How Solar Panels Work in UK Weather

There’s a question we get at almost every home survey: “Will solar actually work here? We don’t exactly get a lot of sun.”

It’s a fair concern. But it’s based on a common misunderstanding about how solar panels generate electricity.

Light, not heat

Solar panels generate electricity from daylight, not from direct sunlight or warmth. They work by converting photons (particles of light) into an electrical current through what’s called the photovoltaic effect. On a bright overcast day, there is plenty of light. The panels are still working.

Countries like Germany and the Netherlands have some of the highest rates of solar adoption in Europe, despite having climates that are broadly comparable to the UK. Germany installed more solar capacity per person than the UK for years before the UK caught up. Weather was never the limiting factor.

What clouds actually do

Heavy cloud cover does reduce output. There’s no getting around that. On a thick, grey January day, your panels might produce around 10 to 20 percent of their peak output. But this is the exception, and it’s rarely the whole day.

What matters more than any single day is the annual average. The UK receives between 1,100 and 1,600 hours of sunshine per year depending on location. London is closer to 1,500, roughly comparable to Berlin. Even in Scotland, panels generate meaningful amounts from spring through autumn, with strong output on long summer days offsetting the shorter, cloudier winters.

The seasonal picture

A well-designed system in the UK will generate roughly 80 percent of its annual output between April and September. June and July are peak months. During these months, a typical 4kWp system on a south-facing roof in central England can generate between 15 and 20 kWh on a good day, more than most households use.

In winter, generation drops significantly. December and January produce perhaps 10 to 15 percent of the summer peak. But bills are not solely about generation. Surplus energy exported to the grid during summer earns payments through the Smart Export Guarantee, and battery storage lets you carry daytime generation into the evening regardless of season.

Temperature actually helps

One thing that surprises people: solar panels are slightly more efficient in cold, bright conditions than in hot summer heat. Photovoltaic cells lose a small amount of efficiency as they heat up. A cool, clear April day in Yorkshire can produce better output than a sweltering August afternoon, depending on the specific panels.

What a survey shows you

The only way to get a reliable picture for your specific home is a proper roof survey. The angle of your roof, which direction it faces, any shading from nearby trees or chimneys. All of these affect the real-world output figure. At SolarCraft, we model expected annual generation for every property before we quote. That figure, based on your roof and your location, is what you should be comparing against your energy usage.

If you’re curious what your roof could generate, the conversation starts with a free survey.