Do solar panels work on cloudy days? (UK weather, shade and snow)

Yes, solar panels work on cloudy days. Under thick overcast a panel typically makes around 10–25% of its bright-sun output, rising to roughly 50–80% under light or broken cloud. Panels run on daylight, not direct sun, so Britain's grey skies slow them down rather than switch them off. Over a full year the number that decides your generation isn't cloud on any single day, it's the season and, more than anything, whatever is shading your specific roof.

This page covers the whole picture: why panels keep generating under cloud, how much you actually lose on a dull day, and the two things that matter far more than cloud (the season and shading). Because "cloudy days" is really a family of questions, we've folded the siblings in as full sections below: shade and trees, and snow.

One thing up front, so we're straight with you: our own roof check and Solarable Report are built around solar PV (electricity), which is exactly what this guide is about. So the sunlight and shading estimates you get from the tool aren't generic weather averages, they're modelled on your actual roof.

Why panels work under cloud at all

The common mental model, "no sun, no power", is wrong. Sunlight reaches your roof in two forms:

• Direct beam radiation: light travelling straight from the sun, the kind that casts a sharp shadow.
• Diffuse radiation: light scattered by clouds, haze, and the atmosphere, plus a little reflected off surrounding surfaces.

A solar panel converts both. On a clear day most of the energy hitting your roof is direct. On a heavily overcast day almost all of it is diffuse, but it's still solar energy and it still generates electricity. That's the whole reason solar is viable in a cloudy country: panels harvest the diffuse light that a grey sky is full of. The UK's climate is why we quote generation as an annual range rather than a peak, but the panels never simply stop.

How much you actually lose on a cloudy day

There's no single "cloudy day" figure, because cloud isn't one thing. A bright hazy sky and a black storm front are worlds apart for a panel. The honest ranges:

Sky conditions	Rough output vs bright sun
Clear, direct sun	100% (the reference)
Light or broken cloud, bright overcast	50–80%
Moderate, uniform grey	25–50%
Heavy, dark overcast	10–25%

So even the gloomiest useful daylight leaves a panel doing real work. What a run of dull days changes is the shape of your generation, not whether it happens. And crucially, a cloudy day in June still handily beats a clear day in December, because day length and sun height matter more than cloud, which is the next point.

The thing that matters more than cloud: the season

If you're worried about British weather, the honest steer is to worry less about individual cloudy days and more about the time of year. UK solar is heavily summer-weighted. A system generates the bulk of its annual total between roughly April and September, and only around 10–15% across November to February, when days are short and the sun sits low. Deep-winter output commonly runs 25–50% below summer levels even on bright days, simply because there's less daylight to work with.

That seasonal shape is baked into every honest savings estimate, and it's why a scattering of cloudy summer days barely dents your year while short winter days do most of the "damage". We cover the lopsided year in detail in solar in winter: what to expect and solar in summer: what to expect. If cloud is your concern, read those two before you read another word about clouds, because that's where the real variation in a UK year lives. (One counterintuitive bonus: panels are slightly more efficient in the cold, so a crisp bright winter day is kinder to a panel than a hot one, as we explain in do solar panels work in a heatwave?.)

Shade, trees and chimneys: the real output killer

Here's the part that actually decides your generation, and it has nothing to do with the weather forecast. Shading is the single biggest avoidable drag on a UK solar system, and its effect is worse than most people expect.

The reason is electrical, not just optical. Panels are usually wired in "strings", and with a basic string inverter, shade falling on one panel can drag down the output of every panel in that string, not just the shaded one. So a chimney's shadow crossing two panels at 4pm can cost you far more than 2 panels' worth of generation. The usual culprits:

• Trees, especially deciduous ones that leaf up in summer exactly when you want the generation, and evergreens that shade year-round.
• Chimneys and dormers on your own roof, which throw a moving shadow across the array as the sun tracks over.
• Neighbouring buildings, which can clip a low winter sun even when summer is fine.

Two things soften this. First, the technology: microinverters and power optimisers let each panel perform independently, so shade on one no longer penalises the whole string. Second, layout: a good installer designs the array around the shadows, keeping panels off the roof sections that get clipped at the worst times. Neither makes shade free, but both turn a dealbreaker into a manageable trade-off.

