Path-Q Solar

What should I request if two installers provide different estimates of annual solar production?

Answer

Request each installer’s complete production-model assumptions and compare them using the same system size, layout, shading, weather data, losses, degradation treatment, and operating conditions. Do not compare annual totals without understanding what each estimate includes.

Key points

  • Ask for monthly production, not only an annual total.
  • Compare usable system size, orientation, tilt, shading, inverter clipping, and system-loss assumptions.
  • Check whether one estimate includes degradation, downtime, curtailment, or export limits.
  • Ask what measurement or performance guarantee, if any, is actually offered.

What it depends on

  • System design and equipment
  • Site-specific shade and orientation
  • Modeling tool and weather dataset
  • Grid operating or export constraints

Risks and trade-offs

  • A higher estimate may result from optimistic assumptions rather than a better design.
  • Different equipment sizes or layouts can make direct comparison misleading.
  • Estimated production is not the same as guaranteed bill savings.

Information you may need

  • Monthly production files
  • Modeling assumptions and loss breakdown
  • Panel layout and equipment schedule
  • Any performance guarantee terms

Your next step

What to do next

Put both estimates into a comparison table and ask each installer to reconcile the largest assumption differences in writing.

Path-Q

Find the right next step

Answer a few questions and we’ll narrow your options.

Loading…

SQ01262