Home & Energy
Home & Energy Calculators
Calculator Matters’ Home & Energy category starts with a Solar Panel Roof-Fit Calculator that turns a roof area into a system size, an estimated yearly generation figure, and a cost and payback estimate for India, the USA, the UK, or any other country — including India’s central rooftop-solar subsidy where it applies. Further home-energy tools are planned; each one will meet this same sourcing and transparency standard before it is published, not the other way around.
Who this is for
Built for homeowners in India, the USA, the UK, or elsewhere who want to size a rooftop solar system from the roof area they actually have, see the estimated yearly generation that size could produce, and get a first-pass installed-cost, incentive, and payback estimate before requesting an installer quote.
How to choose a calculator
Use the Solar Panel Roof-Fit Calculator for the full sizing-to-payback flow in one tool: enter your usable roof area and country to get a system size and panel count, an estimated yearly generation figure, and — with a cost per kW and electricity rate — a net cost, incentive, and simple payback period, plus an optional EMI/loan-payment figure if you plan to finance the system.
Treat every figure as a starting-point estimate, not an installer quote — confirm roof suitability, shading, and final pricing with a licensed installer’s site survey.
Compare home & energy calculators
What each calculator is best for, the main inputs it needs, what it shows, and what to keep in mind.
| Calculator | Best for | Key inputs | Shows | Keep in mind |
|---|---|---|---|---|
| Solar Panel Roof-Fit Calculator | Sizing a rooftop system from your roof area and estimating generation, cost, and payback | Usable roof area, country (India/USA/UK/custom), peak sun hours, cost per kW, electricity rate, optional financing | System size and panel count, yearly generation (kWh), net cost after incentive, payback period, optional EMI | Not a structural survey or installer quote; incentives and rates vary by location and change over time |
Best calculator path
- Measure or estimate your usable roof area (excluding chimneys, vents, skylights, and heavily shaded sections), and pick your country.
- Review the estimated system size in kW and how many standard panels that roof area fits.
- Check the estimated yearly generation in kWh, adjusting the peak-sun-hours figure for your specific region if you know it.
- Enter a cost per kW and your electricity rate to see the net cost after any incentive, and the simple payback period — or switch on financing for an EMI/monthly-payment figure.
Common mistakes and limits
- Entering total roof area instead of usable area — chimneys, vents, skylights, walkways, and shaded sections all reduce what is actually available for panels.
- Assuming the US federal 30% residential solar tax credit still applies in 2026 — it does not; it expired for residential systems installed after December 31, 2025.
- Using a peak-sun-hours figure for the wrong part of a large country — solar irradiance varies substantially by region within India, the USA, and even the UK.
- Treating the estimated generation or payback figure as a guarantee — actual output depends on shading, orientation, tilt, panel quality, and weather that a roof-area estimate cannot see.
When not to rely on calculators alone
This calculator estimates system size, generation, and payback from the figures you enter — it does not replace a licensed installer’s site survey, a structural assessment of your roof, or your utility’s or government’s official incentive-scheme documentation. Subsidy amounts, tax treatment, and electricity rates change over time and vary by exact location; confirm current figures before making a purchase decision.
Source and calculation basis
Roof-area-to-system-size and generation formulas use commonly published rooftop-solar rules of thumb (panel wattage, area per kW, and a performance-ratio/derate factor). India’s subsidy figure follows the published PM Surya Ghar Muft Bijli Yojana central-subsidy structure. Default peak-sun-hours, cost-per-kW, and electricity-rate figures for India, the USA, and the UK are general, sourced starting points — see the calculator’s own Sources section for citations — not a live data feed, so they should be adjusted to your specific location and a current quote.
See the Methodology for how calculators are built and reviewed, who runs the site, the Disclaimer for the full terms, and the Contact page to report an issue.
Frequently asked questions
Common questions about home & energy calculators and how to use them.
What calculators are in the Home & Energy section?
The Solar Panel Roof-Fit Calculator: enter your available roof area and country and it estimates how many panels fit, the resulting system size in kW, an estimated yearly generation figure, and an installed cost, incentive, and simple payback estimate — with built-in defaults for India, the USA, and the UK, plus a manual mode for any other country. More home-energy calculators are planned, each held to the same sourcing and transparency standard before publishing.
Which countries does the Solar Panel Roof-Fit Calculator support?
India, the USA, and the UK have built-in default peak-sun-hours, cost-per-kW, and electricity-rate figures, plus India’s central rooftop-solar subsidy formula. Choosing "Other / custom" lets you enter your own figures for any other country — the underlying roof-area, generation, and payback formulas work the same way everywhere.
Does this include government subsidies or tax credits?
For India, yes — the calculator applies the PM Surya Ghar Muft Bijli Yojana central subsidy formula automatically based on your system size. For the USA, the federal residential solar tax credit does not apply to systems installed in 2026, so no federal credit is assumed by default; enter any state, utility, or other incentive you qualify for manually. For the UK, residential solar is already 0% VAT-rated, and Smart Export Guarantee income (if any) can be added as an optional yearly figure. All of these change over time — verify the current rules before relying on the number.
Is this the same as an installer’s quote or a structural survey?
No. This calculator estimates system size and generation from the roof area, location, and assumptions you enter — it does not assess your roof’s structural suitability, shading, orientation and tilt, or electrical wiring. Get a professional site survey and an installer quote before purchasing a system.
Does this section store or share the figures I enter?
No. Every calculation runs entirely in your browser using your device’s own JavaScript engine — nothing you type into this calculator is sent to or stored on our servers.
Explore other categories
Browse the other calculator categories on Calculator Matters.