cross_axis_slope vs cross_axis_tilt

[williamhobbs]

pvlib.shading.shaded_fraction1d uses 'cross_axis_slope' as an input, while pvlib.tracking.singleaxis uses 'cross_axis_tilt'. I think these are the same thing - is that correct? If so, would it make sense to update one of them to be consistent?

I couldn't seem to find any discussion of this in related PRs, but apologies if I just missed it.

tagging @kandersolar, @mikofski, @AdamRJensen, and @echedey-ls, since you all worked on these functions and/or references.

[kandersolar]

Yes, they represent the same quantity. That they have different names in those two functions was an oversight, and a shame. Thanks for pointing it out.

I'd have to think a bit more to form an opinion on which of them should be changed to match the other.

[mikofski]

I am minus one against “tilt” because the cross axis slope is the angle between adjacent rows. In my opinion tilt refers to the orientation of a tracker axis or module surface.

[mikofski]

I’m also changing my vote, despite what I said previously:

I am minus one against “tilt”

I think I prefer ”tilt” for reason explained in #2543 (comment). Although I’m not deeply invested in either sorry for flip-flopping.

[williamhobbs]

I'll caveat this with noting that I don't think it matters too much, but I still prefer "slope."

For example, I can mention "slope-aware backtracking," and it is relatively unambiguous what I am talking about. If I were instead to mention "tilt-aware backtracking," I think the meaning is lost.

And I informally asked a few non-solar folks in the office about the image below. Everyone said the angle of B should be "tilt" and C should be "slope" or "incline." When I said B has to be "tilt" and asked if A should be "tilt" or "slope", everyone liked "slope" more and said that "tilt" would be confusing. One person did mention that slope makes them think of "rise over run"...

[AdamRJensen]

I also prefer slope for anything related to the ground, and using tilt for the module surface. And of course consistency, even if it requires a deprecation cycle.

[kandersolar]

the “tilt” of the plane containing tracker axes

Yep, it's that plane which is tilted. Note that that plane's orientation is fully defined by axis_tilt and cross_axis_tilt. Seems natural to have the terms use parallel terms when you've got all the geometry loaded up in your head, but as @williamhobbs points out, maybe not so much otherwise.

I'm still not sure which way I'd vote. Abstaining for now :)

[kurt-rhee]

"There are two hard problems in computer science, cache invalidation and naming things" - Phil Karlton

+1 for slope