Do Solar Panels Lose Efficiency Over Time?
Yes, solar panels lose a small amount of efficiency each year. Most panels degrade by 0.3-0.5% annually. After 25 years, they still produce around 85-90% of their original output. This is normal, and factored into every solar investment.
Key Takeaways
- Solar panels typically degrade 0.3-0.5% per year, which is entirely normal.
- After 25 years, most panels still produce 85-90% of original output.
- Manufacturer performance warranties guarantee minimum output levels over time.
- Sudden output drops suggest damage, not normal degradation, and need investigating.
- Quality installation and regular maintenance help panels perform close to expected rates.
Below, we explain exactly why this happens, and what it means for you.
What is Solar Panel Degradation?
Solar panel degradation is the gradual, natural decline in a panel’s power output over time.
It’s not a fault or defect. Every solar panel degrades slightly, year after year.
Think of it like a phone battery. It still works after years of use, just slightly less efficiently.
How Much Efficiency Do Solar Panels Actually Lose?
Most modern panels lose between 0.3% and 0.5% of output per year.
Example: A panel rated at 400W in year one produces roughly 398W by year two.
Over 25 years, total degradation typically reaches 10-15%. That means panels still work well decades later.
| Panel Age | Typical Output Remaining |
| Year 1 | 98-99% |
| Year 5 | 96-97% |
| Year 10 | 93-95% |
| Year 15 | 90-92% |
| Year 20 | 87-89% |
| Year 25 | 84-87% |
These figures reflect standard monocrystalline panels, the most common type installed across the UK today.
Why Do Solar Panels Degrade Over Time?
Several natural factors cause gradual efficiency loss.
a. UV exposure. Constant sunlight slowly affects the panel’s materials over many years.
b. Temperature cycling. Panels expand and contract daily with heat changes. This causes minor wear over time.
c. Microscopic cracking. Tiny cracks can form in solar cells from weather and thermal stress.
d. Moisture ingress. Over decades, tiny amounts of moisture can affect internal components slightly.
None of these cause sudden failure. They simply cause slow, predictable decline.
Do All Solar Panels Degrade at the Same Rate?
No, degradation rates vary by panel type and manufacturing quality.
a. Monocrystalline panels: Typically 0.3-0.4% annual degradation. The most efficient, longest-lasting option.
b. Polycrystalline panels: Typically 0.4-0.5% annual degradation. Slightly less efficient overall.
c. Thin-film panels: Can degrade faster, sometimes 0.5-1% annually, though less common in UK residential installs.
Higher quality panels, from established manufacturers, generally degrade more slowly and predictably.
What’s a Normal Solar Panel Warranty for Degradation?
Manufacturers provide “performance warranties” covering long-term output specifically.
Most reputable brands guarantee:
- 90% output after 10 years
- 80-85% output after 25 years
According to Solar Energy UK, the industry body for UK solar, these performance guarantees are now standard across accredited manufacturers.
Always check this warranty separately from the general product warranty, which covers defects instead.
Does Degradation Affect Your Savings?
Yes, but only gradually, and it’s already factored into typical savings estimates.
A well-installed system still delivers strong savings for 25+ years. Even with expected degradation included.
Real example: A Welton Renewables client in Bedford installed a 4kW system eight years ago. Recent monitoring shows output at roughly 96% of original capacity, in line with expected industry figures.
Their annual savings remain strong, closely matching original projections from installation.
Can You Slow Down Solar Panel Degradation?
Not entirely, since some degradation is unavoidable. But proper care helps panels perform closer to expected rates.
Steps that help:
- Schedule regular cleaning, especially in dusty or rural areas.
- Get annual inspections to catch issues early.
- Choose quality panels from established, accredited manufacturers.
- Ensure correct installation angle and ventilation underneath panels.
- Monitor performance through an app or inverter display.
Poor installation causes far more efficiency loss than natural degradation ever does.
What’s the Difference Between Degradation and Damage?
These are often confused, but they’re very different issues.
Degradation is slow, predictable and expected. It happens to every panel, regardless of quality.
Damage is sudden and unexpected. Caused by storms, debris, faulty installation or manufacturing defects.
If output drops suddenly, rather than gradually, this suggests damage. Not normal degradation.
What to do: Contact your installer promptly if you notice a sharp performance drop.
How Do You Know If Your Panels Are Degrading Normally?
Most modern solar systems include monitoring apps. These track daily and yearly output.
Compare your system’s output year-on-year. A gentle decline of under 1% annually is normal and expected.
A sudden or sharp drop suggests a fault, not degradation. This needs investigating promptly.
Welton Renewables offers performance checks for clients concerned about unexpected output changes.
Are Solar Panels Still Worth It Despite Degradation?
Yes, absolutely. Degradation is minor compared to the savings generated over a panel’s lifetime.
Even at 85% output after 25 years, panels still generate substantial free electricity. Far outweighing the gradual decline.
Most UK homeowners recoup installation costs within 6-10 years. Everything after that is pure savings, degradation included.
Frequently Asked Questions
1. How long do solar panels last before they stop working?
Most solar panels last 25-30 years, continuing to generate electricity even after warranty periods end.
2. Do solar panels degrade faster in the UK climate?
Not significantly. UK weather conditions fall within normal ranges panels are designed and tested to handle.
3. What percentage of efficiency do solar panels lose per year?
Most panels lose 0.3-0.5% of output annually, a normal rate of decline.
4. Should I replace solar panels after 20 years?
Not necessarily. Most panels still perform well after 20 years, often producing 87-89% of original output.
5. Does cleaning solar panels reduce degradation?
Regular cleaning helps maintain performance, though it doesn’t stop natural degradation, which is unavoidable.
6. Do solar panel warranties cover degradation?
Yes, performance warranties specifically guarantee minimum output levels, typically at 10 and 25-year milestones.
7. Can hot weather speed up solar panel degradation?
Extreme heat can slightly increase degradation rates, though UK temperatures rarely cause significant additional wear.
8. Is a sudden drop in solar output always degradation?
No. Sudden drops usually indicate damage or a fault, and should be checked by a professional promptly.
