[RE-wrenches] Bi-facial optimum site

[Kirk Herander]

I do have a 50kw ground-mount of mono-facials alongside 300kw of bifacials
(both @ similar azimuth and tilt).. After calculating both arrays to
watts/sq. ft, the bi's outproduce the monos by 30% in midwinter with snow
ground cover and both arrays 100% clear. I spec only bifacials for ground
mounts as a result.

On Sun, Dec 21, 2025 at 3:53 PM Zeke Yewdall via RE-wrenches <
re-wrenches at lists.re-wrenches.org> 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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-- 


*Kirk Herander / **kirkh at vermont.solar <kirkh at vermont.solar>*

*Owner|Principal, VT Solar, LLC*

*Celebrating our 34st Anniversary 1991-2025!!*

dba Vermont Solar Engineering

802.559.1225
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