Off-grid solar systems are different from the on-grid system in the sense that they are set up independently from the state grid. These systems have an additional battery backup system which is charged by the generated solar energy. Batteries are charged when the generated power is more than the power being consumed. While on paper, battery backed systems sound like a great idea, these systems are generally more costly than on-grid systems and have lower efficiency. The battery needs to be replaced every five years or so but on the positive side, you can use solar energy even in the hours where there is no generation. Off-grid systems are perfect for your rooftop solar plants if you have a very erratic power supply or do not get any power at all.