How efficient are solar panels in the UK during the winter? They keep working through the darkest months, but they generate far less electricity than they do in summer. A south-facing system in Cardiff, modelled with the European Commission’s PVGIS tool, produces about 3.1 percent of its yearly total in December, against about 12.6 percent in June. A December day averages about 1.0 kilowatt hour per kilowatt peak, while a June day averages about 4.4. The panels themselves are not the problem. Cold weather slightly helps them. The problem is the weak, short-lived winter sun, and no panel can generate electricity from light that is not there.

The Short Answer: How Efficient Are Solar Panels in the UK During the Winter?

How efficient are solar panels in the UK during the winter? They work, but at roughly a quarter of their summer output on an average day. In the PVGIS model of a south-facing system at a 35 degree pitch in Cardiff, with 14 percent system losses, December produces about 3.1 percent of the year’s electricity and January about 3.5 percent, while June produces about 12.6 percent and May about 12.7 percent. November to February together produce about 16 percent of a typical year’s electricity. A clear, frosty January day can still beat a dull June day, but averaged across the season, winter is the thin quarter of the solar year.

Why Winter Output Falls So Sharply

Three things change at once in a British winter, and they all push output down. The days are far shorter, so there are simply fewer hours of daylight for the panels to work in. The sun sits much lower in the sky, so its light arrives at a shallow angle and passes through more atmosphere before it reaches your roof. And cloud cover is heavier and more frequent, so a larger share of the light that does arrive has been scattered rather than coming direct from the sun.

The Met Office sunshine averages for Cardiff Bute Park, for 1991 to 2020, show the scale of the change. December averages 50.44 hours of sunshine and January 53.53 hours, against 195.21 hours in June and 199.56 hours in July. July has nearly four times as much sunshine as December. That is the main reason a December day produces roughly a quarter of the electricity of a June day, not a fault in the panels.

Shorter days also mean the sun never climbs high enough to deliver the strong, direct light that panels convert most easily. In midsummer the sun is high for hours around midday. In midwinter it stays low all day, rises late and sets early, and the roof receives weaker light for a shorter time. A south-facing roof still does best, because it catches the low southern sun through the middle of the day, and the Energy Saving Trust notes that panels work best on a south-facing roof with no shading from nearby trees or buildings.

How Efficient Are Solar Panels in the UK During the Winter Compared With Summer?

The table below uses PVGIS, the European Commission’s solar modelling tool, for 1 kilowatt peak of south-facing panels at a 35 degree pitch in Cardiff, with PVGIS’s default 14 percent system losses. It is a model of one roof in one city, not a promise for every home. Your own figures will differ with location, roof direction and pitch, and shading. But the shape of the year is the same across the UK.

April, August and September are not listed with monthly shares in the source, and together they account for the rest of the year’s output. The nine months shown add up to 68.5 percent, so the three unlisted months make up the remaining 31.5 percent. The winter four months, November to February, add up to 15.9 percent, which the source rounds to about 16 percent. The single most useful comparison is December against June: about 1.0 kilowatt hour per kilowatt peak a day against about 4.4. For a 4 kilowatt peak system, that is roughly 4 kilowatt hours on an average December day against roughly 17 to 18 kilowatt hours on an average June day.

Other models of UK systems show the same pattern. A PVGIS model of a 4 kilowatt south-facing system in Keighley, West Yorkshire, with 14 percent losses, puts December at 101 kilowatt hours, or 2.8 percent of its annual total of 3,661 kilowatt hours, and November to February together at about 540 kilowatt hours, or about 15 percent of the year. Another UK guide puts a typical 4 kilowatt system at about 3,400 kilowatt hours a year, generating roughly 270 kilowatt hours from December to February, or about 2 to 4.5 kilowatt hours a day against 13.5 in June, with December output at around 17 percent of June’s. Figures derived from Energy Saving Trust data, as reported by several UK solar guides, tell the same story for a smaller system: a south-facing 3 kilowatt system produces around 300 kilowatt hours in June or July but only around 75 kilowatt hours in December or January.

