[RE-wrenches] NEC 690.8(A) - Bifacial Modules

[Steven Lawrence]

Hi Corey,

I start off by using the BSTC value as the baseline Isc before I do the
classic 1.25x1.25 multiplication.  It does end up causing larger currents
and oversizing the wire. Most of the time our projects have a strict DC
Vdrop requirement so we're always oversizing the wire anyway, so it's not a
big deal.  However, for the Neher-McGrath calculations, I will typically
run a SAM model and re-calculate the ISC that way (on 100kW and larger
projects only).  I base this off the SolarPro article from a few years back
where you calculate Isc0 using nameplate Isc, cell temperature, irradiance,
and the module current coefficient.  For the irradiance, I use the front
side POA and the anti-POA multiplied by the bifaciality factor - usually
70%.

My last run had a situation where SAM was calculating a higher Isc value
than the Isc0 equation value, so I will probably end up using that.  It is,
however, less than the traditional BSTC nameplate x 1.25 method.

Regards
Steven Lawrence, PE
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