Results of TRNSYS simulations of photovoltaic systems with electrical storage are described. Studies of the sensitivity of system performance, in terms of the fraction of the electrical load supplied by the solar energy system, to variables such as array size, battery size, location, time of year, and load shape are reported. An accurate simplified method for predicting array output of max-power photovoltaic systems is presented. A second simplified method, which estimates the overall performance of max-power systems, is developed. Finally, a preliminary technique for predicting clamped-voltage system performance is discussed.