If you’ve lived in the UK for more than a few years, you’ll be familiar with our cold, wet and overcast winters. And if you haven’t, you’ve probably always thought of the UK as grey anyway (it’s not true - we have plenty of sunshine too!)

But yes, UK winters are very grey.

So you may have wondered if solar panels work in winter here. Or at the very least, whether solar panels work on cold, wet and overcast days.

The quick answer is, yes, solar panels do work in the winter. They just work a little less efficiently than on a clear summer’s day.

Let’s find out why...

How do solar panels work in winter?

Solar panels work by converting sunlight into electricity through photovoltaic cells. When photons from sunlight hit these cells, they knock electrons free from atoms, generating a flow of electricity.

We've explained the process in more depth in our detailed solar panel guide.

Fortunately, solar panels rely on light rather than heat to generate energy. So even on cold winter days, the panels will continue producing electricity as long as there's daylight.

The downsides of winter weather on solar panels

There are a few factors that can impact solar panel efficiency in winter:

• Shorter days: With the sun rising later and setting earlier, there are fewer hours in the day when sunlight can hit the panels. This reduces the overall energy output.
• Lower sun: The sun doesn't rise as high during the winter months, which means its light has to pass through more of the atmosphere before reaching your solar panels. This reduces the amount of energy that can be generated.
• Cloud cover: Overcast skies are common during UK winters. This heavy cloud cover can block much of the already weaker winter sunlight from reaching the solar panels. But even the cloudiest day won't prevent a solar panel from generating some energy. ‍
• Snow cover: Thick snow buildup can prevent sunlight from reaching your solar panels until it clears again. But light snowfall usually melts quickly or slides off slanted panels. We don't see too much snow in the UK, so your solar panels shouldn't be out of action for too long, if at all.

The UPSIDE of winter weather on solar panels

That’s right! Did you know that there’s an upside to how winter affects solar panels too?

• Cold temperatures: Solar panels actually operate more efficiently in colder conditions. Lower temperatures allow a solar panel's electrons to move more freely, boosting power generation capacity. A panel's efficiency increases by up to 0.5% per degree below 25C.¹

How much energy do solar panels produce in winter?

In winter, the amount of energy a solar panel produces can drop by around 80% in the UK.

While a single 400-watt solar panel might produce around 2.4 kWh of energy on the sunniest of summer’s day in the UK,² it might produce just 0.4 kWh on the gloomiest winter’s day. This happens because there are less ‘peak sun hours’ in a day during winter than in summer.

A peak solar hour is a measurement of solar energy. But it's not the same as an hour of sunlight. Rather, it represents an hour with a solar intensity of 1,000 watts per square meter.

You can estimate a solar panel's daily energy output using this formula:

Daily output (watt-hours) = Panel rating (watts) × Peak sun hours (hours)  

So in winter, a 400-watt panel in the UK would give you about:

400 watts × 1 hour = 400 watt-hours (0.4 kWh)

These are, of course, just rough estimates. Weather conditions, the angle and direction your panels face, and other factors will affect the actual result.

The good news is that even on the shortest and cloudiest days, solar panels still produce energy. And while a single panel may produce just 400 watts per day, your home might have 12 solar panels. In which case, they'll still produce around 4.8 kWh per day - roughly half the average home's daily energy use during winter.³

Maximising solar panel efficiency in winter

Winter is the most expensive time of the year to heat your home, since even the most efficient home will gradually lose heat. So you'll want to get the most out of your solar panels to help reduce that energy bill.

Here are some tips to maximise the efficiency of your solar panels in winter:

• Keep them clean: Snow and debris can block sunlight, so make sure to keep your panels clean for maximum output. Pointing a garden hose at your roof should do the job, or you could hire a professional to clean them more thoroughly.
• Adjust the tilt: The sun's lower in the sky during winter, so adjusting the tilt of your panels can help capture more light. Consider hiring a professional to do this safely.
• Monitor and maintain: Regular checks can help you spot any issues early on, and some systems let you monitor performance from your phone.
• Remove obstructions: Large trees can block sunlight. If a nearby tree has grown to cast shade on your solar panels, consider trimming it back to maximise the amount of sun reaching the panels.
• Install a battery: You can store excess energy during the sunniest periods for use later on. This won’t increase a panel’s output, but it will help you make the most of the energy your panels do generate. ‍
• Professional check-up: It's worth getting a professional to service your system every so often. They'll be able to spot and fix any issues you might not notice.

So there it is... solar panels do work in the winter, even in the UK! And while they may not generate quite as much energy as during the sunnier seasons, you could still power half your home’s energy needs so long as you take steps to keep your panels in tip-top condition.

To find out how solar panels could boost your home’s energy efficiency, and to discover which grants and payment options you’re eligible for, get your free energy improvement plan from Snugg.