How much does plug-in solar actually produce in the UK?
Between 506 and 833 kWh a year from an 800 W kit, depending on your city and how you mount it. We modelled seven UK cities. Mounting it flat against a railing costs about a quarter of the output.
Rules and product details last checked on .
Key takeaways
- An 800 W kit produces roughly 680 to 830 kWh a year in the UK if tilted at about 35 degrees and facing south.
- Mounted vertically against a balcony railing or wall, the same kit produces 506 to 596 kWh. That is a loss of about a quarter, and it is the single biggest thing nobody tells balcony buyers. Every orientation and tilt option is priced in kilowatt hours here.
- Geography matters less than you would think. Glasgow gets 84% of what Cardiff gets, not half.
- Only the electricity you use while the sun is out saves you money. Output is not the same as saving.
- Figures below are modelled, not measured, and the method is stated so you can check it.
An 800 W plug-in solar kit produces somewhere between 506 and 833 kWh a year in the UK. The range is that wide not because of the weather, but because of how you mount it.
We modelled seven UK cities to find out. The results are below, along with exactly how they were produced, because a number without a method is just a claim.
What an 800 W kit produces, city by city
| City | Tilted 35° | Vertical 90° | Lost by mounting flat |
|---|---|---|---|
| Cardiff | 833 kWh | 596 kWh | 28% |
| London | 815 kWh | 594 kWh | 27% |
| Birmingham | 774 kWh | 568 kWh | 27% |
| Belfast | 735 kWh | 546 kWh | 26% |
| Edinburgh | 722 kWh | 546 kWh | 24% |
| Manchester | 709 kWh | 517 kWh | 27% |
| Glasgow | 682 kWh | 506 kWh | 26% |
How these numbers were produced
They come from PVGIS, the photovoltaic geographical information system published by the European Commission’s Joint Research Centre, queried through its public API on 11 August 2026.
The parameters were identical for every city: 0.8 kWp of panels, 14% system losses, azimuth due south, and two tilt angles, 35 degrees and 90 degrees. City coordinates were the centre point of each city.
Three things this means in practice:
- It is modelled, not measured. PVGIS uses long-run satellite irradiance data. Your actual year will be better or worse than the average.
- It assumes no shading. A tree, a neighbouring building or your own balcony wall will reduce it, sometimes a lot.
- 0.8 kWp of panels is a conservative reading of an 800 W kit. The legal cap of 800 W applies to the inverter’s AC output, and many kits carry more panel capacity than that behind it. A kit with 1,000 Wp of panels behind an 800 W inverter will beat these figures in weaker light while still hitting the same ceiling at midday.
The mounting angle matters more than the city
This is the finding worth taking away, and it is the opposite of what most people assume.
The gap between the sunniest city modelled and the least sunny is 151 kWh, or about 18%. Glasgow gets 84% of what Cardiff gets. If you were expecting Scotland to be hopeless, it is not.
The gap between tilting the panel and mounting it flat against a railing is 24 to 28% in every single city. That is a bigger penalty than moving from Cardiff to Glasgow.
So if you want the largest annual number and the space allows it, tilt it. A frame that tips the panel outward at even 20 or 30 degrees recovers most of the difference.
That advice is too simple, and we have since corrected it. The annual total hides the shape of the year. An upright panel on a railing actually beats a tilted one from November to February, by 27% in December, and gives a much steadier supply across the year. Since winter units are far more likely to be used rather than exported for nothing, the gap in money is narrower than the gap in kilowatt hours. We set that out in does plug-in solar work in a British winter.
If the railing is your only option, the kit still works. Plan the payback on 506 to 596 kWh rather than on the number in the brochure, and do not treat the railing as a failure.
What that is worth in money
Output is not saving. This is where most guides overstate the case.
A kit saves you money only on the electricity you consume while it is generating. Anything you produce and do not use is exported, and without an export tariff you get nothing for it. Plug-in kits are not designed to store energy drawn from your home, which is written into the legal definition itself, so there is no battery smoothing the mismatch.
A worked example, with the assumptions on the table:
- Output: 594 kWh a year, a London kit on a vertical railing
- Self-consumption: 60%, a common planning assumption for a household that is not empty all day
- Unit rate: 26.11p per kWh, the Ofgem price cap for direct debit customers for 1 July to 30 September 2026 (Ofgem, announced 27 May 2026)
594 × 0.60 × £0.2611 = £93 a year
Two things that example does not do, both of which flatter other people’s numbers:
It does not touch the standing charge. That was 57.19p a day over the same period, about £209 a year, and generating your own electricity does not reduce it. Any payback calculation that quietly nets it off is wrong.
It does not count exported units. The 40% you generate and do not use earns nothing without an export arrangement, and a plug-in kit cannot store it for later by design.
Replace the self-consumption fraction with something honest about your household. If nobody is home from nine to five, 60% is optimistic and 30% may be closer, which halves the figure. The price cap changes quarterly, so check the current rate before relying on the total.
At a kit price of £400 to £600, that example implies a payback somewhere between four and six and a half years. Tilt the same kit properly and it improves by about a quarter. Work from home and it improves considerably more. For today’s verified kit prices, see what plug-in solar actually costs.
What we have not verified
Not measured by us. We have not installed a kit and metered it over a year. These are modelled figures from an authoritative source, and we have said so rather than presenting them as test results.
Cited, not modelled. The 26.11p unit rate and the 57.19p daily standing charge are Ofgem’s published cap figures for 1 July to 30 September 2026. They change every quarter.
Not covered here. Kit prices move, and what is genuinely on sale in the UK is a separate question we have looked at in its own guide.
Before you buy anything, check that the kit is one the law actually permits: see whether plug-in solar is legal in the UK, and remember you must tell your network operator before you commission it.
Our editorial policy sets out how we handle modelled figures.
This page carries the date it was last checked. PVGIS updates its datasets periodically; if the figures have moved, tell us and we will re-run the model and update the date.