Solar Panel Output in Winter UK: What Businesses Can Expect

Modelled figures from the European Commission's PVGIS solar database, which installers widely use, show a typical south-facing UK system producing around 29 kWh per kWp in December. The same system produces about 117 kWh per kWp in June and around 950 kWh per kWp across a full year.

Applied to typical commercial system sizes, that means:

• 50kWp system: roughly 1,450 kWh in December, against about 5,850 kWh in June
• 100kWp system: roughly 2,900 kWh in December, against about 11,700 kWh in June
• 250kWp system: roughly 7,250 kWh in December, against about 29,250 kWh in June

Over the winter as a whole, November to February together typically account for about 17% of annual generation, while June to August deliver around 35%. The exact figures vary with location, orientation, tilt and shading, and one dull December can produce noticeably less than a bright one.

In practical terms, a system that comfortably powers a building's daytime load on a June afternoon may cover only a small fraction of it on a grey December morning.

Winter output drops mainly because there is less daylight and the sun sits lower in the sky, not because of the cold. Three factors combine:

• Shorter days: in December much of the UK gets around seven to eight hours of daylight, compared with 16 or more in June, and further north the gap is wider.
• Low sun angle: at midwinter the sun is low even at midday, so its light passes through more atmosphere and strikes the panels at a shallower angle, delivering less energy per square metre.
• More cloud: winter weather brings more overcast days, which cut output further.

Cold weather itself is not the problem. Solar panels become slightly more efficient as they get colder, so a bright, frosty day can produce surprisingly good output for the time of year. Hot summer days actually reduce efficiency a little, which is one reason why spring months such as May can match or beat June in some years.

Location affects winter output even more than summer output, because the difference in day length between north and south is greatest in December. Typical annual yields range from around 850 kWh per kWp in Scotland to about 1,000 to 1,100 kWh per kWp in southern England, and the winter gap is proportionally wider than that.

Some patterns are worth knowing:

• Southern England: the strongest winter output in Great Britain, with Cornwall, Devon and the south coast typically leading.
• Midlands and Wales: close to the UK average, with western areas sometimes holding up better in winter than the south-east.
• Northern England: lower winter output, but still productive on clear days.
• Scotland: the shortest winter days and lowest December output, balanced by very long summer days that lift the annual total.

For a business case, regional yield matters most in the annual payback rather than in winter specifically. A Scottish site generates less in December, but its long summer evenings partly compensate. You can see how output and savings vary by location on our solar panels by area pages.

The biggest hidden winter loss on commercial roofs is shading, and it is often underestimated because most site surveys take place in spring or summer. When the sun is high, a parapet, plant room, neighbouring building or tree may cast a short shadow that barely touches the array. In December, with the sun low in the southern sky, the same obstruction can cast a shadow several times longer across rows of panels.

On flat roofs with tilted frames, the rows themselves cause the same effect. Rows spaced for summer can shade each other for much of the winter day, which is why installers balance row spacing against the number of panels they can fit.

Ask every installer three questions:

• Has shading been modelled for the whole year, including the winter solstice, not just observed on the survey day?
• Does the yield model show monthly output, so you can see the winter months?
• Would optimisers or a different string layout reduce winter shading losses on the affected areas?

A design that looks unobstructed in a June photograph can lose a meaningful share of its winter output to shadows nobody saw. Getting it right costs nothing extra at the design stage.

Most businesses use more electricity in winter, for lighting, heating, longer hours of darkness and sometimes seasonal trade. At exactly the same time, solar output falls to a quarter of its summer level. The result is that solar covers a much smaller share of demand in winter, and almost all winter generation is used on site rather than exported.

That has two consequences for the business case. First, the winter months contribute relatively little to the annual saving, so the payback depends mainly on spring and summer generation. Second, a system sized to your summer daytime demand will rarely export much in winter, so winter output is almost always worth the full import price of 24p to 29p per kWh that most UK businesses paid in 2026.

