PV Panels Prefer the Cold!
When asked to select an ideal location for a solar PV installation most people would suggest somewhere that is hot and sunny all year round. Whilst it is true that solar panels generate the greatest yield in areas with a high irradiance (sun strength), a less well-known fact is that they also lose efficiency in temperatures that are very hot. Solar panel manufacturers describe the potential loss in efficiency as the temperature coefficient, which may be in the region of 0.38% to 0.50% loss for every degree above 25 degrees Celsius. Even in the UK this will have an effect when you consider how hot a south-facing sunny roof space may become. Over the course of a year we would expect the figures to balance in most northern climates but high temperatures could become an issue for those planning an installation near the equator.
Why does this happen?
Solar cells contain semi-conductors with positive charges and negative charges. The gap between them is called the band gap and this is where the conversion of light to electrical energy takes place. The band gap has an inverse temperature dependency meaning its width and the voltage decreases as temperature increases. This in turn reduces the efficiency of the solar cells.
What about the (grey) British weather?
So we know the temperature in the UK is suited to solar panels but how do we tackle the issue of sunlight (or lack of!)? Another common misconception is that solar panels will not produce electricity on cloudy days. Whilst the production levels will certainly be reduced, the panels will continue to generate as long as there is daylight. Some manufacturers have designed panels that are optimised to weak light so they can make the most of grey and overcast days. This can help to boost your yield.
We are also often asked of the effects of rain on panel performance. Rain is actually pretty good for keeping panels clean! In fact, systems that are angled at 30 degrees or more are often said to be ‘self-cleaning’. Dirty panels can significantly reduce the yield from a system so a bit of rain can be helpful, reducing the frequency that you will need to clean your panels.
In the UK we do not often experience prolonged periods of heavy snowfall, although the ‘big freeze’ of the winters in 2009 and 2010 proved they are not unheard of. With a light covering of snow, panels can still generate but once completely covered they may become blocked from the sun. If the panels are free from snow but the surrounding area is covered then this can help to boost production in sunny conditions, as the light is reflected off the snow.
In Switzerland a small town called Tenna became home to the world’s first solar powered ski lift! The chain of panels (pictured) produces three times the amount of electricity required to power the lift, providing a surplus to the regional grid. You can read more about this unusual installation here.
How do we estimate solar panel production?
The weather in the UK can seem very unpredictable at times but there is an excellent range of meteorological data available for hundreds of sites around the country that can help us to make accurate estimates about how much a PV system, in a particular location, is likely to generate. Added to the historical performance data from existing systems we are becoming increasingly confident in our forecasts. However, it is always best to err on the side of caution, which is why analysis of the performance of GMI Energy systems shows the majority are exceeding expectations.