The exact percentages move with location. Southern England gets more sun than northern Scotland, and a south-facing roof at a good pitch beats an east or west facing roof. But no location in the UK escapes the winter trough. December is the weakest month everywhere, and the four winter months together are roughly a sixth of the year everywhere.

Does Cold Weather Help or Hurt Solar Panel Efficiency?

Cold weather slightly helps solar panel efficiency. This surprises most people, because we associate solar panels with heat, but panels are rated at a standard cell temperature of 25 degrees Celsius, and their output falls as the cells get hotter. The manufacturer’s datasheet states a temperature coefficient that tells you how much output changes per degree. For the LONGi EcoLife panels fitted by The Solar House, the datasheet gives a power temperature coefficient of minus 0.26 percent per degree Celsius, measured from a standard cell temperature of 25 degrees Celsius. Output falls by 0.26 percent for every degree the cells run above 25 degrees, and rises slightly when they are cooler.

Cells run warmer than the air around them, because they absorb sunlight. The same datasheet gives a nominal operating cell temperature of 45 degrees Celsius under its test conditions. At 45 degrees, the coefficient points to about 5 percent less output than the panel’s rated power. On a bright, cold winter day the cells stay cooler, so they work a little more efficiently for each unit of light they receive. That does not make up for the weaker winter sun, but it is one reason clear winter days can be productive.

Efficiency and output are not the same thing. Efficiency is how well the panel converts the light it receives, and that is slightly better in the cold. Output is how much electricity it produces, which also depends on how much light arrives. In winter the light is far weaker and lasts for far fewer hours, so the output is far lower even though the efficiency is slightly better. Heat is the real enemy of efficiency, and it is a summer problem: on a hot July afternoon the cells can run far above their rated temperature and lose several percent of their output.

Cloudy Days and Diffuse Light

Solar panels do not need direct sunshine. The Energy Saving Trust states plainly that solar cells do not need direct sunlight to work and can work even on cloudy days, although the stronger the sunshine, the more electricity they make. Sunlight reaches your roof in two forms. Direct light comes in a straight line from the sun. Diffuse light has been scattered by cloud and the atmosphere and arrives from across the whole sky. Panels convert both.

Diffuse light is a large share of what reaches British roofs, and its share is highest in winter. In the European Commission’s PVGIS data for Cardiff, averaged over 2005 to 2023, diffuse light makes up about 48 percent of the sunlight reaching a horizontal surface in June and about 66 percent in December. In other words, about two thirds of the light arriving in December is scattered light. That is why panels keep generating on grey winter days when the sun never appears. The output on a heavily overcast day can be a small fraction of what the same panels produce in bright sun, but over a whole year the cloudy day generation adds up to a real share of the total.

Snow and Frost on Solar Panels

Snow lying on the panels blocks the light, so generation drops to little or nothing until it slides off or melts. Panels are tilted and have smooth glass, which helps snow clear, but how quickly they clear depends on the weather. A light dusting on a sunny morning may slide off as the glass warms. A heavy fall followed by freezing temperatures can keep panels covered for longer.

Do not climb onto the roof or use a ladder to clear snow from your panels. The Solar House guide is direct on this point, and the MCS maintenance schedule only asks homeowners to make visual checks from the ground, including looking for signs of structural distress, particularly after heavy snow. Clearing snow yourself risks a serious fall, and it risks damaging the panels. The right action is to wait for the snow to clear on its own and to check from the ground that the panels have not slipped or been damaged.

Snow loading is part of the design of a properly installed system. Panels are tested for load, and the LONGi datasheet lists a front-side maximum static load of 5,400 pascals. The MCS installation standard also requires a structural engineer for roofs where snow can build up, and panels near roof edges need measures so that sliding snow cannot cause injury or damage. If your monitoring shows nothing at all on a bright day once any snow has cleared, contact your installer, because that points to a fault rather than the weather.

What Winter Means for a Home Battery

A battery changes how you use your solar electricity, and winter changes how useful a battery is. In summer, a battery mostly stores surplus solar for the evening, when the sun has set but the house is still using power. In winter there is much less surplus to store. At about 1 kilowatt hour per kilowatt peak a day in December in the Cardiff model above, a 4 kilowatt peak system would average about 4 kilowatt hours a day. For comparison, the MCS worked example assumes a home using 3,500 kilowatt hours a year, which is about 9.6 kilowatt hours a day. Most winter solar is likely to be used in the house as it is generated, with little left to store.

