BUG: raise ValueError in dirint when use_delta_kt_prime=True and len(times)<2

Author: Omesh37

pvlib/irradiance.py

@@ -1983,6 +1983,9 @@ def dirint(ghi, solar_zenith, times, pressure=101325., use_delta_kt_prime=True,
        SERI/TR-215-3087, Golden, CO: Solar Energy Research Institute, 1987.
     """
 
+    if use_delta_kt_prime and len(times) < 2:
+        raise ValueError('The DIRINT model requires at least two times')
+
     disc_out = disc(ghi, solar_zenith, times, pressure=pressure,
                     min_cos_zenith=min_cos_zenith, max_zenith=max_zenith)
     airmass = disc_out['airmass']

tests/test_irradiance.py

@@ -1142,7 +1142,6 @@ def test_dirindex_min_cos_zenith_max_zenith():
 
 def test_dirint_array_inputs():
     """np.array and pd.Series inputs work correctly. GH #2751"""
-    # dirint requires >= 2 time points
     times = pd.date_range('2023-06-21 10:00', periods=2, freq='h', tz='UTC')
 
     # np.array input → should return pd.Series
@@ -1165,15 +1164,25 @@ def test_dirint_array_inputs():
     assert isinstance(result2, pd.Series)
     assert (result2 >= 0).all()
 
-    # single time point → ValueError regardless of use_delta_kt_prime
+    # single time point + use_delta_kt_prime=True → ValueError
     times_single = pd.DatetimeIndex(['2023-06-21 12:00'], tz='UTC')
     with pytest.raises(ValueError, match="requires at least two times"):
         irradiance.dirint(
             ghi=np.array([500.0]),
             solar_zenith=np.array([45.0]),
-            times=times_single
+            times=times_single,
+            use_delta_kt_prime=True
         )
 
+    # single time point + use_delta_kt_prime=False → no error
+    result3 = irradiance.dirint(
+        ghi=np.array([500.0]),
+        solar_zenith=np.array([45.0]),
+        times=times_single,
+        use_delta_kt_prime=False
+    )
+    assert isinstance(result3, pd.Series)
+
 
 def test_dni():
     ghi = pd.Series([90, 100, 100, 100, 100])