From 630e584481541e90152d8c865e07acf19fdc08bb Mon Sep 17 00:00:00 2001
From: Echedey Luis <80125792+echedey-ls@users.noreply.github.com>
Date: Fri, 23 Oct 2026 17:43:20 +0200
Subject: [PATCH 01/19] Fix deprecated inplace operations

---
 pvlib/iotools/pvgis.py          | 2 +-
 pvlib/iotools/solargis.py       | 5 ++---
 pvlib/iotools/solcast.py        | 3 +--
 pvlib/iotools/surfrad.py        | 2 +-
 pvlib/ivtools/utils.py          | 2 +-
 pvlib/snow.py                   | 2 +-
 tests/spectrum/test_response.py | 3 +--
 tests/test_modelchain.py        | 2 +-
 tests/test_shading.py           | 5 ++---
 9 files changed, 11 insertions(+), 15 deletions(-)

diff --git a/pvlib/iotools/pvgis.py b/pvlib/iotools/pvgis.py
index 61f3eff695..74b044abad 100644
--- a/pvlib/iotools/pvgis.py
+++ b/pvlib/iotools/pvgis.py
@@ -766,7 +766,7 @@ def get_pvgis_horizon(latitude, longitude, url=URL, **kwargs):
     data.columns = ['horizon_azimuth', 'horizon_elevation']
     # Convert azimuth to pvlib convention (north=0, south=180)
     data['horizon_azimuth'] += 180
-    data.set_index('horizon_azimuth', inplace=True)
+    data = data.set_index('horizon_azimuth')
     data = data['horizon_elevation']  # convert to pd.Series
     data = data[data.index < 360]  # remove duplicate north point (0 and 360)
     return data, metadata
diff --git a/pvlib/iotools/solargis.py b/pvlib/iotools/solargis.py
index 375c7ed3e8..2792011c2e 100644
--- a/pvlib/iotools/solargis.py
+++ b/pvlib/iotools/solargis.py
@@ -204,9 +204,8 @@ def get_solargis(latitude, longitude, start, end, variables, api_key,
     if map_variables:
         for variable in VARIABLE_MAP:
             if variable.solargis_name in data.columns:
-                data.rename(
-                    columns={variable.solargis_name: variable.pvlib_name},
-                    inplace=True
+                data = data.rename(
+                    columns={variable.solargis_name: variable.pvlib_name}
                 )
                 data[variable.pvlib_name] = data[
                     variable.pvlib_name].apply(variable.conversion)
diff --git a/pvlib/iotools/solcast.py b/pvlib/iotools/solcast.py
index 451ef58561..01a4081fef 100644
--- a/pvlib/iotools/solcast.py
+++ b/pvlib/iotools/solcast.py
@@ -421,9 +421,8 @@ def _solcast2pvlib(data):
     # rename and convert variables
     for variable in VARIABLE_MAP:
         if variable.solcast_name in data.columns:
-            data.rename(
+            data = data.rename(
                 columns={variable.solcast_name: variable.pvlib_name},
-                inplace=True
             )
             data[variable.pvlib_name] = data[
                 variable.pvlib_name].apply(variable.conversion)
diff --git a/pvlib/iotools/surfrad.py b/pvlib/iotools/surfrad.py
index 948ec5e09e..9c33c07567 100644
--- a/pvlib/iotools/surfrad.py
+++ b/pvlib/iotools/surfrad.py
@@ -158,7 +158,7 @@ def read_surfrad(filename, map_variables=True):
     data = data.where(~missing, np.nan)
 
     if map_variables:
-        data.rename(columns=VARIABLE_MAP, inplace=True)
+        data = data.rename(columns=VARIABLE_MAP)
     return data, metadata
 
 
diff --git a/pvlib/ivtools/utils.py b/pvlib/ivtools/utils.py
index 395678d49c..0d0ef1382a 100644
--- a/pvlib/ivtools/utils.py
+++ b/pvlib/ivtools/utils.py
@@ -160,7 +160,7 @@ def rectify_iv_curve(voltage, current, decimals=None):
 
     df = pd.DataFrame(data=np.vstack((voltage, current)).T, columns=['v', 'i'])
     # restrict to first quadrant
-    df.dropna(inplace=True)
+    df = df.dropna()
     df = df[(df['v'] >= 0) & (df['i'] >= 0)]
     # sort pairs on voltage, then current
     df = df.sort_values(by=['v', 'i'], ascending=[True, False])
diff --git a/pvlib/snow.py b/pvlib/snow.py
index b78a93a2ec..4492abc554 100644
--- a/pvlib/snow.py
+++ b/pvlib/snow.py
@@ -170,7 +170,7 @@ def coverage_nrel(snowfall, poa_irradiance, temp_air, surface_tilt,
     snow_coverage[new_snowfall] = 1.0
     if np.isnan(snow_coverage.iloc[0]):
         snow_coverage.iloc[0] = initial_coverage
-    snow_coverage.ffill(inplace=True)
+    snow_coverage = snow_coverage.ffill()
     snow_coverage -= cumulative_sliding
 
     return snow_coverage.clip(lower=0)
diff --git a/tests/spectrum/test_response.py b/tests/spectrum/test_response.py
index 2ffe572dce..113f09cc0c 100644
--- a/tests/spectrum/test_response.py
+++ b/tests/spectrum/test_response.py
@@ -45,8 +45,7 @@ def sr_and_eqe_fixture():
             [1050, 0.4, 0.338752845368667],
         ],
     )
-    df.set_index("wavelength", inplace=True)
-    return df
+    return df.set_index("wavelength")
 
 
 def test_sr_to_qe(sr_and_eqe_fixture):
diff --git a/tests/test_modelchain.py b/tests/test_modelchain.py
index 15d580aa6c..6b443ac0fc 100644
--- a/tests/test_modelchain.py
+++ b/tests/test_modelchain.py
@@ -602,7 +602,7 @@ def test_prepare_inputs_missing_irrad_component(
         sapm_dc_snl_ac_system, location, missing):
     mc = ModelChain(sapm_dc_snl_ac_system, location)
     weather = pd.DataFrame({'dhi': [1, 2], 'dni': [1, 2], 'ghi': [1, 2]})
-    weather.drop(columns=missing, inplace=True)
+    weather = weather.drop(columns=missing)
     with pytest.raises(ValueError):
         mc.prepare_inputs(weather)
 
diff --git a/tests/test_shading.py b/tests/test_shading.py
index f83f2db47b..82afcb88eb 100644
--- a/tests/test_shading.py
+++ b/tests/test_shading.py
@@ -270,7 +270,7 @@ def sf1d_premises_and_expected():
         (test_data["theta_L"], test_data["theta_R"]),
         (test_data["theta_R"], test_data["theta_L"]),
     )
-    test_data.rename(
+    test_data = test_data.rename(
         columns={
             "theta_L": "shading_row_rotation",
             "theta_R": "shaded_row_rotation",
@@ -279,9 +279,8 @@ def sf1d_premises_and_expected():
             "theta_s": "solar_zenith",  # for the projected solar zenith angle
             "f_s": "shaded_fraction",
         },
-        inplace=True,
     )
-    test_data.drop(columns=["x_L", "z_L", "x_R", "z_R"], inplace=True)
+    test_data = test_data.drop(columns=["x_L", "z_L", "x_R", "z_R"])
     # for the projected solar zenith angle
     # this returns the same psz angle as test_data["solar_zenith"]
     test_data["solar_azimuth"], test_data["axis_azimuth"] = 180, 90

From 889bcb14fb39ca65beb484ec30160638b127e832 Mon Sep 17 00:00:00 2001
From: Echedey Luis <80125792+echedey-ls@users.noreply.github.com>
Date: Sat, 24 Oct 2026 16:53:38 +0200
Subject: [PATCH 02/19] Fix Pandas4Warning: .dayofyear -> .day_of_year

