Path-Q Solar

What should I do if proposed solar system sizes differ because installers use different shading models?

Answer

Ask each installer to rerun the design using the same annual electricity usage, roof layout, shading assumptions, equipment assumptions, and production-report format. Compare modeled annual production and assumptions rather than system size alone.

Key points

  • Request the shading imagery or survey method, shade-loss assumptions, and production estimate for each roof plane.
  • Check whether differences come from panel placement, equipment limits, estimated consumption, or shading rather than from shading software alone.
  • A larger system is not necessarily better if its added panels produce less useful energy or increase cost without improving the project's objective.

What it depends on

  • Roof orientation, tilt, obstructions, and shade changes during the day and year
  • Historical electricity use and expected future loads
  • Panel, inverter, and design assumptions

Risks and trade-offs

  • An optimistic shade model can overstate production and savings.
  • A conservative model may undersize the system, while a larger design may face roof, interconnection, or budget limits.
  • Comparing outputs from different assumptions can make a fair quote comparison impossible.

Information you may need

  • The production report and assumptions from every installer
  • At least twelve months of electricity use, if available
  • A roof plan showing obstructions and any expected future shading

Your next step

What to do next

Give all installers the same usage and roof information, request revised production reports with written shading assumptions, and compare the results side by side.

Path-Q

Find the right next step

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

Loading…

SQ02831