port Purdue bifacial irradiance model

[nappaillav]

• Closes #xxxx
• I am familiar with the contributing guidelines
• Tests added
• Updates entries to docs/sphinx/source/api.rst 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 and Milestone are assigned to the Pull Request and linked Issue.

This is related to issue #863

[cwhanse]

Test failure is for unrelated remote data

[wholmgren]

@nappaillav are you planning on adding the bifacial code to this PR or did you want to split it into two PRs? My preference is a single PR since the trig functions are not explicitly tested and I don't see another near-term use for them.

[nappaillav]

@wholmgren Initially I thought of having separate pull requests, but I guess its better to combine both as you suggest.

[nappaillav]

There are few more steps in the process of completed the port of Purdue bifacial irradiance model, which are as follows

1. Description for the modules/ functions
2. Testing of the individual functions
3. Coding Style has to be corrected

Currently I'm updating the code for your perusal. So that you can suggest me

[nappaillav]

@cwhanse I have updated the description. If you can let me know if the implementation is fine by you, we can proceed further.
I also need help from you to completing the unit test.
I myself will do the write the test_codes, if you can provide me the test data (Input and output) it would be great.

[cwhanse]

@cwhanse I have updated the description. If you can let me know if the implementation is fine by you, we can proceed further.

The new bifacial functions should be added to pvlib.bifacial.py.

I'd suggest
pvlib.bifacial.irradiance_purdue
pvlib.bifacial.ground_reflected_purdue

Although I'm not fond of the ground_reflected name, it will move us ahead.

I also need help from you to completing the unit test.

Sure. Before we do that, we need to clean up the commit - it's not reviewable in current form.

There's a lot of leftover Matlab formalities that need to be dropped or formatted to pass Stickler.

There's a bunch of recent commits to pvlib master in other PRs that show up here as new code changes @wholmgren should this be addressed with a git rebase?

[wholmgren]

Yes

[nappaillav]

I will rebase and make sure the commit is clean

[cwhanse]

Closing due to merge of #717