[WIP] Implement the Plataforma Solar de Almerı́a (PSA) solar position algorithm

[kandersolar]

• [x] Related to #1308
• [x] I am familiar with the contributing guidelines
• [ ] Tests added
• [ ] Updates entries in docs/sphinx/source/reference for API changes.
• [ ] Adds description and name entries in the appropriate "what's new" file in docs/sphinx/source/whatsnew for all changes. Includes link to the GitHub Issue with :issue:`num` or this Pull Request with :pull:`num`. Includes contributor name and/or GitHub username (link with :ghuser:`user`).
• [ ] New code is fully documented. Includes numpydoc compliant docstrings, examples, and comments where necessary.
• [ ] Pull request is nearly complete and ready for detailed review.
• [ ] Maintainer: Appropriate GitHub Labels (including remote-data) and Milestone are assigned to the Pull Request and linked Issue.

The PSA algorithm seems to be as accurate as pvlib's ephemeris method but 3-4 times faster. Here is a brief comparison:

[AdamRJensen]

Are you implementing the 2001 version or the 2020 version?

[kandersolar]

The equations are the same between the two versions; only the coefficients differ. The current function lets the user choose which set of coefficients to use, with 2020 coefficients being the default.

[AdamRJensen]

In the equations in the 2020 paper, it seems that the right ascension ra variable isn't used in any calculations - am I missing something?

[AdamRJensen]

Given that the PSA and Michalsky algorithms are almost the same, maybe we should consider only adding Michalsky?

[adriesse]

almost the same

Could you elaborate on the similarities/differences?

I think the main usage of these algorithms will be to verify or replicate published output from other people or software, so even small differences could be relevant.

[kandersolar]

Closing, will pursue solar position algorithm improvements in fresh PRs.