Solar · Maintenance
What are hot spots and PID, and is a thermal-imaging survey worth it?
Short answer
Hot spots are cells running much hotter than their neighbours because of cracks, shading or failed bypass diodes; PID is voltage-driven leakage that slowly cuts output. Neither is visible by eye. A drone or handheld thermal survey in strong sun finds them quickly and is worth it when output drops unexpectedly or before a warranty claim.
Last checked 24 September 2026 · 1 source
In more detail
- UK study of 3.3 million modules (mainly large assets): 36.5% had thermal defects; ~900,000 modules with hotspots and ~250,000 with heated substrings; defective modules averaged 21.7 C hotter.
- Assets with more thermal defects showed higher degradation rates in the same study.
- Thermal imaging needs strong irradiance (usually >600 W/m2) and the system operating; electroluminescence (EL) imaging shows micro-cracks but needs specialist kit.
- PID is more likely on older p-type modules in high-voltage strings; some inverters offer PID recovery functions.
- Evidence for a warranty claim usually needs the thermal image with irradiance recorded, plus string I-V or flash test.
The facts, dated
- 01Share of UK PV modules surveyed with thermal defects — 36.5 %
market_data · UK · checked 24 September 2026 · nature.com
- 02Average temperature increase on defective modules — 21.7 C
market_data · UK · checked 24 September 2026 · nature.com
Sources
- nature.com — www.nature.com/articles/s41529-023-00331-y
Last checked: 24 September 2026