Solar Panel Degradation Rate: What to Expect Over 25 Years

Here's an uncomfortable fact most solar installers don't discuss: your solar panels will never produce as much electricity 10 years from now as they do today. This inevitable decline is called degradation, and it's completely normal.

Understanding degradation helps you know whether your system is aging normally or experiencing premature failure. It also helps you predict long-term production losses and plan maintenance before problems compound.

What Is Solar Panel Degradation?

Degradation is the gradual loss of a solar panel's ability to convert sunlight into electricity. Several factors cause this:

• UV exposure damages encapsulant materials over decades
• Moisture ingress causes corrosion of internal components
• Thermal cycling — repeated heating and cooling — creates microcracks
• Internal ion migration in the silicon itself reduces carrier mobility

This is not a defect — it's the inevitable result of exposure to the elements over 25+ years. No panel escapes it.

Expected Degradation Rates by Panel Type

Monocrystalline panels (most common): 0.7-0.8% per year degradation. After 25 years, a 400W panel would produce roughly 330W — still usable but 18% less than new.

Polycrystalline panels (older technology): 0.8-0.9% per year. Slightly worse than monocrystalline but still within warranty ranges.

Thin-film panels (CdTe, CIGS): 1.0-2.0% per year initially, with degradation rates slowing over time. They stabilize after 3-5 years.

The good news: manufacturers warrant panels against more than this expected degradation. Most warranties guarantee 90% output after 10 years and 80% after 25 years.

Light-Induced Degradation (LID)

A quirk of older silicon panels: they lose 2-3% of their output in the first few weeks of operation under sunlight. This "light-induced degradation" or LID is well understood and factored into manufacturer ratings.

Newer panels use hydrogen-passivation treatments that minimize LID to less than 1%. This is one of the main improvements in panel technology over the past decade.

If you're checking your system's first-month production, expect it to be slightly below the manufacturer's rated output. That first dip is LID, not a sign of problems.

Potential Induced Degradation (PID)

PID is a phenomenon where high voltage in the panel system causes ions to migrate, degrading the panel faster than normal. This can happen in large systems with many panels in series (which creates high voltage) and is more common in humid climates.

Good news: modern inverters (SolarEdge, Enphase) are designed with PID mitigation features that reverse ion migration and prevent this degradation mode. If you have a modern system with optimizers or microinverters, PID is not a concern.

Older string inverter systems without PID mitigation might experience this. If your system is 8+ years old with a string inverter, PID could be a factor in faster-than-expected degradation.

How to Measure Your Own Degradation

You can estimate your system's degradation rate by comparing production across the same time periods in different years.

Simple method: Compare this January's production to last January's production (accounting for weather variations). Then scale to get an annual degradation rate. This is imperfect but gives you a ballpark estimate.

Better method: Use SolarDoctor. We track your actual production against theoretical expectations (which accounts for weather) and calculate your system's real degradation rate automatically. We flag it if degradation is faster than expected.

When Degradation Is Too Fast

Degradation over 1.5-2% per year is a red flag. Causes of accelerated degradation include:

• Moisture ingress from water damage, cracked panels, or failed sealants
• Delamination — panels separating into layers
• Snail trails — discoloration from cell interconnect corrosion (cosmetic but indicates moisture intrusion)
• Micro-cracks from impacts, thermal stress, or manufacturing defects

If you suspect faster-than-normal degradation, get a professional infrared scan of your array. Failing panels show up as hotter spots on thermal images.

The Bottom Line

0.7-0.8% annual degradation for modern monocrystalline panels is normal and expected. Your 25-year warranty accounts for this decline. If your panels are degrading faster than this, something is wrong and you may have a warranty claim.

Don't assume your system is degrading normally without checking. Most homeowners never measure it, so they don't notice accelerated degradation until years of production have been lost.