Direct and Indirect Sunlight for the UK

Direct and Indirect Sunlight for the UK

We all know the UK is more cloudy than Spain – but just how much direct sunlight do we get?
 
There’s nothing better than sunlight in the form of a clear sky for powering solar panels. A solar panel with the sun shining directly on it will produce the maximum amount of electricity. When the sky is cloudy the indirect light will also power the solar panels and generate electricity – just not as much as when the sky is cloud-free.
 
We wanted to understand the mix of direct sunlight (called ‘beam irradiation’ by the scientists) and indirect sunlight (called ‘diffuse irradiation’) for the UK We pulled data from a European Commission research project on the mix of direct and indirect solar energy hitting the UK. It turns out that for the UK overall, 42% of the solar energy arrives directly. The remaining 58% of the energy arrives indirectly. So we get more energy from the cloudy days and partially cloudy days than we do from the clear days. Not that surprising as we get more cloudy days than clear days in the UK.
 

UK Map of Direct and Indirect Solar Energy

As you might expect, while the average for the UK is 42% direct solar energy, there is quite a lot of regional variation. The picture below shows how this percentage varies across the UK.
 

 
Direct sunlight ranges from a low of 24% of the solar energy to a high of 56% of the solar energy. Areas with 24% direct solar energy are getting the vast majority (76%) of their solar energy indirectly – when the skies are hazy or cloudy. From the chart it’s clear to see these tend to be inland and in the North of the country.
 
Conversely areas with 56% are getting most of their solar energy as beam irradiation – direct from the sun. As you might expect, these areas tend to be further South and closer to the coasts.
 

Every cloud has a silver lining

Is there any good news with living in an area with low levels of direct sunlight? Well there is one benefit: your roof angle and orientation matter much less in determining how much electricity you can generate. For much of the UK the best roof for solar is angled at around 35° and South-facing. If you live in an area with mainly indirect solar energy and your roof is not at 35° and South-facing the reduction in the amount of electricity you can generate will not be that much – certainly compared to a roof in direct sunlight.
 
The interplay between direct / indirect sunlight, roof angle and roof orientation is a complex one. We suggest you use an automatic tool to find out how your roof measures up.