Solar panels in autumn: rain, wind, storms and what to expect (UK)

Yes, solar panels work in the rain. A wet day is just a heavily clouded one, and a UK array typically makes roughly 10–30% of its clear-day output while it's raining, more under a bright shower, less under a dark front that sits over the house all afternoon. Autumn is when that starts to matter, because it is the fast slide from summer to winter: September is still a solid month, October roughly half of a summer month, and November roughly a quarter. Together, September to November produce roughly 15–20% of a UK system's annual total.

Below: what each autumn month does, why the numbers fall (it isn't the temperature), what rain, wind, storms and hail mean for a British roof, and what to check before winter. The cloud physics is kept short because do solar panels work on cloudy days? covers it in full.

What happens month by month

Take the same typical 4 kWp system the summer and winter guides use, one that makes around 3,400–4,000 kWh across a full year. The autumn picture, in rough terms:

• September: typically 300–400 kWh. Days are still 12–13 hours long and the sun is reasonably high at noon, so a bright week can look like a decent August week and many systems still export at midday.
• October: typically 180–270 kWh, roughly half a summer month. Daylight shrinks by close to two hours and the clocks go back in late October. Generation now stops around 4:30pm and the evening peak in household demand falls entirely in the dark.
• November: typically 120–200 kWh, roughly a quarter of a summer month and in line with the winter guide. The noon sun sits below 20 degrees across most of the UK, and a run of dull days can keep daily totals in low single figures.

The shape matters more than any one number: October is where the drop is steepest, and by mid-November you are effectively in winter mode. Our roof check plots this month-by-month curve for your roof specifically. Start at is my roof suitable for solar? or how much sun does my roof get?.

Why output falls, and why it isn't the cold

Two things drive the autumn decline, and neither is temperature:

• Day length. Between the September equinox and the end of November the UK loses roughly four hours of daylight. Fewer hours of light means fewer hours of generation.
• Sun angle. A lower sun spreads the same light over a bigger patch of ground and pushes it through more atmosphere, so each hour of daylight is worth less than it was in July.

The cold is on your side. Panels are rated at 25°C and lose a little efficiency for every degree above that, so cooler autumn air lets them run a few percent more efficiently per unit of light than in a July heatwave, the reverse of the effect in do solar panels work in a heatwave?. A crisp, clear October day is a very good day for a panel. There simply aren't enough hours in it.

Rain: does it help or hurt?

While it's falling, output is down, because the cloud that brings the rain is blocking direct sun. Light rain from broken cloud might leave you at 30–50% of a clear-sky figure; a heavy, all-day downpour sits closer to 10%. That is the cloud, not the water; panels are sealed units.

Once it stops, rain has done you a favour. It is the main reason UK pitched-roof arrays rarely need cleaning: a decent shower rinses off summer dust, pollen and bird droppings, and soiling losses on a typical UK roof stay in the low single digits as a result. Before booking a clean for the dark months, read do solar panels need cleaning in the UK?; in most cases the autumn weather is about to do it for free.

Wind, storms and hail

Autumn is also named-storm season, and the two questions we hear most are "will they blow off?" and "will hail crack them?"

Wind. Panels and their mounting are engineered for far more than an ordinary British gale. Standard modules are tested to mechanical loads of at least 2,400 pascals, and MCS installers must design the fixings for your roof's wind zone, height and exposure under the MCS 012 roof-mounting standard.

After a named storm, spend five minutes checking from the ground, not the roof:

• Look at the array from the garden or street. Panels should sit flush and level; a lifted corner or a gap is a call to your installer.
• Check the tiles and flashing around the array. Displaced tiles or slipped lead near the rails can let water in and need attention quickly.
• Look for debris on the glass. Branches and roofing felt can shade a string until removed.
• Open the monitoring app. A sudden zero, or an inverter fault code, on a day with daylight is worth a call. Most codes clear themselves; a persistent one does not.

Who pays depends on what failed. Fixings or flashing that gave way in weather they were designed for are a workmanship matter for your installer under their installation warranty and MCS-backed guarantee. Damage from something hitting the panels, or a storm well outside design conditions, is an insurance matter; tell your insurer the panels are there and check the wording.

Hail. Panels are tested by firing 25 mm ice balls at around 23 metres per second (over 50 mph) at the glass, bigger and faster than almost any hail the UK produces. Hail damage here is rare, and if it did happen it would be an insurance claim.

