solarposition.ephemeris about pvlib-python HOT 6 CLOSED

I'm inclined to say that we should fix it, but I'm ok with removing it too. If I remember right, @Calama-Consulting is in favor of keeping it. A PR (with tests) is welcome.

from pvlib-python.

We'll keep using this issue to solve the timezone problem in this function.

The pyephem and NREL spa functions use UTC, so as long as Python, pandas, pytz, and dateutils can get the conversion right, DST should be ok there. test_solarposition.py has several tests that use a Golden, CO Location with a DST-allowing America/Denver timezone.

See #41 for a summary of the tz issue.

from pvlib-python.

This code block causes problems.

    # this code is needed to handle the new location.tz format string
    try:
        utc_offset = pytz.timezone(location.tz).utcoffset(
            time[0]).total_seconds() / 3600.
    except ValueError:
        utc_offset = time.tzinfo.utcoffset(time[0]).total_seconds() / 3600.
    pvl_logger.debug('utc_offset={}'.format(utc_offset))

It creates a fixed utc_offset based the first element of the DatetimeIndex. utc_offset should instead be an array so that it can handle a change from DST to non-DST. I wrote this so you can blame me!

To fix it, I suggest using pvlib.tools.localize, and the hours attribute of the returned object in place of UnivHr = DecHours + utc_offset - .5.

I think this also removes the need for

    Hour = time.hour
    Minute = time.minute
    Second = time.second
...
    DecHours = Hour + Minute / float(60) + Second / float(3600)

from pvlib-python.

cc @uvchik.

from pvlib-python.

The Problem is, that I don't really understand the function and it is not well commented. I tried some thing but I didn't succeeded.

I think I won't be able to repair and test this function in an acceptable period. First I have to learn more about Pandas timestamps and how to work with pandas and time zones.

Shall we add another warning, that using this function is on one owns risk. Or does anyone have an idea how to fix an test it?

from pvlib-python.

Thanks for looking. I'll see if I can implement my thoughts above.

from pvlib-python.