coerce and rotate pvgis TMY data to desired tz and year

docs/sphinx/source/whatsnew/v0.11.1.rst

@@ -16,6 +16,10 @@ Enhancements
 * Add new parameters for min/max absolute air mass to
   :py:func:`pvlib.spectrum.spectral_factor_firstsolar`.
   (:issue:`2086`, :pull:`2100`)
+* Add ``utc_offset`` and ``coerce_year`` arguments to
+  :py:func:`pvlib.iotools.get_pvgis_tmy` to allow user to specify time zone,
+  rotate indices of TMY to begin at midnight, and force indices to desired
+  year. (:issue:`2139`, :pull:`2138`)
 
 
 Bug fixes
@@ -45,4 +49,4 @@ Contributors
 * Leonardo Micheli (:ghuser:`lmicheli`)
 * Echedey Luis (:ghuser:`echedey-ls`)
 * Rajiv Daxini (:ghuser:`RDaxini`)
-
+* Mark A. Mikofski (:ghuser:`mikofski`)

pvlib/iotools/pvgis.py

@@ -18,10 +18,10 @@
 import json
 from pathlib import Path
 import requests
+import numpy as np
 import pandas as pd
+import pytz
 from pvlib.iotools import read_epw, parse_epw
-import warnings
-from pvlib._deprecation import pvlibDeprecationWarning
 
 URL = 'https://re.jrc.ec.europa.eu/api/'
 
@@ -390,9 +390,26 @@ def read_pvgis_hourly(filename, pvgis_format=None, map_variables=True):
     raise ValueError(err_msg)
 
 
+def _coerce_and_roll_pvgis_tmy(pvgis_data, tz, year):
+    """
+    After converting TZ, roll dataframe so timeseries starts at midnight
+    and force all indices to a common year. Only works for integer TZ.
+    """
+    tzname = pytz.timezone(f'Etc/GMT{-tz:+d}')
+    new_index = [
+        timestamp.replace(year=year, tzinfo=tzname)
+        for timestamp in pvgis_data.index]
+    new_pvgis_data = pd.DataFrame(
+        np.roll(pvgis_data, tz, axis=0),
+        columns=pvgis_data.columns,
+        index=new_index)
+    return new_pvgis_data
+
+
 def get_pvgis_tmy(latitude, longitude, outputformat='json', usehorizon=True,
                   userhorizon=None, startyear=None, endyear=None,
-                  map_variables=True, url=URL, timeout=30):
+                  map_variables=True, url=URL, timeout=30,
+                  utc_offset=0, coerce_year=1990):
     """
     Get TMY data from PVGIS.
 
@@ -424,6 +441,13 @@ def get_pvgis_tmy(latitude, longitude, outputformat='json', usehorizon=True,
         base url of PVGIS API, append ``tmy`` to get TMY endpoint
     timeout : int, default 30
         time in seconds to wait for server response before timeout
+    utc_offset: int, default 0
+        Use to specify a time zone other than the default UTC zero and roll
+        dataframe by ``utc_offset`` so that it starts at midnight on January
+        1st. If not zero, will also force year to ``coerce_year``.
+    coerce_year: int, default 1990
+        Use to force indices to desired year. Ignored if ``utc_offset`` is
+        zero.
 
     Returns
     -------
@@ -510,6 +534,9 @@ def get_pvgis_tmy(latitude, longitude, outputformat='json', usehorizon=True,
     if map_variables:
         data = data.rename(columns=VARIABLE_MAP)
 
+    if utc_offset != 0:
+        data = _coerce_and_roll_pvgis_tmy(data, utc_offset, coerce_year)
+
     return data, months_selected, inputs, meta
 
 

pvlib/tests/iotools/test_pvgis.py

@@ -435,6 +435,40 @@ def _compare_pvgis_tmy_basic(expected, meta_expected, pvgis_data):
         assert np.allclose(data[outvar], expected[outvar])
 
 
+@pytest.mark.remote_data
+@pytest.mark.flaky(reruns=RERUNS, reruns_delay=RERUNS_DELAY)
+def test_get_pvgis_tmy_coerce_year():
+    """test utc_offset and coerce_year work as expected"""
+    base_case, _, _, _ = get_pvgis_tmy(45, 8)  # Turin
+    assert str(base_case.index.tz) == 'UTC'
+    noon_test_data = [
+        base_case[base_case.index.month == m].iloc[12]
+        for m in range(1, 13)]
+    cet_tz = 1  # Turin time is CET
+    cet_name = 'Etc/GMT-1'
+    # check indices of rolled data after converting timezone
+    pvgis_data, _, _, _ = get_pvgis_tmy(45, 8, utc_offset=cet_tz)
+    jan1_midnight = pd.Timestamp('1990-01-01 00:00:00', tz=cet_name)
+    dec31_midnight = pd.Timestamp('1990-12-31 23:00:00', tz=cet_name)
+    assert pvgis_data.index[0] == jan1_midnight
+    assert pvgis_data.index[-1] == dec31_midnight
+    # spot check rolled data matches original
+    for m, test_case in enumerate(noon_test_data):
+        expected = pvgis_data[pvgis_data.index.month == m+1].iloc[12+cet_tz]
+        assert all(test_case == expected)
+    # repeat tests with year coerced
+    test_yr = 2021
+    pvgis_data, _, _, _ = get_pvgis_tmy(
+        45, 8, utc_offset=cet_tz, coerce_year=test_yr)
+    jan1_midnight = pd.Timestamp(f'{test_yr}-01-01 00:00:00', tz=cet_name)
+    dec31_midnight = pd.Timestamp(f'{test_yr}-12-31 23:00:00', tz=cet_name)
+    assert pvgis_data.index[0] == jan1_midnight
+    assert pvgis_data.index[-1] == dec31_midnight
+    for m, test_case in enumerate(noon_test_data):
+        expected = pvgis_data[pvgis_data.index.month == m+1].iloc[12+cet_tz]
+        assert all(test_case == expected)
+
+
 @pytest.mark.remote_data
 @pytest.mark.flaky(reruns=RERUNS, reruns_delay=RERUNS_DELAY)
 def test_get_pvgis_tmy_csv(expected, month_year_expected, inputs_expected,