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Solar panels work best in bright sunshine, but that doesn’t mean they’re useless on a cloudy day, and even on overcast days, they still generate electricity
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Fitting solar panels to your home is a sizeable undertaking, so it’s understandable in a country like the UK to be concerned about their performance when it’s cloudy.
Thankfully, the short answer is: yes, solar panels work on cloudy days. Even when overcast, the panels continue to generate electricity, which can then be used to power your home, stored for use later, or earn money by being exported to the grid.
It’s true to say solar panels generate less electricity on cloudy days, and that they work best on clear, sunny days. But, importantly, the UK’s climate doesn’t prevent solar panels from being an effective source of household electricity.
Keep reading to understand more about how solar panels work, and what to expect from their performance on cloudy, dull and overcast days.
Solar panels work by using photovoltaic (PV) panels to convert light into electricity. They work in daylight, rather than exclusively when subjected to direct sunlight, so even on cloudy or fully overcast days they will continue to work. That’s because solar panels absorb energy from the visible light spectrum and wavelengths that can pass through clouds.
That said, on cloudy days solar panels generate less electricity than on bright, sunny days. The amount of electricity generated depends on how much light reaches the panels, which in turn is affected by the thickness of the cloud cover, the time of day and year, the angle of the panel (or roof it’s attached to), and local shadowing from nearby objects like trees.
It is also worth remembering that solar panels generate electricity using light, not heat. They don’t need warm weather to function, and can actually perform less efficiently during especially hot weather. So even on a cold winter’s day, clear sunshine will produce a good amount of electricity.
Solar panels generally produce less electricity when it’s cloudy, but the reduction depends on the specific weather conditions. A bright day with occasional light cloud might have relatively little impact on electricity generation, while thick, dark clouds can dramatically reduce the amount produced.
An exact figure can’t be put on how much electricity a solar panel generates on a cloudy day, since there are too many variables to produce a reliable conclusion. However, it is generally claimed that electricity output from solar panels can fall to between 10 and 25 per cent on a grey and overcast day, compared to a sunny day. Heavy cloud cover can see output fall to between 20 and 40 per cent of optimal conditions, while light cloud cover can cut electricity generation to between approximately 60 and 80 per cent.
Read more: Best solar panels, compared
Yes. Solar panels generally generate more electricity when exposed to direct sunlight, since more solar energy reaches their photovoltaic cells. However, this doesn’t necessarily mean the hottest days of the summer are always the best for producing electricity.
This is because high temperatures can make solar panels less efficient. As the temperature of the cells increases, their ability to convert sunlight into electricity tends to decrease slightly.
This doesn’t mean solar panels stop working on hot sunny days. Longer daylight hours and stronger sunlight generally make summer the most productive season for solar generation in the UK, despite efficiency occasionally dropping on especially hot days. Ultimately, the amount of light reaching the panel has a much greater influence on electricity generation than the temperature.
Solar panels can absolutely be a worthwhile investment for your home, despite the UK’s reputation for grey skies and unpredictable weather. As explained earlier, they don’t require constant sunshine to work, and can continue to produce useful amounts of electricity even on cloudy days, and are mostly unaffected by colder temperatures.
In short, a properly installed system can still produce a substantial amount of a home’s electricity demand each year. It is therefore best to zoom out and look at years as a whole, instead of focusing too much on individual days or weeks. Some especially cloudy days will see very little electricity generation, while other days will see much more.
Whether solar panels are worth it to you comes down to their cost and the long-term savings they can deliver. Using electricity generated by your own panels reduces the amount you need to buy from your energy supplier, while exporting surplus electricity back to the grid can provide an additional financial benefit.
Read more: Are Octopus solar panels worth it?
Weather is one of the biggest factors affecting solar panel performance, with the difference between a sunny day and a dull, overcast one having a significant impact on electricity production. However, there are other factors that determine how much electricity your panels can generate.
These include the angle of your roof, local shading caused by nearby objects like trees or other buildings, the size and specification of the panels, and even how clean they are. Dust, pollen, leaves and other objects can reduce electricity generation. A bright side in the UK is that our frequent rainfall can help solar panels stay cleaner and more efficient, according to Switch Together.
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