The effect of the intermittency of solar radiation on the performance of photovoltaic (PV) systems with battery storage is investigated. A model is developed that enables system energy flows to be simulated with one-minute and hourly solar radiation values. It is found that the variations in solar radiation that occur during partly cloudy conditions can cause significant fluctuations in system currents, particularly battery currents. These fluctuations are readily apparent from simulations using one-minute solar radiation data, but not in simulations carried out with hourly data. The implications of these fluctuations for the lifetime of batteries used in solar PV systems is discussed. Differences in the battery state of charge between minute and hourly simulations can arise during periods of intermittent solar radiation.