Example Data Table
| Roof Length |
Roof Width |
Panel Depth |
Panel Width |
Tilt |
Sun Altitude |
Safety Gap |
Expected Use |
| 20 m |
12 m |
2.2 m |
1.13 m |
10° |
20° |
0.3 m |
Commercial flat roof |
| 14 m |
8 m |
1.72 m |
1.13 m |
15° |
18° |
0.4 m |
Small office roof |
| 30 m |
18 m |
2.3 m |
1.3 m |
8° |
22° |
0.25 m |
Large warehouse roof |
Formula Used
Rear height: H = D × sin(T)
Horizontal footprint: F = D × cos(T)
Shadow length: S = H ÷ tan(A)
Adjusted shadow: AS = S × |cos(Z)|
Required clear gap: G = AS + safety gap
Row pitch: P = F + G
Rows: floor((usable roof depth + G) ÷ P)
Panels per row: floor((usable width + panel gap) ÷ (panel width + panel gap))
DC capacity: total panels × panel watts ÷ 1000
How to Use This Calculator
Enter the total roof length and width first. Use north to south length for row spacing depth.
Add edge setbacks for parapets, access rules, drains, and safety zones.
Enter the module depth along the tilt direction. Enter module width across each row.
Choose a tilt angle and a design sun altitude. Lower sun altitude gives larger shadows.
Add service aisle data if part of the roof must stay open.
Press the calculate button. Review row pitch, panel count, and adjusted capacity.
Use CSV or PDF export buttons to save the result for layout comparison.
Flat Roof Solar Spacing Guide
Flat roofs give installers useful control over solar orientation. They also create one important design problem. Tilted rows can shade the row behind them when the sun sits low. A spacing calculator helps estimate a safe gap before a detailed site survey begins.
Why spacing matters
Good spacing protects winter production. It also keeps access paths clear for cleaning, inspection, and fire service movement. When rows are packed too tightly, the array may look efficient on paper. In practice, morning and afternoon shadows can reduce output. Wider gaps may lower the panel count, yet they can improve yearly yield per panel.
Inputs that change the result
The most important inputs are panel height, tilt angle, azimuth, latitude, design sun altitude, and roof usable dimensions. The calculator uses panel height along the tilted plane. It finds the raised rear edge, then projects the shadow using the selected sun altitude. A lower altitude creates a longer shadow. Higher tilt also increases row height and required row pitch.
Roof limits and service paths
Flat roof layouts must respect parapets, drains, skylights, vents, walkways, and edge setbacks. This tool lets you reserve setbacks and service aisles. It then estimates usable roof area, row count, panels per row, total modules, and DC array size. These values support early budgeting and option comparison.
Electrical planning value
Spacing is not only a structural layout issue. It affects electrical design because panel count controls DC capacity, string grouping, inverter sizing, and expected generation. When shading losses are included, the calculator gives an adjusted power estimate. This helps compare compact layouts against safer shadow-free layouts.
Use results carefully
The output is a planning estimate. Real projects need local codes, wind loading, ballast design, roof membrane review, and licensed engineering where required. Use this calculator to screen layouts, test assumptions, and prepare better questions for installers. Always confirm final spacing with measured site data and solar design software.
Practical workflow
Start with conservative tilt and winter sun values. Run one layout for maximum panels. Run another layout for better clearance. Compare the adjusted capacity, access space, and row pitch. The best choice usually balances energy, service safety, weight, and roof warranty requirements before purchase decisions.
FAQs
1. What is row pitch?
Row pitch is the distance from the front of one tilted panel row to the front of the next row. It includes the panel footprint and the required shadow clearance gap.
2. Why does tilt angle change spacing?
A higher tilt raises the back edge of the panel. That taller edge casts a longer shadow. The calculator increases spacing when tilt increases.
3. What sun altitude should I use?
Use a low winter sun altitude for conservative planning. Many designers check the worst useful production period, not only midday summer conditions.
4. Does this replace solar design software?
No. It gives early estimates. Final designs should use measured site data, local code checks, structural review, and professional solar layout software.
5. Why include azimuth offset?
Azimuth offset adjusts the shadow projected behind each row. A direct shadow needs more spacing. A side angle usually reduces the perpendicular row shadow.
6. What is system derate?
System derate reduces rated DC size for wiring, inverter, heat, mismatch, dirt, and other practical losses. It helps show a more realistic usable capacity.
7. Should I add service aisles?
Yes, when access paths are required for maintenance, fire safety, roof drains, or equipment. Aisles reduce usable width but improve service access.
8. Can this calculator handle different panel sizes?
Yes. Enter the panel depth along the tilt direction and the panel width across the row. The layout count updates from those dimensions.