Push breaking test for discussion purposes

Author: markcampanelli

pvlib/irradiance.py

@@ -1042,10 +1042,14 @@ def perez(surface_tilt, surface_azimuth, dhi, dni, dni_extra,
     Perez models determine the diffuse irradiance from the sky (ground
     reflected irradiance is not included in this algorithm) on a tilted
     surface using the surface tilt angle, surface azimuth angle, diffuse
-    horizontal irradiance, direct normal irradiance, extraterrestrial
-    irradiance, sun zenith angle, sun azimuth angle, and relative (not
-    pressure-corrected) airmass. Optionally a selector may be used to
-    use any of Perez's model coefficient sets.
+    horizontal irradiance (DHI), direct normal irradiance (DNI),
+    extraterrestrial irradiance, sun zenith angle, sun azimuth angle, and
+    relative (not pressure-corrected) airmass. Optionally a selector may be
+    used to use any of Perez's model coefficient sets. It is expected that if
+    DHI is zero, then DNI is also zero, otherwise a FloatingPointError is
+    raised due to a division of a nonzero (and not NaN) value by zero. It is
+    also expected that extraterrestrial irradiance is positive. If airmass
+    is NaN, then the total and all components are zero.
 
     Warning
     -------
@@ -1125,6 +1129,11 @@ def perez(surface_tilt, surface_azimuth, dhi, dni, dni_extra,
             * poa_circumsolar
             * poa_horizon
 
+    Raises
+    ------
+    FloatingPointError
+        If dni is zero when dhi is not zero and not NaN.
+
 
     References
     ----------

tests/test_irradiance.py

@@ -456,6 +456,45 @@ def test_perez_array_dhi_and_dni_combos():
     )
 
 
+def test_perez_array_dhi_and_dni_combos_nan_airmass():
+    # Divides zero and non-zero by zero and various NaN division combos, when
+    # airmass is NaN (e.g., for sun below horizon).
+    args = (
+        20, 180,
+        np.array([0.0, 10.0, np.nan, np.nan, 0.0, 100.0, np.nan]),
+        np.array([0.0, 0.0, 0.0, 100.0, np.nan, np.nan, np.nan]),
+        1366.1, 89.96, 256.28, np.nan
+    )
+
+    out = irradiance.perez(*args)
+    poa_sky_diffuse_expected = np.array(
+        [0.0, 0.0, np.nan, np.nan, np.nan, np.nan, np.nan]
+    )
+    assert_allclose(out, poa_sky_diffuse_expected)
+
+    out = irradiance.perez(*args, return_components=True)
+    expected = {
+        "poa_sky_diffuse": poa_sky_diffuse_expected,
+        "poa_isotropic": np.array(
+            [0.0, 9.162258932459126, np.nan, np.nan, np.nan, np.nan, np.nan]
+        ),
+        "poa_circumsolar": np.array(
+            [0.0, 0.5187450944545264, np.nan, np.nan, np.nan, np.nan, np.nan]
+        ),
+        "poa_horizon": np.array(
+            [0.0, -0.2560798402944465, np.nan, np.nan, np.nan, np.nan, np.nan]
+        ),
+    }
+    assert len(out) == len(expected)
+    for key in expected.keys():
+        assert_allclose(out[key], expected[key], err_msg=key)
+
+    assert_almost_equal(
+        out["poa_sky_diffuse"],
+        out["poa_isotropic"] + out["poa_circumsolar"] + out["poa_horizon"],
+    )
+
+
 def test_perez_zero_dhi_nonzero_dni_scalar():
     # Divides nonzero by zero.
     args = (20, 180, 0.0, 100.0, 1366.1, 89.96, 256.28, 37.32)