In an ideal world, it would always be sunny. That’s how most of us picture solar panels in our minds, with the sunlight glinting off the rooftops and perhaps the deck chairs out in the garden below, iced drinks in the cupholders. Wonderful.
Unfortunately, we have to tear that idyllic dream down in a very British way. We live in the UK, and such days are rare. Instead, we get the doom and gloom of long stretches of overcast skies, soft daylight, rain clouds and dark winters.
So, it’s natural to wonder if solar panels are really worth it when it’s cloudy, overcast or otherwise just gloomy and grey.
And there’s good news. Solar panels still work when it’s cloudy. Not at full power, of course, but they’ll still help you generate predictable electrical power. Here’s how.
How solar panels generate energy in cloudy weather
The proper name for a solar panel is a photovoltaic (PV) panel. The ‘photo’ part of that name is really important, because it means these generate electricity from light and light only. It’s nothing to do with heat. In fact, it’s not even particularly tied to the UV light we get from the sun.
In actual fact, heat reduces solar panel efficiency, because higher temperatures affect how the cells themselves work and lower the system’s voltage.
Solar panels actually generate electricity when sunlight hits the cells inside them. The light knocks electrons (tiny, charged particles) loose inside the panel, and those moving electrons create an electrical current. The brighter the light, the more electricity the panel produces.
That means that even when the sky is grey, there’s still some light reaching the earth. Clouds scatter the light and reduce how much makes it through, but they don’t block it entirely, otherwise, we wouldn’t be able to see anything at all.
Thus, your panels continue to generate electricity, even when it’s grey, windy and cold at 12pm at the start of January.
How do solar panels in winter compare to summer?
Let’s be clear, though. In winter, your solar panels generate far less electricity than they do in summer, because there’s far less light. At the peak of summer, we get approximately double the amount of daylight than we do in the depths of winter.
On a bright, clear summer day, your panels might approach their peak output. On a very cloudy day around Christmas time, output could drop to as low as 50% of what you might see in direct sunlight.
There’s no way to forecast this directly because it depends on the thickness of the cloud, your roof position and any other shading from trees or other buildings. However, if you have a monitoring system for your solar panels, you’ll start to learn how dark it has to be to really cut their performance.
It might be helpful to think of the sky as a dimmer switch. Cloud cover turns the dial down, but rarely turns it off except in the most extreme of weather. Even in winter, your system continues to produce energy. Although it’s less, every kilowatt-hour you generate is one you don’t need to buy from the grid.
We find that homeowners are often surprised at how much those ‘background’ savings add up, even in winter. You might not notice much on really cloudy days. Still, across a whole year, the savings can be significant and, overall, consistent.
Why solar still performs well across UK seasons
The UK’s solar performance varies throughout the year, but the overall pattern is reliable. Late spring and summer bring longer days, higher sun and much stronger generation. Autumn and winter bring shorter days and heavier cloud cover, but your system still works. It simply adjusts to the available light.
Across a full year, a properly designed UK solar installation produces far more energy than you might expect based on a run of gloomy days. Even with our island nation’s famously unreliable and dreary weather, we have the data to prove that annual solar output remains steady and predictable.
That’s because solar generation is driven by total daylight hours across the year. A handful of sunny or rainy afternoons doesn’t make much difference to the annual average performance.
With daily use across all the seasons, you’ll find that performance smooths itself out. For example:
- In summer, many homes generate more than they can use, which can be used to charge battery storage systems or exported back to the grid via SEG.
- In winter, even modest output helps offset morning and evening use, especially as demand for light and heat increases.
- In those transition months like April, May, September and October, solar actually performs exceptionally well thanks to long-ish daylight hours and cooler temperatures.
How modern technology boosts cloudy-day performance
There have been many advances in solar panel technology over the past decade. Today’s panels use techniques that significantly improve performance under ‘diffuse light’, the soft, scattered light that dominates our stereotypical weather.
Here are a few examples of how new panels tend to be more efficient year-round than older ones:
High-efficiency panel designs
Modern panels use improved cell structures that capture more light across a wider range of angles. So, even when the sun hides behind thick cloud, enough light scatters across your roof to keep your system working.
Anti-reflective coatings
These help panels absorb more light instead of losing it to reflection. This is particularly helpful during dull weather, when we want to make the most of every ray of light.
String layouts and optimisers
Installers design panel strings (connected panels) or implement power optimisers or micro-inverters to minimise shading losses and encourage panels to perform more independently. That means even if one part of the roof is darker than another, your whole system doesn’t slow down (much).
Smart energy systems
If you have a home battery or smart EV charger, these tools automatically shift your use to match your generation. On cloudy days, this helps you make the most of whatever energy your panels produce.
There’s also warranty. Most manufacturers honour it when only qualified installers handle the system. That’s because poor workmanship often shortens the lifespan of a solar system. Panels, inverters and mounting systems work as a single unit. If any single part goes wrong, you lose performance. That can hardly be said to be an equipment malfunction.
We suggest going with a certified solar panel installer. That way, you get peace of mind that your system works and is safe from day one, and that if any problems do arise, you’re covered. It’s almost always more cost-effective to pay for the installation labour than to get it wrong by doing it yourself.
Solar panels in the UK are actually an advantage
So yes, we aren’t lucky enough to share the weather of Greece, Italy or our friend Down Under. But actually, when it comes to solar, that’s not necessarily a bad thing. Because the cooler temperatures of the UK actually favour solar setups in many cases.
Our weather doesn’t sabotage solar, it simply shapes how we use it. We do have very dark and very long winters compared to most of the world, but actually, that means we also have very light and very long summers. And because our country sits where it does on the globe, our weather is reasonably mild, which means our panels often perform very well across the year as a whole.
Of course, they’re also not as good as other countries in winter, but do you see how it all balances out?
For British homeowners, it’s best to invest in your electrical systems all at once. Install solar panels alongside a battery storage system so you can store daytime energy for use later, and discuss backup options with us if you want the system to support you during power cuts. Sign up for SEG to make a little extra off your surplus. And if you have an EV, invest in a smart charger to make the most of your setup.
If you’re thinking about installing solar panels, Electrical Innovations is here to help. Get in touch for a friendly chat, and let’s explore how solar could support your energy needs all year round.
