Rename "DNI estimation" and "Decomposing & combining irrad" sections for clarity

[mikofski]

As discussed in #1179 (comment) and #1179 (comment) the decomposition functions differ - while Erbs and Boland yield the diffuse fraction (DF) DISC and DIRINT return DNI. Therefore, the documentation subheading "DNI estimation" can be misleading if not all of the functions directly return DNI. Also, these methods (DISC, DIRINT, Erbs, Boland) are often called "Decomposition" methods. However, there is already a subsection called "Decomposing & Combining Irradiance" which contains methods for deriving DNI from GHI & DHI, deriving AOI, calculating extra-terrestrial irradiance, and getting the ground diffuse.

Do folks think these sections subheading could be improved? What would be an improvement? In particular, who would be in favor of switching and renaming these sections like:

• "DNI estimation models" --> "Decomposition models"?
• "Decomposing and combining irradiance" --> "Combing & Calculating Irradiance Components"? or something like that?

[cwhanse]

I would prefer "Direct and diffuse estimation" over "DNI estimation models" and either over "Decomposition models" (novice users may not know what "decomposition" means.) I would put the dni function here.

The current "Decomposing and combining irradiance" looks like a mini-junk drawer of functions that are useful but aren't specific models. What about "Transposing irradiance"? and moving complete_irradiance to Methods for irradiance calculations"? I don't think get_extra_radiation belongs here.

[AdamRJensen]

The current "Decomposing and combining irradiance" looks like a mini-junk drawer of functions that are useful but aren't specific models. What about "Transposing irradiance"? and moving complete_irradiance to Methods for irradiance calculations"? I don't think get_extra_radiation belongs here.

Naming it "transposing irradiance" makes me think of the pvlib.irradiance.get_total_irradiance function and in general seems too similar to the section "Transposition models".