Path-Q Solar

What should I do if solar quotes recommend very different system sizes?

Answer

Do not choose by size alone; ask each installer to reconcile the differences in electricity-use assumptions, future loads, roof layout, shading, production model, export limits, and financial objective before comparing the designs.

Key points

  • Compare the bills and load forecast each installer used, including assumptions about electrification or future consumption.
  • Review roof planes, shading, setbacks, obstructions, equipment limits, and whether all usable areas were considered.
  • Compare modeled production, system losses, expected degradation, and the portion of energy expected to be used or exported.
  • Ask whether the recommended size is limited by roof area, electrical service, utility rules, budget, or an economic target.

What it depends on

  • Historical and forecast electricity use
  • Roof geometry, shading, structural and electrical constraints
  • Production modeling methods and design objectives
  • Current interconnection, billing, and export rules

Risks and trade-offs

  • A larger system can cost more and produce surplus energy whose value depends on the billing arrangement.
  • A smaller system may leave future loads uncovered or make later expansion difficult.
  • Materially different assumptions can make price-per-watt comparisons misleading.

Information you may need

  • All proposals, layouts, production models, and exclusions
  • The utility bills and future-load assumptions used by each installer
  • Electrical service and roof information
  • Current local interconnection and compensation requirements

Your next step

What to do next

Create a side-by-side comparison and ask every installer to revise or explain the proposal using the same current and future load assumptions.

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SQ01088