Maximizing renewables in the country's power system has been a key political agenda in Japan after the Fukushima nuclear disaster. This paper investigates the potential of PV resource, which could be systematically integrated into the Japanese power system, using a high time-resolution optimal power generation mix model. The model allows us to explicitly consider actual PV and wind output variability in 10-min time resolution for 365 days. Simulation results show that, as PV expands, the growth of PV integration into the grid slows down when the installed PV capacity is more than the scale of the peak demand, although Japan has immense potential of installable PV capacity - equivalent to 40 times of the peak. Secondly, the results imply that a large-scale PV integration potentially decreases the usage ratio of LNG combined cycle (LNGCC) in specific seasons, which is a challenge for utility companies to ensure that LNGCC is used as a profitable compensating generator for PV variability. Finally, a sensitivity analysis on rechargeable battery cost suggests that the reason for suppressing the PV output instead of storing its surplus output by the battery can be attributed to the high battery cost; hence, the improvement of its economic performance is significant to integrate the massive PV energy. (C) 2013 Elsevier Ltd. All rights reserved.