Abstract: A method and system of maintaining electrical power to one or more designated loads connected to an electrical bus that is selectively connected to an electric power grid as a first source of power and to an inverter for providing power to the bus from a second source of electrical power. A controller receives an input indicating if the bus is connected to the grid. The inverter is operated to be synchronized with the grid and provide a selected amount of active and reactive electrical power from the second source of electrical power while the one or more designated loads receive electrical power from the grid. Connection of the bus to the grid is monitored and at the time the electrical bus is no longer receiving power from the grid, the inverter is operated to provide required power without interruption to the one or more designated loads of the bus.