As temperatures climb, it’s natural to wonder whether a heatwave will help your solar panels generate more electricity. After all, longer days and brighter skies can mean more power to run fans, air conditioning or other appliances, and potentially more surplus energy to sell back to the grid.
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But solar panels don’t work better simply because it’s hotter. They need sunlight, not heat. In fact, very high temperatures can slightly reduce how efficiently panels convert sunlight into electricity.
For most UK households, though, this drop in efficiency is usually modest. Even during extreme heat, solar panels can still perform strongly, and evidence from Britain’s hottest day on record suggests that heatwaves can still deliver some of the year’s highest solar generation.
If you’re considering installing a system before the hottest months of the year, it’s worth comparing solar panel quotes from trusted UK installers so you can see how system size, panel type, battery storage and roof layout could affect your likely generation.
How do solar panels perform when it’s hot?
Modern solar panels are designed to operate across a wide temperature range. According to trade body Solar Energy UK, most panels are built to work from around -40C to 85C, but they generally perform best when the solar cells are closer to 25C or below.
That can feel counterintuitive. After all, the hottest days are often the sunniest. But solar panels don’t like heat in the same way humans do. Strong sunlight increases the electrical current a panel can generate, yet as the panel warms up, its voltage drops, and power is essentially current multiplied by voltage. In practice, that means bright sunshine can still deliver great generation, but higher panel temperatures shave a little off the top.
Air temperature vs solar panel temperature
One important detail is that it’s the temperature of the solar cells inside the panel that matters most, not the headline temperature on the weather app.
Solar panels are rated in laboratory conditions (often called “standard test conditions”) at 25C. Out on a roof, panels can run significantly hotter than the surrounding air because they absorb solar radiation. While wind and airflow under the panels can cool them, on a still, sunny day it’s common for the panels themselves to be far warmer than the ambient temperature.
How much power do solar panels lose in a heatwave?
The impact of heat is usually described using a panel’s temperature coefficient – a number on the datasheet that indicates how much the panel’s power output falls as its temperature rises above 25C.
As a rule of thumb, for every degree above 25C, solar panels can lose around 0.34 to 0.5 percentage points of power output, depending on the model and the quality of the cells.
To see what that means in the real world, consider Britain’s all-time temperature record of 40.3C, set on 19 July 2022.
If you used the air temperature alone as a rough guide, the difference between 25C and 40.3C is 15.3C. On that basis, a good modern panel would be operating at roughly 5 per cent below its optimum rating.
In reality, panels can be hotter than the air temperature in full sun. But even at the top end of many manufacturers’ operating ranges – around 85C – the loss implied by typical temperature coefficients is still usually in the region of 20 per cent compared with the 25C test condition.
That sounds large, but it’s worth keeping in perspective. First, it’s a comparison to an ideal laboratory reference point. Second, it’s a “moment in time” penalty at a particular panel temperature, not a promise that your annual solar yield will fall by 20 per cent.
For most homeowners, the bigger financial question is how this annual generation compares with the upfront cost of solar panels, rather than what happens during one unusually hot afternoon.
You may also be able to reduce the upfront cost through solar panel grants and funding, including 0 per cent VAT, local schemes or support such as ECO4 if you meet the eligibility criteria.
Heat doesn’t just affect solar panels: the inverter matters, too
If you notice your system output dropping more than the panel maths suggests on very hot days, it may not be the panels at all.
Solar systems rely on an inverter to convert the electricity generated by the panels (DC) into the form used in your home (AC). Inverters generate heat while they operate, and many are designed to protect themselves by reducing output if they get too hot, a behaviour sometimes described as thermal derating or throttling.
That’s one reason installers usually try to position inverters in a cool, well-ventilated place out of direct sunlight. Poor airflow around an inverter – or a unit installed in a hot loft space – can make a bigger difference during a heatwave than the panel temperature coefficient alone.
What happened on the UK’s hottest day on record?
Britain’s record-breaking heat in July 2022 provides a useful real-world test.
According to estimates from Sheffield Solar’s PV Live modelling, cited by Solar Energy UK, solar generated 66.9GWh of electricity over the course of 19 July 2022, supplying around 8.6 per cent of the UK’s power needs that day. Over the previous seven days, solar had provided around 9 per cent.
In other words, even on the hottest day the UK has ever recorded, the national solar fleet still supplied a meaningful share of electricity, and the evidence suggests only a small drop-off in performance.
How to tell if your panels are ‘good in the heat’
If you’re comparing solar panels – or just trying to understand your existing system – a few details can help. These are also useful details to check when comparing the best solar panels, because headline wattage is only one part of long-term performance.
- Temperature coefficient (Pmax): the closer this figure is to zero, the less performance falls as panels heat up.
- NOCT (Nominal Operating Cell Temperature): a clue to how warm a panel tends to run under typical real-world conditions.
- Inverter operating temperature / derating behaviour: some inverters reduce output at high temperatures – good siting and ventilation can minimise this.
Verdict: Do solar panels work in a heatwave?
Solar panels can still work well in a heatwave, but they do not become more efficient simply because it is hot. In fact, very high temperatures can slightly reduce panel efficiency because heat lowers voltage.
For most UK homes, however, this reduction is usually modest. Longer daylight hours and strong summer sunshine often mean solar panels still generate plenty of electricity overall, even if each panel operates a little less efficiently than it would on a cooler, brighter day.
That means a heatwave is not usually a cause for concern about your solar panels underperforming. The bigger lesson is that system design is key. Panels need good airflow, inverters should be kept out of extreme heat where possible, and homeowners should look at generation over days and weeks, rather than judging performance by a single hot afternoon.
As UK summers become hotter and heatwaves more common, understanding this balance will become more important. Solar panels need sunlight, not heat, but a well-designed system should still be able to make strong use of long, bright summer days.
