[RE-wrenches] Bi-facial optimum site

[Bill Battagin]

I hadn't considered the snow melt advantage, which would definitely help 
at this location, 4600' in the Sierra. And yes, the reflection off of 
snow has always been a good boost in output in this area, with the lower 
edge of the array ~18 feet off the ground and a lower sun angle 
reflecting off snow in the winter I'm assuming this is close to ideal 
for bi-facial.

We'll have to check to see if bi-facial is as strong for snow load.  
It's the backside gain in the summer that's stumping us. (white) 
concrete is too energy intensive, whatever is out in front of the array 
will get driven on occasionally (it's more for storage than daily 
driving), its red 3/4" crushed gravel now.

Appreciate the feedback, Gotta love a challenge.

Bill

Feather River Solar Electric
Bill Battagin, owner
4291 Nelson St. (Shipping)
5575 Genesee Rd. (USPS, UPS)
Taylorsville, CA  95983
530-284-7849, 258-1641(cell)
CA. C10 Lic # 874049
Solar Powered since 1982
Home of the Sunny Side Up

On 12/21/2025 12:49 PM, Zeke Yewdall via RE-wrenches wrote:
> We've been using bifacial modules for ground mounts in Colorado this 
> last year and they seem to be doing very well. No hard data with a 
> side by side comparison with a regular module, but it seems that they 
> generate better.  We use snow as our reflection surface.  I've also 
> heard anecdotally that they are good in cloudy conditions in the 
> pacific northwest where you aren't collecting much direct beam 
> radiation, but again, I don't curently have side by side monitoring 
> data. PVwatts claims a 5 to 10% increase in most climates, and less 
> sensitivity to exact orientation, which could also help with off grid 
> sites.  It also seems like the dark backside heats up a little faster 
> on grounmounts and melts snow and ice off just a little faster than 
> regular modules.
>
> As far as backside shading goes. The back side behaves just like the 
> front side from small hard shadows (like from racking).  A significant 
> drop in production.  But diffuse light, which is almost always what 
> the back side is receiving, should be less affected by racking shading 
> -- but I still think it would make sense to try to reduce racking 
> shading of the back side.
>
> The biggest thing that concerns me about bifacial modules is that most 
> of them are not tempered glass.  Two 2mm layers of heat strengthened 
> glass is supposed to be stiffer than one layer of 3.2mm tempered 
> glass, but still less impact resistance if you are in any potential 
> hail area in the 1" to 2" range (higher than 2" is liable to break 
> even the tempered glass modules anyway).  Other than that, I don't see 
> any downsides, as they are usually cheaper per watt than regular 
> modules too.  A lot of people were using them on flush roof mounts 
> because of the cheaper price, though you get zero benefit from the 
> bifacial aspect there.
>
> Z
>
> -- 
> Zeke Yewdall
> PV Engineer
> NABCEP #031508-89
> zeke at darkforestsolar.com
> 303-523-3592
>
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