Solar rooftop systems generate power to reduce your electricity bill. It is very easy to calculate the savings that you can obtain from your solar plant.
Each kilowatt (kW) of your solar system requires about 100 square feet of shadow-free rooftop area. A kW can roughly generate about 1400 kWh (or units) of power each year. Under the system of net-metering, these units are reduced directly from your electricity bill. Thus, you save money from your highest tariff slab in your electricity bill. This is about Rs. 8 / unit generally in Urban areas.
Thus, a kW of solar power saves over Rs. 11,200 per year. This results in a payback period of just about 3 to 4 years on a rooftop solar plant.