Catch exceptions in i_mp_ic computation and update docstring

Author: markcampanelli

pvlib/pvsystem.py

@@ -3048,17 +3048,22 @@ def max_power_point_mismatched(
     previous step may speed up computation. Algorithm falls back to automated
     computation of i_mp_ic if solution fails with provided i_mp_ic. The value
     of i_mp_ic used is returned along with i_mp (same value for all devices),
-    v_mp, and p_mp.
+    v_mp, p_mp, i_mp_string, v_mp_string, and p_mp_string.
     """
     if i_mp_ic is None:
-        i_mp_ic = max_power_point(
-            np.mean(photocurrent),
-            np.mean(saturation_current),
-            np.mean(resistance_series),
-            np.mean(resistance_shunt),
-            np.mean(nNsVth),
-        )["i_mp"]
         retry_ic = False
+        try:
+            i_mp_ic = max_power_point(
+                np.mean(photocurrent),
+                np.mean(saturation_current),
+                np.mean(resistance_series),
+                np.mean(resistance_shunt),
+                np.mean(nNsVth),
+            )["i_mp"]
+        except Exception as exc:
+            raise RuntimeError(
+                f"unsuccessful determination of i_mp_ic"
+            ) from exc
     else:
         retry_ic = True
 

pvlib/tests/test_pvsystem.py

@@ -2648,11 +2648,11 @@ def test_max_power_point_mismatched(inputs):
     print(result)
 
 
-def test_max_power_point_mismatched_error():
+def test_max_power_point_mismatched_exception():
     """
     Test errored max power point computation for mismatched devices in series.
     """
-    photocurrent = -6.2
+    photocurrent = -6.2  # This is bad.
     saturation_current = 1.0e-8
     resistance_series = 0.0001
     resistance_shunt = 5000.0
@@ -2661,7 +2661,7 @@ def test_max_power_point_mismatched_error():
     T_K = scipy.constants.convert_temperature(25.0, "Celsius", "Kelvin")
     nNsVth = 1.1 * 60 * k_B_J_per_K * T_K / q_C
 
-    with pytest.raises(ValueError) as e_info:
+    with pytest.raises(RuntimeError) as e_info:
         pvsystem.max_power_point_mismatched(
             photocurrent,
             saturation_current,