Path-Q Solar

How can I tell whether panel degradation is unusually high?

Answer

Look for a persistent decline in normalized, weather-adjusted production that exceeds the panel's product-specific expectations after ruling out soiling, shading, outages, inverter problems, wiring faults, and monitoring errors. A single low month cannot establish excessive degradation.

Key points

  • Compare the same array or panel group over multiple years using consistent measurement boundaries.
  • Use commissioning data, independent testing, or module-level data when available.
  • Check whether all panels declined similarly or only particular strings or modules are affected.

What it depends on

  • Reliable baseline and long-term production data
  • Panel warranty degradation terms
  • Weather, shading, maintenance, and equipment history

Risks and trade-offs

  • Poor normalization can mistake weather or system downtime for degradation.
  • Module-level testing may cost money and may not be justified for a small apparent decline.

Information you may need

  • Panel model, warranty, and commissioning records
  • Multi-year production and irradiance or weather data
  • Maintenance, shading, outage, and inverter records

Your next step

What to do next

Normalize multi-year output and request installer or manufacturer testing if the sustained decline materially exceeds the product expectation.

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SQ01798