Solar panel degradation is the slow, inevitable decline in the amount of electricity a panel produces over its lifetime. It happens to every solar system, regardless of brand or installation quality. The question isn't whether your panels are degrading — they are — but whether they're degrading at a normal rate, or at a rate that signals a fault you should act on.

This guide covers the science behind degradation, what normal looks like, which failure modes accelerate it, how different brands compare, and how to tell if your system has a problem worth investigating.

What causes solar panels to degrade?

Solar cells are semiconductor devices made primarily from silicon. Over time, several physical and chemical processes gradually reduce their ability to convert sunlight into electricity:

UV-induced degradation is the primary driver of normal ageing. Sustained ultraviolet exposure causes the encapsulant material surrounding the silicon cells to yellow and crack, reducing the amount of light that reaches the cells. This process is slow and largely unavoidable.

Thermal cycling — the repeated expansion and contraction of panel materials as they heat during the day and cool at night — gradually stresses the microwires (busbars) that carry current through the panel. Over thousands of cycles, microcracks can develop in cells and connections.

Potential-induced degradation (PID) is an electrochemical failure mode where voltage stress between the cells and the aluminium frame causes ion migration that progressively reduces cell efficiency. It's accelerated by high humidity and is a particular concern for coastal installations.

Light-induced degradation (LID) occurs primarily in the first few hours to days of a panel's exposure to sunlight. Boron-oxygen defects in the silicon become electrically active, causing an initial efficiency loss of 1–3%. Most panels recover to a stable baseline after this initial period.

Delamination occurs when the bond between the glass, encapsulant, and back sheet breaks down, allowing moisture ingress. This accelerates other degradation modes and is particularly visible as bubbles or yellowing beneath the glass surface.

What's a normal degradation rate?

The industry benchmark comes from the National Renewable Energy Laboratory (NREL), whose meta-analysis of over 2,000 real-world degradation measurements found a median rate of 0.5% per year for crystalline silicon panels.

In practice, this means:

Years in service	Expected output (at 0.5%/year)
1 year	99.5% of original
5 years	97.5% of original
10 years	95% of original
20 years	90% of original
25 years	87.5% of original

Most manufacturers warrant their panels to produce at least 80% of original rated output at 25 years, which implies a maximum degradation rate of around 0.8% per year. Systems degrading faster than 1% per year are exhibiting above-normal decline and warrant investigation.

How warranty degradation claims work

Understanding the difference between your panel's product warranty and its performance warranty is important for knowing what protection you actually have.

The product warranty (typically 10–12 years) covers manufacturing defects — physical failures like delamination, frame damage, or junction box failures.

The performance warranty (typically 25 years) guarantees the panel will produce at least a specified percentage of its original rated output. Most manufacturers use a tiered structure:

Year 1: no more than 2–3% degradation from rated output
Years 2–25: no more than 0.55% per year (cumulative)
At year 25: at least 80% of original rated output

To make a performance warranty claim, you typically need:

Proof of system registration with the manufacturer
Monitoring data showing sustained underperformance
A professional performance test report, usually from a certified inspector

Which factors accelerate degradation?

Not all installations age at the same rate. Several conditions can push degradation well above the 0.5% median:

Climate is the most significant external factor. High-temperature climates with large day-night temperature swings (like inland Australia and the US Southwest) subject panels to more severe thermal cycling. Hot, humid coastal climates accelerate PID and junction box degradation.

Panel quality matters more than brand perception. Premium monocrystalline panels from established manufacturers typically maintain the 0.5% median. Budget PERC panels — particularly from less established suppliers — can degrade at 0.7–1% per year or faster under challenging conditions.

Mounting and ventilation affect operating temperature. Panels mounted flush against a dark roof with no air gap can run 20°C hotter than free-standing rack systems. Every 10°C increase in operating temperature is estimated to reduce long-term panel life by a meaningful fraction.

Soiling doesn't cause permanent degradation, but accumulated dirt, bird droppings, and lichen growth reduce output in a way that can be mistaken for degradation. If panels haven't been cleaned in 2+ years, clean them before concluding degradation is the cause of reduced output.

How different technologies compare

Standard PERC monocrystalline (the most common residential panel technology) typically degrades at 0.5–0.6% per year. This is the baseline.

