Implement Caballero et al. spectral factor model

docs/sphinx/source/reference/effects_on_pv_system_output/spectrum.rst

@@ -10,5 +10,6 @@ Spectrum
    spectrum.get_example_spectral_response
    spectrum.get_am15g
    spectrum.calc_spectral_mismatch_field
+   spectrum.spectral_factor_caballero
    spectrum.spectral_factor_firstsolar
    spectrum.spectral_factor_sapm

docs/sphinx/source/whatsnew/v0.9.6.rst

@@ -33,6 +33,8 @@ Deprecations
 
 Enhancements
 ~~~~~~~~~~~~
+* Added a function :py:func:`pvlib.spectrum.spectral_factor_caballero`
+  to estimate spectral mismatch modifiers from atmospheric conditions. (:pull:`1296`)
 * Added a new irradiance decomposition model :py:func:`pvlib.irradiance.louche`. (:pull:`1705`)
 * Add optional encoding parameter to :py:func:`pvlib.iotools.read_tmy3`.
   (:issue:`1732`, :pull:`1737`)
@@ -90,6 +92,7 @@ Contributors
 * Siddharth Kaul (:ghuser:`k10blogger`)
 * Kshitiz Gupta (:ghuser:`kshitiz305`)
 * Stefan de Lange (:ghuser:`langestefan`)
+* Jose Antonio Caballero (:ghuser:`Jacc0027`)
 * Andy Lam (:ghuser:`@andylam598`)
 * :ghuser:`ooprathamm`
 * Kevin Anderson (:ghuser:`kandersolar`)

pvlib/spectrum/__init__.py

@@ -3,6 +3,7 @@
     calc_spectral_mismatch_field,
     get_am15g,
     get_example_spectral_response,
+    spectral_factor_caballero,
     spectral_factor_firstsolar,
     spectral_factor_sapm,
 )

pvlib/spectrum/mismatch.py

@@ -320,7 +320,7 @@ def spectral_factor_firstsolar(pw, airmass_absolute, module_type=None,
     Returns
     -------
     modifier: array-like
-        spectral mismatch factor (unitless) which is can be multiplied
+        spectral mismatch factor (unitless) which is multiplied
         with broadband irradiance reaching a module's cells to estimate
         effective irradiance, i.e., the irradiance that is converted to
         electrical current.
@@ -446,3 +446,123 @@ def spectral_factor_sapm(airmass_absolute, module):
         spectral_loss = pd.Series(spectral_loss, airmass_absolute.index)
 
     return spectral_loss
+
+
+def spectral_factor_caballero(precipitable_water, airmass_absolute, aod500,
+                              module_type=None, coefficients=None):
+    r"""
+    Estimate a technology-specific spectral mismatch modifier from
+    airmass, aerosol optical depth, and atmospheric precipitable water,
+    using the Caballero model.
+
+    The model structure was motivated by examining the effect of these three
+    atmospheric parameters on simulated irradiance spectra and spectral
+    modifiers.  However, the coefficient values reported in [1]_ and
+    available here via the ``module_type`` parameter were determined
+    by fitting the model equations to spectral factors calculated from
+    global tilted spectral irradiance measurements taken in the city of
+    Jaén, Spain.  See [1]_ for details.
+
+    Parameters
+    ----------
+    precipitable_water : numeric
+        atmospheric precipitable water. [cm]
+
+    airmass_absolute : numeric
+        absolute (pressure-adjusted) airmass. [unitless]
+
+    aod500 : numeric
+        atmospheric aerosol optical depth at 500 nm. [unitless]
+
+    module_type : str, optional
+        One of the following PV technology strings from [1]_:
+
+        * ``'cdte'`` - anonymous CdTe module.
+        * ``'monosi'``, - anonymous sc-si module.
+        * ``'multisi'``, - anonymous mc-si- module.
+        * ``'cigs'`` - anonymous copper indium gallium selenide module.
+        * ``'asi'`` - anonymous amorphous silicon module.
+        * ``'perovskite'`` - anonymous pervoskite module.
+
+    coefficients : array-like, optional
+        user-defined coefficients, if not using one of the default coefficient
+        sets via the ``module_type`` parameter.
+
+    Returns
+    -------
+    modifier: numeric
+        spectral mismatch factor (unitless) which is multiplied
+        with broadband irradiance reaching a module's cells to estimate
+        effective irradiance, i.e., the irradiance that is converted to
+        electrical current.
+
+    References
+    ----------
+    .. [1] Caballero, J.A., Fernández, E., Theristis, M.,
+        Almonacid, F., and Nofuentes, G. "Spectral Corrections Based on
+        Air Mass, Aerosol Optical Depth and Precipitable Water
+        for PV Performance Modeling."
+        IEEE Journal of Photovoltaics 2018, 8(2), 552-558.
+        :doi:`10.1109/jphotov.2017.2787019`