Pandas4Warning: DatetimeIndex.dayofyear is deprecated and will be
removed in a future version. Use DatetimeIndex.day_of_year instead.
---
 benchmarks/benchmarks/solarposition.py        |  2 +-
 .../solar-position/plot_sunpath_diagrams.py   | 12 ++++----
 pvlib/clearsky.py                             |  2 +-
 pvlib/iotools/solrad.py                       |  2 +-
 pvlib/iotools/surfrad.py                      |  2 +-
 pvlib/irradiance.py                           | 12 ++++----
 pvlib/solarposition.py                        |  2 +-
 pvlib/tools.py                                |  2 +-
 tests/test_clearsky.py                        |  4 +--
 tests/test_irradiance.py                      |  2 +-
 tests/test_solarposition.py                   | 28 +++++++++----------
 11 files changed, 35 insertions(+), 35 deletions(-)

diff --git a/benchmarks/benchmarks/solarposition.py b/benchmarks/benchmarks/solarposition.py
index 0ccb379d8c..c3e101955a 100644
--- a/benchmarks/benchmarks/solarposition.py
+++ b/benchmarks/benchmarks/solarposition.py
@@ -51,7 +51,7 @@ def time_sun_rise_set_transit_ephem(self, ndays):
             self.times_daily, self.lat, self.lon)
 
     def time_sun_rise_set_transit_geometric_full_comparison(self, ndays):
-        dayofyear = self.times_daily.dayofyear
+        dayofyear = self.times_daily.day_of_year
         declination = solarposition.declination_spencer71(dayofyear)
         equation_of_time = solarposition.equation_of_time_spencer71(dayofyear)
         solarposition.sun_rise_set_transit_geometric(
diff --git a/docs/examples/solar-position/plot_sunpath_diagrams.py b/docs/examples/solar-position/plot_sunpath_diagrams.py
index 282a8dee43..20de978423 100644
--- a/docs/examples/solar-position/plot_sunpath_diagrams.py
+++ b/docs/examples/solar-position/plot_sunpath_diagrams.py
@@ -32,13 +32,13 @@
 ax = plt.subplot(1, 1, 1, projection='polar')
 # draw the analemma loops
 points = ax.scatter(np.radians(solpos.azimuth), solpos.apparent_zenith,
-                    s=2, label=None, c=solpos.index.dayofyear,
+                    s=2, label=None, c=solpos.index.day_of_year,
                     cmap='twilight_shifted_r')
 # add and format colorbar
 cbar = ax.figure.colorbar(points)
 times_ticks = pd.date_range('2019-01-01', '2020-01-01', freq='MS', tz=tz)
-cbar.set_ticks(ticks=times_ticks.dayofyear, labels=[], minor=False)
-cbar.set_ticks(ticks=times_ticks.dayofyear+15,
+cbar.set_ticks(ticks=times_ticks.day_of_year, labels=[], minor=False)
+cbar.set_ticks(ticks=times_ticks.day_of_year+15,
                labels=times_ticks.strftime('%b'),
                minor=True)
 cbar.ax.tick_params(which='minor', width=0)
@@ -120,13 +120,13 @@
 
 fig, ax = plt.subplots()
 points = ax.scatter(solpos.azimuth, solpos.apparent_elevation, s=2,
-                    c=solpos.index.dayofyear, label=None,
+                    c=solpos.index.day_of_year, label=None,
                     cmap='twilight_shifted_r')
 # add and format colorbar
 cbar = fig.colorbar(points)
 times_ticks = pd.date_range('2019-01-01', '2020-01-01', freq='MS', tz=tz)
-cbar.set_ticks(ticks=times_ticks.dayofyear, labels=[], minor=False)
-cbar.set_ticks(ticks=times_ticks.dayofyear+15,
+cbar.set_ticks(ticks=times_ticks.day_of_year, labels=[], minor=False)
+cbar.set_ticks(ticks=times_ticks.day_of_year+15,
                labels=times_ticks.strftime('%b'),
                minor=True)
 cbar.ax.tick_params(which='minor', width=0)
diff --git a/pvlib/clearsky.py b/pvlib/clearsky.py
index 87c8c78f86..3af86fa771 100644
--- a/pvlib/clearsky.py
+++ b/pvlib/clearsky.py
@@ -245,7 +245,7 @@ def _interpolate_turbidity(lts, time):
 
     isleap = time_utc.is_leap_year
 
-    dayofyear = time_utc.dayofyear
+    dayofyear = time_utc.day_of_year
     days_leap = _calendar_month_middles(2016)
     days_no_leap = _calendar_month_middles(2015)
 
diff --git a/pvlib/iotools/solrad.py b/pvlib/iotools/solrad.py
index f4d446fc61..8e661b74ad 100644
--- a/pvlib/iotools/solrad.py
+++ b/pvlib/iotools/solrad.py
@@ -198,7 +198,7 @@ def get_solrad(station, start, end,
     dates = pd.date_range(start.floor('D'), end, freq='D')
     station = station.lower()
     filenames = [
-        f"{station}/{d.year}/{station}{d.strftime('%y')}{d.dayofyear:03}.dat"
+        f"{station}/{d.year}/{station}{d.strftime('%y')}{d.day_of_year:03}.dat"
         for d in dates
     ]
 
diff --git a/pvlib/iotools/surfrad.py b/pvlib/iotools/surfrad.py
index 9c33c07567..d25651e19a 100644
--- a/pvlib/iotools/surfrad.py
+++ b/pvlib/iotools/surfrad.py
@@ -250,7 +250,7 @@ def get_surfrad(station, start, end, map_variables=True,
     station = station.lower()
 
     filenames = [
-        f"{station}/{d.year}/{station}{d.strftime('%y')}{d.dayofyear:03}.dat"  # noqa: E231,E501
+        f"{station}/{d.year}/{station}{d.strftime('%y')}{d.day_of_year:03}.dat"  # noqa: E231,E501
         for d in dates
     ]
 
diff --git a/pvlib/irradiance.py b/pvlib/irradiance.py
index 38bf122b91..475dc9bed7 100644
--- a/pvlib/irradiance.py
+++ b/pvlib/irradiance.py
@@ -1937,7 +1937,7 @@ def disc(ghi, solar_zenith, datetime_or_doy, pressure=101325,
 
     datetime_or_doy : int, float, array, pd.DatetimeIndex
         Day of year or array of days of year e.g.
-        pd.DatetimeIndex.dayofyear, or pd.DatetimeIndex.
+        pd.DatetimeIndex.day_of_year, or pd.DatetimeIndex.
 
     pressure : numeric or None, default 101325
         Site pressure. See :term:`pressure`. [Pa]
@@ -2765,7 +2765,7 @@ def erbs(ghi, zenith, datetime_or_doy, min_cos_zenith=0.065, max_zenith=87):
         :term:`solar_zenith`. [°]
     datetime_or_doy : int, float, array, pd.DatetimeIndex
         Day of year or array of days of year e.g.
-        pd.DatetimeIndex.dayofyear, or pd.DatetimeIndex.
+        pd.DatetimeIndex.day_of_year, or pd.DatetimeIndex.
     min_cos_zenith : numeric, default 0.065
         Minimum value of cos(zenith) to allow when calculating global
         clearness index `kt`. Equivalent to zenith = 86.273°.
@@ -2865,7 +2865,7 @@ def erbs_driesse(ghi, zenith, datetime_or_doy=None, dni_extra=None,
 
     datetime_or_doy : int, float, array or pd.DatetimeIndex, optional
         Day of year or array of days of year e.g.
-        pd.DatetimeIndex.dayofyear, or pd.DatetimeIndex.
+        pd.DatetimeIndex.day_of_year, or pd.DatetimeIndex.
         Either ``datetime_or_doy`` or ``dni_extra`` must be provided.
 
     dni_extra : numeric, optional
@@ -2992,7 +2992,7 @@ def orgill_hollands(ghi, zenith, datetime_or_doy, dni_extra=None,
 
     datetime_or_doy : int, float, array or pd.DatetimeIndex, optional
         Day of year or array of days of year e.g.
-        pd.DatetimeIndex.dayofyear, or pd.DatetimeIndex.
+        pd.DatetimeIndex.day_of_year, or pd.DatetimeIndex.
         Either ``datetime_or_doy`` or ``dni_extra`` must be provided.
 
     dni_extra : numeric, optional
@@ -3093,7 +3093,7 @@ def boland(ghi, solar_zenith, datetime_or_doy, a_coeff=8.645, b_coeff=0.613,
         :term:`solar_zenith`. [°]
 
     datetime_or_doy : numeric or pd.DatetimeIndex.
-        Day of year or array of days of year e.g. pd.DatetimeIndex.dayofyear,
+        Day of year or array of days of year e.g. pd.DatetimeIndex.day_of_year,
         or pd.DatetimeIndex.
 
     a_coeff : float, default 8.645
@@ -3897,7 +3897,7 @@ def louche(ghi, solar_zenith, datetime_or_doy, max_zenith=90):
 
     datetime_or_doy : numeric, pandas.DatetimeIndex
         Day of year or array of days of year e.g.
-        pd.DatetimeIndex.dayofyear, or pd.DatetimeIndex.
+        pd.DatetimeIndex.day_of_year, or pd.DatetimeIndex.
 
