tests

Author: kandersolar

pvlib/pvarray.py

@@ -474,7 +474,11 @@ def batzelis(effective_irradiance, temp_cell,
     delT = temp_cell - (t0 - 273.15)
     lamT = (temp_cell + 273.15) / t0
     g = effective_irradiance / 1000
-    lnG = np.log(g)
+    # for zero/negative irradiance, use lnG=large negative number so that
+    # computed voltages are negative and then clipped to zero
+    with np.errstate(divide='ignore'):  # needed for pandas for some reason
+        lnG = np.log(g, out=np.full_like(g, -9e9), where=g>0)
+        lnG = np.where(np.isfinite(g), lnG, np.nan)  # also preserve nans
 
     # Eq 9-10
     del0 = (1 - beta_voc * t0) / (50.1 - alpha_sc * t0)
@@ -497,6 +501,10 @@ def batzelis(effective_irradiance, temp_cell,
     imp = g * imp0 * (1 + alpha_imp * delT)
     vmp = vmp0 * (1 + eps0 * lamT * lnG + eps1 * (1 - g) + beta_vmp * delT)
 
+    # handle negative voltages from zero and extremely small irradiance
+    vmp = np.clip(vmp, a_min=0, a_max=None)
+    voc = np.clip(voc, a_min=0, a_max=None)
+
     return {
         'p_mp': vmp * imp,
         'i_mp': imp,

tests/test_pvarray.py

@@ -1,4 +1,5 @@
 import numpy as np
+from numpy import nan
 import pandas as pd
 from numpy.testing import assert_allclose
 from .conftest import assert_series_equal
@@ -114,3 +115,40 @@ def test_huld_errors():
         pvarray.huld(
             eff_irr, temp_mod, pdc0, cell_type='csi', k_version='2021'
         )
+
+
+def test_batzelis():
+    params = {'isc0': 15.98, 'voc0': 50.26, 'imp0': 15.27, 'vmp0': 42.57,
+              'alpha_sc': 0.00046, 'beta_voc': -0.0024}
+    g = np.array([1000, 500, 1200, 500, 1200, 0, nan, 1000])
+    t = np.array([25, 20, 20, 50, 50, 25, 0, nan])
+    expected = {  # these values were computed using the function itself
+        'p_mp': [650.044, 328.599, 789.136, 300.079, 723.401, 0, nan, nan],
+        'i_mp': [ 15.270,   7.626,  18.302,   7.680,  18.433, 0, nan, nan],
+        'v_mp': [ 42.570,  43.090,  43.117,  39.071,  39.246, 0, nan, nan],
+        'i_sc': [ 15.980,   7.972,  19.132,   8.082,  19.397, 0, nan, nan],
+        'v_oc': [ 50.260,  49.687,  51.172,  45.948,  47.585, 0, nan, nan],
+     }
+    
+    # numpy array
+    actual = pvarray.batzelis(g, t, **params)
+    for key, exp in expected.items():
+        np.testing.assert_allclose(actual[key], exp, atol=1e-3)
+
+    # pandas series
+    actual = pvarray.batzelis(pd.Series(g), pd.Series(t), **params)
+    for key, exp in expected.items():
+        pd.testing.assert_series_equal(actual[key], pd.Series(exp), atol=1e-3)
+
+    # scalar
+    actual = pvarray.batzelis(g[1], t[1], **params)
+    for key, exp in expected.items():
+        assert pytest.approx(exp[1], abs=1e-3) == actual[key]
+
+
+def test_batzelis_negative_voltage():
+    params = {'isc0': 15.98, 'voc0': 50.26, 'imp0': 15.27, 'vmp0': 42.57,
+              'alpha_sc': 0.00046, 'beta_voc': -0.0024}
+    actual = pvarray.batzelis(1e-10, 25, **params)
+    assert actual['v_mp'] == 0
+    assert actual['v_oc'] == 0