How to Calculate Solar ROI
The Complete Formula Explained
Stop guessing. Learn the exact formula behind solar ROI calculations and understand what every variable means for your savings.
What is Solar ROI?
Solar ROI measures the financial return from your rooftop solar system compared to its total cost. Unlike most home improvements that depreciate, solar generates increasing returns because electricity tariffs rise while your solar cost stays fixed at zero.
The Formula
Solar ROI Formula
ROI = [(Lifetime Savings − System Cost) ÷ System Cost] × 100
Real example — 3kW system in Maharashtra:
Key Variables
Electricity Tariff (₹/unit)
The single biggest factor. MH at ₹11/unit sees 2x faster payback vs GJ at ₹5.50/unit.
Peak Sun Hours
GJ & RJ lead (5.5–5.8 hrs) while Kerala averages 4.0–4.5 hrs. Directly affects daily generation.
System Capacity (kW)
Must match consumption. Over-sizing wastes investment since surplus credits may lapse or be compensated low.
Panel Degradation
0.5–0.7% per year. A 3kW system: 12 units/day in year 1 → 10.5 units/day in year 25.
Tariff Escalation
Indian tariffs rise 5–8% annually. Your savings grow every year while solar cost stays fixed.
Subsidy Amount
₹78,000 max from PM Surya Ghar. Without subsidy, payback extends by 1.5–2.5 years.
Maintenance Costs
One inverter replacement + cleaning = ₹75K–90K over 25 years. Well-maintained systems generate 15–20% more.
Net Metering Policy
States with 1:1 credit provide better ROI than those with reduced buyback rates.
Payback Period by State
After payback, every unit your system generates is free electricity for the remaining 20+ years:
Real-World Examples
How to Maximise ROI
Right-size your system — Match to actual consumption. Over-sizing wastes money; under-sizing leaves savings on the table.
Clean panels regularly — A ₹2,000 cleaning kit saves ₹6,000–₹9,000 per year. 15–25% efficiency loss from dust.
Choose quality components — Tier-1 panels cost 10–15% more but generate 5–10% more over their lifetime.
Shift heavy loads to daytime — Run ACs, washing machines, and water heaters during 10 AM – 4 PM.
Monitor daily generation — Use your inverter's app. Sudden drops = cleaning needed or equipment issues.
Avoid battery unless needed — Batteries add ₹60K–₹1.2L to cost. Only worth it if you get 2+ hours of power cuts daily.
Ready to calculate your exact ROI? Our free Solar ROI Calculator uses real DISCOM tariff data and 2026 PM Surya Ghar subsidy rates for accurate projections tailored to your state.
Tariff Escalation: Why Your Savings Grow Every Year
Solar ROI calculations that ignore tariff escalation are significantly understating the financial benefit of going solar. Indian electricity tariffs have increased at an average compound annual growth rate (CAGR) of 6.2% over the past decade — meaning the value of every unit your panels generate increases year after year, while your solar system's cost remains fixed at zero.
Here is the compounding effect on a 3kW system in Maharashtra (current tariff: ₹11/unit) over 25 years, using a conservative 5% annual escalation:
| Year | Effective Tariff (₹/unit) | Annual Generation (units) | Annual Savings | Cumulative Savings |
|---|---|---|---|---|
| Year 1 | ₹11.00 | 4,320 | ₹47,520 | ₹47,520 |
| Year 3 | ₹12.13 | 4,277 | ₹51,890 | ₹1,47,900 |
| Year 5 | ₹14.04 | 4,234 | ₹59,440 | ₹2,57,800 |
| Year 10 | ₹17.93 | 4,105 | ₹73,580 | ₹5,90,000 |
| Year 15 | ₹22.88 | 3,980 | ₹91,060 | ₹10,30,000 |
| Year 20 | ₹29.20 | 3,858 | ₹1,12,650 | ₹16,10,000 |
| Year 25 | ₹37.27 | 3,740 | ₹1,39,390 | ₹23,50,000 |
Break-Even Analysis: 3kW System Across 6 States
The break-even point is when cumulative savings equal the net system cost (after PM Surya Ghar subsidy). What happens after break-even is pure profit — your panels generate free electricity for the remaining years of their 25-year life. This analysis uses 2026 benchmark costs: ₹1,80,000 gross cost, ₹78,000 subsidy, ₹1,02,000 net cost, with 5% annual tariff escalation:
Maharashtra
ExceptionalTamil Nadu
ExcellentDelhi
Very GoodUttar Pradesh
Excellent (with UP subsidy)Karnataka
ExcellentGujarat
Good* UP figure reflects ₹1,08,000 combined subsidy (central + UPNEDA). All figures assume 5% annual tariff escalation, 0.5% annual panel degradation, and one inverter replacement at year 12 (₹25,000).
Calculate Subsidy for Your State
Get exact savings based on your DISCOM tariff and 2026 PM Surya Ghar rates.
Frequently Asked Questions
What is the average payback period for solar in India?+
Does solar ROI account for panel degradation?+
Is solar ROI better with or without a battery?+
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