Without the batteries, at daytime, the DC current generated by by solar PV modules, and then it will be inverted to alternating current by a grid-connected inverter and connected with the grid so as to supply power for a load. At present, the energy crisis came into being, it has been a common sense for the world to fulfill environment protective, energy conservation, reduce the Co²  output, so the PV on-grid power plant will be the great trend for the future energy development.