That does not make a battery useless in winter. It changes what the battery is for. The Energy Saving Trust explains that a battery can be charged when a time-of-use tariff is cheap and the stored energy used when prices are higher. On a cheap overnight rate, you can fill the battery from the grid and use that electricity during the expensive evening peak, whether or not the sun shone that day. Whether that works for you depends on your tariff and your usage pattern, so talk it through with your installer rather than assuming a battery pays for itself on solar alone.

The Energy Saving Trust also notes that a battery’s system stops discharging at a set level, perhaps 20 percent, to protect its life. That reserve means the usable capacity is less than the headline figure on the box, which matters when you are sizing a battery for winter evenings. A battery that looks generous on paper may hold less usable charge than you expect once the reserve is taken into account.

If your home is heated by a heat pump, your electricity demand peaks in winter, exactly when solar output is at its lowest. Our guide to how much it costs to run a heat pump in winter sets out what that seasonal demand looks like. Winter solar will cover only a small part of it, so a heat pump home should judge solar on its annual contribution, not on what it delivers in December and January.

The MCS Estimate Already Includes Winter

Every MCS-certified installer must give you an estimate of what your system will generate, and that estimate already includes winter. The MCS estimate on your quote is an annual figure for the first year, given as guidance and not a guarantee. It is calculated as the system size in kilowatt peak, multiplied by a kilowatt hour per kilowatt peak value for your postcode zone, orientation and pitch, multiplied by a shade factor. Those kilowatt hour per kilowatt peak values come from PVGIS data multiplied by 0.8, which builds in a margin for real-world losses. The standard method gives one yearly total rather than a month by month profile, so winter is already built into the annual number.

This is worth understanding before you compare quotes. Two installers quoting the same roof should give similar annual figures, because they are working from the same method. If one quote promises far more than the others, ask how it was calculated. If you would like to see how your system’s output might spread across the months, ask the installer when they prepare your quote.

The estimate is guidance for the first year of generation only, and not a guarantee, because sunlight varies from place to place and from year to year. A dull winter or a bright one will move your real figures either way. Judge a system over a full year, and compare each month against the modelled pattern rather than against summer.

Costs, Savings and Payback in Context

How efficient are solar panels in the UK during the winter? Winter output is only half the question. The other half is whether solar pays for itself over the life of the system, and here the annual total is what counts. The Energy Saving Trust says a typical domestic system is around 4.5 kilowatt peak and costs around 7,600 pounds to install, although the cost depends on the size of the system, access to the roof, whether you choose panels or tiles, and whether the roof covering needs renewing. There are no dedicated solar panel grants from the UK Government, but the Warm Homes Plan is set to invest close to 15 billion pounds in improving the UK’s homes to cut energy bills, with fully funded support for people on low incomes and low and zero interest loans for homeowners.

Payback depends on how much of the solar electricity you use yourself, whether you sign up for export payments such as the Smart Export Guarantee, and where in the UK you live, because areas further south get more direct sunlight. The Energy Saving Trust’s payback figures, with export payments and based on fuel prices as of July 2026, are 9 years in London, 10 to 11 years in Manchester, 9 to 10 years in Aberystwyth and 11 to 12 years in Stirling. Those figures are built from annual generation, so the winter trough is already in them.

There is also a tax point to know about if you are considering solar now. Installed solar panels are energy-saving materials under HMRC’s VAT Notice 708/6, and the zero rate of VAT applies to their installation until 31 March 2027, after which installations revert to the reduced rate of 5 percent from 1 April 2027. The relief applies to the installation, including the panels, cabling, control panel and inverter, in residential accommodation. Materials supplied without installation are standard rated. Our guide to when 0 percent VAT on heat pumps ends explains the same 31 March 2027 expiry, which covers energy-saving materials including solar panels.

