Solar Array Layout Planner
Enter the size of a roof or ground area and your panel size. The planner draws the layout and tells you how many panels fit and how many kilowatts that is.
This planner is for installers and DIY builders who want a quick answer before ordering anything: how many panels go on this roof, or in this patch of ground, and what size system is that? Type in the width and depth of the area, the gap you must keep clear at each edge, and the panel size. You get a drawing to scale, the panel count and the total kW.
It checks portrait and landscape at the same time. On a lot of roofs one of them fits several more panels than the other, and the difference is easy to miss when you plan by eye.
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Planning estimates only. Check the layout against your roof, local fire code setbacks and the racking maker's instructions. Data as of October 2026.
How the solar array layout planner works
The planner takes the area you enter, cuts the setbacks off each edge, and packs panels into what’s left in a tight grid. It counts how many panels fit along a row and how many rows fit up the slope, allowing for the small gap you set between panels. The drawing is to scale, with the setbacks shown as a dashed line.
A roof example
Take a roof face 40 feet wide and 18 feet from eave to ridge, with 3 feet kept clear on every side. That leaves 34 by 12 feet. A 400-watt panel measuring 67.8 by 44.4 inches fits 9 across and 2 rows deep in portrait, which is 18 panels and 7.2 kW. Turned to landscape, the same space takes 5 across and 3 rows, which is 15 panels and 6.0 kW.
Setbacks can flip that answer. Cut them to 1.5 feet and landscape wins: 24 panels (9.6 kW) against 18 in portrait. That’s why the tool shows both.
Tilted rows on a flat roof or the ground
Switch to tilted rows and the planner adds the part that catches people out. Tilted panels shade the row behind them, so the rows can’t sit edge to edge. It uses the same winter shading check as our Row Spacing Calculator, with your ZIP code and shading window, to set how far apart the rows go.
Here’s one from Austin: a 40 by 30 foot pad, 3 feet kept clear on each side, panels tilted at 25 degrees. The rows need to be 9.6 feet apart, so two rows of 9 fit, which is 18 panels. A third row would need 24.3 feet of depth and the pad has 24.0. If the north setback can drop to 2.5 feet, a third row fits and the count jumps to 27 panels, or 10.8 kW. Those 6 inches are worth nine panels. You can also type your own row spacing if your racking maker gives one.
Tip: measure along the roof, not off a floor plan. A roof with a 6-in-12 pitch is about 12% longer from eave to ridge than the plan view suggests, and that’s enough to lose or gain a whole row.
What it doesn’t do
- It only handles rectangles. For an L-shaped roof or one with several faces, run each rectangle on its own and add up the counts.
- It doesn’t draw vents, skylights or chimneys. Take their space off the area, or add setbacks around them.
- It doesn’t check shade from trees or neighbouring buildings, and it doesn’t plan the wiring or strings. The Solar Panel String Calculator does the strings.
Where the numbers come from
- Panel count from plain geometry: the number of panels that fit along each side of the area after the setbacks, with the gap between panels you set.
- Row spacing for tilted rows uses standard solar geometry for December 21, the same method as the SolarYP Row Spacing Calculator.
- The starting panel size (67.8 by 44.4 inches, 400 W) is a typical modern residential panel, not a particular product. Use the size on your panel’s data sheet.
Questions
How many solar panels fit on my roof?
Enter the width and depth of the roof face, the setbacks and your panel size above. As an example, a 40 by 18 foot roof face with 3-foot setbacks takes 18 panels of about 400 W in portrait, which is 7.2 kW.
Should I put panels in portrait or landscape?
Whichever fits more panels in your space. The planner counts both and tells you the difference. On the roof in the example above portrait fits 18 and landscape 15, but with smaller setbacks landscape fits 24.
What setback should I use?
It depends on where you live and the roof. Fire codes often ask for clear paths along the ridge and edges, and the distance changes from one place to the next. The starting figure of 3 feet is a placeholder, not a code number. Ask your local building or fire department what applies.
What size gap goes between panels?
Most racking leaves a small gap for the clamps, often about half an inch to an inch. The planner starts at 0.75 inch. Check your racking maker’s instructions and change it if they say something else.
Do I measure the roof along the slope or on the plan?
Along the slope. A flat plan drawing makes a pitched roof look shorter than it is, and a 6-in-12 roof is about 12% longer from eave to ridge.
What about a roof with several faces or an L shape?
Run the planner once for each rectangle and add the panel counts together. The setbacks for each face go on that face’s own run.
Does the planner check for shade?
No. It only counts panels in the space. For the shade between tilted rows it uses the winter sun, but it doesn’t see trees, chimneys or neighbouring buildings. Check the site for those.
Can I use it for a ground mount?
Yes. Pick tilted rows, enter the size of the ground area, and the planner sets the row spacing for your ZIP code and shows how many rows fit.
Does it work in metric?
Yes. Switch the units to metres and millimetres at the top and every length changes with them.
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