Installing zero-emission power sources including photovoltaic power systems (PV) is necessary to cut greenhouse gas to reduce global warming. In Japan, the target capacity for installed PV in 2020 was set to 28 GW, which was 20 times the 2005 capacity. To achieve this target, PV should be installed in 70% of new houses. The PV output (active power) must be suppressed to sustain adequate voltage (within 101±6V), due to voltage increases by inverse power from PV when clustered residential PV systems are grid-interconnected on a distribution line, even if there is sufficient irradiance. Approaches to this problem should be considered both by power systems and distribution generation. We tried to start to optimize voltage control of clustered residential grid-interconnected PV to reduce loss due to voltage increase. In this research, we evaluated improved generation efficiency through residential PV voltage control on clustered residential grid-interconnected PV.