Panels themselves are long lived. The Energy Saving Trust says your solar panels should last 25 years or more, but if you have a solar inverter, you need to replace it after around 12 years. Most inverters have warranties of five years as a minimum, which you can often extend by up to 15 years. Maintenance is light. In the UK, rain will clean your panels if they are tilted at 15 degrees or more, and the main job is to keep nearby trees well trimmed to minimise shading.

The heating system you pair with solar changes how much of your generation you use yourself, which is the biggest driver of savings. If you are weighing a heat pump against a gas boiler, our comparison of whether it is cheaper to run a gas boiler or a heat pump sets out the running costs.

Nearly 1.7 million installations are already on UK homes, according to UK Government data cited by the Energy Saving Trust. The winter pattern in this article is the lived experience of well over a million households, and the annual figures installers quote are built from it.

What to Do If You Are Considering Solar Panels Now

Winter is not a bad time to think about solar, but it is a bad time to judge a system by looking at a neighbour’s roof in December. Judge it on the annual figure, and check the winter months in the model so you know what to expect. If the installer’s December figure is far above about 3 percent of the annual total, ask why.

Start with the roof. The ideal is a south-facing roof with no shading, but east and west facing roofs can still work well, and the installer can model each option. Check the condition of the roof covering before you commit, because scaffolding and panel removal make a later re-roof far more expensive. Think about how the low winter sun throws shadows across the roof from chimneys, dormers and neighbouring buildings.

Get quotes from at least three MCS-certified installers, as the Energy Saving Trust recommends, and make sure each quote shows the MCS estimate, the system size, the panel and inverter makes, and whether a battery is included. Ask each installer to explain the winter months in their estimate, and ask whether a battery makes sense on your tariff. If you are on a time-of-use tariff with a cheap overnight rate, a battery can earn its keep in winter by charging from the grid. If you are on a flat tariff and use little electricity in the evening, it may not.

Finally, be realistic about what winter solar can do. It will not cover your winter electricity bill on its own. It will trim it, and it will cover a far larger share in spring, summer and autumn. Over a full year, a well sited system generates a meaningful amount of electricity, and the payback figures above show how long that takes to repay the installation cost. Winter is the thin quarter of that year, and knowing that in advance is what stops a disappointing December from feeling like a faulty system.

Frequently Asked Questions

Do solar panels work in winter in the UK?

Yes. Solar panels generate electricity all year in the UK, including on cloudy days, because they use daylight rather than direct sunshine. They produce much less in winter, though. In the PVGIS model of a south-facing system in Cardiff, December produces about 3.1 percent of the year’s electricity and November to February together produce about 16 percent.

How efficient are solar panels in winter in the UK?

How efficient are solar panels in the UK during the winter? They keep working, but at roughly a quarter of their summer output on an average day. In the PVGIS model of a south-facing system in Cardiff, a December day averages about 1.0 kilowatt hour per kilowatt peak against about 4.4 kilowatt hours per kilowatt peak in June. Cold weather slightly helps panel efficiency, so the low output is caused by shorter days, a lower sun and more cloud, not by the cold.

Are solar panels less efficient in cold weather?

No. Solar panels are slightly more efficient when cold. Panels are rated at a standard cell temperature of 25 degrees Celsius, and output falls by 0.26 percent for every degree the cells run above that temperature, according to the LONGi EcoLife datasheet. Winter output is lower because of shorter days and a lower sun, not because of the cold.

Do solar panels work on cloudy days?

Yes. Solar cells do not need direct sunlight, and the Energy Saving Trust says they can work even on cloudy days. Diffuse light, scattered by cloud and the atmosphere, makes up about 66 percent of the sunlight reaching the ground in December in Cardiff, against about 48 percent in June. Output on a heavily overcast day is a small fraction of bright sun output, but cloudy day generation adds up over the year.

Should I clear snow off my solar panels?

No. Do not climb onto the roof or use a ladder to clear snow. Snow usually slides off the tilted, smooth glass or melts on its own. The MCS maintenance schedule only asks homeowners to make visual checks from the ground, including looking for signs of structural distress after heavy snow. If your monitoring shows nothing at all on a bright day once any snow has cleared, contact your installer.

Is a battery worth it for winter solar?

