Do solar panels work on cloudy days?

A cloudy day is an average day on UK soil, and while your primary concern may be whether to don an umbrella for the day, if you’re one for sustainability, next on your mind may be whether your solar panels will be doing their job properly. 

Solar power is one of the cheapest and most abundant forms of energy on earth, but some might be concerned about their usefulness and whether the cost of solar panels is worth it when the weather isn’t at its best.

Solar photovoltaic (PV) panels work using the sun’s light rays to generate electricity. How efficient and how much electricity your solar panels will produce in cloudy weather depends on various factors including the level of cloud cover, how large your solar array is, plus the quality of the solar panels themselves and where they are located. If you are yet to invest in a solar panel installation, but on the fence because of cloud or rain interruption, rest assured that much like you can still catch the sun when it’s overcast in Spain, solar panels can still generate electricity when it’s cloudy in the UK.

Solar panel technology has come a long way and modern designs are built with unpredictable weather in mind, so you’ll see features like better light trapping and less shading highlighted in PV module data sheets from companies like Jinko and JA Solar.

More specifically, monocrystalline solar panels tend to be more efficient in cloud or shade as they are made from higher-quality silicon.

As with cloud cover, solar panels will still work in the rain, but it all depends on how much sunlight can penetrate the clouds. Gilbert Michaud, from School of Environmental Sustainability at Loyola University Chicago, notes how a little rain could even benefit homes with solar panels in cloudy areas as the rain will wash away dirt and grime buildup that could be detrimental to their efficiency. Furthermore, there is a phenomenon known as the edge-of-cloud effect which is where you may see a spike in irradiance as passing cloud cover focuses more sunlight onto your solar panels, essentially magnifying it. Although this may seem like a good thing, cloud enhancement could actually exceed normal daylight conditions and overheating of solar panels can lead to other issues. If rainy conditions turn to snow then the efficiency of a solar panel will diminish but scientists in the US have already invented a solar panel coating strip that causes snow to slide off the panels and therefore not hindering their efficiency when weather conditions deteriorate.

Between spring and summer is when solar panels peak in output, at any individual time, rather than when being measured over the course of a day.

Even the best solar panels don’t work at night as they generate energy using sunlight (the latin routes for photovoltaic translate to light and electricity). Gareth Simkins, Senior Communications Adviser at Solar Energy UK told us that it’s quite simple and without photons, no solar energy can be produced. Although some may think the moonlight will give off enough light, Simkins says the voltage from moonlight simply won’t be meaningful enough to charge your solar panels efficiently so they won’t produce energy at night and will work best during the day.

If your area of the UK is exceptionally renowned for being cloudy and rainy, such as Scotland, don’t let it put you off installing solar panels. However, look for solar panels with high efficiency ratings that are designed with gloomier weather conditions in mind. Also, speak with your MCS accredited solar panel installer about your concerns and they will be able to talk you through the best type and positioning for your home as weather conditions shouldn’t be a major barrier.

Solar batteries, which can store solar energy, are a good investment to make if efficiency in cloudy weather is a concern as the electricity can be ready to use when the panels are generating less. Simkins adds that solar panels generally come equipped with a battery energy storage system (BES) and that this can help to avoid paying extra VAT as a later add-on. Fortunately, as part of the latest UK government energy security announcements, it’s looking to remove this anomaly in the autumn.  

“On average, solar panels will generate 10 to 25 per cent of their normal power output on days when the weather is cloudy,” Says Alan Duncan, Founder of Solar Panels Network. “However, it’s important to note that this figure can vary depending on several factors such as the type and quality of solar panels, their age, the level of cloud cover, and the overall system design. While it’s difficult to provide an exact percentage for every individual panel, this range serves as a reasonable estimate based on extensive industry research and real-world observations.”

If you want to estimate the current UK PV solar power generation from sunlight you can check PVLive, which is a National Grid Electric System Operator-funded tool that estimates the amount of solar being generated for solar PV systems on the UK’s transmission network. It’s updated every 30 minutes and users can go back in time to download previous estimates as well. 

On a very rainy and overcast day (measured mid-afternoon), the generation for solar PV systems on the transmission network is estimated to be 1.33 GW on PVLive. On a brighter, but overcast, morning the estimated solar PV generation was at 2.06 GW, 55 per cent more. In all, brighter weather will see much higher efficiency of solar panels, but the sun’s rays can still penetrate when it’s overcast, so you will be able to continue generating electricity for your home, car, or for the grid, simply at a lower rate.