Your bill is divided by the tariff of ₹ 7 per unit to get monthly consumption.
A kW generates about 4.2 units a day in Gujarat. The system is rounded to the nearest half kW.
Turnkey cost per kW, less the PM Surya Ghar slab your size qualifies for.
Net cost divided by the yearly saving. Most homes recover their money in 3 to 5 years.