     Returns
     -------
diff --git a/pvlib/solarposition.py b/pvlib/solarposition.py
index 4441ed01f1..eb3bcdc81d 100644
--- a/pvlib/solarposition.py
+++ b/pvlib/solarposition.py
@@ -772,7 +772,7 @@ def ephemeris(time, latitude, longitude, pressure=101325.0, temperature=12.0):
     time_utc = tools._pandas_to_utc(time)
 
     # strip out the day of the year and calculate the decimal hour
-    DayOfYear = time_utc.dayofyear
+    DayOfYear = time_utc.day_of_year
     DecHours = (time_utc.hour + time_utc.minute/60. + time_utc.second/3600. +
                 time_utc.microsecond/3600.e6)
 
diff --git a/pvlib/tools.py b/pvlib/tools.py
index 1d9db70369..b519715cb3 100644
--- a/pvlib/tools.py
+++ b/pvlib/tools.py
@@ -214,7 +214,7 @@ def _pandas_to_doy(pd_object):
     -----
     Day of year is determined using UTC, since pandas uses local hour
     """
-    return _pandas_to_utc(pd_object).dayofyear
+    return _pandas_to_utc(pd_object).day_of_year
 
 
 def _pandas_to_utc(pd_object):
diff --git a/tests/test_clearsky.py b/tests/test_clearsky.py
index 0e49b32911..138cc43f26 100644
--- a/tests/test_clearsky.py
+++ b/tests/test_clearsky.py
@@ -782,9 +782,9 @@ def test_bird():
     aod_380nm = 0.15
     b_a = 0.85
     alb = 0.2
-    eot = solarposition.equation_of_time_spencer71(times_utc.dayofyear)
+    eot = solarposition.equation_of_time_spencer71(times_utc.day_of_year)
     hour_angle = solarposition.hour_angle(times, longitude, eot) - 0.5 * 15.
-    declination = solarposition.declination_spencer71(times_utc.dayofyear)
+    declination = solarposition.declination_spencer71(times_utc.day_of_year)
     zenith = solarposition.solar_zenith_analytical(
         np.deg2rad(latitude), np.deg2rad(hour_angle), declination
     )
diff --git a/tests/test_irradiance.py b/tests/test_irradiance.py
index b0d9863ad5..1ee62db6f8 100644
--- a/tests/test_irradiance.py
+++ b/tests/test_irradiance.py
@@ -72,7 +72,7 @@ def relative_airmass(times):
 # setup for et rad test. put it here for readability
 timestamp = pd.Timestamp('20161026')
 dt_index = pd.DatetimeIndex([timestamp])
-doy = timestamp.dayofyear
+doy = timestamp.day_of_year
 dt_date = timestamp.date()
 dt_datetime = datetime.datetime.combine(dt_date, datetime.time(0))
 dt_np64 = np.datetime64(dt_datetime)
diff --git a/tests/test_solarposition.py b/tests/test_solarposition.py
index 9dc0488fe5..ad483eef67 100644
--- a/tests/test_solarposition.py
+++ b/tests/test_solarposition.py
@@ -618,8 +618,8 @@ def test_equation_of_time():
     output = solarposition.spa_python(times, 37.8, -122.25, 100)
     eot = output['equation_of_time']
     eot_rng = eot.max() - eot.min()  # range of values, around 30 minutes
-    eot_1 = solarposition.equation_of_time_spencer71(times.dayofyear)
-    eot_2 = solarposition.equation_of_time_pvcdrom(times.dayofyear)
+    eot_1 = solarposition.equation_of_time_spencer71(times.day_of_year)
+    eot_2 = solarposition.equation_of_time_pvcdrom(times.day_of_year)
     assert np.allclose(eot_1 / eot_rng, eot / eot_rng, atol=0.3)  # spencer
     assert np.allclose(eot_2 / eot_rng, eot / eot_rng, atol=0.4)  # pvcdrom
 
@@ -635,8 +635,8 @@ def test_declination():
                                            sst=True)
     declination = np.deg2rad(declination)
     declination_rng = declination.max() - declination.min()
-    declination_1 = solarposition.declination_cooper69(times.dayofyear)
-    declination_2 = solarposition.declination_spencer71(times.dayofyear)
+    declination_1 = solarposition.declination_cooper69(times.day_of_year)
+    declination_2 = solarposition.declination_spencer71(times.day_of_year)
     a, b = declination_1 / declination_rng, declination / declination_rng
     assert np.allclose(a, b, atol=0.03)  # cooper
     a, b = declination_2 / declination_rng, declination / declination_rng
@@ -652,14 +652,14 @@ def test_analytical_zenith():
     output = solarposition.spa_python(times, lat, lon, 100)
     solar_zenith = np.deg2rad(output['zenith'])  # spa
     # spencer
-    eot = solarposition.equation_of_time_spencer71(times_utc.dayofyear)
+    eot = solarposition.equation_of_time_spencer71(times_utc.day_of_year)
     hour_angle = np.deg2rad(solarposition.hour_angle(times, lon, eot))
-    decl = solarposition.declination_spencer71(times_utc.dayofyear)
+    decl = solarposition.declination_spencer71(times_utc.day_of_year)
     zenith_1 = solarposition.solar_zenith_analytical(lat_rad, hour_angle, decl)
     # pvcdrom and cooper
-    eot = solarposition.equation_of_time_pvcdrom(times_utc.dayofyear)
+    eot = solarposition.equation_of_time_pvcdrom(times_utc.day_of_year)
     hour_angle = np.deg2rad(solarposition.hour_angle(times, lon, eot))
-    decl = solarposition.declination_cooper69(times_utc.dayofyear)
+    decl = solarposition.declination_cooper69(times_utc.day_of_year)
     zenith_2 = solarposition.solar_zenith_analytical(lat_rad, hour_angle, decl)
     assert np.allclose(zenith_1, solar_zenith, atol=0.015)
     assert np.allclose(zenith_2, solar_zenith, atol=0.025)
@@ -675,16 +675,16 @@ def test_analytical_azimuth():
     solar_azimuth = np.deg2rad(output['azimuth'])  # spa
     solar_zenith = np.deg2rad(output['zenith'])
     # spencer
-    eot = solarposition.equation_of_time_spencer71(times_utc.dayofyear)
+    eot = solarposition.equation_of_time_spencer71(times_utc.day_of_year)
     hour_angle = np.deg2rad(solarposition.hour_angle(times, lon, eot))
-    decl = solarposition.declination_spencer71(times_utc.dayofyear)
+    decl = solarposition.declination_spencer71(times_utc.day_of_year)
     zenith = solarposition.solar_zenith_analytical(lat_rad, hour_angle, decl)
     azimuth_1 = solarposition.solar_azimuth_analytical(lat_rad, hour_angle,
                                                        decl, zenith)
     # pvcdrom and cooper
-    eot = solarposition.equation_of_time_pvcdrom(times_utc.dayofyear)
+    eot = solarposition.equation_of_time_pvcdrom(times_utc.day_of_year)
     hour_angle = np.deg2rad(solarposition.hour_angle(times, lon, eot))
-    decl = solarposition.declination_cooper69(times_utc.dayofyear)
+    decl = solarposition.declination_cooper69(times_utc.day_of_year)
     zenith = solarposition.solar_zenith_analytical(lat_rad, hour_angle, decl)
     azimuth_2 = solarposition.solar_azimuth_analytical(lat_rad, hour_angle,
                                                        decl, zenith)
@@ -814,8 +814,8 @@ def test_sun_rise_set_transit_geometric(expected_rise_set_spa, golden_mst):
     latitude = golden_mst.latitude
     longitude = golden_mst.longitude
     eot = solarposition.equation_of_time_spencer71(
-        times_utc.dayofyear)  # minutes
-    decl = solarposition.declination_spencer71(times_utc.dayofyear)  # radians
+        times_utc.day_of_year)  # minutes
+    decl = solarposition.declination_spencer71(times_utc.day_of_year)  # radians
     with pytest.raises(ValueError):
         solarposition.sun_rise_set_transit_geometric(
             times.tz_convert(None), latitude=latitude, longitude=longitude,

