There are two main types of solar energy technology: photovoltaics (PV) and solar thermal. Solar PV is the rooftop solar you see on homes and businesses – it produces electricity from solar energy directly. Solar thermal technologies use the sun’s energy to generate heat, and electricity is generated from that.

The PV Solar system can be ON-Grid or OFF-Grid. The 2 videos below will explain the difference (Source: http://www.solarpowernrg.com)