Any solar electric system that is grid-tied has the ability to generate excess electricity and actually put it back into the electric grid. By inverting the DC power from the solar panels to AC and putting it in your household AC Breaker Panel, you can offset your utility company electricity usage so much as to wind back the dial on your two-way Kilowatt-Hour meter. That would mean selling electricity back to the utility company. Many companies will credit this excess energy generation and apply it to your bill another month when you may use more electricity. That is known as net billing or net metering. You will have to contact your utility company about getting a two-way kWh meter installed (usually free of charge), and the regulations in your area about net metering.