From 9f3ae9b87efde78baa9ecf57f43e95b5679e3fcd Mon Sep 17 00:00:00 2001
From: Echedey Luis <80125792+echedey-ls@users.noreply.github.com>
Date: Sat, 24 Oct 2026 16:59:28 +0200
Subject: [PATCH 03/19] Fix Pandas4Warning: deprecated passing a list to
 DataFrame.from_dict -> DataFrame constructor instead

Pandas4Warning: Passing a list to DataFrame.from_dict is deprecated. Use
the DataFrame constructor instead.
---
 pvlib/iotools/solcast.py      |  2 +-
 tests/iotools/test_solcast.py | 20 ++++++++++----------
 2 files changed, 11 insertions(+), 11 deletions(-)

diff --git a/pvlib/iotools/solcast.py b/pvlib/iotools/solcast.py
index 01a4081fef..96ed677097 100644
--- a/pvlib/iotools/solcast.py
+++ b/pvlib/iotools/solcast.py
@@ -473,7 +473,7 @@ def _get_solcast(
 
     if response.status_code == 200:
         j = response.json()
-        df = pd.DataFrame.from_dict(j[list(j.keys())[0]])
+        df = pd.DataFrame(j[list(j.keys())[0]])
         if map_variables:
             return _solcast2pvlib(df)
         else:
diff --git a/tests/iotools/test_solcast.py b/tests/iotools/test_solcast.py
index 23989ecb2e..d6df24c222 100644
--- a/tests/iotools/test_solcast.py
+++ b/tests/iotools/test_solcast.py
@@ -39,7 +39,7 @@ def test__get_solcast(requests_mock, endpoint, params, api_key, json_response):
             endpoint, params, api_key, True
         ),
         pvlib.iotools.solcast._solcast2pvlib(
-            pd.DataFrame.from_dict(
+            pd.DataFrame(
                 json_response[list(json_response.keys())[0]])
         )
     )
@@ -49,7 +49,7 @@ def test__get_solcast(requests_mock, endpoint, params, api_key, json_response):
         pvlib.iotools.solcast._get_solcast(
             endpoint, params, api_key, False
         ),
-        pd.DataFrame.from_dict(
+        pd.DataFrame(
             json_response[list(json_response.keys())[0]])
     )
 
@@ -93,7 +93,7 @@ def test_get_solcast_live(
         pd.testing.assert_frame_equal(
             function(**params, map_variables=map_variables)[0],
             pvlib.iotools.solcast._solcast2pvlib(
-                pd.DataFrame.from_dict(
+                pd.DataFrame(
                     json_response[list(json_response.keys())[0]]
                 )
             ),
@@ -101,7 +101,7 @@ def test_get_solcast_live(
     else:
         pd.testing.assert_frame_equal(
             function(**params, map_variables=map_variables)[0],
-            pd.DataFrame.from_dict(
+            pd.DataFrame(
                 json_response[list(json_response.keys())[0]]
             ),
         )
@@ -145,7 +145,7 @@ def test_get_solcast_tmy(
         pd.testing.assert_frame_equal(
             function(**params, map_variables=map_variables)[0],
             pvlib.iotools.solcast._solcast2pvlib(
-                pd.DataFrame.from_dict(
+                pd.DataFrame(
                     json_response[list(json_response.keys())[0]]
                 )
             ),
@@ -153,7 +153,7 @@ def test_get_solcast_tmy(
     else:
         pd.testing.assert_frame_equal(
             function(**params, map_variables=map_variables)[0],
-            pd.DataFrame.from_dict(
+            pd.DataFrame(
                 json_response[list(json_response.keys())[0]]
             ),
         )
@@ -232,7 +232,7 @@ def test_get_solcast_historic(
         pd.testing.assert_frame_equal(
             function(**params, map_variables=map_variables)[0],
             pvlib.iotools.solcast._solcast2pvlib(
-                pd.DataFrame.from_dict(
+                pd.DataFrame(
                     json_response[list(json_response.keys())[0]]
                 )
             ),
@@ -240,7 +240,7 @@ def test_get_solcast_historic(
     else:
         pd.testing.assert_frame_equal(
             function(**params, map_variables=map_variables)[0],
-            pd.DataFrame.from_dict(
+            pd.DataFrame(
                 json_response[list(json_response.keys())[0]]
             ),
         )
@@ -288,7 +288,7 @@ def test_get_solcast_forecast(
         pd.testing.assert_frame_equal(
             function(**params, map_variables=map_variables)[0],
             pvlib.iotools.solcast._solcast2pvlib(
-                pd.DataFrame.from_dict(
+                pd.DataFrame(
                     json_response[list(json_response.keys())[0]]
                 )
             ),
@@ -296,7 +296,7 @@ def test_get_solcast_forecast(
     else:
         pd.testing.assert_frame_equal(
             function(**params, map_variables=map_variables)[0],
-            pd.DataFrame.from_dict(
+            pd.DataFrame(
                 json_response[list(json_response.keys())[0]]
             ),
         )

From 279dec735b0faacdee73e1828e6ad1703b72a6c0 Mon Sep 17 00:00:00 2001
From: Echedey Luis <80125792+echedey-ls@users.noreply.github.com>
Date: Sat, 24 Oct 2026 17:05:41 +0200
Subject: [PATCH 04/19] Fix Pandas4Warning: assert_index_equal will check the
 'freq' attribute

Pandas4Warning: assert_index_equal will check the 'freq' attribute by
default in a future version; these freqs <Minute> and None do not match.
Pass check_freq=True or check_freq=False to silence this warning
    pd.testing.assert_index_equal(left, right, **kwargs)
---
 tests/conftest.py                   | 2 +-
 tests/iotools/test_solaranywhere.py | 6 +++++-
 tests/iotools/test_tmy.py           | 6 +++++-
 tests/test_conftest.py              | 5 +++++
 4 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/tests/conftest.py b/tests/conftest.py
index 8a1c1180d8..bda29842ae 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -56,7 +56,7 @@ def _check_pandas_assert_kwargs(kwargs):
 
 def assert_index_equal(left, right, **kwargs):
     kwargs = _check_pandas_assert_kwargs(kwargs)
-    pd.testing.assert_index_equal(left, right, **kwargs)
+    pd.testing.assert_index_equal(left, right, **kwargs, check_freq=False)
 
 
 def assert_series_equal(left, right, **kwargs):
diff --git a/tests/iotools/test_solaranywhere.py b/tests/iotools/test_solaranywhere.py
index 54216a7ab0..c4ff5858c3 100644
--- a/tests/iotools/test_solaranywhere.py
+++ b/tests/iotools/test_solaranywhere.py
@@ -74,7 +74,11 @@ def test_read_solaranywhere_high_resolution(high_resolution_index):
     assert data.loc['2021-01-01 07:00:00-05:00', 'Albedo'] == 0.6
     assert data.loc['2021-01-01 07:00:00-05:00', 'WindSpeed (m/s)'] == 0
     # Assert that the index is parsed correctly
-    pd.testing.assert_index_equal(data.index, high_resolution_index)
+    pd.testing.assert_index_equal(
+        data.index,
+        high_resolution_index,
+        check_freq=False,
+    )
 
 
 def test_read_solaranywhere_map_variables():
diff --git a/tests/iotools/test_tmy.py b/tests/iotools/test_tmy.py
index 02ffe7042f..0659c416f6 100644
--- a/tests/iotools/test_tmy.py
+++ b/tests/iotools/test_tmy.py
@@ -111,7 +111,11 @@ def test_solaranywhere_tmy3(solaranywhere_index):
     # included to test files with  00:00 timestamps are parsed correctly
     data, meta = tmy.read_tmy3(TMY3_SOLARANYWHERE, encoding='iso-8859-1',
                                map_variables=False)
-    pd.testing.assert_index_equal(data.index, solaranywhere_index)
+    pd.testing.assert_index_equal(
+        data.index,
+        solaranywhere_index,
+        check_freq=False,
+    )
     assert meta['USAF'] == 0
     assert meta['Name'] == 'Burlington  United States'
     assert meta['State'] == 'NA'
diff --git a/tests/test_conftest.py b/tests/test_conftest.py
index fc8b14c31c..dbc9cedaaf 100644
--- a/tests/test_conftest.py
+++ b/tests/test_conftest.py
@@ -33,5 +33,10 @@ def test__check_pandas_assert_kwargs(mocker, function_name, pd_version,
         expected_kwargs = {'atol': tol, 'rtol': tol}
     else:
         expected_kwargs = {'check_less_precise': check_less_precise}
+    if function_name == "assert_index_equal":
+        # assert_index_equal in Pandas 3.1.0 warns:
+        # Pandas4Warning: assert_index_equal will check the 'freq' attribute by default in a future version; these freqs <Minute> and None do not match. Pass check_freq=True or check_freq=False to silence this warning
+        # pd.testing.assert_index_equal(left, right, **kwargs)
+        expected_kwargs['check_freq'] = False
 
     spy.assert_called_once_with(*args, **expected_kwargs)

