Solar Panel Degradation: How Much Output Do You Lose?

All solar panels gradually lose output over time. This is called degradation, and it's a normal, expected part of solar panel aging. The good news is that modern panels degrade very slowly — losing less than half a percent per year. Here's what that means in practice.

What Causes Degradation?

Solar panel degradation is primarily caused by:

Light-Induced Degradation (LID)

When panels are first exposed to sunlight, a chemical reaction occurs in the silicon cells that slightly reduces their efficiency. This happens in the first few days to weeks and accounts for a 1–3% output loss. LID is a one-off event — it doesn't continue after the initial exposure.

Some premium panels use n-type silicon cells (like the LONGi Hi-MO 6) which have significantly lower LID than traditional p-type cells.

Potential-Induced Degradation (PID)

High system voltages can cause a gradual loss of performance in certain conditions (humidity, temperature). Modern panel designs and proper system earthing minimise PID risk. Quality inverters with PID prevention features essentially eliminate this concern.

Thermal Cycling

Daily temperature changes (heating during the day, cooling at night) cause microscopic expansion and contraction in panel materials. Over years, this can create micro-cracks in cells that slightly reduce output.

UV Exposure

Ultraviolet light gradually degrades the encapsulant material that protects the cells. High-quality panels use UV-resistant encapsulants that minimise this effect.

Moisture Ingress

If the panel's edge seals or backsheet deteriorate, moisture can enter and accelerate cell degradation. Well-manufactured panels with robust sealing have minimal moisture ingress over their rated lifespan.

How Much Output Do You Actually Lose?

For a typical 4kW system generating 3,600kWh in year one:

After 25 years, you're still generating over 90% of the original output. After 30 years, nearly 89%. The panels don't stop working at 25 years — they just produce a bit less than when new.

Manufacturer Warranty Guarantees

Panel warranties typically include a performance guarantee:

Premium panels from brands like LONGi, Trina, and Canadian Solar now offer 30-year performance warranties guaranteeing 87.4% output at year 25 and 84.8% at year 30.

If your panels degrade faster than the warranty guarantees, you have a valid warranty claim against the manufacturer.

Comparing Panel Types

Degradation rates vary by technology:

The trend is clear: newer n-type technologies degrade more slowly than older p-type designs. If long-term output retention is important to you, n-type panels are worth the modest price premium.

GivEnergy All-in-One 5kW Hybrid Inverter

£1,200

rated power kw

5

max pv input kw

7.5

mppt channels

2

battery voltage v

48V

View on Amazon

Affiliate link — we may earn a small commission at no extra cost to you

What About the Inverter?

While panels degrade slowly, the inverter is a separate component with a different lifespan. String inverters typically last 10–15 years before needing replacement. Microinverters and optimisers last 20–25 years.

Inverter failure isn't degradation — it's a complete stop in generation until replaced. Budget for one inverter replacement over the 25–30 year panel lifespan.

JA Solar JAM54D41 450W N-type TOPCon

£82

watt peak

450

efficiency pct

22.8

dimensions mm

1722 x 1134 x 30

weight kg

21.5

View on Amazon

Affiliate link — we may earn a small commission at no extra cost to you

Financial Impact of Degradation

Degradation is already factored into most payback calculations. Over a 25-year system life, the cumulative output is approximately 93–95% of what it would be without any degradation.

For a 4kW system:

• Without degradation (theoretical): 90,000kWh over 25 years
• With 0.4% annual degradation: approximately 84,500kWh over 25 years
• Difference: 5,500kWh (~6%) over the full 25 years

At 24p/kWh, that's approximately £1,320 less over 25 years — or £53 per year on average. Significant but not dramatic, and already accounted for in reputable installers' generation estimates.

Can You Reduce Degradation?

There's limited control over the physical degradation process, but you can:

• Choose quality panels — Premium brands with lower degradation rates and better quality control
• Ensure proper installation — Correct mounting reduces thermal stress and moisture risk
• Keep panels clean — Soiling isn't degradation, but it reduces output similarly. Regular maintenance keeps panels performing at their degraded maximum
• Monitor performance — Catch actual faults early rather than dismissing lost output as "normal degradation"

Share this article