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How much do solar panels degrade each year?

Short answer

UK field studies measure roughly 0.5% to 1% output loss a year: a Sheffield Solar analysis of over 7,000 UK systems found about 0.8% a year, and a ten-year study of UK and Irish homes found 0.4% to 1.0%. Current warranties promise less, around 0.35% to 0.4% a year after the first year.

Last checked 24 September 2026 · 3 sources

In more detail

  • Sheffield Solar (2015, >7,000 UK systems): mean degradation -0.8 +/-0.1 %/yr; mean performance ratio 83%.
  • Dhimish (2020, 7 residential systems, 10 years): Ireland -0.4 to -0.6 %/yr; England -0.7 to -0.9 %/yr; Aberdeen/Glasgow -1.0 %/yr; average -0.74 %/yr.
  • Those studies cover older (pre-2015) modules; modern n-type TOPCon/HJT/back-contact modules carry warranties of 0.35-0.40 %/yr after year 1.
  • Monitoring apps rarely separate degradation from weather: compare kWh per kWp for the same month across years, or use a neighbouring reference.
  • Faster loss (several % per year) points to a fault: PID, hot spots, cracked cells, failing optimiser or a string down.

The facts, dated

  1. 01
    Mean degradation of >7,000 UK distributed PV systems — -0.8 +/-0.1 %/yr

    market_data · UK · checked 24 September 2026 · researchgate.net

  2. 02
    Average degradation of 7 UK/Irish residential systems over 10 years — -0.74 %/yr

    market_data · UK · checked 24 September 2026 · eprints.whiterose.ac.uk

  3. 03
    Jinko Tiger Neo linear power warranty: 0.40%/yr, 87.4% after 30 years — 0.40 %/yr

    manufacturer · n/a · checked 24 September 2026 · jinkosolarcdn.shwebspace.com

What we saw in the field

[QA review 2026-09-24] I-9 AGREES (conservative for current modules). | Earlier notes: Installer claim '80-85% output guaranteed after 25 years' matches older warranties (e.g. 80.7-84.8%); current premium warranties are higher (87.4% at 30 years Jinko; 84.8-89.4% JA Solar; AIKO 88.85% at 30 years). Measured UK degradation (~0.7-0.8%/yr) would leave ~80-83% after 25 years for older modules, so the claim is realistic for older kit and conservative for new.

Sources

Last checked: 24 September 2026