From b2aba024b6d6b52cbdcc011b42d7e333df36a683 Mon Sep 17 00:00:00 2001
From: Echedey Luis <80125792+echedey-ls@users.noreply.github.com>
Date: Sun, 25 Oct 2026 14:52:59 +0100
Subject: [PATCH 05/19] Fix pandas 3.1.0 unexpected behavior on .map (may defer
 until pandas GH#71567 is resolved)

pvlib/iotools/tmy.py:226: in read_tmy3
    data_ymd.iloc[-1] = data_ymd.iloc[-1].replace(year=coerce_year+1)
    ^^^^^^^^^^^^^^^^^
venv/lib/python3.14/site-packages/pandas/core/indexing.py:1010: in __setitem__
    iloc._setitem_with_indexer(indexer, value, self.name)
venv/lib/python3.14/site-packages/pandas/core/indexing.py:2653: in _setitem_with_indexer
    self._setitem_single_block(indexer, value, name)
venv/lib/python3.14/site-packages/pandas/core/indexing.py:2985: in _setitem_single_block
    self.obj._mgr = self.obj._mgr.setitem(indexer=indexer, value=value)
                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
venv/lib/python3.14/site-packages/pandas/core/internals/managers.py:625: in setitem
    return self.apply("setitem", indexer=indexer, value=value)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
venv/lib/python3.14/site-packages/pandas/core/internals/managers.py:456: in apply
    applied = getattr(b, f)(**kwargs)
              ^^^^^^^^^^^^^^^^^^^^^^^
---
 pvlib/iotools/tmy.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pvlib/iotools/tmy.py b/pvlib/iotools/tmy.py
index 28d20ffc2d..2dcd2b529f 100644
--- a/pvlib/iotools/tmy.py
+++ b/pvlib/iotools/tmy.py
@@ -222,7 +222,7 @@ def read_tmy3(filename, coerce_year=None, map_variables=True, encoding=None):
     # shifted_hour is a pd.Series, so use pd.to_timedelta to get a pd.Series of
     # timedeltas
     if coerce_year is not None:
-        data_ymd = data_ymd.map(lambda dt: dt.replace(year=coerce_year))
+        data_ymd = data_ymd.transform(lambda dt: dt.replace(year=coerce_year))
         data_ymd.iloc[-1] = data_ymd.iloc[-1].replace(year=coerce_year+1)
     # NOTE: as of pvlib-0.6.3, min req is pandas-0.18.1, so pd.to_timedelta
     # unit must be in (D,h,m,s,ms,us,ns), but pandas>=0.24 allows unit='hour'

From 65371c88827eeb65d42fc8f4406777920f979cbf Mon Sep 17 00:00:00 2001
From: Echedey Luis <80125792+echedey-ls@users.noreply.github.com>
Date: Sun, 25 Oct 2026 15:13:31 +0100
Subject: [PATCH 06/19] Fix Pandas4Warning: DatetimeIndex.values will change
 from UTC ndarray to pd.DatetimeArray

Pandas4Warning: DatetimeIndex.values returning an ndarray that drops
timezone information is deprecated. In a future version, this will
return the underlying DatetimeArray instead. Use
'DatetimeIndex.tz_convert(None).to_numpy()' to get a NumPy array of UTC
values, or 'DatetimeIndex.array' to get the ExtensionArray.
---
 pvlib/soiling.py       | 4 ++--
 pvlib/tools.py         | 5 ++++-
 tests/test_clearsky.py | 2 +-
 3 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/pvlib/soiling.py b/pvlib/soiling.py
index dfcd60529e..6fdad506e6 100644
--- a/pvlib/soiling.py
+++ b/pvlib/soiling.py
@@ -192,9 +192,9 @@ def kimber(rainfall, cleaning_threshold=6, soiling_loss_rate=0.0015,
     # convert grace_period to timedelta
     grace_period = datetime.timedelta(days=grace_period)
 
-    # get indices as numpy datetime64, calculate timestep as numpy timedelta64,
+    # get indices as np.datetime64 (UTC), calculate timestep as np.timedelta64,
     # and convert timestep to fraction of days
-    rain_index_vals = rainfall.index.values
+    rain_index_vals = rainfall.index.tz_convert(None).to_numpy()
     timestep_interval = (rain_index_vals[1] - rain_index_vals[0])
     day_fraction = timestep_interval / np.timedelta64(24, 'h')
 
diff --git a/pvlib/tools.py b/pvlib/tools.py
index b519715cb3..3a51f1e2b4 100644
--- a/pvlib/tools.py
+++ b/pvlib/tools.py
@@ -428,7 +428,10 @@ def _get_sample_intervals(times, win_length):
     """ Calculates time interval and samples per window for Reno-style clear
     sky detection functions
     """
-    deltas = np.diff(times.values) / np.timedelta64(1, '60s')
+    deltas = (
+        np.diff(times.tz_convert(None).to_numpy())  # UTC np.datetime64
+        / np.timedelta64(1, '60s')
+    )
 
     # determine if we can proceed
     if times.inferred_freq and len(np.unique(deltas)) == 1:
diff --git a/tests/test_clearsky.py b/tests/test_clearsky.py
index 138cc43f26..332fd70216 100644
--- a/tests/test_clearsky.py
+++ b/tests/test_clearsky.py
@@ -660,7 +660,7 @@ def test_detect_clearsky_arrays(detect_clearsky_data):
 
 def test_detect_clearsky_irregular_times(detect_clearsky_data):
     expected, cs = detect_clearsky_data
-    times = cs.index.values.copy()
+    times = cs.index.tz_convert(None).to_numpy()  # UTC np.datetime64
     times[0] += pd.Timedelta(1, unit='s')
     times = pd.DatetimeIndex(times)
     match = "does not yet support unequal time intervals"

From 4045155731a5186aa28b7176e71e8caeae91092c Mon Sep 17 00:00:00 2001
From: Echedey Luis <80125792+echedey-ls@users.noreply.github.com>
Date: Sun, 25 Oct 2026 20:22:45 +0100
Subject: [PATCH 07/19] Fix previous commit - use localize to ignore tz, and
 not fail when input is tz-naive

---
 pvlib/tools.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pvlib/tools.py b/pvlib/tools.py
index 3a51f1e2b4..aa58b280ad 100644
--- a/pvlib/tools.py
+++ b/pvlib/tools.py
@@ -429,7 +429,7 @@ def _get_sample_intervals(times, win_length):
     sky detection functions
     """
     deltas = (
-        np.diff(times.tz_convert(None).to_numpy())  # UTC np.datetime64
+        np.diff(times.tz_localize(None).to_numpy())  # tz-naive np.datetime64
         / np.timedelta64(1, '60s')
     )
 

From 10b9c3032cc6a7928bff7358f4891201384c6d17 Mon Sep 17 00:00:00 2001
From: Echedey Luis <80125792+echedey-ls@users.noreply.github.com>
Date: Sun, 25 Oct 2026 20:37:14 +0100
Subject: [PATCH 08/19] Fix prior Pandas4Warning - we need a writable array,
 not just a ro view

---
 tests/test_clearsky.py | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/tests/test_clearsky.py b/tests/test_clearsky.py
index 332fd70216..752d5043b0 100644
--- a/tests/test_clearsky.py
+++ b/tests/test_clearsky.py
@@ -660,7 +660,10 @@ def test_detect_clearsky_arrays(detect_clearsky_data):
 
 def test_detect_clearsky_irregular_times(detect_clearsky_data):
     expected, cs = detect_clearsky_data
-    times = cs.index.tz_convert(None).to_numpy()  # UTC np.datetime64
+    times = (cs.index
+        .tz_convert(None)  # converted to UTC
+        .to_numpy(copy=True)  # np.datetime64 + required writability
+    )
     times[0] += pd.Timedelta(1, unit='s')
     times = pd.DatetimeIndex(times)
     match = "does not yet support unequal time intervals"

