Solar on Grid/of Grid
On-Grid Systems are solar PV systems that only generate power when the utility power grid is available. They must connect to the grid to function. They can send excess power generated back to the grid when you are overproducing so you credit it for later use. These are simplest systems and the most cost-effective to install. These systems will pay for themselves by offsetting utility bills in 3-8 yrs. These do not provide power during a grid outage.
Off-Grid/Hybrid Solar
These systems allow you to store your solar power in batteries for use when the power grid goes down or if you are not on the grid. Hybrid systems provide power to offset the grid power whenever the sun is shining and will even send excess power to the grid for credit for later use. Provides power for your critical loads when the power grid is down.