Rear POA as an input to modeling bifacial PV

Hello,

I am using SAM to model bifacial PVs, and am wondering if SAM can take the rear POA irradiance as an input in addition to the front side POAI in the weather file? 

In case it matters: I'm running open source SAM on a Windows machine via .lk scripts.

Thanks,
Caitlin 

Hi Caitlin,

SAM's bifacial model calculates the rear-side irradiance as a fraction of the front-side irradiance. It is not possible to provide the rear-side irradiance as an input.

Best regards,
Paul.

HI Paul,

Thanks for your reply! I just had a clarifying follow up question: Do you mean that when only the front POAI is fed into SAM as an input, the rear irradiance is calculated as a ratio of that front side irradiance? If GHI, DHI or DNI is fed in, rear side irradiance is still calculated via the view factor model, correct? (As detailed here :  www.nrel.gov/docs/fy17osti/67847.pdf   )

Thanks,
Caitlin 

Hi Caitlin,

Yes, that is correct. SAM calculates the incident irradiance (or plane-of-array, POA irradiance) as described in Chapter 6 of the SAM Photovoltaic technical reference manual.

Gilman, P.; Dobos, A.; DiOrio, N.; Freeman, J.; Janzou, S.; Ryberg, D. (2018) SAM Photovoltaic Model Technical Reference Update. 93 pp.;
NREL/TP-6A20-67399. ( PDF 1.8 MB )

The bifacial model calculates the backside irradiance as described in the paper you referenced:

Marion, B.; MacAlpine, S.; Deline, C.; Asgharzadeh, A.; Toor, F.; Riley, D.; Stein, J.; Hansen, C. (2017). A Practical Irradiance Model for
Bifacial PV Modules. NREL/CP-5J00-67847 ( PDF 1 MB )

Note that the SAM PV reference manual was published before the bifacial model was implemented in SAM.

Best regards,
Paul.

Great, thanks so much, Paul!