Path-Q Solar

How should I compare measured solar production with the expected output?

Answer

Compare measured energy with the original site-specific model for the same period, using monthly or longer intervals and accounting for weather, shading, snow, soiling, outages, curtailment, and data gaps. Do not compare a single day's output directly with an annual estimate.

Key points

  • Use the same measurement boundary, such as inverter output versus utility-metered export.
  • Check monitoring timestamps, missing data, inverter availability, and system changes.
  • Normalize cautiously for sunlight and weather rather than relying only on a simple percentage.

What it depends on

  • Model assumptions and measurement location
  • Time period, weather, and site conditions
  • Monitoring accuracy and system uptime

Risks and trade-offs

  • Utility export is not the same as total solar production when the home uses energy directly.
  • Short periods and incomplete monitoring can produce misleading conclusions.

Information you may need

  • Original monthly production model
  • Inverter and utility data for matching dates
  • Outage, shading, snow, cleaning, and weather information

Your next step

What to do next

Create a month-by-month comparison using consistent data sources and investigate sustained unexplained shortfalls.

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SQ01785