From 3f64bb69c379d36c03eabfb13fb80e4a24cc2560 Mon Sep 17 00:00:00 2001
From: Echedey Luis <80125792+echedey-ls@users.noreply.github.com>
Date: Sun, 25 Oct 2026 20:48:33 +0100
Subject: [PATCH 09/19] Fix error in prior commit due to check_freq nonexistent
 in pandas<3.1.0

---
 tests/conftest.py | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/tests/conftest.py b/tests/conftest.py
index bda29842ae..ce1459fb62 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -56,7 +56,10 @@ def _check_pandas_assert_kwargs(kwargs):
 
 def assert_index_equal(left, right, **kwargs):
     kwargs = _check_pandas_assert_kwargs(kwargs)
-    pd.testing.assert_index_equal(left, right, **kwargs, check_freq=False)
+    try:  # check_freq was added in pandas 3.1.0
+        pd.testing.assert_index_equal(left, right, **kwargs, check_freq=False)
+    except TypeError:  # this branch supports prior versions
+        pd.testing.assert_index_equal(left, right, **kwargs)
 
 
 def assert_series_equal(left, right, **kwargs):

From bd73b06a4d116a3e17e1c059b61a507d6c19310b Mon Sep 17 00:00:00 2001
From: Echedey Luis <80125792+echedey-ls@users.noreply.github.com>
Date: Sun, 25 Oct 2026 20:49:04 +0100
Subject: [PATCH 10/19] Fix style issues - flake8

---
 tests/test_clearsky.py      | 3 ++-
 tests/test_conftest.py      | 5 +++--
 tests/test_solarposition.py | 2 +-
 3 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/tests/test_clearsky.py b/tests/test_clearsky.py
index 752d5043b0..20d88679ff 100644
--- a/tests/test_clearsky.py
+++ b/tests/test_clearsky.py
@@ -660,7 +660,8 @@ def test_detect_clearsky_arrays(detect_clearsky_data):
 
 def test_detect_clearsky_irregular_times(detect_clearsky_data):
     expected, cs = detect_clearsky_data
-    times = (cs.index
+    times = (
+        cs.index
         .tz_convert(None)  # converted to UTC
         .to_numpy(copy=True)  # np.datetime64 + required writability
     )
diff --git a/tests/test_conftest.py b/tests/test_conftest.py
index dbc9cedaaf..56dfb48519 100644
--- a/tests/test_conftest.py
+++ b/tests/test_conftest.py
@@ -35,8 +35,9 @@ def test__check_pandas_assert_kwargs(mocker, function_name, pd_version,
         expected_kwargs = {'check_less_precise': check_less_precise}
     if function_name == "assert_index_equal":
         # assert_index_equal in Pandas 3.1.0 warns:
-        # Pandas4Warning: assert_index_equal will check the 'freq' attribute by default in a future version; these freqs <Minute> and None do not match. Pass check_freq=True or check_freq=False to silence this warning
-        # pd.testing.assert_index_equal(left, right, **kwargs)
+        # Pandas4Warning: assert_index_equal will check the 'freq' attribute
+        # by default in a future version; these freqs <Minute> and None do not
+        # match. Pass check_freq=True or check_freq=False to silence
         expected_kwargs['check_freq'] = False
 
     spy.assert_called_once_with(*args, **expected_kwargs)
diff --git a/tests/test_solarposition.py b/tests/test_solarposition.py
index ad483eef67..cc7151d5fb 100644
--- a/tests/test_solarposition.py
+++ b/tests/test_solarposition.py
@@ -815,7 +815,7 @@ def test_sun_rise_set_transit_geometric(expected_rise_set_spa, golden_mst):
     longitude = golden_mst.longitude
     eot = solarposition.equation_of_time_spencer71(
         times_utc.day_of_year)  # minutes
-    decl = solarposition.declination_spencer71(times_utc.day_of_year)  # radians
+    decl = solarposition.declination_spencer71(times_utc.day_of_year)  # rad
     with pytest.raises(ValueError):
         solarposition.sun_rise_set_transit_geometric(
             times.tz_convert(None), latitude=latitude, longitude=longitude,

From b62991682e48f7928b61b4ff75fb552771d02d6f Mon Sep 17 00:00:00 2001
From: Echedey Luis <80125792+echedey-ls@users.noreply.github.com>
Date: Sun, 25 Oct 2026 23:02:58 +0100
Subject: [PATCH 11/19] Fix check_freq not in pandas<3.1.0; iotools

---
 tests/iotools/test_solaranywhere.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tests/iotools/test_solaranywhere.py b/tests/iotools/test_solaranywhere.py
index c4ff5858c3..5f4dedfbe1 100644
--- a/tests/iotools/test_solaranywhere.py
+++ b/tests/iotools/test_solaranywhere.py
@@ -6,6 +6,7 @@
     TESTS_DATA_DIR,
     RERUNS,
     RERUNS_DELAY,
+    assert_index_equal,
     requires_solaranywhere_credentials,
 )
 
@@ -74,10 +75,9 @@ def test_read_solaranywhere_high_resolution(high_resolution_index):
     assert data.loc['2021-01-01 07:00:00-05:00', 'Albedo'] == 0.6
     assert data.loc['2021-01-01 07:00:00-05:00', 'WindSpeed (m/s)'] == 0
     # Assert that the index is parsed correctly
-    pd.testing.assert_index_equal(
+    assert_index_equal(  # from conftest; doesn't compare index frequency attr
         data.index,
         high_resolution_index,
-        check_freq=False,
     )
 
 

From 058848caef29b79a196c8913ef882ca94c37890a Mon Sep 17 00:00:00 2001
From: Echedey Luis <80125792+echedey-ls@users.noreply.github.com>
Date: Sun, 25 Oct 2026 23:55:10 +0100
Subject: [PATCH 12/19] Fix check_freq not in pandas<3.1.0; iotools (II)

---
 tests/iotools/test_tmy.py | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/tests/iotools/test_tmy.py b/tests/iotools/test_tmy.py
index 0659c416f6..c95f89986b 100644
--- a/tests/iotools/test_tmy.py
+++ b/tests/iotools/test_tmy.py
@@ -1,7 +1,7 @@
 import numpy as np
 import pandas as pd
 from pvlib.iotools import tmy
-from tests.conftest import TESTS_DATA_DIR, PVLIB_DATA_DIR
+from tests.conftest import TESTS_DATA_DIR, PVLIB_DATA_DIR, assert_index_equal
 import pytest
 
 # test the API works
@@ -111,10 +111,9 @@ def test_solaranywhere_tmy3(solaranywhere_index):
     # included to test files with  00:00 timestamps are parsed correctly
     data, meta = tmy.read_tmy3(TMY3_SOLARANYWHERE, encoding='iso-8859-1',
                                map_variables=False)
-    pd.testing.assert_index_equal(
+    assert_index_equal(  # from conftest; doesn't compare index frequency attr
         data.index,
         solaranywhere_index,
-        check_freq=False,
     )
     assert meta['USAF'] == 0
     assert meta['Name'] == 'Burlington  United States'

From 6a656c11da8d1b3984cbe3d7a8ee2921da7b5075 Mon Sep 17 00:00:00 2001
From: Echedey Luis <80125792+echedey-ls@users.noreply.github.com>
Date: Mon, 26 Oct 2026 16:56:31 +0100
Subject: [PATCH 13/19] Review: tidy check_freq logic

---
 tests/conftest.py | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/tests/conftest.py b/tests/conftest.py
index ce1459fb62..b58670d194 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -51,15 +51,16 @@ def _check_pandas_assert_kwargs(kwargs):
     else:
         kwargs.pop('rtol', None)
         kwargs.pop('atol', None)
+    if Version(pd.__version__) >= Version('3.1.0'):
+        # check_freq was added in pandas 3.1.0
+        # tests written prior to it, may have not taken it into account
+        kwargs['check_freq'] = False
     return kwargs
 
 
 def assert_index_equal(left, right, **kwargs):
     kwargs = _check_pandas_assert_kwargs(kwargs)
-    try:  # check_freq was added in pandas 3.1.0
-        pd.testing.assert_index_equal(left, right, **kwargs, check_freq=False)
-    except TypeError:  # this branch supports prior versions
-        pd.testing.assert_index_equal(left, right, **kwargs)
+    pd.testing.assert_index_equal(left, right, **kwargs)
 
 
 def assert_series_equal(left, right, **kwargs):

From db5f399e38c13fd3c66ac97c34f700f5ed4244b4 Mon Sep 17 00:00:00 2001
From: Echedey Luis <80125792+echedey-ls@users.noreply.github.com>
Date: Mon, 26 Oct 2026 17:04:39 +0100
Subject: [PATCH 14/19] Whatsnew

