Path-Q Solar
How can I tell whether two installers are using comparable production estimates?
Answer
Compare the inputs and reporting method, not just the annual kilowatt-hour result. The estimates should use comparable system size, layout, shading, weather assumptions, equipment characteristics, degradation, losses, and operating constraints.
Key points
- Check whether both estimates use the same roof planes, azimuth, tilt, shading, and system capacity.
- Compare assumptions for weather, soiling, snow, temperature, wiring, inverter, and availability losses.
- Check whether production is shown monthly as well as annually and whether degradation is included.
- Ask for the modeling tool, assumptions, and any production guarantee.
What it depends on
- Final site measurements and shade analysis
- Equipment specifications
- Modeling assumptions and loss factors
- Whether battery operation or export limits affect modeled output
Risks and trade-offs
- A higher estimate may reflect optimistic assumptions rather than a better system.
- A lower estimate may be more conservative and not necessarily inferior.
- Annual totals can hide seasonal differences that matter for bills or backup.
Information you may need
- Full production reports
- System layout and equipment list
- Loss and shading assumptions
- Monthly output and degradation treatment
Your next step
What to do next
Place both production reports side by side and ask each installer to explain every material difference in inputs and assumptions.
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SQ00345