How Many Solar Panels Do I Need? (UK Guide, 2026)

By Rob Hammond · Updated September 2026 · How we score

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The honest answer is enough to cover the electricity you can actually use or store, within your roof and budget. Getting to a number takes four steps, and the figures below all come from sources you can check.

Step 1: Find your annual electricity use

Take it from a bill or your smart meter app. If you can’t, Ofgem’s typical domestic consumption values, implemented on 1 July 2026, are the official reference points:

Those are lower than the numbers you’ll see quoted elsewhere, because Ofgem cut them in 2026, from 2,700kWh to 2,500kWh for a medium single-rate household, because British homes genuinely use less electricity than they did. If you’re planning around an EV or a heat pump, size against the consumption you’ll have, not the one you have now.

Step 2: Convert usage into system size

The rule of thumb is “1kWp makes about 900kWh a year”, which is close enough for a south-facing roof and badly wrong for anything else. You can do better in two minutes.

The European Commission’s PVGIS is a free, authoritative model of solar yield built on 2005–2023 satellite irradiance data. Here is what it returns for a 4kWp array at 35° pitch, facing south, with PVGIS’s default 14% system losses:

So a 4kWp system on a good roof makes rather more than 3,600kWh, and the north–south spread is smaller than the “half as much up north” folklore: Manchester generates 15.8% less than Exeter (equivalently, Exeter generates 19% more than Manchester). Run your own coordinates; it takes a minute and it is the single highest-value thing you can do before talking to an installer.

Step 3: Derate for orientation and pitch

This is where the rule of thumb falls apart. Same 4kWp array, same Midlands location, same 35° pitch, varying only the direction it faces (PVGIS):

And varying only the pitch, facing south:

Two practical readings. Pitch barely matters between about 25° and 50°, which covers nearly every UK pitched roof, so stop worrying about it. Orientation matters, but less than people fear: east and west roofs at roughly 80% are perfectly viable, and an east–west split array spreads generation across the morning and evening, which raises the share you use yourself. Only north is genuinely marginal.

Shading is the exception to all of this, because it isn’t linear: a chimney or a neighbouring tree across part of the array can cost far more than the shaded fraction suggests. If you have shading, that is a conversation with an installer about panel-level optimisation, not a number you can look up.

Step 4: Turn kWp into a panel count

Current residential panels sit around 440–470W. From the catalogue:

Ten 440W panels is 4.4kWp. Aiko’s Neostar 2S54 datasheet gives module dimensions of 1,757 × 1,134 × 30mm, just under 2m² per panel, so ten panels is about 20m² of roof plane before edge and access clearances. That fits comfortably on most UK pitched roofs.

Efficiency is what decides how much power you fit in a fixed area, not how much you get per panel. If your roof is tight, a higher-efficiency panel buys you real capacity; if you have plenty of roof, it’s mostly buying you a smaller number of panels. Compare them on our solar panels page.

What it costs, and what it saves

DESNZ publishes official cost statistics drawn from the MCS database. The 2025/26 edition, published 28 May 2026, covers 264,742 installations in total, of which 177,014 were domestic. Those domestic installations give these mean domestic costs per kW installed, VAT included, excluding battery storage:

Read that twice. On the official data, a 4.4kW system costs less in total than a 4kW system, because cost per kW falls sharply once you cross into the larger band. Costs fell for every size band against 2024/25. These are averages across thousands of real jobs, not a quote. Scaffolding, roof condition and region all move them, but they are the best benchmark available for judging whether a quote is sane.

We pull that release apart, medians as well as means, what the figure includes, and the 25-year cost per kWh, in how much solar panels cost.

There is no VAT to add: HMRC zero-rates solar panel installation in residential accommodation until 31 March 2027, after which it returns to the 5% reduced rate.

The worked example. A 4.4kWp south-facing array at 35° in the Midlands, generating about 4,360kWh a year, costing about £7,238. Every kWh you use yourself avoids the Ofgem price cap rate of 26.32p (1 October to 31 December 2026). Every kWh you export earns your export tariff: 12p/kWh on Outgoing Octopus.

