Solar Calculators: Cost, Output, Payback, Battery and Roof Tools

All Our Solar Calculators: The Question Each One Answers

Each calculator below answers one question; pick the question closest to yours. Two more tools are not open yet: a solar roof checker and one to check a solar quote.

• Solar Panel Savings Estimator and Payback CalculatorSaving, export income and payback years, from a quote or our estimate.
• Solar Power Calculator UKThe kWh a year a system would generate on your roof.
• Solar Panel CheckerA check of roof direction, pitch, shade and roof type, and whether the home is listed or in a conservation area. Not open yet.

What Would Solar Cost and Save on Your Roof?

The full cost calculator estimates what solar would cost and save on your home, and gives a verdict.

• You enter: your postcode, roof, electricity use, time at home and tariff, plus a battery if you want one.
• You get: system size in kWp, installed cost, yearly saving, export income and payback years.
• Runs on: cost data for April 2025 to March 2026 from DESNZ (the Department for Energy Security and Net Zero), the Ofgem price cap unit rate and PVGIS.

Roof direction, pitch and shade are questions in this calculator.

How Many Panels and What kWp Does Your Home Need?

Sizing starts from your yearly kWh use: our sizing calculator works out the number of solar panels your home needs and its kWp, capped at the number of panels you say fit your roof, if you enter one.

• You enter: postcode, yearly use or monthly bill, roof direction, pitch and shade, panel wattage and, if you know it, how many panels fit.
• You get: panels and kWp matched to your use, the recommended size, and its cost and payback.
• Runs on: typical use of 2,500 kWh a year if you give none (Ofgem), plus the same cost and generation data.

How Many Panels Fit on Your Roof?

The usable area of each roof face sets how many panels it holds: our roof space calculator works out how many solar panels fit on your roof and the kWp they make.

• You enter: the length and width of each roof face you can use, the panel size from a maker's datasheet or your own, and, if you know them, your installer's edge clearance, the gap between panels and the panel wattage.
• You get: the panels that fit on each face and in total, the layout, the usable area and the kWp those panels make.
• Runs on: the panel sizes printed on makers' datasheets and the edge clearance in the MCS installation standard.

How Much Electricity Would Your Roof Generate?

The solar output calculator estimates how much electricity a system on your roof would generate at your postcode: its yearly output in kWh.

• You enter: postcode, system size (in kWp, as panels x watts, or "size it for me"), roof direction, pitch and shade.
• You get: yearly kWh, kWh per kWp, the average per day and the share of your use covered.
• Runs on: our calculation from PVGIS 5.3 (European Commission Joint Research Centre) for 121 postcode areas.

How Many Years Would Solar Take to Pay Back?

The solar panel payback calculator gives the payback period in years, with the yearly saving and export income behind it.

• You enter: a quote total or our estimate for a size in kWp, then the same answers about your home, with a battery if you want one.
• You get: yearly saving, export income, payback years and the 25-year net figure.
• Runs on: the Ofgem price cap unit rate and an export rate of 13p per kWh (our calculation from Ofgem figures), both held flat.

What Would a Battery Cost, and What Size?

A battery's price depends on its size in kWh, and our battery calculator works out solar battery cost and payback for the size you pick.

• You enter: whether you have panels, your electricity use, time at home and a battery size; day and night rates are optional.
• You get: fitted price, extra yearly saving, payback years set against the makers' warranty length, and a verdict (none for a battery priced on its own with no day and night rates).
• Runs on: DESNZ battery installation statistics for April 2025 to March 2026: the median price per kWh in each size band.

The battery calculator does not recommend a size.

What Do Panels and a Battery Cost Together?

The price of panels and a battery fitted together is on our page about solar panels with a battery, a cost guide and not a calculator. For your own home, "Show both" in the payback calculator puts panels alone next to panels with a battery.

Can You Get a Grant or Funded Scheme?

Whether you can get a grant depends on each scheme's rules, and no calculator on this site decides it. Our page on solar panel grants in the UK sets out the schemes in each nation, who each one is for and how to apply. Only the scheme can say whether you qualify. The next section puts the questions in order.

