Photovoltaic systems are typically grouped according to their relationship to the utility grid.

Grid-tied Systems

Grid-tied systems are configured so that the power they generate is fed directly into the utility grid. The electricity produced is not stored; instead it is delivered directly to the local electric company whenever the system is active. The electric company then uses “your” power to meet the general demand and depending on your state’s utility credit policies, you can receive a credit for the electricity that your system produces. Grid-tied systems are commonly found in homes and businesses that wish to offset the cost of their power usage.

 

Off-grid Systems

As the name implies, off-grid systems are not connected to the public utility grid and are often referred to as “stand-alone” systems. During the day, the electricity generated is used either by powering loads or to charge storage batteries. At night, power is supplied by the energy stored in the batteries. When the sun comes up the next day, the cycle begins again.
Off-grid systems are typically found in remote homes, weather stations or radio sites and parks.
Off-grid systems can also be used to supply electricity to vacation homes that are not connected to the utility grid. In developing countries, off-grid systems frequently represent the only solution to supplying remote villages with electricity. The demand for these types of systems is extremely large. To date, approximately two billion people worldwide still live without electricity in regions far away from public utility grids.