---
 docs/sphinx/source/whatsnew/v0.16.2.rst | 1 +
 1 file changed, 1 insertion(+)

diff --git a/docs/sphinx/source/whatsnew/v0.16.2.rst b/docs/sphinx/source/whatsnew/v0.16.2.rst
index 64132a2547..e4084cf22b 100644
--- a/docs/sphinx/source/whatsnew/v0.16.2.rst
+++ b/docs/sphinx/source/whatsnew/v0.16.2.rst
@@ -24,6 +24,7 @@ Bug fixes
 
 Enhancements
 ~~~~~~~~~~~~
+* Add ``pandas==3.1.0`` support. (:pull:`2924`)
 * Add ``dataset`` parameter to :py:func:`~pvlib.iotools.get_era5`
   allowing for choosing between ERA5 and ERA5-Land datasets.
   (:pull:`2780`)

From d1120386ec4938aa79f6d05aac71d400647c1b3c Mon Sep 17 00:00:00 2001
From: Echedey Luis <80125792+echedey-ls@users.noreply.github.com>
Date: Tue, 27 Oct 2026 19:48:59 +0100
Subject: [PATCH 15/19] Fix _check_pandas_assert_kwargs test (after tidying
 code)

---
 tests/test_conftest.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tests/test_conftest.py b/tests/test_conftest.py
index 56dfb48519..740de33cb5 100644
--- a/tests/test_conftest.py
+++ b/tests/test_conftest.py
@@ -33,7 +33,7 @@ def test__check_pandas_assert_kwargs(mocker, function_name, pd_version,
         expected_kwargs = {'atol': tol, 'rtol': tol}
     else:
         expected_kwargs = {'check_less_precise': check_less_precise}
-    if function_name == "assert_index_equal":
+    if function_name == "assert_index_equal" and pd_version == '3.1.0':
         # assert_index_equal in Pandas 3.1.0 warns:
         # Pandas4Warning: assert_index_equal will check the 'freq' attribute
         # by default in a future version; these freqs <Minute> and None do not

From a6ec50d435ae086149ebfff9657e23c351db7bbd Mon Sep 17 00:00:00 2001
From: Echedey Luis <80125792+echedey-ls@users.noreply.github.com>
Date: Tue, 27 Oct 2026 22:35:27 +0100
Subject: [PATCH 16/19] Fix index check_freq implementation and tests

check_freq is exclusively supported in assert_index_equal, added in
pandas==3.1.0
---
 tests/conftest.py      | 8 ++++----
 tests/test_conftest.py | 4 ++--
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/tests/conftest.py b/tests/conftest.py
index b58670d194..19a44de38f 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -51,15 +51,15 @@ def _check_pandas_assert_kwargs(kwargs):
     else:
         kwargs.pop('rtol', None)
         kwargs.pop('atol', None)
-    if Version(pd.__version__) >= Version('3.1.0'):
-        # check_freq was added in pandas 3.1.0
-        # tests written prior to it, may have not taken it into account
-        kwargs['check_freq'] = False
     return kwargs
 
 
 def assert_index_equal(left, right, **kwargs):
     kwargs = _check_pandas_assert_kwargs(kwargs)
+    if Version(pd.__version__) >= Version('3.1.0'):
+        # check_freq was added in pandas 3.1.0
+        # tests written prior to it, may have not taken it into account
+        kwargs['check_freq'] = False
     pd.testing.assert_index_equal(left, right, **kwargs)
 
 
diff --git a/tests/test_conftest.py b/tests/test_conftest.py
index 740de33cb5..7a177177ec 100644
--- a/tests/test_conftest.py
+++ b/tests/test_conftest.py
@@ -6,7 +6,7 @@
 @pytest.mark.parametrize('function_name', ['assert_index_equal',
                                            'assert_series_equal',
                                            'assert_frame_equal'])
-@pytest.mark.parametrize('pd_version', ['1.0.0', '1.1.0'])
+@pytest.mark.parametrize('pd_version', ['1.0.0', '1.1.0', '3.1.0'])
 @pytest.mark.parametrize('check_less_precise', [True, False])
 def test__check_pandas_assert_kwargs(mocker, function_name, pd_version,
                                      check_less_precise):
@@ -28,7 +28,7 @@ def test__check_pandas_assert_kwargs(mocker, function_name, pd_version,
     assert_function = getattr(conftest, function_name)
     args = [None, None]
     assert_function(*args, check_less_precise=check_less_precise)
-    if pd_version == '1.1.0':
+    if pd_version in {'1.1.0', '3.1.0'}:
         tol = 1e-3 if check_less_precise else 1e-5
         expected_kwargs = {'atol': tol, 'rtol': tol}
     else:

From 1c6c0c74fcac573ad8784d5ce719987ffc3b9c08 Mon Sep 17 00:00:00 2001
From: Echedey Luis <80125792+echedey-ls@users.noreply.github.com>
Date: Tue, 27 Oct 2026 22:51:30 +0100
Subject: [PATCH 17/19] Fix Pandas4Warning - Series.values returning an ndarray
 that drops timezone information for DatetimeTZDtype is deprecated.

tests/test_solarposition.py::test_sun_rise_set_transit_geometric

/home/echedey/Documents/10_Programming/pvlib-python/tests/test_solarposition.py:835:
Pandas4Warning: Series.values returning an ndarray that drops timezone
information for DatetimeTZDtype is deprecated. In a future version, this
will return the underlying DatetimeArray instead. Use
'Series.dt.tz_convert(None).to_numpy()' to get a NumPy array of UTC
values, or 'Series.array' to get the ExtensionArray.
  See
https://pandas.pydata.org/docs/dev/whatsnew/v3.1.0.html#whatsnew-310-deprecations-values
for more details.
    expected_sunset =
pd.DatetimeIndex(expected_rise_set_spa.sunset.values,
---
 tests/test_solarposition.py | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/tests/test_solarposition.py b/tests/test_solarposition.py
index cc7151d5fb..fc31094362 100644
--- a/tests/test_solarposition.py
+++ b/tests/test_solarposition.py
@@ -830,12 +830,15 @@ def test_sun_rise_set_transit_geometric(expected_rise_set_spa, golden_mst):
     test_sunset = solarposition._times_to_hours_after_local_midnight(ss)
     test_transit = solarposition._times_to_hours_after_local_midnight(st)
     # convert expected SPA sunrise, sunset, transit to local datetime indices
-    expected_sunrise = pd.DatetimeIndex(expected_rise_set_spa.sunrise.values,
-                                        tz='UTC').tz_convert(golden_mst.tz)
-    expected_sunset = pd.DatetimeIndex(expected_rise_set_spa.sunset.values,
-                                       tz='UTC').tz_convert(golden_mst.tz)
-    expected_transit = pd.DatetimeIndex(expected_rise_set_spa.transit.values,
-                                        tz='UTC').tz_convert(golden_mst.tz)
+    expected_sunrise = pd.DatetimeIndex(
+        expected_rise_set_spa["sunrise"].dt.tz_convert(None).to_numpy(), tz="UTC"
+    ).tz_convert(golden_mst.tz)
+    expected_sunset = pd.DatetimeIndex(
+        expected_rise_set_spa["sunset"].dt.tz_convert(None).to_numpy(), tz="UTC"
+    ).tz_convert(golden_mst.tz)
+    expected_transit = pd.DatetimeIndex(
+        expected_rise_set_spa["transit"].dt.tz_convert(None).to_numpy(), tz="UTC"
+    ).tz_convert(golden_mst.tz)
     # convert expected times to hours since midnight as arrays of floats
     expected_sunrise = solarposition._times_to_hours_after_local_midnight(
         expected_sunrise)

From 8df4f73977d949899c8ce292e7928420b865c8c1 Mon Sep 17 00:00:00 2001
From: Echedey Luis <80125792+echedey-ls@users.noreply.github.com>
Date: Tue, 27 Oct 2026 23:46:45 +0100
Subject: [PATCH 18/19] Fix Pandas4Warning: A future version of pandas will
 return a BaseOffset object instead of a string from infer_freq

A future version of pandas will return a BaseOffset object instead of a
string from infer_freq. Use
pd.set_option('future.infer_freq_returns_offset', True) to get the
future behavior, or set to False to keep the old behavior and silence
this warning. To preserve the string representation, use
``infer_freq(...).freqstr``.
---
 pvlib/snow.py  | 10 ++++++++--
