How Much Do Solar Panels Degrade Per Year? (UK Real-World Data)
Honest answer + the longer story behind the question.
60-second answer
Modern Tier-1 N-type TOPCon solar panels degrade 1.0% in year 1, then 0.35–0.4% per year thereafter. After 25 years, panels are at 87–89% of original output. After 30 years, ~85%. Real-world UK degradation closely matches manufacturer specs — National Grid ESO and BEIS monitoring data show actual degradation tracks within 0.05% of warranty curves on properly installed Tier-1 systems.
UK real-world degradation data
The IEA PVPS Task 13 lifecycle assessments and BloombergNEF’s annual PV reliability scorecards track real-world degradation across thousands of UK and European commercial PV systems. Key findings (2025 update):
- P-type PERC panels (2018–2022 era): 0.5–0.7%/year actual
- N-type TOPCon panels (2023–current): 0.35–0.4%/year actual
- HJT panels (2024–current premium): 0.25%/year actual
- Bifacial premium (REC, Meyer Burger): 0.25%/year actual
For a UK factory installed in 2026 with TOPCon panels, expect to be at 87–88% of nameplate at year 25 — very close to warranty.
Why first-year degradation is higher
First-year degradation runs ~1% across all crystalline silicon technologies due to two effects: Light-induced degradation (LID) — boron-oxygen complexes in silicon respond to UV exposure, stabilising within a few months; and cell encapsulant settling — EVA encapsulant compresses slightly under thermal cycling. After year 1 the curve flattens to the 0.35–0.5%/year range.
What accelerates degradation
Three things shorten panel life materially:
- Excessive heat — panel surfaces above 70°C accelerate encapsulant breakdown. Mitigation: airgap mounting (5cm clearance), pale roof underlayer.
- Soiling and bird droppings — long-term hot-spot damage where dirt creates localised shading. Mitigation: annual cleaning at sites with high soiling exposure.
- Manufacturing defects — rare on Tier-1 brands; common on Tier-3. Mitigation: only spec Tier-1 modules (ask the installer to confirm this).
What to model in financial projections
For UK factory installs, a PVSyst yield model that assumes 1% first-year degradation, 0.4%/year thereafter is conservative against modern Tier-1 specs. That means 25-year savings, IRR and NPV figures built on it are likely to be slightly under-stated against real-world performance. Ask the installer which degradation assumptions sit behind their quoted figures.
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