Last reviewed: 4 September 2026. Sun angles and day lengths in the table are our own calculations from latitude and solar declination, rounded; product requirements are from the DESNZ Interim Product Specification version 2.0 (July 2026).
Expect very little, and plan around it. Between November and February a plug-in solar kit in Britain produces a small fraction of what it produces in summer — the sun is low, the days are short, and the weather is the weather. The consolation is that almost all of the little it does make gets used, because a dark, cold house with the heating on is a house that is consuming. The honest framing is this: plug-in solar is a summer and shoulder-season purchase that happens to keep ticking over in winter. It is not a way to cut a January bill, and anyone selling it as one is not being straight with you.
The two things that collapse: angle and daylight
Everything else is secondary. On the shortest day the sun at its highest point in southern England is barely fifteen degrees above the horizon, and in the Highlands it is nine. That has two consequences: the light arrives through a much thicker slice of atmosphere, and it strikes a tilted panel at a glancing angle. At the same time, the number of hours in which anything at all is possible falls to around seven, and a good part of those hours is twilight.
| Location (latitude) | Noon sun, 21 Dec | Noon sun, 21 Jun | Day length, 21 Dec | Day length, 21 Jun | Dec noon: vertical vs 30° tilt | Jun noon: vertical vs 30° tilt |
|---|---|---|---|---|---|---|
| London (51.5°N) | 15.1° | 61.9° | ~7 h 50 m | ~16 h 40 m | vertical +36% | vertical −53% |
| Birmingham (52.5°N) | 14.1° | 61.0° | ~7 h 40 m | ~16 h 50 m | vertical +39% | vertical −51% |
| Manchester (53.5°N) | 13.1° | 60.0° | ~7 h 30 m | ~17 h 05 m | vertical +43% | vertical −50% |
| Edinburgh (56.0°N) | 10.6° | 57.5° | ~7 h 00 m | ~17 h 35 m | vertical +51% | vertical −46% |
The last two columns are the useful, counter-intuitive part. A vertical panel — the balcony-rail case — catches midwinter noon sunlight better than a 30°-tilted one, by more than a third in London and by half in Edinburgh, because at those tiny sun angles the vertical panel is nearly face-on to the beam and the tilted one is not. In June the position reverses completely. Vertical mounting does not fix winter; it does mean the seasonal curve of a balcony installation is flatter than the curve of a tilted one, which is worth knowing if you were about to feel bad about your railing.
How much will it actually make?
As a rule of thumb across Great Britain, a fixed array produces roughly a tenth of its June output in December, and the four months from November to February together account for well under a tenth of the year. That is a rule of thumb, and we will not dress it up as a measurement.
[VERIFICAR: month-by-month output for an 800 W array at four UK locations, modelled in PVGIS and published as a dated table of our own, to replace the rule of thumb above.] Until that is done, our savings calculator gives annual figures only, on assumptions that are declared on the page, and how much electricity plug-in solar makes explains the reasoning behind them.
What we can say without a model: the DESNZ illustrative savings of roughly £70 to £110 a year are annual figures for a whole year of an 800 W device. Do not divide them by twelve. Roughly two-thirds of a British solar year arrives between April and September.
The one thing that gets better in winter
Self-consumption. Because a plug-in kit earns nothing for exported units — no MCS certificate, no export meter point, no Smart Export Guarantee tariff — the only kilowatt-hours worth anything are the ones your house uses at the moment they are produced. In June, a household out at work exports most of a bright midday peak for £0. In December there is no peak to export: output is low, spread thin across a short day, and the house is heated, lit and occupied. Very close to all of it gets used.
So the winter saving per kilowatt-hour generated is at its best exactly when the kilowatt-hours are scarcest. That does not rescue the arithmetic, but it does mean the honest winter figure is closer to “small” than to “nothing”. See why plug-in solar cannot get SEG payments and how to use more of your solar at home.
Winter shading is a different problem from summer shading
This catches people who sited their panel in July. A hedge that casts no shadow when the sun is at 62° will cast one four times longer when the sun is at 15°, and in midwinter the sun also rises and sets much further south — so the fence, shed or neighbour’s conifer that was irrelevant in summer sits squarely in the beam for the whole of December.