Monthly bills will reflect this pattern. Expect solar to make a large dent in your electricity bills from April to September and a modest one from November to February. If you budget on a flat monthly saving, the winter bills will look disappointing even though the system is performing exactly as designed.

Snow stops panels generating while it covers them, but in most of the UK it rarely lies long enough to matter. A light covering usually slides off tilted panels within a day or two once the sun reaches them, helped by the dark surface warming up.

Do not send staff onto a roof to clear panels. Working on a commercial roof in winter conditions is dangerous, the lost generation is small, and scraping can scratch the glass or damage the anti-reflective coating. If snow persists on a low-pitch array, it is usually better to wait.

Frost and cold do no harm to modern panels, which are tested to withstand freezing conditions and hail. Winter does bring a few practical checks:

• Leaves and debris can collect along the lower edges of panels, especially on low-pitch roofs.
• Storms can loosen roof fixings or cable trays, so include the array in any post-storm roof inspection.
• Monitoring should show steady, if low, output on clear days. A sudden drop to zero usually means an inverter fault rather than the weather.

Usually not very much. A battery stores surplus solar generation for later use, but in winter a business typically uses all its solar output as it is generated, so there is little or no surplus to store. A battery that earns its keep shifting summer surplus into the evening may sit largely unused by solar from November to February.

There is one exception. Many commercial batteries can also charge from the grid at cheaper overnight rates and discharge during expensive daytime or peak periods. If your tariff has a large enough price difference between those times, a battery can earn value all year round, including in winter, independently of the solar array.

That is why battery payback should be modelled using your full year of half-hourly data and your actual tariff, not a summer-only calculation. For most offices, factories and shops that use their solar output during working hours, the battery case rests on summer exports and tariff arbitrage rather than on winter solar. Our commercial solar payback guide explains how storage affects the overall numbers.

Winter output is low, but winter is often the best time to plan and order a commercial system, so that it is generating at full strength through spring and summer. Commercial projects take time to move from enquiry to switch-on:

• Survey, design and quotes: typically several weeks
• G99 grid application: the network operator has up to 45 working days to issue an offer on a full application
• Structural checks, procurement and scheduling: further weeks, depending on the project
• Installation and commissioning: from a few days on a small roof to several weeks on a large site

Start in November and a straightforward project can realistically be generating by spring, ready to capture the months that deliver most of the annual saving. Start in May and the same project may miss much of that summer.

Installers also tend to have more scheduling flexibility in winter than in the busy spring and summer months, which can help with timing on sites that need work done around operations. Our guide to sizing a commercial solar system explains what information to gather first.

Most commercial systems come with an online monitoring portal, and winter is when owners most often worry that something has gone wrong. A few checks distinguish normal seasonal behaviour from a real fault:

• Compare with the forecast, month by month: your installer's yield model should show expected output for each month. Compare December against December, not against the annual average.
• Compare inverters with each other: on larger systems with several inverters facing the same way, output should track closely. One inverter well below the others points to a fault or shading issue.
• Look at clear days: on a bright winter day the system should produce a clean curve peaking around midday. A flat line or a curve that stops abruptly suggests a problem.
• Check for zero output: even on dull days, a working system produces something. Zero generation during daylight almost always means a tripped isolator, inverter fault or communications failure.

If your system has an operation and maintenance contract, the provider should flag faults automatically.

A well-designed commercial system accepts that winter output will be low and is sized and laid out to deliver the best value across the whole year. In practice, that means:

• Sizing to your spring and summer daytime baseload, so the system is not oversized and exporting heavily in summer
• Modelling shading at the winter solstice as well as in summer, particularly near parapets, plant and neighbouring buildings
• Asking for a month-by-month yield forecast rather than a single annual figure
• Budgeting for uneven monthly savings, with most of the benefit arriving between April and September
• Planning installation in autumn or winter, so the system is generating by spring

Our commercial solar cost guide sets out typical prices by system size, and our guide to comparing commercial solar quotes explains how to check the assumptions behind each forecast. When you are ready, compare quotes from up to three MCS-certified commercial installers for your site.