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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