The UK’s solar fleet generated 10.7 GW on 10 July 2024, a new record. Yet on the same day, the mercury hit 32°C in parts of southern England, and every rooftop panel was losing efficiency with each degree rise. The Telegraph reports that solar panels can overheat as temperatures soar, raising questions for the 1.5 million UK households with solar installations.
As reported by The Telegraph, solar panels are tested at 25°C under standard test conditions. For every degree above that, output falls by about 0.3-0.5%. On a 35°C roof, that is a 5-10% loss. For a typical 4 kW system generating 3,500 kWh a year, a heatwave week could cost around 15-20 kWh, roughly £3-4 at current price cap rates. Not a disaster, but not trivial either.
Who qualifies, and who doesn’t
The overheating effect applies to all silicon-based photovoltaic panels, which cover over 95% of UK installations. Thin-film panels have slightly lower temperature coefficients but are rare in residential setups. The loss is temporary: as soon as the panel cools, efficiency returns. No permanent damage occurs unless the panel exceeds its maximum operating temperature, typically 85°C, which UK roofs almost never reach.
But the catch is that roof colour and ventilation matter. Dark roofs absorb more heat, raising panel temperature by up to 5°C compared to a light-coloured roof. Panels mounted flush to the roof with no air gap can run 10-15°C hotter than those with a proper stand-off mount. The Energy Saving Trust recommends a minimum 10-15 cm air gap for rear ventilation.
What it costs a typical 3-bed semi
A typical 3-bed semi with a 4 kW south-facing system might generate 3,500 kWh annually. If summer temperatures average 20°C, the temperature loss is negligible. But during a 30°C heatwave week, that system loses roughly 5% of its daily output, about 3-4 kWh per day. Over a two-week heatwave, that is 50-60 kWh lost, worth about £10-12 at current rates.
Ofgem’s price cap for July-September 2024 is 22.36p per kWh for electricity, so every kWh counts. Households on time-of-use tariffs who export at peak rates may feel the loss more acutely. Octopus Energy’s Outgoing Agile tariff pays different rates by half-hour; a lost kWh at 4pm on a 35°C day could mean missing out on 50p-£1 of export revenue.
How to prevent overheating
Three practical steps can reduce heat-related losses. First, ensure panels are mounted with an air gap, most MCS-certified installers do this by default, but check the installation spec. Second, use microinverters or power optimisers so that one hot panel does not drag down the whole string. Third, keep the roof and panels clean; dust and debris trap heat.
What this misses is that heat is a second-order problem. The bigger issue for UK solar is shading, orientation, and inverter sizing. A panel at 30°C still outperforms a shaded panel at 20°C. The Telegraph’s reporting highlights a real but manageable effect, one that should not deter new installations.
What to do next
Households with existing solar should check their inverter app on hot days. If output drops more than 10% below typical summer generation, contact your installer to check for ventilation issues. Those considering solar should ask installers about the temperature coefficient of the panel, most premium brands like SunPower or LG have lower coefficients (0.3%/°C) than budget panels (0.5%/°C).
The Great British Insulation Scheme closed on 31 March 2026. It funded insulation measures only and never covered windows or glazing. Heatwave or not, solar remains one of the best long-term investments for UK homes, with typical payback periods of 10-15 years. The heat is a hiccup, not a hazard.
Frequently Asked Questions
No, they do not stop working. They lose some efficiency, typically 0.3-0.5% per degree above 25°C, but still generate electricity. Even at 40°C, a panel produces about 80-85% of its rated output.
Extreme UK heat (up to 40°C) is well within the operating limits of modern solar panels, which are tested to withstand 85°C. No permanent damage occurs from heat alone, though thermal cycling over many years can cause microcracks in poorly manufactured panels.
