Minimal functionality for early feedback

Author: markcampanelli

pvlib/pvsystem.py

@@ -7,11 +7,13 @@
 import functools
 import io
 import itertools
+import numbers
 import os
 import inspect
 from urllib.request import urlopen
 import numpy as np
 from scipy import constants
+import scipy.optimize
 import pandas as pd
 from dataclasses import dataclass
 from abc import ABC, abstractmethod
@@ -3022,3 +3024,58 @@ def combine_loss_factors(index, *losses, fill_method='ffill'):
         combined_factor *= (1 - loss)
 
     return 1 - combined_factor
+
+
+def _negative_total_power(current, *args):
+    """
+    Compute negative of total power generated by devices in series at specified current.
+    """
+    return -np.sum(current * v_from_i(current, *args))
+
+
+def max_power_point_mismatched(
+        photocurrent, saturation_current, resistance_series, resistance_shunt, nNsVth,
+):
+    """Compute maximum power info for (possibly) mismatched set of devices in series."""
+    if all([isinstance(input, numbers.Number) for input in (
+       photocurrent, saturation_current, resistance_series, resistance_shunt, nNsVth 
+    )]):
+        # There cannot be mismatch, so fall back to non-mismatch function.
+        return {
+            **max_power_point(
+                photocurrent,
+                saturation_current,
+                resistance_series,
+                resistance_shunt,
+                nNsVth
+            )
+        }
+
+    i_mp_0 = max_power_point(
+        np.mean(photocurrent),
+        np.mean(saturation_current),
+        np.mean(resistance_series),
+        np.mean(resistance_shunt),
+        np.mean(nNsVth),
+    )["i_mp"]
+    args = photocurrent, saturation_current, resistance_series, resistance_shunt, nNsVth
+    sol = scipy.optimize.minimize(_negative_total_power, i_mp_0, args)
+
+    if sol.success:
+        i_mp = sol.x[0]
+        v_mp = v_from_i(
+            i_mp,
+            photocurrent,
+            saturation_current,
+            resistance_series,
+            resistance_shunt,
+            nNsVth,
+        )
+
+        return {
+            "i_mp": i_mp,
+            "v_mp": v_mp,
+            "p_mp": i_mp * v_mp,
+        }
+
+    raise RuntimeError(f"unsuccessful solution: {sol}")

pvlib/tests/test_pvsystem.py

@@ -4,6 +4,7 @@
 import numpy as np
 from numpy import nan, array
 import pandas as pd
+import scipy.constants
 
 import pytest
 from .conftest import (
@@ -2549,3 +2550,47 @@ def test_Array_temperature_missing_parameters(model, keys):
         array.temperature_model_parameters = params
         with pytest.raises(KeyError, match=match):
             array.get_cell_temperature(irrads, temps, winds, model)
+
+
+@pytest.mark.parametrize(
+    'inputs', 
+    [
+        {
+            "photocurrent": 6.2,
+            "saturation_current": 1.0e-8,
+            "n": 1.1,
+            "resistance_series": 0.0001,
+            "resistance_shunt": 5000.0,
+            "Ns": 60,
+            "T": 25.0,
+        },
+        {
+            "photocurrent": np.array([5.8, 6.2]),
+            "saturation_current": 1.0e-8,
+            "n": 1.1,
+            "resistance_series": 0.0001,
+            "resistance_shunt": 5000.0,
+            "Ns": 60,
+            "T": 25.0,
+        }
+    ]
+)
+def test_max_power_point_mismatched(inputs):
+    """Test max power point computaiton for mismatched devices in series."""
+
+    photocurrent = inputs["photocurrent"]
+    saturation_current = inputs["saturation_current"]
+    resistance_series = inputs["resistance_series"]
+    resistance_shunt = inputs["resistance_shunt"]
+    q_C = scipy.constants.value("elementary charge")
+    k_B_J_per_K = scipy.constants.value("Boltzmann constant")
+    T_K = scipy.constants.convert_temperature(inputs["T"], "Celsius", "Kelvin")
+    nNsVth = inputs["n"] * inputs["Ns"] * k_B_J_per_K * T_K / q_C
+
+    pvsystem.max_power_point_mismatched(
+        photocurrent,
+        saturation_current,
+        resistance_series,
+        resistance_shunt,
+        nNsVth,
+    )