Leaves, debris and shade

A quieter autumn risk is the leaf pile. Panels are usually wired in strings, and with a basic string inverter a wedge of wet leaves stuck on one panel can drag down every panel in that string.

• Low-pitch and flat arrays are the most exposed, because leaves settle rather than slide. If you have a flat-roof system under trees, a look every couple of weeks in October and November is sensible.
• Gutters matter more than glass. Blocked gutters back water up under the bottom row of panels and around the flashing. Clearing them is the one bit of autumn maintenance worth doing every year.
• Don't go up. Anything you can't reach safely from the ground is a job for the installer or a roofer, and a stuck leaf pile usually blows off within days anyway.

Autumn and batteries

Through summer a battery's job was storing your midday surplus for the evening. In autumn that surplus shrinks fast: by late October many 4 kWp systems cover the daytime base load and little more, so there is nothing left to store.

The battery doesn't become useless; it changes jobs. On a time-of-use tariff it charges from cheap overnight electricity, typically at a quarter to a third of the daytime rate, and discharges through the expensive evening peak that now falls after dark, with whatever the roof adds during the day as a top-up. Set up that way, a battery tends to save nearly as much in November as it did in June.

Your autumn checklist

• Check your monitoring baseline. Note what a clear September day produces, then compare autumn on autumn, not autumn on summer.
• Clear the gutters once the leaves are mostly down, ideally before the first hard frost.
• Look after every named storm. From the ground: panels flush, tiles and flashing intact, no debris, no persistent fault codes.
• Check where the inverter lives. A garage or loft that gets cold and damp with no ventilation is hard on electronics; a small vent or a relocation is cheaper than a replacement.
• Review your tariff if you have a battery. Cheap overnight charging carries the savings once the solar surplus has gone.

What a good autumn day still does

For all the decline, autumn is not winter. A clear, cool day in late September can still produce 15–20 kWh from a 4 kWp roof, and a bright day in early November can deliver 6–9 kWh, which covers a working-from-home household's daytime use. Knowing the season sets the baseline, so a grey week doesn't look like a fault and a good week doesn't set false expectations.

Panels work in the rain, storms are a design condition rather than a threat to a properly fitted array, and autumn's roughly 15–20% share of the year is already counted in any honest savings figure. To see what your own roof does across September to November, run the roof check and look at the monthly-sun chart. The savings calculator works on annual figures, so autumn and winter are priced in before you start. When you're ready for a firm number, an MCS-certified installer covering your postcode will survey the roof and confirm suitability in person.

Frequently asked questions

Do solar panels work in the rain?

Yes. Rain arrives with cloud, and cloud is what cuts the output, not the water. While it is raining a UK array typically produces roughly 10–30% of what it would on a clear day, more under light showers, less under a dark all-day front. Panels are sealed units, so the rain does no harm, and it rinses dust and droppings off the glass.

How much do solar panels generate in autumn in the UK?

For a typical 4 kWp system making 3,400–4,000 kWh a year, September is roughly 300–400 kWh, October roughly 180–270 kWh and November roughly 120–200 kWh. Together that is around 15–20% of the annual total. October is where the decline is steepest, because the loss of daylight and the falling sun angle stack up fastest. Your roof's direction, pitch and shading move these figures up or down.

Can strong wind damage solar panels?

Rarely, on a properly installed system. Panels are tested to mechanical loads far above an ordinary British gale, and MCS installers must design the fixings for your roof's wind zone, height and exposure. Panels that lift or come loose in a storm nearly always point to a fixing not installed to standard, which is a workmanship matter for the installer, rather than to the panel or the wind itself.

Do solar panels get damaged by hail in the UK?

Very rarely. Panels are tested by firing 25 mm ice balls at the glass at around 23 metres per second, larger and faster than almost any hail the UK produces. If a freak storm did crack a panel it would be visible from the ground and would be a claim on your home insurance, so tell your insurer the panels are there.

Is a battery still worth it in autumn?

Yes, but it changes jobs. Through summer a battery stores your midday surplus for the evening; by late October there is little surplus left to store. On a time-of-use tariff it instead charges on cheap overnight electricity and discharges through the expensive evening peak, with any daytime solar as a top-up. Set up that way, a battery typically saves nearly as much in November as it did in June.

Related

• Solar panels in summer: what to expect
• Solar in winter: what to expect
• Do solar panels work on cloudy days?
• Do solar panels need cleaning in the UK?
• Solar with Octopus Go and time-of-use tariffs
• How much sun does my roof get?
• Is my roof suitable for solar?