[kadyrbekovhamit-cyber]

On DST-transition days, elapsed time since local midnight differs from the local clock time. hour_angle already subtracts the UTC offset at each input timestamp, so combining it with elapsed hours can introduce a 15-degree discrepancy. Geometric sunrise/set conversion has the corresponding one-hour shift.

Use naive local wall-clock subtraction for the forward calculation, and construct the inverse UTC instant from the date, wall-clock hours and timestamp-specific offset. This also avoids an ambiguous/nonexistent local midnight. The return types and function signatures remain unchanged. Related #2132/#2133 addressed midnight handling; this proposal addresses the remaining numerical discrepancy.

Regression validation on current main 0c6ab77: six transition/ambiguous-midnight checks fail before and pass after. The complete test_solarposition.py module has 65 passes and 21 skips (optional dependencies unavailable), versus 59 passes, six failures and 21 skips before. Current solarposition.py and tests ran over the existing pvlib installation; not a full source install or full project suite. No measured annual-production or financial-loss claim.

Prepared by Xamit Kadirbekov and Daniyal Kadirbekov with Codex/ChatGPT assistance for investigation, patch, tests and writing. Synthetic tests use a direct UTC hour-angle equation and timezone-invariance checks.

• No new issue; related NonExistentTimeError when calling hour_angle #2132 and Handle time normalization for nonexistent and ambiguous times #2133, which are not reopened or claimed as resolved here.
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• Tests added
• Updates entries in docs/sphinx/source/reference for API changes.
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Documentation CI follow-up (24 October)

Read the Docs build 35380797 failed. Its raw log reports ten gallery-example failures in pvlib/iotools/tmy.py:226, ValueError: Cannot modify read-only array, plus downstream undefined-variable errors in the clearsky guide. The tmy.py Git blob is identical on the base and this branch. I have not run a complete documentation build on the base, so I am not claiming that the whole CI pipeline is clean. The scoped solar-position regression results above remain unchanged.

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