Do solar panels work in winter?

Yes, but far less. Solar panels respond to light, not heat, so they generate on overcast December days as well as bright June ones — just at a fraction of the output. The reduction is driven by three things at once: fewer daylight hours, a lower sun angle meaning light passes through more atmosphere and strikes the panel more obliquely, and more frequent cloud. Expect a British array to produce the great majority of its annual total between spring and autumn, with the midwinter months contributing very little. A well-designed system accounts for that rather than pretending otherwise.

Light, not temperature

This is the part most people have backwards. Photovoltaic cells convert light. Their electrical output actually improves slightly as cell temperature falls, which is why a crisp, clear, cold February morning can produce a surprisingly strong instantaneous reading — often better than a hazy, baking July afternoon at the same irradiance.

What collapses in winter is the amount of light available. Short days, low sun and thick cloud between them reduce the total energy arriving at the roof dramatically.

Why the sun angle matters so much

In midsummer the sun rises high. Its light passes through relatively little atmosphere and arrives close to perpendicular to a typical pitched roof.

In midwinter it barely clears the rooftops. Light travels a longer path through the atmosphere, and it strikes a standard roof pitch at a shallow angle, so less of it is captured per square metre.

This is also why shading gets worse in winter. Obstructions that clear the array entirely in June — a neighbouring house, a hedge, a chimney — cast long shadows across it in December, sometimes for most of the short day.

What this means for design

Several practical consequences follow.

Do not size for winter. An array large enough to meet December demand would be enormously oversized for July, exporting most of what it makes for half the year. Sizing normally works from annual consumption and self-consumption instead.

Pitch is a compromise. A steeper pitch favours the low winter sun; a shallower one favours summer. Almost nobody rebuilds a roof for this. In practice you take the pitch you have, and the design works around it.

Winter shading deserves separate assessment. A shading survey done in summer is only half a survey. We assess obstructions across the year, because a December shadow path can be very different from a June one.

Heat pumps invert the pattern. A heat pump raises electricity consumption exactly when solar output is lowest. Solar and a heat pump work well together over a year, but the seasonal mismatch is real and should be understood rather than glossed over.

Batteries in winter

A battery shifts energy by hours, not by seasons. In summer it moves midday surplus into the evening. In winter there is frequently not enough surplus to fill it from the array at all.

That does not make storage useless from November to February — it changes its job. On a time-of-use tariff a battery can charge from cheap off-peak import overnight and cover expensive daytime and evening hours. Households on flat tariffs get less from storage in winter, which is worth knowing before buying capacity on the strength of a summer demonstration.

Snow, frost and debris

Snow sitting on a panel stops generation while it is there. On a normal pitched roof it usually slides off within a day or two as the surface warms, helped by the smooth glass. Flat and low-pitch arrays hold it longer.

Do not go up to clear it. Roof access in icy conditions is genuinely dangerous, and panels can be damaged by scraping. The output lost over a couple of snowy days is trivial compared with the risk.

Winter is, however, when debris accumulates: wet leaves at the bottom edge of an array, moss growth on north-facing roofs, and bird nesting material building up underneath. Those are worth dealing with, and they are jobs for someone with proper access equipment.

Reading your monitoring in winter

Households often panic at their first December figures. Some perspective helps: compare the current month against the same month in previous years, not against the summer. A year-on-year comparison at the same season is the only meaningful check.

If winter output has dropped noticeably against the previous winter, that is worth investigating — a failing optimiser, a soiled array, a string offline. A big drop from August to December is simply the season.

Published seasonal profiles from independent bodies are illustrative industry figures, not Solar Fx figures for your roof. Actual generation, savings and payback depend on the property, roof orientation and pitch, shading, system design, your electricity usage and tariff, export rates and future energy prices. Figures shown are estimates and are not guaranteed.