There are 4 types of solar electrical (PV) systems: Direct, off-grid with batteries, on-grid with batteries, and on-grid without batteries.
1. Direct PV system is simply a solar panel connected to a DC device like a solar-powered attic fan that is not connected to your building wiring or the utility grid. The fan operates only when the sun shines.
2. Off-grid PV system with batteries is used to power millions of homes and electrical devices around the world that do not have utility power. Off-grid PV with batteries use special batteries designed to be charged and discharged for many years. The batteries in an off-grid PV system store energy to provide autonomous power at night and on cloudy days.
3. On-grid PV system with batteries operates similar to off-grid with batteries except that the battery stored energy is used to provide emergency power during grid power outages. Batteries and other parts increase PV system complexity and its cost by about 30% more than on-grid PV without batteries.
4. On-grid PV system without batteries is the most popular (and practical) urban and suburban solar solution because of its much lower initial cost, virtually maintenance and trouble-free operation, and the fact that it offsets costly and polluting grid electricity.