Do Solar Panels Work in Cloudy UK Weather?

Key Takeaways

• Solar panels don’t just need direct sunlight to work. Diffused sunlight on overcast days is sufficient. 
• Even on overcast days, panels typically produce 10–50% of their output compared to sunny days.
• Cloudy day output will be around 10% in the Winter Vs 50% in the Summer. 
• This is likely to be enough to meet the energy requirements of your home, even on cloudy days
• We’ve taken data from the grid and from our actual customers to show you real life examples

Can Solar Panels Work in Cloudy UK Weather?

The short answer? Yes – they 100% do. 

When you think of solar panels, you might imagine the need for endless sunny skies, but that’s unnecessary. Even in cloudy weather, solar panels generate electricity from natural daylight, meaning diffused sunlight, i.e. sunlight that is shining through clouds, works just fine. 

The UK’s daylight hours, which vary from 8 to 16 hours depending on the time of year, and mild climate make solar energy a viable year-round solution. 

To prove this claim, let’s look at some real-life data to show how UK solar generation compared on two very different days regarding the weather. 

Friday, 9th May 2025 – Sunny day across the UK. 

Here, we can see the total solar generation to the National Grid in Gigawatt Hours (GWh). 

Thursday, 6th June 2025 – cloudy and wet across the UK.

Here we can see the cloud cover across the UK:

And here is the comparable total solar generation to the National Grid in Gigawatt Hours (GWh) on this cloudy day. 

Let’s compare these two days’ half-hourly generation (showing every hour for ease). We get the following data showing the overall average variance in solar output on a cloudy day across the UK, which was 43.6% of a sunny day with no clouds. 

Time	Friday, 9th May (Gigawatts)	Thursday, 6th June (Gigawatts)	Variance % (Cloud Vs Sunny)
07:00am	0.622	0.246	39.5%
08:00am	2.321	0.897	38.6%
09:00am	4.724	1.621	34.3%
10:00am	7.642	2.624	34.3%
11:00am	10.150	3.763	37.1%
12:00pm	12.055	4.564	37.9%
13:00pm	12.901	5.514	42.7%
14:00pm	12.721	6.203	48.8%
15:00pm	12.049	5.735	47.6%
16:00pm	10.645	5.510	51.8%
17:00pm	8.731	4.176	47.8%
18:00pm	6.129	2.993	48.8%
19:00pm	3.602	1.916	53.2%
20:00pm	1.566	0.751	48.0%

Source: https://www.energydashboard.co.uk/historical 

Here we have images from a The Solar Co customer proudly showing us how, despite cloudy conditions, his solar set-up was still generating enough electricity to meet his demand and producing a little extra to sell back to the grid.

Whilst this data shows a drop in solar generation, as you would expect, solar panels continue to generate electricity even on cloudy days. Also, let’s not forget that if it rains, that will help clean the solar panels, removing dust and dirt that will otherwise start to reduce the panel’s efficiency. 

The results shown above explain, in part at least, why record numbers of UK consumers are opting to invest in solar panels to reduce their energy bills and carbon footprint and ultimately help the environment. Latest data from the UK government shows how solar panel sales are surging:

Over 75% of solar panel installations have been domestic, and the remaining 25% commercial. Of the domestic installations, 80% are retrofitted to existing properties, and 20% have been installed on new builds. 

In addition to producing free electricity all year round, most solar panels come with an output warranty of around 30 years. Depending on the quality of the panel, e.g. Monocrystalline or Polycrystalline, the loss of power output against the minimum peak power at standard test conditions should be around +80% after 30 years of use. 

For context, if you have a system installed with an Annual Solar Energy Production of 5,000 kilowatt hours (kWh), your panels will be under warranty to still be producing +80% of that after 30 years which would equate to an Annual Solar Energy Production of 4,000 kilowatt hours (kWh). Remember, that is what the manufacturer is willing to put under warranty, so the reality is that output should be higher than this over a more extended period.

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What Affects Solar Panel Efficiency?

Several factors determine how efficient your system performs:

• Weather: Clouds reduce direct sunlight but still allow diffused light to generate electricity.
  
• Panel quality: Higher-end panels like monocrystalline perform better in cloudy conditions.
  
• Tilt & orientation: Aim for a 30–40° angle, facing due south for optimal results.
  
• Temperature: Unlike hot countries, the UK’s cooler climate boosts output. Panels work best at around 25°C.

In terms of overall efficiency, solar panels can last for 25-30 years with the output of your panels only degrading by around 0.3% to 1.0% per year. 

These factors mean a well-installed system will perform consistently – even in Winter.

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What Happens to Solar Panels on Cloudy Days?

Solar panels generate electricity without direct sunlight thanks to photovoltaic (PV) cells that absorb light, whether direct or diffused when the sun’s rays shine through clouds. 

“Germany – with weather very similar to the UK – is one of the global leaders in solar energy production.”

Whilst output on overcast days drops to 10–50% of full sunlight levels, newer technologies and premium panels help improve efficiency and solar production. 

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Seasonal Solar Performance in the UK

Yes, Winter reduces solar output – but it doesn’t stop it. In the UK, we average around 12 hours of daylight each day, varying between 8 hours in the Winter and 16 hours in the Summer. For a more detailed breakdown, here is how many hours of daylight we see by month in the UK:

If we look at overall UK solar generation at a grid level, this also gives a good illustration of how your solar output performs throughout the year:

As we can see, solar output during Autumn/Winter will be lower (around 25.0% of your annual solar energy production), while your electricity consumption increases (around 57.0% of your annual electricity consumption). Therefore, to enhance your setup even further, you can pair your solar panels with a battery storage unit to store your solar power for later in the day when the nights draw in. 

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Benefits of Solar in the UK

Energy Savings

• 4kW system = ~3,500 kWh/year = UK average electricity consumption is 2,700kWh/year
  
• Offsets exposure to energy price volatility – electricity prices have risen by 6% per year since 2019
  
• Reduces reliance on the grid

Environmental Impact

• Offsets ~1.5 tonnes of CO₂ annually
  
• Equivalent to planting 50 trees each year
  
• Moves you closer to energy independence

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Long-Term Value & Government Support

Longevity & Maintenance

1. Panels usually come with 25-30 year warranties, but their lifespan can be much more with minimal upkeep
   
2. Cleaning and annual inspections usually sufficient

Smart Export Guarantee (SEG)

• Earn by exporting unused electricity to the grid
  
• SEG rates vary (e.g., Octopus pays ~15p/kWh)
  
• SEG payments are tax-free income

Payback Period

• Typical systems pay for themselves in 8–12 years, faster with SEG

Investing in solar is a strategic move, environmentally and financially.

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In Summary: Are Solar Panels Worth It in the UK despite it often being cloudy?

Solar is right for you if…	You may reconsider if…
You live in the UK and want to cut bills	You want full power output in Winter
You care about reducing carbon emissions	You have poor roof orientation or shading
You want protection from volatile energy costs	You’re expecting 100% off-grid living
You want long-term investment value
You have suitable roof orientation, i.e. south facing
You want energy security

Even in cloudy weather, UK homeowners can benefit from solar power thanks to efficient technology, smart installations, and long daylight hours – up to 16 hours during Summer months. 

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Get a Quote from The Solar Co

Live in the South-East? Let us design your perfect system.

We will:

• Review your energy usage (now & future)
  
• Visit on-site to assess your roof
  
• Design the most efficient system
  
• Estimate your annual output & payback period

Whether you’re in Kent, Surrey, Essex or Sussex – we’re here to help.

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