Path-Q Solar

How much can cloudy weather reduce the expected annual savings from a solar system?

Answer

Clouds reduce solar irradiance and therefore production, but the effect cannot be expressed as one universal percentage. Use a site-specific, long-term production model that includes local weather variability, then value the reduced output using the applicable bill and export assumptions.

Key points

  • Panels still produce under diffuse light, but output is generally lower than in clear conditions.
  • The relevant measure is long-term annual production, not one cloudy day or month.
  • Cloud effects vary by climate, season, roof orientation, shading, and system design.
  • Savings depend on when production occurs, your electricity use, storage, export compensation, and fixed bill charges.

What it depends on

  • Local historical weather and solar resource
  • System orientation, shading, and equipment
  • Household load timing and storage
  • Current bill and export-credit treatment

Risks and trade-offs

  • Using a clear-sky estimate can overstate annual savings.
  • A system may produce close to its energy estimate but save less if much output is exported at a lower value.
  • Weather variability creates year-to-year differences even when the system is functioning normally.

Information you may need

  • Site-specific production estimate with weather assumptions
  • Several years of electricity use by month or interval
  • Storage and export assumptions
  • Current bill structure and credit treatment

Your next step

What to do next

Ask the installer for a weather-based production range and recalculate savings under low, expected, and high production cases.

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SQ00395