Path-Q Solar

How can I verify that actual solar production matches the installation proposal?

Answer

Compare measured production with the proposal's estimated production over comparable periods, using the same system size, shading assumptions, weather basis, and loss assumptions. A single day or month is not enough; use at least several months and account for unusual weather, outages, shading, and system degradation.

Key points

  • Obtain the proposal's annual and monthly production estimates, not just a savings figure.
  • Use inverter or monitoring-system records showing energy produced by the array.
  • Compare actual and estimated production by month or season, then review cumulative performance.
  • Check whether the proposal assumed a different array layout, equipment configuration, shading level, or operating date.
  • Separate low production from high electricity bills, since bills also depend on consumption, rates, export treatment, and billing structure.

What it depends on

  • The proposal's monthly or annual production model and assumptions
  • Reliable inverter or monitoring data
  • Weather, shading, soiling, outage, and equipment-performance conditions
  • The period available for comparison

Risks and trade-offs

  • Short-term weather variation can make a correctly modeled system appear underperforming.
  • Monitoring data may measure inverter output rather than energy delivered after all system losses.
  • A production shortfall may indicate shading, soiling, equipment faults, communication problems, or an inaccurate original model.

Information you may need

  • The signed proposal and production estimate
  • Monthly monitoring records and system commissioning date
  • Any outage, maintenance, shading, or equipment-alert history
  • Recent electricity bills if bill impact is also being evaluated

Your next step

What to do next

Create a month-by-month comparison of modeled and measured production, document material deviations, and ask the installer to explain any sustained shortfall using the original modeling assumptions.

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