Do solar panels overheat in hot weather?

No, not in any way that should worry a UK homeowner. A panel's power drops slightly as its cells get hotter, and every datasheet states by how much: the temperature coefficient of Pmax, typically around −0.24% to −0.29% per °C on current panels. But the extra sunshine in summer outweighs that loss by far. For a south-facing system in London, PVGIS estimates June and July as the most productive months, with more than three times the output of December.

So hot weather does not make solar panels a poor summer performer. It is one more reason to compare the heat figures on the datasheets in your quote, and to check where the inverter will be fitted.

Why panels lose a little power in the heat

Panel ratings are measured at a cell temperature of 25 °C (standard test conditions, STC). On a sunny roof the cells run much hotter than the air around them, so their output at that moment is below the rated power. That is normal, and manufacturers publish it.

The temperature coefficient tells you how much output is lost for each degree above 25 °C. The closer it is to zero, the better the panel copes with heat. On four current datasheets:

The nominal operating cell temperature describes a mild day: 800 W/m² of sunshine, 20 °C air and a light 1 m/s breeze. Even then, the cells run about 25 °C warmer than the air.

An illustration. Suppose that on a hot, still afternoon the cells reach 60 °C, which is 35 °C above the test temperature (an illustrative figure: real cell temperature depends on sunshine, air temperature, wind and how the panels are mounted). A −0.29%/°C panel then delivers about 10.2% less than its rating at that sunshine level (35 × 0.29%); a −0.24%/°C panel about 8.4% less (35 × 0.24%). That is a snapshot of one moment, not the loss over a day or a year.

Why summer is still the best season

Heat takes off a few per cent at the hottest moments. Long, bright summer days add far more. For a 1 kWp south-facing system at a 35° pitch in London, PVGIS (the European Commission's solar model, 2005–2023 data, free-standing mounting) estimates:

These are long-term averages from a model, not a forecast for your roof. PVGIS already allows for heat: over a whole year it puts the combined loss from temperature and low light at about 4.8% for this London example with its free-standing setting (panels on a frame with air behind them). Its building-integrated setting, for panels with no air gap behind them, gives about 7.8%. Further north and west, May is often the best month: in Glasgow, PVGIS puts May ahead of June and July.

The example below shows production and use month by month for a 2,500 kWh household without a battery, using our calculator's own sizing rather than the 4 kWp in the table; change the yearly use to see how the seasons shift the balance.

The UK rarely gets truly hot. The national record is 40.3 °C, set at Coningsby in Lincolnshire on 19 July 2022. Panels run hotter than the air, but the AIKO, JinkoSolar and LONGi panels above are rated to operate at up to +85 °C (and down to −40 °C). The days that really hold a system back are the dull, short ones in winter, which solar panels in winter looks at in detail.

Where heat makes more difference

• Panels with little air behind them. Panels fixed close to a dark roof, or built into it, have less air flowing underneath to carry heat away than panels on a frame with a clear gap.
• Full sun in the middle of the day, when the panels are already at their hottest.
• Panels with a less favourable coefficient. The difference between −0.24% and −0.29% per °C is small, but it adds up over many sunny hours. It is a fair point to compare between quotes, alongside price and warranty. The best solar panels sets out what else to compare.

Check where the inverter and battery go

Heat also matters for the electronics. Inverter datasheets give an ambient temperature range: for example, Enphase's IQ8 microinverters are rated for –40 °C to 65 °C air temperature. Inverters and batteries are often fitted in lofts or garages, and a loft can get very warm in summer. Ask the installer where each device will go, whether that space stays within its rated range, and whether the manufacturer's clearance for ventilation will be kept. See solar inverters for more on choosing and siting one.

What to ask, and what to avoid

Ask for the temperature coefficient of Pmax of the panel model offered and how the panels will be mounted, including the gap behind them. Both are quote questions, not DIY fixes.

Do not try to cool panels yourself. Hosing down a roof means working at height and near live electrics, and it can go against the manufacturer's instructions; follow the guidance in cleaning solar panels instead. If you want to get more value from sunny summer days, run the dishwasher, washing machine or EV charger while the sun is out. That raises how much of your solar power you use yourself, which is worth more than exporting it: each kWh you use saves the full import price, while export pays less. Solar self-consumption explains how.

Frequently asked questions

Can solar panels overheat in the UK?

Not in normal use. They lose a little output as they warm up, but they are built for heat: three of the four panels compared above are rated to operate at up to +85 °C, while the UK's hottest recorded air temperature is 40.3 °C (July 2022).

Do solar panels produce less in a heatwave?

At any given level of sunshine, a hotter panel produces slightly less. But a heatwave usually means long, bright days, so daily output is still high. The loss is roughly the temperature coefficient times the degrees above 25 °C in the cells.

Do panels in the north of the UK produce more because it is cooler?

No. More sunshine matters more than cooler air. PVGIS estimates about 1,121 kWh a year per kWp in Plymouth against about 853 kWh in Glasgow for the same south-facing set-up, around 32% more in the warmer south-west.

Which month do solar panels produce the most in the UK?

It depends on where you are. In the PVGIS estimate for London, June has the highest daily average (4.09 kWh per kWp) with July close behind (3.97 kWh). In most other UK locations, including Bristol, Manchester, Belfast and Glasgow, May produces the most: in Glasgow, 115.8 kWh per kWp against 110.0 in June and 111.0 in July. December is the lowest month almost everywhere (in Manchester it is January).

Is the temperature coefficient the same for all panels?

No. It varies by model and cell technology and is printed on every datasheet. The four compared above range from −0.24% to −0.29% per °C.