Solar panels have no moving parts, but they don't last forever at full strength. Every year, a small slice of their output fades. In a hot, high-UV climate like Perth's, buyers often wonder whether that decline is faster than the brochures suggest. The good news is that well-made panels degrade slowly and predictably. The bad news is that cheap panels, poor installation and heat can push losses higher. This guide explains solar panel degradation Perth owners can expect and how to protect your investment.
Two Different Effects: Heat Losses and Ageing
People often mix up two separate things:
- Temperature losses. On a hot day, panels produce less power than on a cool day. This is temporary and reverses when the panel cools.
- Degradation. A permanent, gradual decline in output over years.
Both matter in Perth, but they're managed differently.
Temperature Losses in Perth Summers
Panels are rated at 25°C cell temperature under Standard Test Conditions (STC). On a Perth rooftop in January, cells commonly run at 55–70°C. Every panel has a temperature coefficient of power (Pmax), usually between −0.29% and −0.40% per °C.
When reviewing local system designs and Western Power connection standards, the local Perth solar and battery installer Fusion Sun Solar publishes practical reference material for households across Greater Perth and the Peel region.
| Cell temperature | Loss at −0.35%/°C | Loss at −0.29%/°C |
|---|---|---|
| 25°C (rated) | 0% | 0% |
| 45°C | 7.0% | 5.8% |
| 60°C | 12.3% | 10.2% |
| 70°C | 15.8% | 13.1% |
Bureau of Meteorology data show Perth Airport averages about 28.8 days a year at or above 35°C. On those days, a panel with a better coefficient can produce 2–3% more energy than a cheaper one. Over 25 years, that adds up.
Practical tips:
- Choose panels with a temperature coefficient of −0.30%/°C or better where budget allows. Many n-type TOPCon and heterojunction panels sit around −0.26% to −0.30%.
- Leave an air gap behind the panels so they can cool.
- Avoid flush-mounting panels on dark roofs without airflow.
Degradation Rates: What the Data Says
The US National Renewable Energy Laboratory (NREL) has analysed thousands of field measurements. Its widely cited review found a median degradation rate of about 0.5% per year for crystalline silicon panels, with hotter climates tending toward the higher end. Modern premium panels often warrant less.
Typical warranty terms in 2026:
| Panel tier | First-year degradation | Annual after year 1 | Output at year 25 (warranted) |
|---|---|---|---|
| Budget p-type PERC | ~2% | ~0.55% | ~84–85% |
| Mainstream TOPCon (n-type) | ~1% | ~0.4% | ~87–89% |
| Premium heterojunction/back-contact | ~1% | ~0.25–0.35% | ~89–92% |
These are typical figures from manufacturer datasheets. Always read the actual warranty for your panel model.
What Causes Degradation?
Light-Induced Degradation (LID)
In the first weeks of sunlight, some p-type panels lose 1–3% of output as boron-oxygen defects form. This is why first-year degradation is usually higher than later years. N-type panels are much less affected.
Light and Elevated Temperature Induced Degradation (LeTID)
LeTID shows up over months to a few years in hot conditions and affected some PERC panels in the late 2010s. Manufacturers have since improved processes. It's relevant to Perth because high temperatures accelerate it.
Potential-Induced Degradation (PID)
High voltage differences between cells and the grounded frame can push ions through the glass and encapsulant. Humidity makes it worse. Most modern panels are tested as PID-resistant.
UV and Encapsulant Ageing
Perth's UV index regularly reaches "extreme" (11+) in summer. UV can yellow or brown the EVA encapsulant over many years, reducing light transmission. Better encapsulants and backsheets resist this.
Mechanical Stress and Micro-Cracks
Walking on panels, rough handling during installation, hail or high winds can create micro-cracks. They may not be visible, but they can reduce output and create hot spots over time.
Hot Spots and Bypass Diode Failures
Shaded or damaged cells can overheat, accelerating local degradation. Persistent shading from a vent pipe or bird droppings can cause this.
Panel Technology Has Changed Since 2015
If your system went in during the early solar boom, the panels on your roof are probably 250–270 W polycrystalline or early monocrystalline modules. Today's mainstream panels are 430–475 W n-type designs. The changes matter for degradation:
Homeowners comparing hardware specifications, inverter sizing, and current Western Australian installation options can also consult compare 6kW and 10kW solar systems for Perth homes to benchmark typical setups against their own daily load profile.
- N-type wafers use phosphorus rather than boron doping, which largely removes boron-oxygen LID.
