In recent years, a substantial amount of photovoltaic (PV) generations have been installed in Japanese power systems. However, the power output from the PV is random and intermittent in nature. As is known, the PV generation poses many challenges to the power system operation. To evaluate impact of the behavior of PV, we developed power supply reliability evaluation model considering a large penetration of PV generation into the power system. As a result, power supply reliability is getting worse as the PV penetration increases. To mitigate these issues, we proposed that pumped storage power plant (PSPP) is used to improve the reliability. This paper presents a fundamental study on the impact of the operation scheduling of PSPP taking into account the excess power caused by PV generations on the power supply reliability, which is evaluated by Monte Carlo simulation.