Solar Panels: What If The Sun Doesn’t Shine?

I’ve lost count of the number of times I have been asked whether solar panels really work in the UK’s cloudy climate and no doubt there will be many more inquisitive and apprehensive clients asking the same thing in the future.

Whilst solar panels both photovoltaic (PV) and thermal benefit greatest during nice bright sunny days as soon as the inevitable cloud rolls in does not spell doom for the technology. This week we find out why.

Solar Panels DO Work In The UK!

Solar energy is harvested in a number of ways; light consists of a huge range of wavelength frequencies all capable of transferring energy to the photo cell or light absorbing surface on a solar thermal panel/tube.

When clouds roll in we notice a reduction in the visible light and clouds inevitably interfere with the level of photon energy reaching the surface of the earth but there is still a substantial amount of visible, infra-red and ultra-violet light hitting the earth ready for capture.

If you have ever been sunburnt on what you though was a cloudy day you have been absorbing ultra-violet light through the day.

Most panels rely on certain visible and infra-red wavelengths to produce most of their energy but there are certain products in use, and numerous others in development, that have been tuned to capture more light energy than their predecessors.

I have seen figures of 10%-25% quoted as the expected relative output compared to 100% when the cloud passes by but of course the level of cloud we receive every day varies wildly! A “cloud edge magnification” affect has even been recorded when the edge of a passing cloud actually focuses light and increase the level of light onto the collector. This is only fleeting but an interesting side-effect of an otherwise suboptimal phenomenon.

Practically speaking often only when snow or hard shade cover solar panels do they produce zero output and whilst there are a handful of days where little energy is created, most of the year in the UK produces some usable energy for electricity or hot water use. There are now accurate tables for almost every orientation and inclination depending on your location within the UK so you can see what even a “cloudy” UK sky can practically deliver to your nearest rooftop. Have a look at this Solar Energy Calculator from the Energy Savings Trust.

Whilst the electricity generated or hot water produced should never be used as a primary source of energy for most UK homes they do provide a very useful input during typical summer months and bright cold winter days too.

You can always find some comfort in the fact that manufacturers spend millions of pounds each year testing their products to meet rigorous European technical efficiency standards. If the technology and the useful output from photovoltaic and solar thermal panels are good enough for over 650,000 domestic homes in the UK and numerous acres of UK farmers’ fields then there is a pretty good chance they will suit you too!

Doug Johnson

Doug is a chartered mechanical engineer and has had the pleasure of being involved in the UK renewable sector since 2008. With wide-ranging operational and design experience in both the domestic and commercial sectors across a wide range of recognised technologies he hopes to be able to share his experience to help enlighten and save you hassle along the way.