How efficient are solar panels in the UK during the winter? A battery stores less solar in winter because there is little surplus to store. A 4 kilowatt peak system averages about 4 kilowatt hours a day in December in the Cardiff model, against a typical home using about 9.6 kilowatt hours a day, so most winter solar is used as it is generated. A battery can still be worth it if your time-of-use tariff lets you charge it on a cheap rate and use the stored energy when prices are higher.

The Verdict: How Efficient Are Solar Panels in the UK During the Winter?

How efficient are solar panels in the UK during the winter? Efficient enough to keep generating, but not efficient enough to carry your winter electricity use. December delivers about 3 percent of the year’s electricity, the four winter months together deliver about 16 percent, and a December day averages roughly a quarter of a June day. The cold helps the panels slightly, the cloud does not switch them off, and snow is a temporary blockage rather than a lasting problem. None of that changes the basic fact: the winter sun is weak, low and short lived, and the panels can only convert the light they receive.

That is not a reason to avoid solar. It is a reason to buy it with open eyes. Judge a system on its annual generation, check the winter months in the installer’s estimate, and size any battery for what it can do on your tariff rather than for summer surplus alone. A system bought on that basis will do exactly what it promised, including in December, and the thin winter quarter will be part of the plan rather than a surprise.

Sources

• Energy Saving Trust, Solar panels: costs, savings and benefits explained. Supports: panels work on cloudy days, cells do not need direct sunlight, south-facing roof best, typical 4.5 kWp system around 7,600 pounds, no dedicated UK Government solar grants, Warm Homes Plan close to 15 billion pounds, payback by city at July 2026 fuel prices, panels last 25 years or more, inverter replacement after around 12 years, rain cleans panels tilted at 15 degrees or more, nearly 1.7 million installations, quotes from at least three MCS-certified installers. https://energysavingtrust.org.uk/advice/solar-panels/
• The Solar House, Do solar panels work in winter? Updated 12 October 2026. Supports: PVGIS Cardiff model monthly shares and daily output, Met Office Cardiff Bute Park sunshine hours 1991 to 2020, diffuse light shares, LONGi EcoLife temperature coefficient minus 0.26 percent per degree Celsius and nominal operating cell temperature 45 degrees Celsius, snow guidance and MCS ground checks, MCS estimate method and PVGIS multiplied by 0.8, battery winter figures and MCS 3,500 kWh a year worked example, battery charged on a cheap time-of-use rate and discharge floor of perhaps 20 percent as explained by the Energy Saving Trust, LONGi front-side maximum static load 5,400 pascals. https://www.thesolarhouse.co.uk/news/do-solar-panels-work-in-winter/
• PVGIS, Photovoltaic Geographical Information System, European Commission Joint Research Centre. Supports: the solar modelling tool behind the monthly figures and the MCS estimate tables. https://re.jrc.ec.europa.eu/pvg_tools/en/
• HMRC, Energy-saving materials and heating equipment, VAT Notice 708/6, GOV.UK. Supports: zero rate of VAT on installed energy-saving materials including solar panels until 31 March 2027, reverting to the reduced rate of 5 percent from 1 April 2027, and materials supplied without installation being standard rated. https://www.gov.uk/guidance/vat-on-energy-saving-materials-and-heating-equipment-notice-7086
• P4 Solar, Do solar panels work in the winter? Supports as corroboration only: PVGIS model of a 4 kW south-facing system in Keighley, West Yorkshire, December 101 kWh (2.8 percent of annual), annual total 3,661 kWh, November to February about 540 kWh (about 15 percent). https://p4solar.co.uk/advice/do-solar-panels-work-in-the-winter/
• Home Energy Quotes, Solar panels winter UK electricity generation. Supports as corroboration only: typical 4 kW system about 3,400 kWh a year, roughly 270 kWh from December to February, about 2 to 4.5 kWh a day against 13.5 kWh a day in June, December output around 17 percent of June’s. https://www.homeenergyquotes.co.uk/solar-panels-winter-uk-electricity-generation/
• Met Office sunshine averages for Cardiff Bute Park, 1991 to 2020, as reported by The Solar House. Supports: 50.44 sunshine hours in December, 53.53 in January, 195.21 in June, 199.56 in July.