There are two types of grid-tie systems, those with storage batteries and those without. Systems without batteries use PV modules connected directly to an inverter to create 120-volt utility-grade electricity. Power is produced during sunlight hours and is fed directly into a building`s electrical load center. This solar power supplements the utility power and reduces the amount of utility power used. If there is extra solar generation above what is needed in a house, it is sent back to the utility grid, spinning the customer`s meter backwards.

These systems are simple, reliable, and produce the most kilowatt-hours (kWh) per dollar invested. But there`s one thing they won`t do - keep the lights on during a power outage.

The second type of grid-tie PV system, those with batteries, overcome this limitation by use of a battery bank to store energy and a special "bi-modal" inverter. During a brownout or blackout, the inverter will disconnect from the utility and draw energy from the sun or battery bank to power house loads. The number of appliances that can be run, and the length of time they can run, depends on the size of the inverter and the battery bank.