Fact check: Solar power works best in the summer

More solar power is produced in the summer than any other time – regardless of how hot it gets.

Why the marginal impact of hot weather on solar photovoltaic panel efficiency is not the story.

With mainstream media delivering yet another ill-considered click-bait headline; ‘Britain fires up coal plant as solar panels suffer in hot weather’, Chris Hewett of Solar Energy UK checks the facts and explains why efficiency should not be confused with total output.

A gross misapprehension

Solar photovoltaic panels convert a slightly lower proportion of sunlight into electricity in hotter conditions. That is why peak power output generally occurs at midday in April or May.

But clearer skies, longer days and more sunlight add up to mean that significantly more power is produced overall during the summer. With over 14 hours of daylight each day between May and August, it’s a great time to generate renewable electricity – which can also be stored and used when less is being generated.

So, the idea that solar panels wilt in the heat is a gross and fundamental misapprehension.

A marginal effect

“It’s not actually a big deal. High temperatures only marginally affect the overall output of solar power – it’s a secondary effect. If it’s sunny and hot, you are going to get good power output. It doesn’t fall off a cliff,” said the UK’s leading technical expert on the technology, Alastair Buckley, Professor of Organic Electronics at the University of Sheffield.

Electrical generation data provides clear evidence for this. If solar power failed to function properly in the heat, it would not have been serving 25-30% of the UK’s power needs each lunchtime for the past week.

Over 24-hour periods, the rapidly expanding sector powered its way to supply an estimated 9.5% of demand on Saturday and 8.9% on Sunday.

“Cooler weather is marginally better for efficiency but ultimately, more light means more power. Solar power works perfectly well in the Saudi Arabian desert – and the same panels are being installed there as on rooftops in Birmingham or a field in Oxfordshire,” said Solar Energy UK chief executive Chris Hewett.

An important part of the energy mix

Put together, UK photovoltaics supply far more than any conventional thermal power station – which are also affected by the heat. The output of gas, coal and nuclear generation is cut when the temperature of their cooling water rises, a function of the laws of thermodynamics. This effect will worsen as climate change continues to bite.

Over a million homes can now attest to the performance of solar power, simply by looking at how their utility bills have been slashed. More rooftop installations are expected to be completed this year than any since the end of subsidies in 2019.

More generally, solar farms are helping to cut bills and reliance on imported natural gas for everyone in the nation. In combination with grid-scale storage, they will become a more and more important part of the energy mix as the UK’s energy mix steadily decarbonises.

Photovoltaic panels are typically warranted rated to function from -40 to +85°C, with performance falling by 0.34 percentage points per °C, compared to standard conditions at 25°C. So, even at close to boiling point, power output would only be around 20% lower, all other things being equal. Nominal operating temperature, which reflects more real-world conditions, is around 42°C.[4]

Temperature is even less of an influence for some newer products on the market.