There is a danger of power generation efficiency decreasing due to voltage increase when clustered residential PV systems are grid-interconnected to a single distribution line. As a countermeasure, installation of the reactive power control of an inverter at each residence has been considered. In the previous research we demonstrated that about 20 percent of the output suppression loss was eliminated with reactive power control including PV voltage control when 225 residential PV were grid-interconnected. However, this was on a typical sunny spring day, the seasonal change of PV output and load power was not considered. So in this research we evaluated improved and smoothed generation efficiency among all residences with power factor and reactive power operating voltage through residential PV voltage control on clustered residential grid-interconnected PV for a period of one year.