A solar shading calculator determines the minimum row spacing for ground-mounted or flat-roof solar arrays from your latitude, module length and panel tilt. It models the shadow one row throws across the next on the winter solstice, the lowest-sun day of the year, and reports the base-to-base pitch that keeps the array clear at solar noon, from 10AM to 2PM, or across the standard 9AM to 3PM design window.
Array Parameters
Spacing Results
Enter a site latitude and a module length. Spacing is sized on the winter solstice, at the hour you pick above.
Shadow Projection — Winter Solstice
Solar Site Survey Gear
Before installing a large ground-mount solar array, you must map the site's true south (or north, in the southern hemisphere) and measure local horizon shading from trees or buildings. A simple smartphone compass is easily thrown off by magnetic interference. We highly recommend using a professional sighting compass for locking in your array's azimuth. To quickly measure the distance between rows during layout without dragging a dirty tape measure through the mud, use a laser distance measurer.
How to Calculate Solar Panel Row Spacing
When installing multiple rows of solar panels (whether on a flat roof or ground mount), the front row casts a shadow backward. If this shadow falls onto the next row, it can severely cripple your energy production, as shaded solar cells drag down the performance of the entire string. SunClear sizes that gap on the winter solstice, the day the sun sits lowest and shadows run longest.
The solstice fixes the date but not the hour, and that distinction is where most spacing numbers go wrong. A row's shadow keeps growing from noon until sunset and runs to infinity as the sun touches the horizon, so no finite spacing is clear across a whole winter day. You have to pick the window you want protected - solar noon, 10AM to 2PM, or the common 9AM to 3PM rule - and accept shading outside it. The calculator returns the base-to-base pitch that criterion demands, along with the sun's altitude and bearing at the governing hour so you can check the assumption yourself.
The geometry assumes rows running east-west on level ground and facing the equator, which is what lets the azimuth term reduce to a single cosine. A sloped site, a row axis rotated off east-west, or a tracker changes the answer and needs a site-specific study.
Frequently Asked Questions
How do you calculate solar panel row spacing to avoid shading?
Row spacing depends on latitude, panel tilt, module length and the hour you design for. Measured base to base, the pitch is Module Length × cos(tilt) + Module Length × sin(tilt) × cos(sun azimuth) ÷ tan(sun elevation), with the sun taken on the winter solstice and the azimuth measured from the equator-facing direction. A 1.72 m module at 30° tilt on latitude 40.7° sees a 25.8° sun at solar noon and needs 3.26 m. Hold the same array clear until 9:00 solar time and the sun drops to 13.4°, which pushes the pitch to 4.17 m.
Why is winter solstice used for solar shading calculations?
The winter solstice (21 December in the Northern Hemisphere, 21 June in the Southern) puts the sun at its lowest noon altitude and casts the longest shadows of the year. It fixes the date but not the hour: shadows keep lengthening either side of noon and run to infinity at sunrise and sunset, so no finite spacing is clear across a whole day. Designers pick a window and accept shading outside it. This calculator offers solar noon, 10AM-2PM and the common 9AM-3PM rule, and defaults to 9AM-3PM.
Does row spacing affect total solar panel output?
Yes — wider spacing means fewer panels fit in the same area, reducing total system capacity and energy output. But panels shaded by the row in front lose 20-80% of their output. The optimal balance depends on land costs vs. energy value. Ground-mounted farms with cheap land use wider spacing; constrained rooftops use tighter spacing and accept some winter shading.