A synchronous inverter is an electrical inverter that changes direct current (DC) electricity to alternating current (AC) electricity to be fed into the utility grid. A power system equipped with a synchronous inverter effectively uses the utility company as a storage battery, ensuring that the power provided is in phase and at the same frequency as the external power source.
Take the case of a home that is partly powered partly by a solar photovoltaic system. When the sun is shining, electricity is delivered to appliances in the home from the PV array, via the inverter. If the PV array is making more power than is being consumed, the excess is sold to the utility power company through a second electric meter. If more power is used than the PV array can supply, the utility makes up the difference. This type of system makes the most sense if you have utility power, because there are no batteries to maintain or replace, but it has a very long payback period and may not be cost-effective at today's electric rates. Using a multifunction inverter allows you to sell excess power to the utility, and also maintain a battery bank for stand-by power in the event of a utility power failure.