Path-Q Solar
How can I tell whether afternoon shade from a neighboring building will materially reduce solar production?
Answer
Measure or model the building's shadow across the affected roof plane during different seasons and compare the resulting annual production with an unshaded or alternative layout. Afternoon shade can matter substantially, but its effect depends on timing, height, distance, roof orientation, panel placement, and whether only part of the array is affected.
Key points
- Observe the roof at different times and seasons, not only on one clear day.
- Ask for a shade analysis that shows losses by roof plane or panel group.
- Compare placing panels away from the shadow with using another roof plane or location.
- Check whether the building's height or distance is likely to change.
What it depends on
- Building height, distance, and azimuth
- Roof orientation, pitch, and panel location
- Seasonal sun path and shade duration
- Electrical design and whether shaded panels share equipment
- Future changes to the neighboring property
Risks and trade-offs
- A visual assessment can understate winter or low-angle sun shading.
- Avoiding shade may reduce system size or require a more expensive layout.
- Predictions are uncertain if the neighboring building may be expanded or modified.
Information you may need
- Roof and neighboring-building dimensions
- Time-stamped shade observations or imagery
- Installer's modeled shade-loss estimate
- Alternative roof or ground locations
- Expected future changes nearby
Your next step
What to do next
Request a site-specific shade study with seasonal assumptions and compare the shaded layout with an alternative panel placement before accepting the production estimate.
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