What is solar panel degradation?
Solar panel degradation is the slow fall in output as panels age, typically around 0.5% a year. That means after 25 years a panel still produces roughly 85% of its original output. Performance warranties guarantee a minimum output (often 85% to 90%) at year 25, so the gentle decline is predictable and built into payback estimates.
What degradation means in practice
A small annual drop adds up slowly, not suddenly. A system generating 4,000 kWh in year one might generate around 3,400 kWh in year 25, still a substantial output. Most savings happen well within the warranty period, and the panels keep working beyond it.
Check the performance warranty
- Look for a 25-year performance warranty (or longer).
- Check the guaranteed output at year 25 (often 85% to 90%).
- A lower first-year degradation step is a sign of quality.
- The product (defect) warranty is separate, often 12 to 25 years.
Frequently asked questions
- Do solar panels stop working after 25 years?
- No. 25 years is the typical warranty period, but panels keep generating at a slightly reduced output well beyond it.
- How fast do panels lose output?
- Around 0.5% a year for quality panels, after a slightly larger drop in the first year.
Related questions
Indicative estimates based on UK average data. Last updated 27 May 2026.