Partial shading matters more than its area suggests, because shading part of a module drags down the string it is in. With at most four modules and no more than two in series per string, a plug-in array has little redundancy to lose. If you can, choose the winter position first and accept a slightly worse summer one: the summer sun is generous enough to forgive a compromise, and December is not. See ground-mounted plug-in solar.
The winter safety checks
Winter is when the mounting is tested and the wiring is wettest. These are the checks worth doing in October, from the ground.
- Fixings and ballast. The specification requires the manufacturer to give fastening or ballasting information for expected wind and snow load, with structural analysis to BS EN 1991-1-3 (snow) and BS EN 1991-1-4 (wind) and their UK National Annexes. Re-check the fixings against that guidance before the first named storm, not after it. Improvised mountings — cable ties, rope, string, adhesive tape, bungee cords, straps — are prohibited as the mounting method in any season.
- Cables and connectors. A visual check of fixings, cables and connectors is part of the maintenance the specification asks manufacturers to schedule. Look for chafing, standing water, and connectors lying in a puddle.
- The socket. Outdoor sockets must be IP55 or better. A cracked lid, a perished seal or a socket that has been rained into all autumn is a job for an electrician before winter, not after. Never bridge the gap with an extension lead — see extension leads and plug-in solar.
- The RCBO test button. The specification asks consumers to press the test button on the RCBO periodically while the plug-in unit is generating, because older residual current protection can be desensitised by devices that leak DC current into an AC circuit. Winter is a fine time to do it — but pick a day when the panel is actually producing, or the test proves nothing.
- Snow: leave it. Do not climb, do not scrape, do not use hot water on cold glass. A tilted or vertical panel sheds snow on its own within a day or two, and the generation you would recover by climbing on something icy is worth a few pence.
Cold is not the enemy; darkness is
Photovoltaic modules are slightly more efficient cold than hot — their output falls as cell temperature rises, which is why the sunniest afternoons underperform their nameplate. A crisp, bright February day with a low sun and a cold panel can produce a surprisingly respectable half-hour. What winter takes away is not efficiency but photons: less time, lower angle, more cloud and more atmosphere in the way.
Two consequences follow. A generously sized DC array — up to the specification’s 2,000 W ceiling, four modules maximum, no more than two in series — earns its keep mainly in the shoulder seasons and winter, because that is when the inverter is nowhere near its 800 VA limit and every extra watt of panel converts directly into output. And bifacial modules, which pick up light reflected from the ground behind them, do relatively better over snow and wet paving than over summer grass. See how many panels behind an 800 W inverter and are bifacial panels worth it.
Frequently asked questions
Should I take the kit down for winter?
Only if the mounting position genuinely worries you in a gale — in which case fix the mounting, not the season. Bear in mind that removing a device is itself notifiable to your distribution network operator, and so is reconnecting it. See telling your DNO you removed a device.
Will it work on a dull day at all?
Yes, at a much reduced level. Diffuse light from an overcast sky still generates; it is why the annual figure is not simply the sunny hours. It is also why the direct-beam column in our table above is only part of the picture.
Would a battery fix the winter problem?
No — a battery moves energy through the day, it does not create any, and in December there is little to move. It is also not permitted in a plug-in kit: SI 2026/848 excludes devices designed to import electricity in order to store it, and the specification requires a prominent warning against pairing one. See can I add a battery to plug-in solar and home battery storage.
Does my payback calculation change?
No, if it was an annual calculation to begin with. It changes a great deal if you were extrapolating from a good week in June. See the payback period and are plug-in solar panels worth it.
Is it worth angling the panel more steeply for winter?
A steeper tilt does help in winter and costs you in summer, and for a plug-in kit that trade is less lopsided than for a rooftop array because winter output is used at home while summer surplus is exported for nothing. A near-vertical mount is a legitimate choice, not a compromise — see the table above and balcony solar panels in the UK.
Primary sources.
DESNZ, Plug-in Solar Device Interim Product Specification version 2.0, July 2026 (PDF) ·
DESNZ, plug-in solar government response and impact assessment ·
European Commission Joint Research Centre, PVGIS ·
Sheffield Solar, PV_Live GB solar generation estimates ·
Ofgem, Smart Export Guarantee.
General information, not electrical advice. Do not work at height or on a roof to inspect or clear a panel — see our editorial methodology.