Solar ROI Estimator
System size, savings & payback from your bill and roof area
Free · No sign-up · Computed instantly on your device
Your Details
Estimates assume ~4 units/kW/day generation, 80 sq.ft per kW, and a tariff of ₹8/unit. Net of PM Surya Ghar central subsidy (up to ₹78,000). Final sizing follows a free on-site survey.
Recommended system capacity
4.2kW
Covers ~100% of your current bill
Estimated monthly savings
₹4,000
₹48,000 per year
Payback period
4.8 yrs
Then ~22 years of near-free power
Indicative investment
₹2,29,167
Net of PM Surya Ghar central subsidy (up to ₹78,000).
CO₂ offset per year
5.2 t
≈ 234 trees planted
These are indicative estimates for education and planning. Actual sizing depends on a site survey, shadow analysis, and DISCOM sanction. Read the PM Surya Ghar guidelines or browse the vendor directory to take the next step.
About This Calculator
The Solar ROI Estimator answers the first question every rooftop journey starts with: what does solar actually save me? It sizes a system from two numbers you already know — your average monthly electricity bill and your usable roof area — and returns the recommended capacity in kW, projected monthly savings in rupees, the indicative investment, and the payback period in years.
The model uses typical Indian rooftop economics: ~4 units of generation per kW per day, 80 sq.ft of shadow-free roof per kW, and current residential and commercial tariff bands. Results are indicative — a proper site survey and shadow analysis refine the final design — but they are accurate enough to decide whether solar is worth pursuing and what budget range to expect.
How the Calculation Works
The estimator works backwards from your bill. It converts your monthly bill to units using your tariff, divides by roughly 4 units of generation per kW per day to find the system size, then checks that size against your roof area at about 80 sq ft of shadow-free space per kW.
Savings are the units your system generates multiplied by your tariff; payback is the net investment divided by those annual savings. For homes, net investment is after the PM Surya Ghar subsidy — the subsidy guide explains how much applies to you.
Worked example (rules of thumb, assuming ₹8 per unit)
- A ₹4,000 monthly bill at ₹8 per unit is about 500 units a month, or 16.7 units a day.
- At roughly 4 units per kW per day, that needs about 4.2 kW of solar.
- At about 80 sq ft per kW, you need roughly 333 sq ft of shadow-free roof.
- Your actual tariff slab and shading will move these numbers — use the calculator above with your own bill.
Go Deeper
Frequently Asked Questions
- How Accurate Is a Solar ROI Calculator?
- Within roughly ±15% for typical rooftops. The two biggest real-world variables are shading on the roof and your DISCOM tariff slab. Use the result to shortlist budget and system size, then validate with an on-site survey.
- Does the Estimate Include the PM Surya Ghar Subsidy?
- Yes — residential cost assumptions are net of the central subsidy (up to ₹78,000 on the first 3 kW). Commercial and society estimates use scale pricing without capital subsidy.
More Free Solar Calculators
Found this useful? Send it to someone planning solar.