[RE-wrenches] Bi-facial Open Circuit voltage testing

[Dave Angelini Offgrid Solar]

I am curious why you care?  Is it close to maxing out cold weather Voc for
one more panel in the string? If so I would be conservative and use one
less panel.

I have an old Sanyo Bi Array and it pretty much has never gone outside the
cold weather Voc that is logged by the controller. The 600v mppt just
cranks out the power when the snow is off the array. It does pretty well
also when the snow is on it. 

Just curious what you are doing? Testing used panels to make sure they are
good? If so I would line them all up exactly the same and have a second set
of eyes to record it all.


Dave Angelini Offgrid Solar
"we go where powerlines don't"
http://members.sti.net/offgridsolar/
e-mail offgridsolar at sti.net
text 209 813 0060

On Mon, 2 Nov 2020 10:18:29 -0500, Jason Kechijian <solarj at me.com> wrote:
> Hey wrenches,
> 
> Does anyone have any guidance to which values to use when testing open
> circuit voltage on bi-facial modules, considering you take the
temperature
> reading from the cell vs. the back sheet? Also, what would be the
correct
> module Voc to use since there are values for both the front and back?
> 
> 405W Module: Front/Back
> Pmpp: 405 / 285
> Vmpp: 40.89 / 41.10
> Impp: 9.91 / 6.94
> Voc: 48.42 / 46.99
> Isc: 10.38 / 7.28
> Module efficiency: 19.7% / 13.9% 
> Temp coefficient Pmpp: -0.3528%/ºC
> Temp coefficient Isc: +0.0400%/ºC
> Temp coefficient Voc: -0.2769%/ºC
> Nominal: 44+/-2ºC
> 
> I was using the front Voc and Voc temp coefficient, but I am getting
some
> results which are not in line with the 5% of expected.
> 
> Jason D. Kechijian, LEED AP
> NABCEP Certified PV Installation Professional™
> 
> 
> 
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