Recently, many people in the world pay attention to the renewable energy and a photovoltaic system becomes especially worthy for the future of the earth. In this paper, we investigate the operation of PV system with storage battery by using next-day residential load forecast. First, we propose the application of a simple and high-precision modeling method, i.e., Just-In-Time Modeling to the forecast of residential load. And we carry out the improvement in predictive accuracy by the input selection and the weighting method. Next, we simulate the operation of PV system with storage battery by using the load forecast information. The result shows that the introduction of load forecast into PV system operation contributes to environmental conservation and reduction of operating cost.