# Thread: Musings on snow on panels and production estimating

1. ## Musings on snow on panels and production estimating

Do the values in PV watts take into account snow covering the modules for significant periods during the winter? Anyone heard of an analysis of different panel tilts and its effect on snow shedding?

Ideal fixed tilt here near Albany NY is 34 degrees. 22 degrees only results in 2% less annual production - in theory. But how much quicker will they shed snow? Dec Jan and Feb together are 17% of annual production. This gets back to the first question, but I assume that assumes no snow cover. WAG, 1/4 of the time covered with snow at 34 degrees, 3/4 of the time at 22 degrees?

2. Very old, but interesting. In particular, see page 11:

https://www.osti.gov/scitech/servlets/purl/5232456

A brief primer on a model in SAM:

https://sam.nrel.gov/sites/default/f...Snow_Model.pdf

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Keep in mind that snow reflectance from the ground can increase irradiance and thus increase winter output beyond the expected. A higher tilt is better for that, too. I can't point to any kind of robust analysis but my intuition says to go with the higher tilt, all else being equal.

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Originally Posted by electrofelon
Do the values in PV watts take into account snow covering the modules for significant periods during the winter? Anyone heard of an analysis of different panel tilts and its effect on snow shedding?

Ideal fixed tilt here near Albany NY is 34 degrees. 22 degrees only results in 2% less annual production - in theory. But how much quicker will they shed snow? Dec Jan and Feb together are 17% of annual production. This gets back to the first question, but I assume that assumes no snow cover. WAG, 1/4 of the time covered with snow at 34 degrees, 3/4 of the time at 22 degrees?
When you measure tilt that way, are you talking about raising the top from horizontal, or raising the bottom from vertical?

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From horizontal.

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Originally Posted by jaggedben
From horizontal.
That didn't seem to make sense, so I went here and confirmed my hunch that it is from vertical, as in pin the top of the panel like it's the rear door of a hatch-back and lift from the bottom. 90 degrees would be parallel to the ground, 0 degrees is perpendicular to the ground. According to the calculator the ideal sun angle for Albany, NY varies from 24 in December to 70 in June.

7. Originally Posted by jaggedben
Keep in mind that snow reflectance from the ground can increase irradiance and thus increase winter output beyond the expected. A higher tilt is better for that, too. I can't point to any kind of robust analysis but my intuition says to go with the higher tilt, all else being equal.
Yeah good point.

That didn't seem to make sense, so I went here and confirmed my hunch that it is from vertical, as in pin the top of the panel like it's the rear door of a hatch-back and lift from the bottom. 90 degrees would be parallel to the ground, 0 degrees is perpendicular to the ground. According to the calculator the ideal sun angle for Albany, NY varies from 24 in December to 70 in June.
This site has the equations:

http://www.solarpaneltilt.com/

The common theory of "set them to your latitude" is incorrect.

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That didn't seem to make sense, so I went here and confirmed my hunch that it is from vertical.
You found a site using that convention. This thread has been using the other convention, as does the site that electrofelon mentioned, as does the (non-optimal) rule of thumb "tilt angle = latitude".

Cheers, Wayne

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