Path-Q Solar

How should I compare solar proposals that use different assumptions about annual production?

Answer

Normalize the production estimates before comparing economics. Ask each provider to show system size, modeled losses, shading, orientation, weather data, degradation, availability, and the production probability or confidence level, then compare expected energy and savings using the same utility and export assumptions.

Key points

  • A larger production estimate is not necessarily more credible.
  • Check whether estimates are annual totals, monthly profiles, or guaranteed output.
  • Review losses from temperature, shading, wiring, inverter efficiency, snow or soiling, and downtime where relevant.
  • Use conservative and downside production cases when calculating payback or financing affordability.

What it depends on

  • System size and equipment
  • Roof orientation, tilt, shading, and site conditions
  • Modeling method and weather dataset
  • Loss, degradation, and availability assumptions
  • Utility rates and export terms

Risks and trade-offs

  • An optimistic production estimate can overstate savings and shorten apparent payback.
  • A conservative estimate may understate upside but supports safer budgeting.
  • Production guarantees may use conditions or measurement rules that differ from proposal estimates.

Information you may need

  • Detailed production reports for each proposal
  • Site survey and shading assumptions
  • Monthly production profile
  • Production guarantee and remedy terms

Your next step

What to do next

Have an independent reviewer or all providers rerun the proposals with a common production model and identical financial assumptions.

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