Which Calculator Should You Start With?

Start with the full cost calculator if you want cost, savings and payback together; use a single-purpose tool when you need one figure.

A solar decision runs in four steps, in this order.

1. Check your roof with the roof questions in the full cost calculator.
2. Size the system to your yearly use.
3. Compare the installed cost with the payback years.
4. Add a battery, or test a quote total.

You can run any tool again with new answers. Each run starts from the same few facts about your home.

What You Need Before You Start

Every calculator has a box for your postcode and your electricity use; the other questions depend on the tool.

Five things are worth having to hand.

• Your postcode
• Your yearly electricity use in kWh (kilowatt-hours, the unit on your bill), or your monthly bill
• Your roof's direction, pitch and any shade
• Your panel count, if an installer has told you how many fit
• Your quote's total and size in kWp, for the payback calculator

You can use a calculator without knowing your yearly use: it then works from your monthly bill, your number of bedrooms (full cost calculator only) or Ofgem's typical value of 2,500 kWh a year, and says which it used. The other half of every estimate is our data.

What Data Do the Calculators Use, and How Recent Is It?

Every calculator reads one shared data table, and each figure carries its source and date.

Six datasets sit in that table.

All the calculators use the same figures, so a change to the table changes every tool at once.

Why Do Solar Calculators Give Different Answers?

Solar calculators give different answers because each one makes different assumptions: the cost data and its date, the sunshine figure for your area, the panel size, the electricity price and whether export is limited.

The table sets out all five and what our calculators do.

To compare two calculators, compare these five assumptions, not the headline figure. They also set how close an estimate comes to a real price.

How Accurate Is a Calculator Estimate?

A calculator result is an estimate, not a quote: it can differ from an installer's price because of scaffolding, roof work, wiring or a different panel layout.

An estimate is good for deciding whether a survey is worth asking for and for checking that a quote is in range. Only a survey settles the measured roof, the exact design and the firm price. Every estimate holds electricity prices flat, and none models an electric car, a heat pump or an export limit.

We give an estimate, Leads 2 Trade arranges a survey, and installers give the quote. The result says what comes next.

What Happens After You Get a Result?

Each calculator result ends with a verdict: Good fit, Borderline or Poor fit, with the reason. A battery priced on its own, with no day and night rates, gets a price and no verdict.

After a Poor fit result there is no survey offer: the tool says what would change the answer and offers "Run it again". A tenant gets the estimate to share with the landlord.

The survey step is inside each calculator, not on this page. You will get phone calls. That is how surveys are arranged. The request form is not open yet. The calculators cost nothing to use. We are paid by Leads 2 Trade Limited when a homeowner we refer asks for a survey. You are never charged. It does not change our figures.

Do the Calculators Work Across the UK?

Yes: the calculators take postcodes in England, Scotland, Wales and Northern Ireland, with two differences for Northern Ireland.

Generation uses your postcode area in every nation. The Ofgem price cap and the Smart Export Guarantee cover Great Britain only, so a Northern Ireland (BT) postcode gets its savings on standard Power NI rates. DESNZ cost data leaves out Northern Ireland, so the panel cost there uses the Great Britain figure, with a note on the result. These rates change on known dates.

When Are the Calculators Updated?

DESNZ publishes its cost data once a year, next on 27 May 2027, and the export rate follows Ofgem's yearly SEG report. A change to a formula gets a new method version (now 1.0).

Until 31 March 2027 each result shows a VAT clock: home solar panels and batteries carry 0% VAT until then and 5% from 1 April 2027 (HMRC VAT Notice 708/6). Four subjects fall outside the calculators.

What These Calculators Do Not Cover

These calculators cover rooftop solar panels and home batteries; four related subjects sit outside them.

• Plug-in solar kits (legal to buy and use in Great Britain from 27 August 2026): the tools price rooftop systems, not plug-in solar cost and rules.
• Solar water heating: a different product, which heats water and makes no electricity.
• Business premises: the tools are for homes and do not work out commercial solar cost per kW.
• Off-grid systems and sizing for single appliances.

Solar Calculator Questions