Lets say we can fix a 5.4kW system at your home. You can get a loan at 4% interest upto 10 years repayment period. Your monthly installment will be about Rs 8600/-. You can generate about 600 units per month. And for the first 7 years CEB is paying Rs 22/- per unit. Lets say your monthly electricity usage is 150 units. Then you can give 450 units to CEB per month. That means CEB is paying you 450x22=9900. After deducting your loan installment you have Rs 1300 in your hand every month (plus electricity bill is zero).
Conclusion is "loan repays it self!"