Solar Panel Roof-Fit Calculator

It turns a usable roof area into an estimated solar system size, using a standard "roof area per kW" rule of thumb (around 70 sq ft, or 6.5 sq m, per kW, which already accounts for fire-code setbacks and spacing between panel rows). From there, system size × peak sun hours × 365 days × a performance-ratio (derate) factor gives an estimated yearly generation in kWh, and system size × cost per kW gives an estimated installed cost.

Select India, enter your usable roof area (in sq ft or sq m), and the calculator estimates your system size in kW and panel count, applies the PM Surya Ghar Muft Bijli Yojana central subsidy automatically based on that system size, and — once you enter a cost per kW and your electricity rate — a net cost and payback period in rupees.

Enter your usable roof area (excluding chimneys, vents, skylights, and shaded sections) in the calculator above; it divides that area by the roof space one kW typically needs, then converts the resulting system size into a panel count using the panel wattage you choose (400W by default).

The PM Surya Ghar Muft Bijli Yojana central subsidy gives ₹30,000 per kW for the first 2 kW, ₹18,000 for the 3rd kW, capped at ₹78,000 total for systems of 3 kW or more. This calculator applies that formula automatically when India is selected. Special-category states can receive a higher amount, which this calculator does not model — check the official portal linked in Sources for your state.

No — this is an independent calculator built by Calculator Matters and is not affiliated with, endorsed by, or produced by Tata Power Solar or any other installer or brand. It performs the same kind of roof-area-to-system-size and cost estimate that installer calculators typically offer, using published formulas and government scheme figures rather than any one company’s proprietary pricing.

Estimated yearly generation (kWh) = system size (kW) × peak sun hours per day × 365 × a performance-ratio factor (typically 0.75-0.85, accounting for inverter losses, wiring, dirt, and heat). The calculator does this for you once it knows your system size and location, and shows both a yearly and a monthly-average figure.

Typical installed cost before incentives is roughly ₹45,000-₹75,000 per kW in India, $2,400-$3,300 per kW ($2.40-$3.30/watt) in the USA, and £1,400-£2,000 per kW in the UK, though actual quotes vary by equipment, roof type, and installer. The calculator pre-fills a starting figure for each country in the Cost & incentive section — replace it with your own quote for an accurate number.

Yes — turn on "I’m financing this" in the Financing section. Enter the share of the net cost you’re borrowing, an annual interest rate, and a tenure in years, and it calculates the monthly EMI and total interest using the standard reducing-balance loan formula.

There’s no separate PDF, but every formula on this page is written out in full in the Formula section below, so you can rebuild it directly in a spreadsheet: system size = roof area ÷ area-per-kW; generation = system size × peak sun hours × 365 × performance ratio; cost = system size × cost per kW, minus any incentive.

No — the 30% federal residential Section 25D credit expired for systems installed after December 31, 2025, under 2025 legislation. This calculator does not assume a federal credit for the USA by default; enter any state, utility, or other incentive you separately qualify for in the "Other incentive" field.

Yes — installing solar panels (with the inverter, battery, and labour) on a residential property in the UK is zero-rated for VAT under a relief currently extended through 31 March 2027. This is usually already reflected in an installer’s quoted price, so the calculator treats UK cost per kW as VAT-inclusive already rather than subtracting it separately.

This is a free, online calculator — no signup, download, or app required. It runs entirely in your browser on desktop or mobile.

Yes — choose "Other / custom," then enter your own peak-sun-hours, cost-per-kW, and electricity-rate figures. The roof-area, generation, and payback formulas work the same way everywhere; only the pre-filled defaults and the automatic subsidy are India/USA/UK-specific.

No. This calculator estimates size, generation, and cost from the figures you enter — it does not assess your roof’s structural suitability, shading, orientation, tilt, or electrical wiring. Get a professional site survey and an installer quote before purchasing a system.