Question on cell temperature model for BIPV

Dear colleagues

I'm participating in a collaborative group for an Activity on BIPV yield calculation of IEA-PVPS Task 15. In this group we have applied SAM to model six different BIPV installations around the world. Some questions have arisen in the cell temperature model while we are discussing our results. According to the SAM PV model report by NREL we wee some modifications to the NOCT  for Eq. 10.36, where the “building integrated” category appears to be identical to “ground/rack mounted”. We would like to  fully understand the underlying assumptions behind this allocation, which would help us a lot in our discussions.  And, more generally, we would appreciate to have more references that document or deal with  the derivation of the relationships between mounting stand-off type and adjusted NOCT?

Any help would be greatly appreciated

Thanks so much in advance and best wishes

Jesus Polo 


 

Hi Jesus,

The source code that determines the adjustment for different standoff heights for the NOCT cell temperature model implementation in SAM is here:

github.com/NREL/ssc/blob/338b58e677152b491e0c2b6934310df806ee018e/shared/lib_pv_io_manager.cpp#L1101

The way the code is set up, an adjustment is only applied for the options shown in the orange box:



This means that for building integrated, greater than 3.5 inches, and ground and rack mounted, an adjustment is not applied.

Based on that information, the "building integrated" option in SAM allows for free flow of air behind the module.

I think the original source of this approach is from the "Estimating INOCT from NOCT and Mounting Configuration" section starting on page 10 of the attached Fuentes, M. (1987). A Simplified Thermal Model for Flat-Plate Photovoltaic Arrays. Sandia National Laboratories. SAND85-0330. However, he does not mention a "building-integrated" option.

The NOCT Cell Temperature model is also described in Sandia's PVPMC modeling guide: pvpmc.sandia.gov/modeling-guide/2-dc-module-iv/cell-temperature/noct-cell-temperature/

Best regards,
Paul.