Shading is also the one factor a desktop tool reads least perfectly, because a satellite sees the roof from above at one moment, not the tree's shadow tracking across it at 3pm in December. Our roof check estimates sun and obstructions from Google's solar data, but final shading is exactly what an installer survey on site is for.

Snow on solar panels

Snow is a short-lived, self-solving problem in most of the UK. While cells are physically covered, output drops to near zero, because no light reaches them. But three things work in your favour:

• Pitched roofs shed snow. A typical UK roof pitch of around 30–40 degrees lets snow slide off rather than settle.
• Panels clear themselves faster than the roof around them. Their smooth, dark glass warms in daylight and the snow slips off sooner than it does from surrounding tiles.
• UK snow rarely lasts. For most of the country, lying snow is a day or two at a time, and it happens in the depths of winter when your system is generating little anyway, so the annual cost is tiny.

Don't climb up to clear snow yourself: it's dangerous and rarely worth it. The days you'd be clearing are low-generation days regardless. Let it slide.

Why an average can't answer this for your roof

Every figure on this page is a national average dressed up as a range. Useful for understanding the physics, useless for a decision, because "how much will cloud and shade cost me" depends entirely on your roof. Two identical houses on the same street can generate meaningfully different amounts once you account for which way each faces and what's casting shadows on it.

That gap is what our roof check is built to close. It finds your home, estimates your roof's direction, usable area and sunlight from Google's Solar API (which models per-roof solar flux, not a regional average), and combines that with sunlight data from PVGIS, the EU's solar-yield database. The savings calculator then turns that into an honest generation and bill-saving range for your roof, not a generic house. It takes about a minute and it's a far better answer to "does the weather here make solar worth it" than any table, including ours.

None of it replaces a proper survey. An MCS-certified installer measuring your roof and reading its shading in person is the only way to a firm number, and you should always get one before you commit. Our installer directory lists MCS-certified installers covering your postcode.

Frequently asked questions

Do solar panels work on cloudy days in the UK?

Yes. Panels run on daylight rather than direct sun, so they convert the diffuse light a cloudy sky is full of. Output typically falls to around 10–25% of bright-sun levels under heavy overcast, and 50–80% under light or broken cloud. It's why solar is viable in Britain's climate: the panels slow down under cloud, they don't switch off.

How much less electricity do solar panels make when it's cloudy?

It depends on how thick the cloud is. A bright overcast or lightly clouded sky might still give 50–80% of clear-sky output; a dark, heavy overcast day can drop it to 10–25%. Over a whole year, though, the season matters far more than any single cloudy day: UK systems make only around 10–15% of their annual total across November to February, when days are shortest.

Does shade from trees affect solar panels more than clouds?

Usually yes. Cloud reduces output evenly across the whole array, but shade on even one panel can drag down a whole wired string with a basic string inverter, so its effect is disproportionate. Trees, chimneys and neighbouring buildings are the biggest avoidable drag on a UK system. Microinverters or power optimisers, and a layout designed around the shadows, reduce the penalty. Precise shading is what an installer survey is for.

Do solar panels work when covered in snow?

Not while the cells are physically covered, but that's usually brief. Pitched UK roofs shed snow, and panels' smooth dark glass clears faster than the surrounding roof. UK snow rarely lasts more than a day or two and falls in deep winter when generation is low anyway, so the annual cost is minimal. Don't climb up to clear it, it isn't worth the risk.

Is solar worth it in a cloudy country like the UK?

Yes, and millions of UK installs are the proof. Panels are designed to work on diffuse light, and the UK gets enough usable daylight across the year for a well-sited system to cut bills significantly. The deciding factors for your home aren't the clouds, they're your roof's direction, its shading, and how much of your own generation you use. The only way to know for your roof is to estimate it, then get a survey.

Related

• Solar in winter: what to expect
• Solar in summer: what to expect
• How much electricity does a solar panel produce?
• Solar inverter types explained
• Do solar panels work in the UK?
• Is my roof suitable for solar?
• Estimate your savings