Path-Q Solar

How can I compare production from two arrays when their roofs have different orientations?

Answer

Compare the arrays using orientation-adjusted, time-matched production rather than raw energy totals. Account for tilt, azimuth, shading, module count and capacity, inverter limits, weather, and the different times of day each roof receives sunlight; a design model or irradiance-based analysis is more reliable than a simple percentage comparison.

Key points

  • Normalize output by installed capacity, such as energy per unit of rated capacity.
  • Compare equivalent periods and examine hourly profiles, not only monthly totals.
  • A west-facing array may produce less daily energy than a south-facing array but more later in the day; this is not necessarily a fault.

What it depends on

  • Array orientation, tilt, capacity, and module technology
  • Shading and horizon obstructions
  • Inverter or optimizer configuration
  • Weather and data quality

Risks and trade-offs

  • Over-normalizing can hide real faults if the assumptions are wrong.
  • Different orientations may be intentionally chosen to match load timing rather than maximize annual energy.

Information you may need

  • Array layout and rated capacity
  • Orientation, tilt, and shading information
  • Time-stamped production by array
  • Weather or irradiance data and original design model

Your next step

What to do next

Create a capacity-normalized, time-matched comparison and ask the designer or installer to explain deviations from the expected orientation-specific model.

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SQ02340