Correct dtype bug in temperature.fuentes (pvlib#2745)

* fix dtype bug

* whatsnew

* add new test

* Update tests/test_temperature.py

Co-authored-by: Kevin Anderson <kevin.anderso@gmail.com>

* Update docs/sphinx/source/whatsnew/v0.15.2.rst

Co-authored-by: Kevin Anderson <kevin.anderso@gmail.com>

* pvsystem test

* Update docs/sphinx/source/whatsnew/v0.15.2.rst

Co-authored-by: Kevin Anderson <kevin.anderso@gmail.com>

---------

Co-authored-by: Kevin Anderson <kevin.anderso@gmail.com>

Author: cwhanse

docs/sphinx/source/whatsnew/v0.15.2.rst

@@ -14,7 +14,10 @@ Deprecations
 
 Bug fixes
 ~~~~~~~~~
-
+* Corrects a bug in :py:func:`pvlib.temperature.fuentes`. If inputs were
+  data type integer, users can expect modeled cell temperature values to
+  increase slightly.
+  (:issue:`2608`, :pull:`2745`)
 
 Enhancements
 ~~~~~~~~~~~~
@@ -46,3 +49,4 @@ Maintenance
 Contributors
 ~~~~~~~~~~~~
 * :ghuser:`Omesh37`
+* Cliff Hansen (:ghuser:`cwhanse`)

pvlib/temperature.py

@@ -6,7 +6,6 @@
 import numpy as np
 import pandas as pd
 from pvlib.tools import sind
-from pvlib._deprecation import warn_deprecated
 from pvlib.tools import _get_sample_intervals
 import scipy
 import scipy.constants
@@ -883,7 +882,7 @@ def fuentes(poa_global, temp_air, wind_speed, noct_installed, module_height=5,
     windmod_array = wind_speed * (module_height/wind_height)**0.2 + 1e-4
 
     tmod0 = 293.15
-    tmod_array = np.zeros_like(poa_global)
+    tmod_array = np.zeros_like(poa_global, dtype=float)
 
     iterator = zip(tamb_array, sun_array, windmod_array, tsky_array,
                    timedelta_hours)

tests/test_pvsystem.py

@@ -711,7 +711,7 @@ def test_PVSystem_fuentes_celltemp(mocker):
     assert_series_equal(spy.call_args[0][1], temps)
     assert_series_equal(spy.call_args[0][2], winds)
     assert spy.call_args[0][3] == noct_installed
-    assert_series_equal(out, pd.Series([52.85, 55.85, 55.85], index,
+    assert_series_equal(out, pd.Series([52.884, 56.835, 56.836], index,
                                        name='tmod'))
 
 

tests/test_temperature.py

@@ -271,7 +271,16 @@ def test_fuentes_timezone(tz):
     out = temperature.fuentes(df['poa_global'], df['temp_air'],
                               df['wind_speed'], noct_installed=45)
 
-    assert_series_equal(out, pd.Series([47.85, 50.85, 50.85], index=index,
+    assert_series_equal(out, pd.Series([48.042, 51.845, 51.846], index=index,
+                                       name='tmod'))
+    # GH 2608
+    df = pd.DataFrame({'poa_global': 1000., 'temp_air': 20., 'wind_speed': 1.},
+                      index)
+
+    out = temperature.fuentes(df['poa_global'], df['temp_air'],
+                              df['wind_speed'], noct_installed=45)
+
+    assert_series_equal(out, pd.Series([48.042, 51.845, 51.846], index=index,
                                        name='tmod'))