Capacity degradation of lead-acid batteries under variable-depth cycling operation in photovoltaic system

Grid-connected photovoltaic systems with local energy consumption can be equipped with additional energy buffer to increase self consumption when feed-in-tariffs are low or to reduce the negative impact on power network in some periods. The buffer is typically implemented with a lead-acid battery dedicated for day-to-night energy storage. Since the solar energy fluctuates highly during the day, the battery operates with many variable-depth charge/discharge cycles, rather than with one full cycle per day. This paper shows the method of estimation the battery service life in a photovoltaic system under variable irradiance. The results are computed for one year period and presented in respect to PV and consumption ratio for various buffer sizes.