomous photovoltaic systems require an energy buffer to match the generation with the time distribution of demand, as photovoltaic is time and weather dependent. The Valve Regulated Lead Acid (VRLA) battery is commonly used for photovoltaic storage because of its low cost, low maintenance, and wide availability. A Hybrid Energy Storage System (HESS) integrates the VRLA battery and ultracapacitor, drawing on their respective advantages at appropriate times. By combining an ultracapacitor with a VRLA battery, the power density of the overall system is increased. The ultracapacitor operates under high power conditions reducing the strain of large current draw from the VRLA battery. This paper outlines a methodology to optimize the combination of VRLA batteries and ultracapacitors in the photovoltaic system taking the load demand, solar irradiation, and ambient temperature into account. A photovoltaic system is simulated in Matlab Simulink to analyze the results of the optimization.