Our editorial method

Solar Report starts from the question a homeowner is trying to answer: what a system costs, what it could save, which rules apply where they live and what to check before signing. Every page aims to give a usable answer first and to keep the conditions that change it, such as a date, a nation or a tariff requirement, next to the figure they apply to. About Solar Report explains who runs the site and how it is funded.

Where our facts come from

We take rules, rates and official figures from primary sources:

• legislation.gov.uk for the law itself, such as VAT reliefs and permitted development rules;
• government departments and agencies, including HMRC, the Department for Energy Security and Net Zero, and the Scottish and Welsh Governments and Northern Ireland departments for their own schemes;
• Ofgem for the price cap and the Smart Export Guarantee, and MCS for installer standards;
• the Energy Networks Association and network operators for grid connection;
• energy suppliers' own tariff pages and published price lists for export and import rates;
• manufacturers' datasheets and UK warranty documents for products.

News reports, trade press and other comparison sites can point us to a change, but they are never the only source for a rule, a rate or a price. A rule from another country is never assumed to apply in the UK, and a rule that differs between England, Scotland, Wales and Northern Ireland is given for the nation it covers.

We link an official source where you need it to act, for example to check a scheme's eligibility. The full record of every source stays in our working files.

How a page is checked before it goes live

Every page goes through the same four stages:

1. A brief. It sets out the question readers search for, what the current top results leave unanswered and what our page must do better.
2. A claim ledger. Every factual sentence and number in the draft gets a row: the value, the nation it applies to, the source, the passage in that source and the date we opened it. Each calculation gets its own row with the full arithmetic. A fact we cannot source is cut, or replaced with an explanation and the check you should make yourself.
3. Three separate reviews. One re-checks every claim and every calculation against its source. One checks the page against UK advertising and consumer rules: the Advertising Standards Authority's CAP Code, the Competition and Markets Authority's guidance, the Digital Markets, Competition and Consumers Act 2024, and the Financial Conduct Authority's rules on promoting finance. One checks that the page answers the reader's question clearly, in British English, with useful links. Nobody reviews a page they wrote.
4. Approval. A page is ready only when all three reviews pass the same version of the text. Any later change goes back to the reviewer whose area it touches, and nothing is published without the publisher's go-ahead.

These are checks on documents and calculations. They are not a physical test of any product or an inspection of any installation.

Dates, nations and figures that change

Some figures change on a timetable, so we date them in the text. Ofgem sets the price cap every quarter: 26.32p/kWh for electricity is the average for Direct Debit from 1 October to 31 December 2026, and the cap for January to March 2027 is due to be announced on 25 November 2026. The 0% VAT on installed solar panels and batteries runs until 31 March 2027. Export rates are set by each supplier: variable rates can change at any time and fixed ones end with their term, so we check them on the day we quote them.

Pages that carry these figures are on a maintenance list and are re-checked when the figure changes. The date on a page shows when it was last updated; it does not promise that every rule is unchanged since.

How we handle money figures

• Assumptions next to the number. A saving or payback figure always comes with the system size, location, yearly electricity use, the import price and its date, the export rate and its condition, and whether a battery or a special tariff is included.
• Bill savings and net savings are different. A lower bill is not a saving until the installed cost is taken into account, so payback figures always include it. The standing charge stays on your bill and is never counted as a saving.
• Each unit counted once. Electricity you use yourself saves your unit rate; electricity you export earns your export rate. A battery's value is the extra you use at home, minus the export income it gives up and its losses.
• No "up to" figures. We give worked examples for stated households instead of a best case few people would reach.
• Examples are labelled. Every worked example shows its arithmetic and says which household it describes. For a battery, we always say which household, because a battery's value depends on how much electricity is used and when.

Export rates: 12p, 6p and a 2% price rise

The export rate can change the answer a lot: for our London reference home below, payback is 12.3 years with exports at 12p/kWh and 19.0 years at 6p. The higher rates we found come with a condition, such as buying your electricity from the same company. So our savings figures follow one convention across the site:

• The headline values exports at 12p/kWh, the rate of Octopus Outgoing, which needs Octopus as your electricity supplier on a compatible tariff. The condition always appears next to the figure.
• Beside it, a "keep your supplier" case values exports at 6p/kWh, the rate of E.ON Next Flex Export, which is open to customers of any supplier.
• A third line shows electricity prices rising 2% a year, in line with the Bank of England's inflation target. It is a sensitivity, not a forecast, and the headline stays at today's prices. Export rates are kept flat, because suppliers set and change them themselves.

