Do Solar Panels Work Less Efficiently in Hot Weather? The Real Numbers

Yes — solar panels lose efficiency as they heat up, and a scorching July afternoon can produce less power per panel than a cool, clear day in April. This surprises most homeowners, because it runs against the obvious assumption: more sun equals more heat equals more power. In reality, sunlight and heat are two separate inputs, and only one of them helps your panels. The other works against them.

Here's the actual physics, the real production numbers, and what it means for sizing a system in a hot climate.

Last updated: 2026-07-14

Why Heat Hurts Panel Output

Solar panels are semiconductor devices, and semiconductors generate more electrical resistance as they get hotter. That resistance eats into the voltage the panel can produce, even while the amount of sunlight hitting it stays the same or increases.

Every panel has a temperature coefficient, usually listed on the spec sheet as a percentage per degree Celsius above 25°C (77°F) — the standard testing temperature manufacturers use to rate output. A typical monocrystalline panel has a coefficient around -0.35% to -0.45% per °C. That means for every degree above 25°C the panel's surface reaches, you lose roughly a third to a half a percent of rated output.

The catch: panel surface temperature runs far hotter than the air temperature around it. On a 95°F (35°C) day with direct sun, a roof-mounted panel can reach 140–160°F (60–70°C) at the cell level, because dark panels absorb heat and rooftop mounting limits airflow underneath them.

Run the math on that: a panel sitting at 65°C is 40°C above its 25°C rating point. At a -0.4%/°C coefficient, that's a 16% efficiency loss — on what looks, from the ground, like a perfect solar day.

Real Production Numbers: Summer Heat vs. Peak Efficiency

To make this concrete, compare a 10kW system's output on two different days with identical sun exposure but different temperatures, based on standard temperature-coefficient modeling:

Cool, sunny day — 60°F air / panel surface ~95°F (35°C):

Temperature loss from rating point: ~4%
Effective output: ~9.6 kW of rated capacity

Hot, sunny day — 100°F air / panel surface ~155°F (68°C):

Temperature loss from rating point: ~17%
Effective output: ~8.3 kW of rated capacity

That's a real-world swing of roughly 1.3 kW of lost capacity on the hottest days — precisely when air conditioning is driving your household's peak demand. This is why homeowners in Phoenix, Las Vegas, or Dallas sometimes see their system's best single-day output numbers show up in May or October, not July or August, even though those summer months still produce more total energy because the days are longer.

The distinction that matters: heat reduces efficiency, not total daily or monthly production. Long summer days with more peak sun hours generally still out-produce shorter, cooler months overall — the heat penalty is a discount on an already-larger number, not a wipeout. But it does mean your system's rated capacity and its real-world summer performance are two different figures, and any installer quote that doesn't account for this gap is overselling.

Heat is only one of several environmental factors that swing daily output. See how cold weather affects production and what actually happens on cloudy days for the fuller picture of how conditions beyond simple sun hours change your system's real numbers.

Where This Matters Most: Hot-Climate States

The temperature penalty isn't evenly distributed. It matters most in states where summer heat is extreme and sustained:

Arizona, Nevada, and inland Southern California — surface temperatures regularly exceed 65°C for weeks at a time
Texas, especially inland areas without coastal breeze — see Texas solar guide for state-specific numbers
Florida, where heat is paired with high humidity — see Florida solar guide
Interior Southwest states generally

In these climates, the gap between a panel's rated capacity and its actual mid-summer output can run 15–20%, which is exactly why installers in hot regions should be sizing systems to account for it — not just quoting rated wattage and letting homeowners assume that's what they'll get every day.

If your installer's proposal doesn't mention temperature derating at all, that's worth asking about directly. EnergySage is a useful way to get multiple proposals side by side and see whether one installer is modeling this more conservatively — and more honestly — than another.

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Not All Panels Handle Heat the Same Way

Temperature coefficient varies by panel technology, and it's one of the more overlooked specs homeowners should compare when getting quotes.

Monocrystalline panels typically run -0.35% to -0.40%/°C — generally the best heat tolerance among mainstream panel types.

Polycrystalline panels run closer to -0.40% to -0.45%/°C, a modest but real difference. For a full breakdown of how these panel types compare beyond just heat performance, see our monocrystalline vs. polycrystalline guide.

