A power system for connecting a power source, an energy storage unit and a grid includes a power inverter, an energy storage power converter and a controller. The power inverter is electrically coupled to the power source through a DC bus and converts DC power from the DC bus to AC power output to the grid. The power converter is electrically coupled between the DC bus and the energy storage unit and stores power in the energy storage unit and discharges power from the energy storage unit. The controller controls the power converter to store excess power from the power source that cannot be output to the grid in the energy storage unit, and control the energy storage power converter to discharge power stored in the energy storage unit to the power inverter to output to the grid.