Both export rates were last checked on 24 September 2026. Our export tariffs comparison shows other rates and their conditions.

How the calculator works

The calculator covers homes in England, Scotland and Wales.

1. Your roof. Where map data exists for your address, it uses Google's Solar API to find the usable roof faces, their direction, pitch and space.
2. Generation comes from PVGIS, the European Commission's solar model, for your location, roof direction and pitch. It is a long-term average and varies from year to year.
3. Use at home comes from an hourly model of your household's demand, set to the MCS self-consumption tables for your answer to "is someone usually at home during the day?". If you don't answer, it uses "in half the day", the MCS default.
4. Value is each kWh used at home times your unit rate, plus each kWh exported times your export rate.
5. Payback adds up each year's value, with output falling 0.4% a year, until it covers the installed price. The projection runs for 25 years, before any repairs or a replacement inverter.

The installed price is our own model, not a quote: £2,200 for each installation plus £800 per kWp, plus the panels and inverter chosen. With the default equipment, a 4 kWp system comes to £2,200 + (4 × £800) + £800 of panels + a £900 inverter = £7,100, or £1,775 per kW. That sits between the mean costs in the government's 2025/26 solar PV cost data for systems fitted to existing homes, per kW of installed panel capacity and including VAT: £2,109 per kW for systems up to 4 kW and £1,651 per kW for 4 to 10 kW. A battery fitted with the panels adds £2,200 plus £200 per kWh of capacity, so £3,200 for 5 kWh. Prices include VAT at 0%.

The result is an estimate to help you plan. It is not the performance estimate an MCS installer must give you in writing before you sign, and the installer's figures and price will differ from ours.

How we test the calculator

The calculator is checked against a fixed set of reference homes, which we call golden cases. Their results are written into automated tests that run whenever the calculator's code changes, so a change that moves a result fails the tests until the recorded figures are deliberately updated. Guides that quote one of these reference homes use its figures. Some older guides still work their examples by hand, including the London home in our export guides, and we are replacing those with the golden cases so that the same household gives the same answer across the site. Where the calculator doesn't model a case, such as a battery charged only from the grid or one battery size in the MCS self-consumption tables, the guide says which method it uses instead, labels its figures as an illustration and shows the arithmetic.

A selection, at 26.32p/kWh, exports at 12p (Octopus Outgoing, which needs Octopus as your electricity supplier), someone at home for half the day and a south-facing roof at 35°:

"Used at home" is the share of generation the household uses; "MCS table" is the figure from the MCS self-consumption tables for the same home. The golden cases use a generic 5 kWh battery with 90% round-trip efficiency; when you choose a real battery, the calculator uses its own figures. Taking London as the check: 701 kWh used at home × 26.32p = £184.50, plus 3,374 kWh exported × 12p = £404.88, gives £589 in the first year.

Brand and product pages

A brand gets a page only if it is present in the UK market: its products are in the MCS product directory or on the Energy Networks Association's type-test register, it has a UK distributor or support company, and UK installers quote it. We also check the company's status, because a warranty is only as good as the company behind it.

Specifications come from the manufacturer's datasheet, and warranty terms from the UK warranty document, with the edition we checked. Conditions go next to the warranty: some depend on registering the product or keeping it connected to the internet. A brand page describes what the brand sells and what to check on a quote; it does not say the brand is right for your roof.

Our best-of pages use a similar test, and each one sets out its own criteria and the date we checked. A product is included only if it is present in the UK market, for example in the MCS product directory, and we could read its current datasheet and the manufacturer's warranty terms. We don't score products or rank them overall: shortlists group them by the situation they suit, and where a table is sorted by one datasheet figure, such as efficiency, the page says so. We don't shortlist a product whose company has stopped trading. Nobody pays to be included.

We don't publish star ratings or scores. If we rank or score products in future, the criteria and how they are weighted will be published on this page first, and every product will be compared on the same basis. Nobody pays to appear on a page or for a better position.

What we don't do

We don't test products in a laboratory, visit roofs, inspect installations or check installers' work. We don't host customer reviews, and we don't give financial advice. When a page mentions loans, it explains how a scheme works; it doesn't recommend a lender.

Corrections

If you think something on a page is wrong or out of date, email info@solarreport.co.uk with the page's address and what you think is wrong, and include your source if you have one. We check it against the primary source. If it is wrong, we correct the text and any worked example that depends on it, not just a footnote, and the corrected sentences are reviewed again before they go live. The page's update date changes when we do. More ways to reach us are on our contact page.