# What angle do you mount solar panels?

17/06/2021
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A tilted array on a flat roof poses different challenges than a basic array flush mounted on the conventionally sloped roof. In particular, as the photo above illustrates, each row of modules must be separated by extra spacing. Otherwise, when the sun is low in the sky, each row closer to the sun will shade the one behind it. This grim situation cannot be allowed under any circumstances.

Professional designers have formulas to help them work out the minimum distance between rows on tilted arrays. It’s kind of a fun challenge, too, because they get to play with the legendary Pythagorean Theorem. Here are the variables needed to compute the spacing:

• local latitude of the city
• lowest sun altitude angle at either 9 a.m. or 3 p.m. on winter solstice
• module height when tilted
• highest tilt angle of the array

The easiest approach to calculating row space is to start with the conventional formula based on local latitude. Here’s how local latitudes for most of the populated world dictate row spacing:

As the blue line in the graph above illustrates, you can pinpoint the “factor” you need by drawing up from where your city latitude lies to the curving red line, which represents the impact of shading at 9 a.m. and 3 p.m. on the winter solstice. Then you draw from that intersection horizontally to the factor scale on the left. Practically speaking, the result translates as follows:

• Latitude – – – – – – – Formula for Calculating Distance between Rows
• 30° – – – – – – – – – – – 2 X Module Height
• 35° – – – – – – – – – – – 2.5 X Module Height
• 40° – – – – – – – – – – – 3 X Module Height
• 45° – – – – – – – – – – – 4 X Module Height
• 50° – – – – – – – – – – – 6 X Module Height

If your latitude is not exactly 30°, 35°, 40°, etc., the formula should be either adjusted for accuracy, or you can simply use the next higher one listed above. For instance, a 38.5° latitude is more than halfway between 35°and 40°, so you want to stay near (or use) the 3 X Module Height. If you estimate an in between amount, lean towards a higher value — in this case 2.9 — so as not to be in danger of coming up short on the space necessary to avoid shading.

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