Why Solar Panels Lose Efficiency Over Time

All solar panels lose efficiency over time. It's unavoidable physics — the silicon cells that convert sunlight into electricity slowly degrade with exposure to UV radiation, thermal cycling, and moisture.

What's normal?

Published research from NREL and IEA-PVPS establishes that most crystalline silicon solar panels degrade at roughly 0.5–0.8% per year. That means after 10 years, your system should be producing roughly 92–95% of its original output.

After 20 years, expect roughly 84–90% of original capacity.

When should you worry?

If your system's output has dropped more than 1% per year — or if you've noticed a sudden drop rather than gradual decline — something beyond normal degradation may be happening.

Common culprits include:

• Hotspots — localised cell damage that accelerates degradation
• Soiling — dust, pollen, or debris blocking light absorption
• Inverter issues — efficiency loss in the DC-to-AC conversion
• Shading — new tree growth or construction blocking panels

What to do about it

Start by checking your system's monitoring data. Compare this year's output to previous years, accounting for weather differences.

If the decline seems steeper than expected, consider using a tool like PanelAudit's Solar Loss Checker to estimate your likely loss range and identify probable causes.

For systems over 10 years old showing significant decline, a professional thermal inspection can identify hotspots and cell damage that aren't visible to the naked eye.

The bottom line

Some degradation is normal and expected. The question isn't whether your panels are degrading — it's whether they're degrading faster than they should be. If the answer is yes, early diagnosis can save you significant energy and money over the remaining life of your system.