Last reviewed: 3 September 2026, against the Ofgem price cap
for 1 October to 31 December 2026. This page is rewritten every time the cap changes — four times a
year.
A well-sited 800 W plug-in kit saves a British household somewhere around
£60 to £110 a year, and our own model reaches roughly £140 for the best cases. The
government’s headline figure is “up to £110”, which we treat as the conservative version. Get the
siting or the self-consumption wrong and it is a third of that. The single largest variable is not the panel, the brand
or even the region — it is what share of the electricity you manage to use inside the house at the
moment it is generated, because none of what you export is paid for.
The calculation, step by step
Four multiplications. Anyone quoting you a saving without showing all four is guessing.
1. Generation before losses
Panel capacity in kilowatts-peak × the annual yield for your part of the country. Yields for a
well-oriented, well-tilted array in Great Britain run from roughly 750 kWh per kWp in
the far north of Scotland to around 1,050 on the south coast of England, with about
900 as a national average. Those ranges derive ultimately from the same PVGIS irradiance dataset that
sits behind the MCS tables used for accredited installations.
2. Real-world derating
Three factors, applied in turn. The values below are our own rounded estimates
used for illustration and in our calculator — they are not published MCS figures, and we label them
as estimates every time we use them.
| Factor | Range | Comment |
|---|---|---|
| Orientation | South 1.00 · SE/SW 0.95 · E/W 0.80 · NE/NW 0.60 · North 0.45 | The biggest single lever after shading |
| Mounting angle | Angled frame 1.00 · fence/ground at a shallow angle 0.95 · vertical balcony rail 0.70 | Vertical mounting is the hidden cost of the classic balcony install |
| Shading | None 1.00 · light 0.90 · moderate 0.75 · heavy 0.55 | A single railing shadow across a panel costs more than the label suggests |
| Inverter clipping | Up to about 12% for a large DC array behind an 800 W inverter | Only bites in summer, and only on well-oriented arrays |
3. Self-consumption — the step everyone skips
Multiply by the share of generation you actually consume. A household with someone at home during
the day typically captures a large majority of an 800 W output, because 800 W is roughly what a
fridge, a freezer, a router, a couple of laptops and a boiler pump draw between them. A household
empty from eight to six may capture half or less. We use 70% as a default for an occupied home and
50% for an empty one, and both are estimates rather than measurements.
4. Value
Multiply by your unit rate. Under the price cap for 1 October to 31 December 2026, a typical
direct-debit customer in England, Scotland or Wales pays 26.32p per kWh, with a daily
standing charge of 54.83p. There is no VAT on domestic electricity in Great Britain between 1 October
2026 and 31 March 2027, a temporary zero rate announced in July 2026. If you are on a fixed or
time-of-use tariff, use your own rate — it can differ from the cap substantially in both directions.
Worked examples
| Household | Setup | Approx. usable kWh/yr | Approx. annual saving |
|---|---|---|---|
| Terraced house, Midlands, someone home during the day | 0.9 kWp on a south-facing fence frame, no shading, 70% self-consumption | ≈ 540 | ≈ £142 |
| Flat, London, working from home | 0.9 kWp vertical on a south-west balcony, light shading, 75% self-consumption | ≈ 390 | ≈ £103 |
| Semi, Yorkshire, empty 8am–6pm | 0.8 kWp on a west-facing fence, no shading, 50% self-consumption | ≈ 265 | ≈ £70 |
| Flat, central Scotland, north-east balcony | 0.8 kWp vertical, moderate shading, 70% self-consumption | ≈ 145 | ≈ £38 |
The bottom row is the one worth staring at. It is not a bad product badly made — it is the same kit
in the wrong place, and no brand choice fixes it. Run your own configuration through the
savings calculator, which uses exactly
these factors and lists every one of them on the page.
Why there is no export income
The Smart Export Guarantee obliges larger suppliers to pay for exported electricity, but it
requires the installation to be certified under MCS or an accepted equivalent, and to have an export
meter point. A self-installed plug-in kit has neither, and a supplier cannot offer a regulated SEG
tariff to an uncertified installation.
So every kilowatt-hour you generate and do not use is a gift to your neighbours. This has two
practical consequences that matter more than anything else on this page:
- Any calculator that adds export income to a plug-in kit is producing a fiction.
If you see one, stop using it. - The cheapest way to improve your return is free. Moving the washing machine,
dishwasher, hot water timer or EV charge into the middle of the day converts exported units into
saved units at no cost. See
using more of your solar at home.
Payback
Payback is what you paid divided by what you save each year. Compliant kits span roughly £300 to
£1,000 depending on panel count and mounting hardware, so:
| Annual saving → Kit price ↓ |
£40 | £70 | £100 | £140 |
|---|---|---|---|---|
| £300 | 7.5 | 4.3 | 3.0 | 2.1 |
| £500 | 12.5 | 7.1 | 5.0 | 3.6 |
| £750 | 18.8 | 10.7 | 7.5 | 5.4 |
| £1,000 | 25.0 | 14.3 | 10.0 | 7.1 |
Two honest observations about this table. First, the bottom-left corner is a bad purchase and no
amount of enthusiasm changes that. Second, the table assumes today’s electricity price for the whole
period; if electricity gets more expensive the payback shortens, and the temporary removal of VAT on
electricity until March 2027 currently pushes it the other way. We do not model future prices, because
nobody can, and a calculator that quietly assumes 5% annual energy inflation is flattering itself.
More on both halves: what a kit costs and
payback period.
What is not included in the saving
- The standing charge. 54.83p a day, or roughly £200 a year, is payable whether
you generate or not. Solar does not touch it. - Export income. Nil, as above.
- Gas. A plug-in kit does nothing for heating or hot water unless you heat water
electrically. - Winter. The annual figure is dominated by April to September. December
contributes almost nothing, and any monthly average is misleading.
When a battery changes the answer
A plug-in kit cannot have a battery — the regulations exclude storage from the device. A separately
installed home battery is a different purchase with different economics, driven mostly by the spread
between cheap overnight electricity and peak-rate evening electricity rather than by solar at all. If
your problem is that you are exporting half your generation because the house is empty, a battery
solves it, but it costs several thousand pounds to solve a £30 problem — so do it because the tariff
arbitrage stacks up, not because of the panels. See
home battery storage and
can I add a battery to plug-in solar?
Frequently asked questions
Is the government’s “£110 a year” realistic?
As a good case, yes. As an average, no. It assumes decent siting and decent self-consumption.
Does a bigger panel array save more?
Up to a point. Past roughly 1 kWp behind an 800 W inverter you start losing summer output to
clipping, and the marginal panel earns less than the one before it.
Will my saving go up if energy prices rise?
Yes, proportionally — the kit saves units, and units get more valuable. The reverse is also true.
Do I save more with a smart meter?
No. A smart meter measures; it does not change what you save. It does let you see your half-hourly
consumption, which is genuinely useful for improving self-consumption.
Is it worth it if I move house in two years?
Often, yes — unlike rooftop solar, the kit comes with you. That is the strongest argument for
plug-in solar in a rented or short-term home.
Sources.
Ofgem, price cap unit rates and standing charges, 1 October –
31 December 2026 ·
GOV.UK, zero rate of VAT on domestic electricity from 1
October 2026 ·
Ofgem, Smart Export Guarantee ·
DESNZ, plug-in solar.
Derating and self-consumption factors are our own estimates and are labelled as such — see
editorial methodology.