Japan has faced the rapid penetration of solar PV, and specific power service areas actually experience technical difficulty in integrating massive PV into the power grids. By developing an optimal power grid model with 352 buses and 441 power transmission lines in an hourly temporal resolution through 8,760 h, this manuscript aims to analyze the optimal integration of solar PV into a bulk power transmission network in Japan and to identify the best location of PV to be installed in the grid so as to minimize total power system cost. For optimizing PV installation in Japan, computational results recommend the deployment of PV system in the area with sufficient grid capacity and higher solar radiation, because enough grid adequacy is necessary to efficiently control PV output and higher solar insolation leads to reduce required PV capacity and the associated investment cost. In order to realize optimal PV integration in Japan, policy recommendation is to institutionalize the scheme informing preferable locations of PV integration in a power grid, such as developing a PV installable map or implementing a zoning regulation of the grid connection. (C) 2019 Elsevier Ltd. All rights reserved.