TOPCon (Tunnel Oxide Passivated Contact) — used in Jinko Tiger Neo, LONGi Hi-MO 6, and others — shows lower degradation rates in early data, typically warranted to 0.4% per year. The technology is newer, so long-term real-world data is still accumulating.

HJT (Heterojunction) — used in REC Alpha and some Panasonic panels — has the lowest temperature coefficient and strong early degradation data, also warranted around 0.25–0.3% per year. Considered the most degradation-resistant technology currently available at scale.

Older polycrystalline panels (common in pre-2018 installations) typically degrade at 0.6–0.8% per year — faster than modern monocrystalline.

Brand comparison: degradation performance

Independent testing organisations including PVEL (PV Evolution Labs) and Fraunhofer ISE publish annual degradation testing scorecards. Based on available data:

Brand / Series	Cell type	Warranted annual degradation
SunPower Maxeon	Maxeon	0.25%
REC Alpha	HJT	0.25%
LONGi Hi-MO 6	TOPCon	0.40%
Jinko Tiger Neo	TOPCon	0.40%
Canadian Solar HiKu	PERC	0.55%
JA Solar DeepBlue	PERC	0.55%
Standard PERC (industry)	PERC	0.55%

Note that "warranted" rates are the worst-case guarantee — most panels in good conditions outperform the warranty threshold. Real-world median rates from field studies tend to cluster around 0.5% for PERC and 0.3–0.4% for HJT/TOPCon.

Normal degradation vs. a genuine fault

The most important skill for a solar owner is distinguishing between expected age-related decline and a problem that warrants professional investigation.

Normal degradation looks like:

Gradual, consistent output decline across all panels
Decline in line with the warranty curve (0.5–0.8% per year)
Decline that correlates with system age rather than any specific event
Performance broadly matching regional benchmark data for similar systems

A fault looks like:

Output dropping suddenly (not gradually)
One or more panels producing significantly less than their neighbours
Decline rate exceeding 1% per year
Visible physical damage: bubbling, discolouration, cracking, delamination
Inverter fault codes appearing alongside performance decline

The most common mistakes owners make are:

Assuming seasonal output variation is degradation (winter output is always lower)
Ignoring gradual decline because it's not dramatic enough to notice day-to-day
Not comparing output to the same month in previous years — the only valid comparison

How to check your system's degradation rate

Without professional equipment, you can estimate your degradation rate using your monitoring data:

Find your system's Year 1 output in kWh (from your installer, monitoring app, or utility bills)
Find your current annual output for the same 12-month period
Calculate: (Year 1 kWh - Current kWh) / Year 1 kWh × 100 = total % decline
Divide by system age in years to get approximate annual degradation rate

Example: A 6kW system that produced 8,400 kWh in year 1 and now produces 7,980 kWh in year 8 has declined by 5%, or approximately 0.6% per year — within normal range.

Adjustments to make: compare like-for-like weather years where possible, and account for any soiling events or panel cleaning that might distort the comparison.

When to get a professional assessment

A professional thermal imaging inspection is worth arranging if:

Your calculated degradation rate exceeds 1% per year
Any individual panel consistently produces 10%+ less than adjacent panels
You notice any visual changes to panels (discolouration, bubbling, cracks)
Your system is more than 10 years old and has never been inspected
You're planning to sell your property and want to document system condition

Thermal imaging identifies hotspots, microcracks, and delamination that are invisible to the naked eye and don't always show up clearly in monitoring data. A full inspection typically costs £150–£400 in the UK or $200–$500 in Australia, depending on system size and access.

The economics of acting early

Degradation left unchecked compounds. A single hotspot that reduces one panel's output by 20% has a limited impact in isolation — but if the fault propagates to adjacent cells, or if a failing junction box causes the whole string to underperform, the economic loss quickly outweighs the cost of an inspection and repair.

The general principle: the earlier a fault is identified, the cheaper it is to fix, and the more of your warranty coverage remains active.

For most residential solar owners, an inspection every 5 years is a reasonable baseline. For coastal installations, systems showing any anomalies in monitoring data, or systems approaching the end of their product warranty, more frequent checks make financial sense.

Solar Panel Degradation: The Complete Guide