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
[email protected]
303-523-3592
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