Clear answer, explained.
The clearest signal of underperformance is a consistent gap between actual monthly generation — available from the system's monitoring portal — and the projected output from the original project model. Most commercial solar projects include a production forecast on an annual or monthly basis as part of the financial analysis. If actual generation is running 10% or more below this forecast over several billing cycles, there is likely a fault or maintenance issue requiring attention.
Underperformance causes range from minor to significant. Common causes include panel soiling accumulation, shading from new obstructions, string or wiring faults, inverter degradation or failure, and module-level defects identified through thermographic inspection. Monitoring errors — where the system appears to be producing normally but data is incorrect — also occur and can mask real faults.
Systems without active monitoring are particularly vulnerable to extended underperformance because there is no automatic alert when production drops. For many system owners, a performance review is the first time they discover that generation has been below design specifications for months or years — representing cumulative financial loss that could have been avoided with earlier detection. If you do not have access to production data or are uncertain whether your system's output matches its design, a professional performance review is the appropriate starting point.
What this means in practice.
- Compare actual generation to original project model each month
- A sustained gap of 5–10%+ below forecast warrants investigation
- Common causes: soiling, shading, wiring faults, inverter issues, module defects
- Systems without monitoring are particularly vulnerable to extended faults
- Monitoring errors can mask real underperformance
- Professional performance review is the starting point for unknown systems
Best-fit environments.
- Systems more than 3–5 years old without recent performance review
- Facilities that acquired a property with an existing solar system
- Systems where production data appears lower than expected
- Any installation without active real-time monitoring and fault alerts