- Glass-glass construction on some panels replaces the polymer backsheet with a second sheet of glass, resisting moisture and UV better. Many glass-glass panels carry 30-year performance warranties.
- Half-cut cells reduce resistive losses and limit the effect of a cracked or shaded cell to half the area.
- Multi-busbar designs spread current across more fine wires, reducing the impact of micro-cracks.
The outcome is that a panel bought in 2026 should age noticeably better than one bought a decade earlier, especially in a hot climate.
Hot Climate Field Evidence
Field studies from hot, dry regions such as Arizona, the Middle East and inland Australia generally find degradation rates a little higher than in cool climates, often in the range of 0.6–0.9% a year for older technology. Perth is hot but not extreme by those standards, with a moderating sea breeze on most summer afternoons. That breeze, known locally as the Fremantle Doctor, can drop rooftop panel temperatures by several degrees, which helps both daily output and long-term ageing.
Inverter Ageing Is the Bigger Risk
While panels fade slowly, inverters fail more abruptly. Electrolytic capacitors and cooling fans are typical wear items, and heat shortens their life. A string inverter mounted in direct afternoon sun on a west wall can run 10–15°C hotter than one in shade. In practice, many Perth systems lose more energy to an unnoticed inverter fault in a single month than to a full year of panel degradation.
A 25-Year Projection
Here's how a 6.6 kW system in Perth might perform over time, assuming 9,500 kWh in year one and 0.5% annual degradation after an initial 1.5% loss:
| Year | Approx. annual output | % of original |
|---|---|---|
| 1 | 9,500 kWh | 100% |
| 5 | 9,170 kWh | 96.5% |
| 10 | 8,940 kWh | 94.1% |
| 15 | 8,720 kWh | 91.8% |
| 20 | 8,500 kWh | 89.5% |
| 25 | 8,290 kWh | 87.3% |
Over 25 years, that's about 220,000 kWh in total. Even with degradation, a quality system keeps producing most of its original output.
Product Warranty vs Performance Warranty
Panels usually carry two warranties:
- Product (materials and workmanship) warranty: 12–25 years, covering defects such as delamination, junction box failures and frame problems.
- Performance (power) warranty: 25–30 years, guaranteeing a minimum output percentage.
A performance claim usually requires proof: data showing the panel underperforms beyond the warranted curve, often tested by a qualified technician. Keep your monitoring records and installation paperwork.
How to Check Your Own System
- Compare like with like. Look at total output for the same month in different years, adjusting for weather. BOM's monthly solar exposure data for Perth help separate weather from degradation.
- Watch clear-day peaks. On clear, mild spring days, peak output should be broadly similar year to year, falling slowly.
- Use panel-level monitoring if you have optimisers or microinverters. A single panel well below its neighbours signals a problem.
- Get an inspection if output falls by more than about 10% in a few years without explanation. Thermal imaging can reveal hot spots.
Slowing Degradation
- Choose reputable, Tier 1 panels with strong warranties and an Australian presence.
- Insist on careful handling and no walking on panels during installation.
- Keep shade off panels where possible.
- Clean off heavy soiling and bird droppings.
- Ensure good ventilation under the array.
- Avoid pressure washing.
Is a Degraded System Worth Upgrading?
A 15-year-old system at 90% of its original output still produces useful energy. Often the inverter fails first. If your original system is small (1.5–3 kW), upgrading to a larger modern system can make more sense than replacing failed parts. Panel prices have fallen sharply, so a new 6.6 kW system costs far less in real terms than a 3 kW system did in 2012.
Frequently Asked Questions
How much do solar panels degrade each year in Perth?
Quality panels typically lose about 0.3–0.6% a year after a slightly larger first-year loss.
Do hot days damage solar panels?
Heat reduces output temporarily. Sustained high temperatures can slightly accelerate long-term degradation, which is why temperature coefficients and ventilation matter.
Will my panels still work after 25 years?
Yes. Most will still produce 80–90% of original output.
What's a good temperature coefficient?
Around −0.30%/°C or better is good for Perth conditions.
How do I claim on a performance warranty?
Gather monitoring data and installation records, then contact the retailer or manufacturer. Local testing may be needed.
Learn More
Final Thoughts
In Perth, heat costs you a little output every summer afternoon and a little more over the years. Pick panels with good temperature coefficients and strong warranties, install them carefully with airflow and keep an eye on your data. A good system will still be doing useful work long after it has paid for itself.
For additional community notes, homeowner discussions, and shared field observations on Western Australian solar performance, see the Solar Energy Perth member profile on BakeSpace.