# Thread: Musings on snow on panels and production estimating

1. Senior Member
Join Date
Oct 2007
Location
New Jersey
Posts
6,090
Originally Posted by electrofelon
This site has the equations:

http://www.solarpaneltilt.com/

The common theory of "set them to your latitude" is incorrect.
If you look at the site I had gone to, for Albany NY the tilt angle is 70 degrees. Per Google, Albany NY is at 42.6526 degrees North. Using your web site's equation for 4-season adjustment, the summer angle, converting for my site's convention, is 71.4 degrees. Not very different. Optimization asks two questions; when do you need the most electricity vs the sun angle at that time.

If you're looking for the maximum utility offset for a single fixed angle, the sun angle will be biased toward the summer angle as that's when you have the longest collection period. In concept it's a pretty simple max/min problem, but I'm so far removed from high school senior year calculus I can't even set it up now.

If you look at the site I had gone to, for Albany NY the tilt angle is 70 degrees. Per Google, Albany NY is at 42.6526 degrees North. Using your web site's equation for 4-season adjustment, the summer angle, converting for my site's convention, is 71.4 degrees. Not very different. Optimization asks two questions; when do you need the most electricity vs the sun angle at that time.

If you're looking for the maximum utility offset for a single fixed angle, the sun angle will be biased toward the summer angle as that's when you have the longest collection period. In concept it's a pretty simple max/min problem, but I'm so far removed from high school senior year calculus I can't even set it up now.
Yeah to be clear I was thinking fixed angle for max annual production in my previous posts. Yes that site has other situations that an off gridder might want such as adjusting the angle several times a year or setting at the ideal winter angle. The ideal winter angle would def shed the snow nicely!

3. Senior Member
Join Date
Nov 2015
Location
CA, USA
Posts
646
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?
PV Watts is pretty primitive. If you go into the loss calculator you can enter an annual loss percentage for snow coverage and that's it. If you want to do more advanced simulations then you need to use SAM or PVSyst.

Simulating loss from snow is actually pretty complex. There are a number of papers on it available on the internet. I found it particularly interesting to find out the huge effect having a place for the snow to slide off too has on losses. If the array is not high enough off the ground for the sliding snow to drop clear of the modules the increase in annual losses is quite large.

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