Calculator
Solar Payback and Savings Calculator
Most payback calculators divide cost by first-year savings and stop. That ignores two things: panels get weaker every year, and electricity gets costlier every year. This one works out all 25 years, one at a time.
The formula
What this assumes
- Panel ageing is taken as 0.6% a year, which matches most manufacturer warranties.
- Tariff rise is taken as 4% a year, based on how Indian tariffs have moved historically. Nobody can promise the future.
- Inverter replacement around year 12 to 15 is NOT included. Budget Rs 25,000 to Rs 50,000 for it.
- Assumes you use most of what you generate. If your state does net billing, your savings will be lower.
- Cleaning and maintenance costs are not included. They are small but not zero.
Common questions
How many years does solar take to pay back?
For a normal home system with subsidy, usually 4 to 6 years. After that the electricity is effectively free for another 20 years. Your exact number depends on your tariff and how much sun your area gets.
Why is your answer different from other calculators?
Most of them multiply your first year saving by 25. That treats electricity in 2050 as costing the same as today, which it will not. We work out each year separately. The difference is usually 15 to 20%.
Do panels really stop working after 25 years?
No. They keep working, just at lower output, usually around 80 to 85% of new. Twenty five years is the warranty period, not the death date.
What about inverter replacement?
The inverter usually needs replacing once, around year 12 to 15. Budget Rs 25,000 to Rs 50,000. We do not include it in the projection, so subtract it mentally from the 25 year figure.