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Fix perez ZeroDivisionError on scalar dhi=0 #2826

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Fix perez ZeroDivisionError on scalar dhi=0 #2826

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436293f
Fix perez ZeroDivisionError on scalar dhi=0
chuenchen309 Jul 17, 2026
5920f91
Add whatsnew entry for perez scalar dhi=0 fix
chuenchen309 Jul 17, 2026
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4 changes: 4 additions & 0 deletions docs/sphinx/source/whatsnew/v0.16.0.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,9 @@ Deprecations

Bug fixes
~~~~~~~~~
* :py:func:`~pvlib.irradiance.perez` no longer raises ``ZeroDivisionError`` on
scalar ``dhi=0`` input (e.g. nighttime); the scalar path now returns the same
finite value as the array path. (:pull:`2826`)


Enhancements
Expand Down Expand Up @@ -48,3 +51,4 @@ Maintenance
Contributors
~~~~~~~~~~~~
* Carolina Crespo (:ghuser:`cbcrespo`)
* Andrew Chen (:ghuser:`chuenchen309`)
8 changes: 6 additions & 2 deletions pvlib/irradiance.py
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Expand Up @@ -1146,8 +1146,12 @@ def perez(surface_tilt, surface_azimuth, dhi, dni, dni_extra,
delta = dhi * airmass / dni_extra

# epsilon is the sky's "clearness"
with np.errstate(invalid='ignore'):
eps = ((dhi + dni) / dhi + kappa * (z ** 3)) / (1 + kappa * (z ** 3))
# np.true_divide so a Python-scalar dhi=0 yields inf/nan like the array
# path (handled below via digitize) instead of raising ZeroDivisionError,
# which np.errstate cannot suppress for native scalar division.
with np.errstate(invalid='ignore', divide='ignore'):
eps = (np.true_divide(dhi + dni, dhi) + kappa * (z ** 3)) \
/ (1 + kappa * (z ** 3))

# numpy indexing below will not work with a Series
if isinstance(eps, pd.Series):
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10 changes: 10 additions & 0 deletions tests/test_irradiance.py
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Expand Up @@ -429,6 +429,16 @@ def test_perez_scalar():
assert_allclose(out, 109.084332)


def test_perez_scalar_dhi_zero():
# dhi=0 (e.g. nighttime) is documented-valid input (dhi >= 0). A native
# Python scalar division raised ZeroDivisionError (which np.errstate cannot
# suppress) while the array path returns a finite value; they must match.
out = irradiance.perez(30, 180, 0.0, 800.0, 1400.0, 40.0, 120.0, 1.5)
expected = irradiance.perez(30, 180, np.array([0.0]), np.array([800.0]),
1400.0, 40.0, 120.0, np.array([1.5]))
assert_allclose(out, expected[0])


def test_perez_driesse_scalar():
# copied values from fixtures
out = irradiance.perez_driesse(40, 180, 118.458, 939.954,
Expand Down