Solar panels lose output as they heat up, typically around 0.3 to 0.5 percent for every degree Celsius above 25C, and they keep working well past any temperature the weather produces. Panels are rated to operate up to about 85C, which outdoor air never reaches even where panel surfaces do.
The practical answer is that heat costs you production rather than causing damage. A panel in Arizona in July is producing meaningfully less than its rated output, and it is not at risk.
Quick Answer
Panels are rated for cell temperatures up to roughly 85C and lose efficiency steadily as they warm. Expect 10 to 25 percent below rated output on a hot summer day. Airflow underneath the array matters more than anything else you can control.
What the Temperature Coefficient Means
| Panel type | Typical coefficient | Loss at 65C cell temp |
|---|---|---|
| Monocrystalline | -0.30 to -0.40 %/C | 12 to 16% |
| Polycrystalline | -0.38 to -0.45 %/C | 15 to 18% |
| Thin film | -0.20 to -0.28 %/C | 8 to 11% |
Panels are rated at Standard Test Conditions, which assume a cell temperature of exactly 25C. That is a laboratory reference rather than a field measurement, and cell temperature in real installations runs considerably above the surrounding air.
The coefficient tells you the penalty. A panel with a coefficient of -0.4 percent per degree, running at 65C, is 40 degrees above the reference and therefore producing about 16 percent below its rating.
Cell Temperature Runs Far Above Air Temperature
This is the part that surprises people. On a 35C day, panel cell temperature commonly sits between 55C and 70C.
Dark glass absorbing full sun heats considerably beyond the surrounding air, and the panel has limited ability to shed that heat other than by radiating and convecting from its surfaces.
Roof-mounted arrays run hottest, since the roof beneath is also hot and the gap between panel and roof restricts airflow.
Ground mounts and pole mounts run cooler because air moves freely on both sides, which is one reason the same panel produces differently in different installations, covered in solar panel orientation and output.
Why Panels Do Not Fail From Heat
Manufacturers specify an operating range that typically extends to 85C cell temperature, which is above what installations reach in practice.
Certification includes thermal cycling, meaning repeated heating and cooling across wide ranges without delamination or cracking.
What heat does accelerate is long-term degradation. Panels lose a fraction of a percent of output per year, and consistently high operating temperatures push that toward the higher end of the range.
That is a decades-long effect rather than a summer one, covered in how long solar panels last.
What Actually Suffers in Heat
Batteries
Lithium and lead acid both degrade faster at high temperatures, and unlike panels this is a genuine lifespan issue rather than a temporary output loss.
Inverters
Most derate above a threshold, reducing output to protect internal components, and some shut down entirely in extreme heat, covered in why inverters shut off.
Charge controllers
Same behavior. Enclosed electronics in direct sun are working harder than the panels are.
Wiring insulation
Rated for specific temperature ranges, and conduit on a hot roof can exceed what standard insulation was specified for.
Why NOCT Is the More Useful Number
Panel labels carry two ratings, and the second one describes real conditions rather than laboratory ones.
Standard Test Conditions assume 25C cell temperature, 1000 watts per square meter of irradiance, and no wind. That combination essentially never occurs outdoors, which is why STC output is a comparison figure rather than a prediction.
Nominal Operating Cell Temperature is measured at 20C ambient, 800 watts per square meter, and a light breeze. Most panels report a NOCT somewhere between 42C and 48C, which tells you how hot the cells run in fairly mild conditions.
A lower NOCT means the panel sheds heat better, and comparing two panels on NOCT alongside the temperature coefficient gives a far better sense of hot-weather performance than wattage alone.
The rated power at NOCT, sometimes listed as NMOT power, is usually 20 to 25 percent below the STC figure. That number is closer to what a panel actually delivers on a normal day.
People comparing panels on peak wattage alone are comparing laboratory numbers, which is fine for ranking similar panels and misleading if the two have different thermal behavior.
Reducing Heat Losses
Leave airflow under the array. A gap of four to six inches between panel and roof allows convection that a flush mount does not, and this is the single biggest controllable factor.
Choose panels with better temperature coefficients if you are in a consistently hot climate. The difference between -0.29 and -0.45 percent per degree compounds across every hot hour of every summer.
Mount electronics in shade. Inverters, charge controllers, and batteries in direct sun run hotter than they need to and derate sooner.
Keep panels clean, since dust reduces output independently and a dirty panel absorbs slightly more heat than a clean one, covered in how often to clean solar panels.
Reading Your Own System in Heat
Knowing what normal looks like on a hot day prevents the common mistake of diagnosing a fault that is not there.
Compare production against a cool clear day rather than against the rated wattage. A 400 watt panel delivering 300 watts at midday in summer is behaving correctly, and comparing it to 400 makes it look broken.
Watch the shape of the curve rather than the peak. A healthy hot-weather curve rises through the morning, flattens or dips slightly at the hottest part of the day, and recovers a little as temperature falls in the late afternoon.
That midday dip is the signature of heat rather than shading. Shading produces sharp irregular drops, and heat produces a broad shallow depression across the middle hours.
Monitor panel or cell temperature if your equipment reports it, since that number tells you directly how far above 25C the array is running and therefore what loss to expect.
A sudden drop that does not match temperature is worth investigating properly, since that pattern points at soiling, a connection problem, or a failing component rather than at the weather.
The Counterintuitive Part
Cold sunny days produce more per panel than hot sunny days. Panels are more efficient below 25C, so a clear winter day at 5C can outproduce a hazy summer day at 35C on a per-hour basis.
Summer still wins on total production because of daylight hours and sun angle, and the hourly peak often occurs in spring rather than midsummer.
That is why winter output is better than people expect in cold sunny climates, covered in whether solar panels work in winter.
It also means system sizing based on summer peak alone can misjudge what a system produces across a year.
Related Reading
- solar panel efficiency
- underproduction reasons
- panels in winter
- how long panels last
- mono against poly
- batteries in cold weather
Frequently Asked Questions
How hot is too hot for solar panels?
Panels are rated to roughly 85C cell temperature, which real installations do not reach. Heat costs output rather than causing damage, typically 10 to 25 percent below rating on a hot day.
How much output do I lose in summer?
Commonly 10 to 25 percent below the rated figure, depending on the panel’s temperature coefficient and how hot the cells actually run.
Why is cell temperature higher than air temperature?
Dark glass absorbing full sun heats well above the surrounding air. On a 35C day, cells commonly sit between 55C and 70C.
Do roof mounts run hotter than ground mounts?
Yes. The roof beneath is also hot and the gap restricts airflow, where a ground mount has air moving freely on both sides.
Can heat permanently damage panels?
Not at normal operating temperatures. Sustained high heat does push long-term degradation toward the faster end of the range, which is a decades-long effect.
What suffers more than the panels?
Batteries, inverters, and charge controllers. Batteries degrade faster in heat, and inverters derate or shut down to protect themselves.
What is NOCT and why does it matter?
Nominal Operating Cell Temperature, measured under realistic conditions rather than laboratory ones. A lower NOCT means the panel sheds heat better, and the power rating at NOCT is closer to real output.
Do panels produce more in cold weather?
Per hour of sunlight, yes. Panels are more efficient below 25C, so a clear cold day can outproduce a hot hazy one despite fewer daylight hours.
Sources
- National Renewable Energy Laboratory. PV Performance and Temperature. https://www.nrel.gov/pv/
- United States Department of Energy. Solar Performance and Efficiency. https://www.energy.gov/eere/solar/solar-performance-and-efficiency
Recommended Reading
See our note on choosing solar panels.
