Why are back & front POA the same?

[mikofski]

[nevermind] Help! I am trying to use infinite shreds but front & back POA are coming out the same?
https://gist.github.com/mikofski/1517ef35cd5fadafc1ebf2f5191e8ead

[mikofski]

[update] Maybe it’s because I only sanity checked January 1st and it’s a purely diffuse day all day? The graphs for July imply that it is differentiating front and back. I think this is just me being lazy sorry!

Yes, it was entirely because Jan 1 is all diffuse, and for vertical pv and isotropic diffuse, it would be the same on both sides. But here's a look at July 5 showing that poa global does differ when direct differs, but diffuse is same on both sides.

I thought maybe Hay-Davies would make some distinction based on solar zenith? If the sun were behind the panel, then the projection ratio should be zero, AHA! but if DNI is zero then this term AI * Rb is also zero, so Rb doesn't matter.

OK, I get it now. I guess I can either close or delete this discuss?