We asked experts if there's any truth in claims it can be too hot for solar panels

When the heatwave hit in June — rather than oodles of electricity being spare, Britain was firing up its coal-fired power stations to cope with a surge in demand.

Prior to this there had been a 46-day hiatus from the fossil fuel, leaving some scratching their heads as to why there was a sudden need for more power. Soon, people were joining the dots and pointing the finger at solar panels saying it was "too hot for solar panels" and that was the cause for the increase in demand.

One MP, Sammy Wilson, for the DUP, even made the claim that: "The UK has had to start coal fired generators during this heatwave because the sun is too strong and solar panels have had to be taken offline."

But is this really true? Can higher temperatures cause solar panels to be "taken offline"? Can it really be "too hot" for solar panels in a similar way that it can be "too windy" for wind turbines? Here we take a look at why coal-fueled power was really needed, if it was linked to a dip in solar panel output and whether there is any truth in the claims that it can be too hot solar panels.

What caused the spike in demand for electricity?

Contrary to claims that solar PV struggles in hot temperatures, the recent firing up of a coal power station in June was not due to any limitations of solar energy. 

Instead, the decision was due to an increase in demand for electricity caused by people switching on air conditioning —  which often will run all day and night — in both residential homes and, probably more pertinently, commercial buildings.

The BBC reports that electricity interconnectors between the UK and Norway had lower capacity due to a technical fault too so less electricity was imported. The news outlet also said that maintenance on gas power stations reduced their output and it was less windy so wind-generated power was also down. 

Solar Energy UK also points out that thermal power stations (gas, coal and nuclear) are less efficient in the heat as the temperature of the cooling water rises, which is needed for creating power due to the laws of thermodynamics.

Let us not forget that only last winter, the National Grid announced that there were power shortage concerns and a risk of blackouts due to electricity supplies from Europe being affected by the Ukraine war as well as a drop in domestic output due to plans to decommission British coal-fueled power plants to help with the UK's carbon targets.

So, can it ever be 'too hot' for solar panels?

Essentially, the weather can never be too hot for solar panels to work and it is not true that solar panels have to be "taken offline" in extreme heat. In fact it is quite the opposite, with most solar energy in the UK being generated during the summer months, according to Solar Energy UK. 

“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,” Solar Energy UK Chief Executive Chris Hewett told Euro News.

That said, like other forms of power generation, solar panels can be ever so slightly less efficient when temperatures exceed 25C as Homebuilding & Renovating's heating expert, David Hilton explains.

"Solar photovoltaic (PV) panels are affected by heat but it is very marginal. The optimum temperature for a solar PV panel is around 25C and if the temperature of the cell rises above this then you lose around 1% for every 3 degrees," he said.

"Therefore on a really hot, windless day you may have a cell temperature around 46C which means you lose around 7% of the generation. The glass acts as a very good heat sink and the prevailing winds (even thermal drafts), angle of the sun and strength of the sun all help to keep the temperatures low. 

"Even considering wire resistance and additional fan power required to cool the inverter in hot spaces on a hot day the losses are not really above around 10% to 14% for very short periods of time."

Hilton summarised that "when the sun is that hot it is often over 1000W/square meter," which can lead to greater yields of energy generation from solar panels. Therefore, higher temperatures can improve solar panel performance.

Main risk to solar panels is lack of investment 

Around 1.2 million homes in the UK have undertaken installing solar panels, which accounts for 4.1% of the country's 29 million households, according to the latest MCS installations data. The UK's total electricity production from solar panels stands at 13,258 megawatts per year, enough to power approximately three million homes nationwide.  This marks a significant increase from the 5,488.6 megawatts generated in 2014. 

The International Energy Agency (IEA) even projects that the UK's solar panel capacity will nearly triple by 2030. This surge in solar power adoption is expected to result in a reduction of UK emissions, estimated at 4.7%.

However, a recent report from SolarPower Europe highlights that the main obstacle to the UK's solar panel rollout is the "chronic underinvestment" in the country's transmission and distribution networks, rather than any limitations imposed by the sun itself. 

What grants for solar panels are out there?

Basically there are no significant grants running at the moment to help with solar panel installation costs despite coal power being scheduled to be phased out by October 2024.

However, the Energy Company Obligation Scheme has allocated £4 billion to facilitate the installation of solar panels and heat pumps, increasing the likelihood of grants for solar panels in the coming years to alleviate the initial financial burden.

Chancellor Rishi Sunak did announce a reduction in VAT for solar panels to 0% for five years in early 2022, but critics allege more schemes should used to encourage solar panel instalment, such the recently removed FiT, Renewable Heat Incentive and the Green Homes Grant.