Path-Q Solar

What should I ask an installer about expected solar production?

Answer

Ask the installer to show how annual and month-by-month production were modeled, which site assumptions were used, and the expected range rather than only a single production number.

Key points

  • Request the modeled annual production and monthly estimates, including any expected seasonal variation.
  • Ask which roof planes, shading conditions, system losses, equipment specifications, and degradation assumptions were included.
  • Ask for the production estimate in a form you can compare across proposals, such as expected energy by year and the assumptions behind it.
  • Ask what monitoring will be provided and how actual production will be compared with the estimate.

What it depends on

  • Roof orientation, tilt, shading, and usable area
  • System size, equipment, layout, and expected losses
  • Historical electricity use and future changes in consumption
  • The method and weather data used for production modeling

Risks and trade-offs

  • A single annual estimate can hide substantial seasonal variation and uncertainty.
  • Production estimates are not guarantees; shading changes, equipment outages, weather, and soiling can reduce output.
  • A larger system may produce more energy but may not improve the economics if surplus energy has limited value.

Information you may need

  • A copy of the production model or proposal assumptions
  • Recent electricity bills and any planned changes in electricity use
  • A comparison of production estimates from more than one installer

Your next step

What to do next

Ask each installer for a written production model with monthly output, assumptions, losses, degradation, and an uncertainty explanation, then compare the models on the same basis.

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SQ01069