+    """
+
+    if module_type is None and coefficients is None:
+        raise ValueError('Must provide either `module_type` or `coefficients`')
+    if module_type is not None and coefficients is not None:
+        raise ValueError('Only one of `module_type` and `coefficients` should '
+                         'be provided')
+
+    # Experimental coefficients from [1]_.
+    # The extra 0/1 coefficients at the end are used to enable/disable
+    # terms to match the different equation forms in Table 1.
+    _coefficients = {}
+    _coefficients['cdte'] = (
+        1.0044, 0.0095, -0.0037, 0.0002, 0.0000, -0.0046,
+        -0.0182, 0, 0.0095, 0.0068, 0, 1)
+    _coefficients['monosi'] = (
+        0.9706, 0.0377, -0.0123, 0.0025, -0.0002, 0.0159,
+        -0.0165, 0, -0.0016, -0.0027, 1, 0)
+    _coefficients['multisi'] = (
+        0.9836, 0.0254, -0.0085, 0.0016, -0.0001, 0.0094,
+        -0.0132, 0, -0.0002, -0.0011, 1, 0)
+    _coefficients['cigs'] = (
+        0.9801, 0.0283, -0.0092, 0.0019, -0.0001, 0.0117,
+        -0.0126, 0, -0.0011, -0.0019, 1, 0)
+    _coefficients['asi'] = (
+        1.1060, -0.0848, 0.0302, -0.0076, 0.0006, -0.1283,
+        0.0986, -0.0254, 0.0156, 0.0146, 1, 0)
+    _coefficients['perovskite'] = (
+        1.0637, -0.0491, 0.0180, -0.0047, 0.0004, -0.0773,
+        0.0583, -0.0159, 0.01251, 0.0109, 1, 0)
+
+    if module_type is not None:
+        coeff = _coefficients[module_type]
+    else:
+        coeff = coefficients
+
+    # Evaluate spectral correction factor
+    ama = airmass_absolute
+    aod500_ref = 0.084
+    pw_ref = 1.4164
+
+    f_AM = (
+        coeff[0]
+        + coeff[1] * ama
+        + coeff[2] * ama**2
+        + coeff[3] * ama**3
+        + coeff[4] * ama**4
+    )
+    # Eq 6, with Table 1
+    f_AOD = (aod500 - aod500_ref) * (
+        coeff[5]
+        + coeff[10] * coeff[6] * ama
+        + coeff[11] * coeff[6] * np.log(ama)
+        + coeff[7] * ama**2
+    )
+    # Eq 7, with Table 1
+    f_PW = (precipitable_water - pw_ref) * (
+        coeff[8]
+        + coeff[9] * np.log(ama)
+    )
+    modifier = f_AM + f_AOD + f_PW  # Eq 5
+    return modifier

pvlib/tests/test_spectrum.py

@@ -269,3 +269,47 @@ def test_spectral_factor_sapm(sapm_module_params, airmass, expected):
         assert_series_equal(out, expected, check_less_precise=4)
     else:
         assert_allclose(out, expected, atol=1e-4)
+
+
+@pytest.mark.parametrize("module_type,expected", [
+    ('asi', np.array([0.9108, 0.9897, 0.9707, 1.0265, 1.0798, 0.9537])),
+    ('perovskite', np.array([0.9422, 0.9932, 0.9868, 1.0183, 1.0604, 0.9737])),
+    ('cdte', np.array([0.9824, 1.0000, 1.0065, 1.0117, 1.042, 0.9979])),
+    ('multisi', np.array([0.9907, 0.9979, 1.0203, 1.0081, 1.0058, 1.019])),
+    ('monosi', np.array([0.9935, 0.9987, 1.0264, 1.0074, 0.9999, 1.0263])),
+    ('cigs', np.array([1.0014, 1.0011, 1.0270, 1.0082, 1.0029, 1.026])),
+])
+def test_spectral_factor_caballero(module_type, expected):
+    ams = np.array([3.0, 1.5, 3.0, 1.5, 1.5, 3.0])
+    aods = np.array([1.0, 1.0, 0.02, 0.02, 0.08, 0.08])
+    pws = np.array([1.42, 1.42, 1.42, 1.42, 4.0, 1.0])
+    out = spectrum.spectral_factor_caballero(pws, ams, aods,
+                                             module_type=module_type)
+    assert np.allclose(expected, out, atol=1e-3)
+
+
+def test_spectral_factor_caballero_supplied():
+    # use the cdte coeffs
+    coeffs = (
+        1.0044, 0.0095, -0.0037, 0.0002, 0.0000, -0.0046,
+        -0.0182, 0, 0.0095, 0.0068, 0, 1)
+    out = spectrum.spectral_factor_caballero(1, 1, 1, coefficients=coeffs)
+    expected = 1.0021964
+    assert_allclose(out, expected, atol=1e-3)
+
+
+def test_spectral_factor_caballero_supplied_redundant():
+    # Error when specifying both module_type and coefficients
+    coeffs = (
+        1.0044, 0.0095, -0.0037, 0.0002, 0.0000, -0.0046,
+        -0.0182, 0, 0.0095, 0.0068, 0, 1)
+    with pytest.raises(ValueError):
+        spectrum.spectral_factor_caballero(1, 1, 1, module_type='cdte',
+                                           coefficients=coeffs)
+
+
+def test_spectral_factor_caballero_supplied_ambiguous():
+    # Error when specifying neither module_type nor coefficients
+    with pytest.raises(ValueError):
+        spectrum.spectral_factor_caballero(1, 1, 1, module_type=None,
+                                           coefficients=None)