Abstract. With the expected spread of photovoltaic (PV) systems, high power generation in spring and summer is expected to cause abnormally high voltage in distribution systems. As described in herein, we propose a method to improve the utilization efficiency of a small-scale PV generator connected to a distribution system by short-term (30 min) forecasting of solar power generation output in a small area of a few kilometers. As a countermeasure against abnormally high voltage, a method exists to adjust the voltage by switching a tap of the substation transformer. However, the switching frequency of the tap with mechanical contact is limited to once or twice per hour. Under these conditions, if short-term forecasting of solar power generation were possible, then tap changing of a substation transformer efficiently could maintain voltage within an appropriate range, which enables effective use of solar power. This paper is organized as follows. After a short-term forecast method of solar power is proposed. The method of adjusting the sending end voltage of a distribution substation based on the PV output forecast data is proposed. Finally, reduction of the PV disconnection frequency is verified numerically.