deprecate Sandia ephemeris model

[mikofski]

Should we deprecate the Sandia ephemeris solar position model? The first line of the docstring says:

The accuracy of this code is not guaranteed. Consider using the built-in spa_c code or the PyEphem library.

The reference reads:

Grover Hughes’ class and related class materials on Engineering Astronomy at Sandia National Laboratories, 1985.

Therefore, I worry that users may be choosing to use this and ignoring the note to use either SPA or PyEphem. If looking for a faster implementation I would recommend SOLPOS over either of these two methods.

AFAIK, the mission of pvlib is both to be a curated tool library but also an educational platform that directs users to the most appropriate tool for a particular task. There is a decision trap of too many choices summarized well in this NYT sketch.

Therefore, perhaps it's time to archive some of the methods, and lean more into the 2nd part of our mission of guiding users with a better set of recommendations. Input?

[cwhanse]

A bit of history: when we started PVLib in Matlab in 2012, the only solar position code we had was that ephemeris function (that's why it is called ephemeris and not Hughes or Sandia or something.) It got ported to python when pvlib-python was born. SPA and SOLPOS came later.

I doubt anyone at Sandia would oppose retiring the ephemeris function.

[williamhobbs]

Just a thought: is there a way to "archive" a function and still have it come with the latest version of pvlib, as opposed to removing it and having it only be available in old versions of pvlib? Maybe that's a bad idea from a long-term maintenance perspective, though.

[adriesse]

Just a thought: is there a way to "archive" a function and still have it come with the latest version of pvlib, as opposed to removing it and having it only be available in old versions of pvlib? Maybe that's a bad idea from a long-term maintenance perspective, though.

Perhaps we could find a standard one-liner to put in the docstring of functions in that category?