Premium panels from manufacturers like SunPower/Maxeon and REC often push closer to -0.29% to -0.34%/°C, thanks to cell architecture designed specifically to reduce resistance losses at high temperatures. In consistently hot climates, that difference compounds across an entire summer and can meaningfully close the production gap versus a standard panel — sometimes enough to justify the price premium on its own.

If you live somewhere that regularly sees 100°F+ summers, ask any installer for the temperature coefficient on the specific panel model in your quote — not just the brand name. It's listed on every manufacturer spec sheet and takes thirty seconds to compare across proposals. Once your system is installed, a solar monitoring system makes it easy to see exactly how much heat is cutting into your output on any given afternoon, rather than guessing from your utility bill weeks later.

Airflow and Mounting: The Overlooked Efficiency Lever

Because heat buildup — not ambient air temperature — is the real driver of loss, how a panel is mounted matters more than most homeowners realize.

Standard roof-mount racking typically leaves 4–6 inches of air gap between the panel and the roof surface, allowing some convective cooling. This is the baseline most residential systems use.

Flush or low-profile mounts that hug the roofline trap more heat and can run several degrees hotter at the cell level — worth asking about if you're choosing a sleeker aesthetic option in a hot climate. See our flat roof solar guide if this applies to your home.

Ground-mount and carport systems generally run cooler than roof-mount, since air can circulate on all sides. If you're in a hot climate and have the yard space, this is a legitimate efficiency argument in favor of ground mounting beyond just convenience — see our ground mount guide and solar carport guide for cost comparisons.

None of these differences are dramatic on their own, but in a climate where you're already fighting a 15%+ heat penalty for months at a time, a mounting choice that shaves a few more degrees off cell temperature adds up over a 25-year system life.

Why This Matters for System Sizing

The practical takeaway isn't "solar doesn't work in hot climates" — it clearly does, and hot, sunny states like Arizona and Texas remain some of the best solar markets in the country because of how many total sun hours they get. The takeaway is that rated wattage and real summer output are not the same number, and a system sized purely off rated capacity without accounting for temperature derating will underperform its own paperwork on the hottest days of the year — right when your air conditioner needs it most.

A properly sized system for a hot climate should:

Account for temperature derating in production estimates, not just rated panel wattage
Factor in peak summer demand, since AC load and the heat-driven efficiency dip hit at the same time
Consider panel temperature coefficient as a real comparison point between quotes, not just price per watt
Weigh mounting type if ground space is available and heat is severe

This is also where battery storage earns its keep in hot climates. If your system's summer output dips right as your AC load peaks, a battery charged during high-efficiency morning hours can help cover the afternoon gap without pulling from the grid at your utility's most expensive rate. If you're weighing how much storage actually makes sense for your climate and usage, see our guide to how much solar battery storage you need.

For homeowners without a full home battery yet, a portable power station is a reasonable interim step for critical loads during a summer grid event. The EcoFlow DELTA Pro offers 3.6kWh of storage (expandable to 25kWh) and 3,600W of output — enough to carry a refrigerator, fans, medical equipment, and lighting through an extended outage or utility shutoff, which are more common during extreme summer heat events when grid demand spikes across an entire region.

For lighter backup needs — keeping devices charged and a fan or two running during a shorter outage — the Jackery Explorer 2000 Plus covers most scenarios at a lower price point, and can be recharged from solar if you already have panels installed.

The Bottom Line on Heat and Solar Efficiency

Solar panels do lose efficiency as they heat up — often 10–20% below rated capacity on the hottest days in hot climates. This is normal, well-documented physics, not a sign of a defective system. What it means practically is that a system sized purely off manufacturer rated wattage, without accounting for real-world temperature derating, will underdeliver on paper versus what actually shows up on your roof in August.

The fix isn't avoiding solar in hot climates — those remain among the best solar markets in the country on an annual-production basis. The fix is making sure your installer's proposal accounts for temperature loss explicitly, comparing temperature coefficients between panel options, and sizing your system (and any battery storage) around your actual summer performance, not just the number printed on the panel's spec sheet.

Get Quotes That Account for Real Summer Performance

The best way to know what a system will actually produce on your roof, in your climate, is to compare proposals that model temperature derating explicitly rather than quoting rated capacity alone.

Get competing solar quotes on EnergySage →

Compare installer proposals side by side, ask about panel temperature coefficients, and get a realistic summer production estimate before you sign anything.

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The exact questions to ask before signing — temperature derating, monthly output, and panel comparison. Free, no spam.