A hot Perth summer day seems ideal for solar. In terms of sunshine, it is close. But here is a surprising twist: very high temperatures actually cut the efficiency of a solar panel. This guide explains how heat affects output. It also explains why summer still produces the most energy overall. Finally, it shows why panel quality matters most when temperatures climb.
The short version: heat slightly lowers how efficiently each panel works. But the long, intense sunshine of a Perth summer more than makes up for it. Summer remains the highest-producing season. Better panels simply lose less to the heat.
Panels Run on Light, Not Heat
Solar panels generate electricity from light, not from warmth. This is why they work on cool, bright days and even on overcast ones. Heat is not what makes them produce. Sunlight is. While a hot day usually is a sunny day, the heat itself is not helping the panels. Beyond a point it works against them.
Why High Temperatures Lower Efficiency
Solar panels are rated at a standard cell temperature of 25 degrees. Their efficiency falls as the cells get hotter than that. Every panel has a temperature coefficient. It is typically around a third to four tenths of a percent of output lost for each degree above 25. On a 40 degree Perth day, a panel sitting in full sun can reach a cell temperature of 65 to 70 degrees. This can trim its output by somewhere in the region of 10 to 18 percent compared with the same sunshine at a milder temperature.
This is a real effect. This is why a system sometimes produces a little less at 3pm on a blazing hot day than expectations based on the sunshine alone would suggest. It is normal. It is understood. It is designed around rather than being a fault.
| Situation | Approx. cell temperature | Effect on a panel output |
|---|---|---|
| Rated test conditions | 25 degrees | Full rated output |
| Warm sunny day | Around 45 degrees | Slightly reduced |
| Hot 40-degree day, full sun | 65 to 70 degrees | Around 10 to 18 percent below rated |
| Cool, bright day | Low | Efficient per panel, though less total sunlight |
Why Summer Still Wins Overall
Despite that efficiency loss, summer is comfortably the highest-producing season for a Perth system. The reason is simple: the days are far longer. The sun is far stronger and higher in the sky. So the panels generate for many more hours at much greater intensity. That extra generation vastly outweighs the percentage lost to heat. A summer day still produces more energy than a mild spring or autumn day. It produces far more than a short winter one. The heat shaves a slice off the peak. But the sheer size of the summer resource means the total is still the largest of the year.
Why Panel Quality Matters Most in the Heat
This is where the choice of panel makes a genuine difference. A key measure of a quality panel is a low temperature coefficient. This means it loses less output for each degree of heat. On a mild day, a low-cost panel and a premium panel might perform similarly. On a 40 degree Perth afternoon, the premium panel holds noticeably more of its output. Over the many hot days a Perth system sees each year, that difference adds up to real energy. It is one of the reasons Positive Energy Solutions installs premium panels built to perform in the conditions they will actually face. Not the conditions of a laboratory.
Heat also affects the rest of the system. Inverters and batteries have their own thermal limits. They can throttle back to protect themselves if they get too hot. This is why quality gear matters. Good ventilation matters. Sensible placement out of the worst afternoon sun matters. All of these count for real-world summer performance.
Getting the Best From a System in Summer
A well-designed installation already accounts for Perth heat: quality panels with a low temperature coefficient, an inverter and battery placed and rated for hot conditions, and mounting that lets air move behind the panels to help them shed heat. For a household, the main thing to know is simple. A small midday dip on the hottest days is normal. The summer total is still the best of the year. Monitoring the system through its portal shows exactly how it performs across the seasons.
How Positive Energy Solutions Can Help
Positive Energy Solutions designs systems for real Perth conditions. We choose quality panels that hold their output in the heat. We site inverters and batteries so they run cool and reliably through summer. Every installation is completed by our accredited installers and signed off to Positive Energy’s completion standards. It is backed by a 10-year installation workmanship warranty. Positive Energy Protection, powered by Omnidian, includes monitoring. A household can see its real output on hot days and across the year.
Frequently Asked Questions
Does heat reduce solar panel output?
Yes, a little. Panels are rated at 25 degrees and lose efficiency as they get hotter. Loss is typically around a third to four tenths of a percent per degree above that. On a 40 degree Perth day a panel can lose in the region of 10 to 18 percent of its output to heat. Though the strong summer sunshine more than compensates overall.
Do solar panels work better in summer or winter?
Summer, comfortably. Although heat lowers efficiency slightly, summer days are much longer. The sun is much stronger. So a Perth system produces far more energy in summer than in winter. The heat trims the peak. But it does not come close to outweighing the extra sunshine.
Do heatwaves damage solar panels?
No. Panels are built to operate in high temperatures. They are not damaged by a normal Perth heatwave. They simply run at slightly lower efficiency while very hot. Quality panels with a low temperature coefficient lose less output in those conditions.
Why does my solar produce less on very hot afternoons?
Because the panels get hot enough to lose some efficiency, even in full sun. A cell temperature of 65 to 70 degrees on a 40 degree day reduces output. This is compared with the same sunshine at a milder temperature. It is a normal, expected effect rather than a fault. Better panels minimise it.
Get Panels Built for the Perth Sun
Perth heat is exactly why panel quality and good design matter. Choosing a system that holds its output through a hot summer is precisely what a Positive Energy Solutions consultation is for.
Talk to the local team about solar built for Perth conditions: request your quote from Positive Energy
About the Author
Jason Wiktorowicz
Sales Manager, Positive Energy Solutions | Perth, WA
Jason has been at the centre of Western Australia’s energy transition for over a decade. As Orchestration Lead on Project Symphony, WA’s largest virtual power plant pilot, and Stream Lead on Project Encore, he worked directly with AEMO, Western Power and Energy Policy WA. He shaped how distributed energy resources connect and operate on the SWIS. That work included developing and rolling out CSIP-AUS, now mandatory for all new WA grid connections. He also led Emergency Solar Management. It was the first program of its kind in WA. VPP for Schools provided direct market benefits through Supplementary Reserve Capacity. REBAR was the WA Residential Battery Rebate scheme.
At Positive Energy Solutions, Jason leads sales with a focus on system design accuracy and long-term performance. Positive Energy Solutions installs solar and battery systems, EV chargers and heat pumps. We hold partner accreditations with Fronius, SigEnergy, iStore and SunPower.
10-year installation workmanship warranty. Positive Energy Protection, powered by Omnidian, performance monitoring included on all systems.