We are not going to tell you what your self-consumption rate will be, because it depends entirely on when you’re home and what you run, and the widely-quoted “about 50%” has no source we’re willing to stand behind. What the table shows is that at a 12p export rate the answer is not very sensitive to it, because the spread across that whole range is under £200 a year. On a low-single-digit export tariff, though, the exported kWh are worth a quarter as much and self-consumption becomes the dominant variable. Check your export rate before you size the array, not after.

Put your own roof in. The calculator starts on the worked example (4.4kWp, Midlands, south, pitched, £7,238) and every input is one of the tables above:

If you’re weighing a battery alongside the panels, the battery sizing calculator sizes that separately.

When the answer is “fewer”, or “not yet”

• Low consumption and a poor export rate. A 1,600kWh household on a single-digit SEG tariff is buying an array that mostly sells electricity cheaply. Size to consumption, get on a better export tariff, or wait.
• A north-facing roof and nothing else. At 54% of south, the economics roughly halve while the cost doesn’t.
• A roof that needs work. Panels last 25 years and come with a 25-year product and 30-year performance warranty from Aiko. Putting them on tiles with ten years left means paying to remove and refit them. Do the roof first.
• Significant shading you can’t remove. Get a site-specific shading assessment before you commit; this is the one variable a model can’t give you.
• A flat roof. 83% of the south-facing figure at 0°, and in practice you fit fewer panels per square metre, because a ballasted, tilted array needs spacing to stop each row shading the next. A flat roof also has its own planning limit, 0.6m above the highest part of the roof, and a prior approval step on protected land, which we quote in do I need planning permission for solar panels.

None of these make solar a bad idea in general. They make a particular array a bad idea, which is a different thing, and worth knowing before you sign. We take each of them apart, with the payback arithmetic at both a good and a poor export rate, in are solar panels worth it.

All prices, rates and generation figures were checked on 20 September 2026. The price cap is reset quarterly and export tariffs change, so re-check before committing.

What’s changed (changelog)

• 21 September 2026 (third revision, same day). Corrected the JA Solar DeepBlue 4.0 Pro row from 440W/22.5% to 440W/22.0%: JA Solar’s JAM54D40/LB datasheet (Global-EN-20240423A) puts the 440W bin at 22.0% and the 22.5% we held belongs to the 450W bin. The product page had also been showing a different bin again (445W/22.8%) from an old scrape; it now shows this one.

• 21 September 2026 (second revision, same day). Corrected the Jinko Tiger Neo 3.0 row from 445W/23.0% to 460W/23.02%. The catalogue entry had been mixing bins, a “485W” model label over a 445W/23.0% spec, and was rebuilt on a single bin from JinkoSolar EU’s JKM460-485N-48QL6-DV-F2-EU datasheet, which runs 460-485W at 23.02-24.27% and has no 445W bin.

• 21 September 2026. Corrected the Aiko Neostar 2S efficiency in the panel table from 23.2% to 22.3%. Aiko’s own datasheet (AIKO-A-MAH54Mb, V4.1, 202510) lists the 445W bin at 22.3%; 23.2% matches no bin in the range. The catalogue entry was corrected the same day.

• 20 September 2026 (second revision, same day). Corrected the installation count attached to the domestic cost table: 264,742 is the release-wide figure, and the domestic subset behind those mean costs is 177,014 (DESNZ Solar Costs 2025-26 (TIC), “Domestic costs” sheet). Made the FAQ’s generation figure agree with the worked example (4,360kWh, not 4,400), and reworded the north–south spread so its direction is unambiguous.

• 20 September 2026. Rebuilt on sourced data: PVGIS generation by region, orientation and pitch, the DESNZ/MCS 2025/26 installation cost statistics, Ofgem’s updated consumption values and a worked payback at the October 2026 price cap. The previous version’s “roughly 900kWh per kWp”, “1.7–2.0m² per panel” and household usage bands were unsourced, and its relatedProducts slugs did not match the catalogue, so the product links were silently dropped.

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