PV systems can be grid-tied (operate only when the utility grid is working), off-grid (not connected to the grid at all), or hybrid (operate in grid-parallel or stand alone mode).

If your site is remote and grid electricity is not available, then an off-grid system is the only choice. However, when when the grid is available, the benefits of a hybrid system (which provide power when the grid is down) need to be weighed against the added cost of battery storage and the 10-15% energy that is lost keeping the batteries charged.

Depending on grid reliability and the length of power outages in a particular service area, some people opt for the simplicity of a grid-tied system with a portable generator for emergency back-up power.