Reindl model bug fix to close #1153 (#1154)

* fixed reindl model to generate zeros when irradiance is zero.  Also revised the test

* typo fix

* stickler-ci edits

* added to what's new

* added to what's new

* formatting

Author: jsstein

docs/sphinx/source/whatsnew/v0.9.0.rst

@@ -100,7 +100,8 @@ Bug fixes
 * Pass weather data to solar position calculations in
   :ref:meth:`~pvlib.modelchain.ModelChain.prepare_inputs_from_poa`.
   (:issue:`1065`, :pull:`1140`)
-
+* Reindl model fixed to generate sky_diffuse=0 when GHI=0.
+  (:issue:`1153`, :pull:`1154`)
 Testing
 ~~~~~~~
 

pvlib/irradiance.py

@@ -886,8 +886,9 @@ def reindl(surface_tilt, surface_azimuth, dhi, dni, ghi, dni_extra,
     # these are the () and [] sub-terms of the second term of eqn 8
     term1 = 1 - AI
     term2 = 0.5 * (1 + tools.cosd(surface_tilt))
-    term3 = 1 + np.sqrt(HB / ghi) * (tools.sind(0.5 * surface_tilt) ** 3)
-
+    with np.errstate(invalid='ignore', divide='ignore'):
+        hb_to_ghi = np.where(ghi == 0, 0, np.divide(HB, ghi))
+    term3 = 1 + np.sqrt(hb_to_ghi) * (tools.sind(0.5 * surface_tilt)**3)
     sky_diffuse = dhi * (AI * Rb + term1 * term2 * term3)
     sky_diffuse = np.maximum(sky_diffuse, 0)
 

pvlib/tests/test_irradiance.py

@@ -203,7 +203,7 @@ def test_reindl(irrad_data, ephem_data, dni_et):
         40, 180, irrad_data['dhi'], irrad_data['dni'], irrad_data['ghi'],
         dni_et, ephem_data['apparent_zenith'], ephem_data['azimuth'])
     # values from matlab 1.4 code
-    assert_allclose(result, [np.nan, 27.9412, 104.1317, 34.1663], atol=1e-4)
+    assert_allclose(result, [0., 27.9412, 104.1317, 34.1663], atol=1e-4)
 
 
 def test_king(irrad_data, ephem_data):