Photovoltaic (PV) systems are rapidly gaining acceptance as some of the best alternative energy sources. In installation area of large PV/battery system, it requires appropriate operation for example of a method considering power output fluctuation and insolation forecasts errors. In addition, it is better to minimize the size of battery and its capital cost. This paper proposes an optimization approach to determine operational planning of power output for large PV/battery system. This approach includes the determination method of charge/discharge amount for battery of electric vehicle as a demand response. The method aims to obtain more benefit deal with electrical power selling. The optimization method applies genetic algorithm (GA) to smooth the fluctuating power output due to PV system, and also to determine the initial state of charge of battery. The validity of proposed method is confirmed by simulation results.