Path-Q Solar

What should I ask an installer about estimated solar production?

Answer

Ask the installer to show how the estimate was calculated, what system layout and equipment were assumed, how shade and weather were modeled, what losses were included, and how the estimate compares with your actual or expected electricity use. Request the assumptions and exclusions in writing.

Key points

  • Ask for expected production by month or period, not only an annual total.
  • Clarify whether the estimate is before or after system losses and whether degradation is considered.
  • Ask what happens if the design changes, roof conditions differ, or monitoring later shows underperformance.
  • Compare estimates using the same system boundaries and assumptions.

What it depends on

  • System size, orientation, tilt, and equipment
  • Shading, weather, soiling, temperature, and other loss assumptions
  • Your usage pattern and future electricity needs
  • Whether the estimate is a forecast, guarantee, or contractual commitment

Risks and trade-offs

  • A higher production estimate may reflect optimistic assumptions rather than a better system.
  • An estimate is not necessarily a promise of output or savings.

Information you may need

  • The proposed layout and equipment list
  • Production model and assumptions
  • Monthly production estimate and loss breakdown
  • Any performance commitment and its measurement method

Your next step

What to do next

Ask each installer for the same written production assumptions and compare them with your bills and an independent or second-provider review.

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SQ01820