 pvlib/tools.py | 39 ++++++++++++++++++++++++++++++++++++++-
 2 files changed, 46 insertions(+), 3 deletions(-)

diff --git a/pvlib/snow.py b/pvlib/snow.py
index 4492abc554..85774568bd 100644
--- a/pvlib/snow.py
+++ b/pvlib/snow.py
@@ -5,7 +5,13 @@
 
 import numpy as np
 import pandas as pd
-from pvlib.tools import sind, cosd, tand
+
+from pvlib.tools import (
+    _pandas_infer_freq_BaseOffset_transition_handler,
+    cosd,
+    sind,
+    tand,
+)
 
 
 def _time_delta_in_hours(times):
@@ -58,7 +64,7 @@ def fully_covered_nrel(snowfall, snow_depth=None, threshold_snowfall=1.,
     hourly_snow_rate = snowfall / timestep
     # if we can infer a time frequency, use first snowfall value
     # otherwise the first snowfall value is ignored
-    freq = pd.infer_freq(snowfall.index)
+    freq = _pandas_infer_freq_BaseOffset_transition_handler(snowfall.index)
     if freq is not None:
         timedelta = pd.tseries.frequencies.to_offset(freq) / pd.Timedelta('1h')
         hourly_snow_rate.iloc[0] = snowfall.iloc[0] / timedelta
diff --git a/pvlib/tools.py b/pvlib/tools.py
index aa58b280ad..ce92fbd681 100644
--- a/pvlib/tools.py
+++ b/pvlib/tools.py
@@ -9,6 +9,7 @@
 
 import numpy as np
 import pandas as pd
+from packaging.version import Version
 import zoneinfo
 
 
@@ -434,7 +435,8 @@ def _get_sample_intervals(times, win_length):
     )
 
     # determine if we can proceed
-    if times.inferred_freq and len(np.unique(deltas)) == 1:
+    if (_pandas_infer_freq_BaseOffset_transition_handler(times)
+        and len(np.unique(deltas)) == 1):
         sample_interval = times[1] - times[0]
         sample_interval = sample_interval.seconds / 60  # in minutes
         samples_per_window = int(win_length / sample_interval)
@@ -448,6 +450,41 @@ def _get_sample_intervals(times, win_length):
         raise NotImplementedError(message)
 
 
+def _pandas_infer_freq_BaseOffset_transition_handler(times):
+    """
+    Pandas 3.1.0 introduced the following deprecation [^1]:
+        Pandas4Warning: A future version of pandas will return a BaseOffset
+        object instead of a string from infer_freq.
+        Use pd.set_option('future.infer_freq_returns_offset', True) to get the
+        future behavior, or set to False to keep the old behavior and silence
+        this warning.
+        To preserve the string representation, use ``infer_freq(...).freqstr``
+
+    Side-effects must be avoided in user-code.
+
+    pd.infer_freq documentation is at [^2].
+    pd.tseries.offsets.BaseOffset documentation is at [^3].
+
+    Parameters
+    ----------
+    times : DatetimeIndex | TimedeltaIndex | Series | DatetimeLikeArrayMixin
+
+    Returns
+    -------
+    str
+
+    [^1]: pandas PR GH#64679: https://github.com/pandas-dev/pandas/pull/64679
+    [^2]: https://pandas.pydata.org/docs/reference/api/pandas.infer_freq.html
+    [^3]: https://pandas.pydata.org/docs/reference/api/pandas.tseries.offsets.BaseOffset.html
+    """
+    if Version(pd.__version__) < Version("3.1.0rc0"):
+        return pd.infer_freq(times)
+    with pd.option_context({'future.infer_freq_returns_offset': True}):
+        # relies on BaseOffset to work seamlessly with Pandas 4
+        base_offset = pd.infer_freq(times)
+        # base_offset:=None if unable to infer
+        return getattr(base_offset, "freqstr", None)
+
 def _degrees_to_index(degrees, coordinate):
     """Transform input degrees to an output index integer.
     Specify a degree value and either 'latitude' or 'longitude' to get

From 8ccdb20f8cdbdeaf5f750cd781418cd59be74113 Mon Sep 17 00:00:00 2001
From: Echedey Luis <80125792+echedey-ls@users.noreply.github.com>
Date: Wed, 28 Oct 2026 14:35:11 +0100
Subject: [PATCH 19/19] Review: Fix Pandas4Warning: assert_index_equal will use
 check_freq by default

tests/iotools/test_era5.py::test_get_era5_land

/home/runner/work/pvlib-python/pvlib-python/tests/iotools/test_era5.py:69:
Pandas4Warning: assert_index_equal will check the 'freq' attribute by
default in a future version; these freqs None and <Hour> do not match.
Pass check_freq=True or check_freq=False to silence this warning
    pd.testing.assert_index_equal(df.index, expected.index)

tests/iotools/test_nasa_power.py::test_get_nasa_power

/home/runner/work/pvlib-python/pvlib-python/tests/iotools/test_nasa_power.py:42:
Pandas4Warning: assert_index_equal will check the 'freq' attribute by
default in a future version; these freqs None and <Hour> do not match.
Pass check_freq=True or check_freq=False to silence this warning
    pd.testing.assert_index_equal(data.index, data_index)

tests/iotools/test_nasa_power.py::test_get_nasa_power_pvlib_params_naming

/home/runner/work/pvlib-python/pvlib-python/tests/iotools/test_nasa_power.py:57:
Pandas4Warning: assert_index_equal will check the 'freq' attribute by
default in a future version; these freqs None and <Hour> do not match.
Pass check_freq=True or check_freq=False to silence this warning
    pd.testing.assert_index_equal(data.index, data_index)
---
 tests/iotools/test_era5.py       | 9 +++++++--
 tests/iotools/test_nasa_power.py | 6 +++---
 2 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/tests/iotools/test_era5.py b/tests/iotools/test_era5.py
index 6e0703be28..3afab97ffd 100644
--- a/tests/iotools/test_era5.py
+++ b/tests/iotools/test_era5.py
@@ -8,7 +8,12 @@
 import pvlib
 import requests
 import os
-from tests.conftest import RERUNS, RERUNS_DELAY, requires_ecmwf_credentials
+from tests.conftest import (
+    RERUNS,
+    RERUNS_DELAY,
+    assert_index_equal,
+    requires_ecmwf_credentials,
+)
 
 
 @pytest.fixture
@@ -66,7 +71,7 @@ def test_get_era5_land(params, expected):
     df, meta = pvlib.iotools.get_era5(**params)
     assert np.isclose(meta['longitude'], -80.0)
     assert np.isclose(meta['latitude'], 40.0)
-    pd.testing.assert_index_equal(df.index, expected.index)
+    assert_index_equal(df.index, expected.index)
     assert set(df.columns) == {'ghi', 'temp_air'}
     assert df.notna().all().all()
 
diff --git a/tests/iotools/test_nasa_power.py b/tests/iotools/test_nasa_power.py
index dd09d7b1ca..7d7ffeab32 100644
--- a/tests/iotools/test_nasa_power.py
+++ b/tests/iotools/test_nasa_power.py
@@ -2,7 +2,7 @@
 import pytest
 import pvlib
 from requests.exceptions import HTTPError
-from tests.conftest import RERUNS, RERUNS_DELAY
+from tests.conftest import RERUNS, RERUNS_DELAY, assert_index_equal
 
 
 @pytest.fixture
@@ -39,7 +39,7 @@ def test_get_nasa_power(data_index, ghi_series):
     assert meta['time_standard'] == 'UTC'
     assert meta['title'] == 'NASA/POWER Source Native Resolution Hourly Data'
     # Assert that the index is parsed correctly
-    pd.testing.assert_index_equal(data.index, data_index)
+    assert_index_equal(data.index, data_index)
     # Test one column
     pd.testing.assert_series_equal(data['ALLSKY_SFC_SW_DWN'], ghi_series,
                                    check_freq=False, check_names=False)
@@ -54,7 +54,7 @@ def test_get_nasa_power_pvlib_params_naming(data_index, ghi_series):
                                               end=data_index[-1],
                                               parameters=['ghi'])
     # Assert that the index is parsed correctly
-    pd.testing.assert_index_equal(data.index, data_index)
+    assert_index_equal(data.index, data_index)
     # Test one column
     pd.testing.assert_series_equal(data['ghi'], ghi_series,
                                    check_freq=False)