Our region just came off its warmest April on record, and summer hasn’t even started. As temperatures climb, we hear a question that surprises a lot of people: “Don’t solar panels work worse when it’s hot?”
It’s true, sort of. Heat does lower a solar panel’s efficiency a little. But summer is still, by far, your system’s best season. Here’s why both things are true, with real numbers.
Solar Panels Run on Light, Not Heat
Solar panels turn sunlight into electricity. Heat isn’t part of the recipe. In fact, like most electronics, panels work a bit better when they’re cool.
Every panel is rated at a cell temperature of 25°C (77°F). For every degree the cells get hotter than that, output drops slightly. That rate is called the temperature coefficient, and for most modern panels it’s somewhere around -0.3% to -0.4% per °C (roughly -0.2% per °F).
What That Looks Like on a 90°F Afternoon
Panels on a roof in direct sun run much hotter than the air around them, often 20°C to 40°C (about 35°F to 70°F) hotter.
Here’s a realistic example for a hot summer afternoon here:
- Air temperature: 90°F (about 32°C)
- Bright, full sun
- Estimated cell temperature: about 63°C (about 145°F)
- Temperature coefficient: -0.35% per °C
That’s about 38°C above the 25°C rating, so the panel produces roughly 13% less than its nameplate rating at that moment. A 400-watt panel would be making closer to 350 watts.
That sounds like a lot until you look at the whole season.
Why Summer Is Still Your Best Season
Heat costs you a little, but summer more than makes up for it:
- Longer days. Late June brings close to 15 hours of daylight here, compared with about 9.5 hours in late December.
- Higher sun. The summer sun is nearly overhead at midday, so its energy hits your panels more directly.
- More total sunlight. In central Ohio, a June day delivers about 2.8 times as much usable sunlight as a December day.
So even running a bit less efficiently, your system produces the most energy in late spring and summer. And those crisp, sunny 70-degree days in April, May and September? They’re often your best days of the year, with plenty of sun and cool panels.
Solar Production Lines Up With Air Conditioning
Here’s the best part about summer solar: your panels produce the most on the same sunny, hot days your air conditioner is working hardest. Much of that cooling happens while the sun is up, which means more of your solar power goes straight to work in your own home.
That matters more than ever in places where the credit for exported solar is less than the retail rate, like Indiana and Kentucky. Using your solar as it’s produced is where the biggest savings come from. (We explain how that works in Indiana and Kentucky.)
Evening is another story. Air conditioning often runs well after sunset, when panels aren’t producing. A home battery can store extra midday solar for those hot evenings and keep things cool during a summer outage.
How Solar Systems Are Built for Heat
A good installation accounts for summer heat from the start:
- Airflow under the panels. Panels are mounted on racking with a gap above the roof so air can circulate and carry heat away.
- Panel choice. Some panel technologies have better (smaller) temperature coefficients than others. It’s one of the specs worth comparing in a quote.
- Accurate estimates. Production estimates should already factor in local temperatures, so your summer numbers shouldn’t come as a surprise.
Your Panels Also Keep Your Roof Cooler
There’s a bonus. The section of roof under your panels stays shaded all summer. In a UC San Diego study, the ceiling under solar panels was about 5°F cooler than under exposed roof. We cover that and more in Do Solar Panels Damage Your Roof?
Make the Most of Summer Sun
If you’re thinking about solar, now is a great time to get started, and we can walk you through realistic production numbers for your home and your roof.
Icon Solar has helped homeowners across Ohio, Kentucky and Indiana go solar since 2009. Learn how many solar panels your home may need, explore solar for your home, review solar financing options, or request your free quote. You can also call us at (866) 396-4266.
Frequently Asked Questions
Do solar panels work in hot weather?
Yes. Solar panels run on sunlight, not heat. High temperatures lower efficiency slightly, but long, sunny summer days still make summer the most productive season for most systems in Ohio, Kentucky and Indiana.
How much efficiency do solar panels lose in the heat?
Most panels lose about 0.3% to 0.4% of their output for every degree Celsius above 25°C (77°F). On a 90°F afternoon, rooftop panels can run around 145°F and produce roughly 13% below their rating at that moment.
What month do solar panels produce the most electricity in Ohio?
Production is usually highest in late spring and summer, when days are longest and the sun is highest. In central Ohio, June delivers about 2.8 times as much usable sunlight per day as December.
Are cool, sunny days good for solar panels?
Yes. Cool, bright days are often among the best production days of the year because panels get plenty of sun while staying cooler and more efficient.
Can solar panels help with summer air conditioning costs?
Yes. Solar production peaks on sunny days when air conditioners work hardest, so much of your solar power can be used right away in your home. A home battery can store extra daytime solar for evening cooling.
