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NEC 690.31
Validated against the standard.
PDF export
Pro-only. Generate professional reports.
$2.99 Pro
Lifetime unlock. No subscriptions.
How it works
Enter your values
Type in your inputs — the app fills code tables and constants for you, so there's nothing to look up.
Get a code-checked result
Instant answer with a clear PASS / FAIL and the exact NEC 690.31 reference behind every number.
Save & export
Keep a history of calculations and export a clean PDF report to share or attach to a permit (Pro).
What this calculator does
Ground-mount and flat-roof arrays need the right row spacing so the front row does not shade the one behind it in winter. This app computes inter-row spacing, tilt, and ground coverage ratio from your latitude and the winter sun angle.
What it computes
- Minimum row spacing to avoid shading at the worst-case winter sun angle (often the December 21 solar noon altitude, or 9 a.m. to 3 p.m. window).
- Module tilt and the resulting shadow length for a given row height.
- Ground coverage ratio (GCR) — module area to land area — which trades density against shading losses.
Worked example
A row of modules tilted 30° with a 6-foot vertical rise casts a long winter shadow at a low sun angle; the app returns the row pitch needed to keep the next row clear during the design solar window.
Related calculators
Size the system with the panel sizing calculator and estimate output with the production estimate calculator.
Ground mount FAQ
How is row spacing determined?
From the array tilt, row height, and the winter sun altitude at your latitude. The spacing keeps the front row from shading the next during the design hours, typically 9 a.m. to 3 p.m. on the shortest day.
What is ground coverage ratio?
GCR is the ratio of module area to total ground area. A higher GCR packs more power per acre but increases inter-row shading losses, so it is a design trade-off.
Does latitude matter?
A lot. Higher latitudes have lower winter sun and longer shadows, requiring more spacing for the same tilt.
Does it work offline?
Yes, it runs 100% offline with no account. Free with rewarded ads; a one-time $2.99 Pro unlock adds PDF export and saved history.
Get Ground Mount Calculator on your phone
Free with rewarded ads · $2.99 lifetime Pro · iOS & Android. Works 100% offline on the job site.