Solar Power in Winter: What Really Happens When the Days Get Short

_Published: 7 January 2026 | Reading Time: 6 minutes | Last Updated: 7 January 2026_


Introduction

When you picture solar panels, you probably think of long summer days and bright blue skies. But winter is a very different story — shorter days, low sun angles and often overcast skies. This article explains what really happens to solar panels in winter (especially in the UK), why some effects are surprising, and what you can do to get the best year-round performance.

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The Cold Weather Surprise

Here's something that catches most people off guard: solar panels actually work better in cold weather. This seems odd at first, but it's true.

Solar panels are designed to work best at around 25°C. When it gets hotter than this, they become less efficient. But when temperatures drop, they perk up. On a cold, crisp winter day at 5°C, your panels could be working 5 to 10% more efficiently than their rated capacity.

The catch? Whilst each ray of sunlight is being converted more efficiently, there are simply far fewer rays of sunlight reaching your panels in winter. The efficiency boost from cold weather is easily overwhelmed by shorter days and low sun angles. Think of it like having a more efficient car but only being able to drive it for half the distance.

Batteries Don't Like the Cold

If cold weather helps solar panels, you'd hope it would help batteries too. Unfortunately, this is where things get tricky.

Most home solar batteries use lithium-ion technology, the same as your mobile phone. These batteries rely on chemical reactions, and those reactions slow right down when it's cold. At around 0°C, your battery might lose 20% or more of its capacity. Below freezing, that can climb to 30 or 40%.

This doesn't mean your battery is broken. Once it warms up, either from the ambient temperature rising or from the heat generated whilst charging and discharging, the capacity comes back. It's temporary, but it's something to be aware of during cold snaps.

Many modern battery systems have heating features to combat this, or they're installed in locations where they stay relatively warm. If you're getting a battery installed, it's worth asking about where it will go and whether it has any cold weather protection.

When Snow Covers Your Panels

Snow is dramatic when it happens, but it's actually less of an issue than you might think in the UK. When snow does settle on your panels, it blocks sunlight almost completely until it melts or slides off.

The good news is that solar panels are dark and angled, which helps snow slide off once the sun appears. Even if there's snow around your panels, the dark surface absorbs whatever light gets through and warms up, speeding up the melting process.

Heavy, wet snow is more problematic than light, powdery snow. And if temperatures stay below freezing for days, snow can persist and knock out your generation for that period.

Should you clear snow from your panels? Most experts say no. It's dangerous to get on a roof in winter, and you can damage panels if you're not careful. In most cases, the snow will clear naturally within a day or two, and it's not worth the risk.

Rain and Clouds: The Real Challenge

In the UK, persistent grey skies are a much bigger issue than snow. Solar panels can still generate electricity on cloudy days, but the output drops dramatically.

On a heavily overcast day, your panels might only produce 10 to 25% of their normal capacity. Light cloud with some breaks might allow 30 to 50%, whilst thick storm clouds can reduce things to just 5 to 10%.

Rain itself isn't harmful at all. In fact, it's helpful because it washes away dirt, pollen and bird droppings that build up on your panels. Clean panels work better, and many people notice improved generation after a good downpour clears weeks of grime.

The problem is the clouds that come with the rain. When thick clouds block the sun, it doesn't matter how efficient your panels are or how cold the air is. Without light, there's no power.

The Real Problem: Geometry

The biggest challenge for winter solar isn't actually weather, it's the basic geometry of Earth's tilt.

In winter, the sun rises late and sets early. In London near the winter solstice, you get about eight hours between sunrise and sunset. But "daylight" doesn't mean eight hours of good solar generation. The sun spends most of that time low in the sky, which means weaker light hitting your panels at awkward angles.

Most solar panels in the UK are installed at an angle that works reasonably well year-round rather than being perfect for any one season. This is a sensible compromise, but it means winter generation is never going to match summer output.

The combination of short days and low sun angles means a solar system in the UK might only generate 15 to 25% as much energy in December as it does in June. This isn't a fault or a failure, it's just physics. There's genuinely four to six times less solar energy available in midwinter.

Does Solar Still Make Sense?

Given all these challenges, you might wonder whether solar panels are worth it in the UK at all. The answer is actually yes, for several reasons.

First, solar systems pay for themselves based on yearly generation, not winter generation. Your panels might only generate 15 to 25% of their annual output during the October to March period, but they've already done most of their work during the sunnier months from April to September.

Second, electricity is expensive. Even modest winter generation has value when you're paying 25 to 35 pence per kilowatt-hour for grid electricity. Every bit your panels generate saves you money, even on grey February days.

Third, solar panels last for 25 to 30 years. They might take 7 to 12 years to pay for themselves, but after that, you're getting essentially free electricity for another 15 to 20 years. Over that long timeframe, even the modest winter generation adds up.

Modern panels are also much better than older ones at capturing light, including the diffuse light from cloudy skies. Technology keeps improving, which helps with winter performance.

What to Expect

If you have solar panels or are thinking about getting them, here's what's realistic for winter:

This is completely normal.

Your panels won't make you energy-independent in winter unless you have a huge system and lots of battery storage. Most home systems are sized to meet 40 to 70 per cent of your annual electricity needs, which means they fall short during winter when generation is low but consumption is often high.

Don't obsess over daily generation figures in winter. It's more useful to look at weekly or monthly trends. A few poor days mean nothing, but if your system is consistently underperforming compared to previous years, that might indicate a problem worth checking.

Keep your panels clean going into winter. A professional clean in late autumn ensures they're as efficient as possible for the darker months ahead. When there's less light available, you can't afford to lose any generation to dirty panels.

The Bigger Picture

Winter solar generation has real limitations, but it's just one part of the story. Solar panels remain one of the best investments for reducing energy bills and environmental impact, even in the UK.

The key is understanding it's a long-term game. Your panels won't meet all your needs all the time, and winter will always be challenging. But over the years, they'll generate substantial amounts of free electricity, protect you against rising energy costs, and reduce your carbon footprint.

Solar in the UK isn't about powering your home in December. It's about cutting your annual electricity bills significantly, making the most of brilliant generation during the longer months, and knowing that even on short winter days, you're still producing some clean energy.

Yes, winter performance is modest. But the solstice passes, spring arrives, and suddenly your panels are working hard again. The sun always comes back, and when it does, your panels will be ready.

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