Migrate spectral modifier functions to pvlib.spectrum

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

@@ -10,3 +10,5 @@ Spectrum
    spectrum.get_example_spectral_response
    spectrum.get_am15g
    spectrum.calc_spectral_mismatch_field
+   spectrum.first_solar_spectral_correction
+   spectrum.sapm_spectral_correction

docs/sphinx/source/whatsnew/v0.9.5.rst

@@ -12,6 +12,11 @@ the ``pvlib`` `conda channel<https://anaconda.org/pvlib/pvlib>`_.  We recommend
 
 Deprecations
 ~~~~~~~~~~~~
+* Functions for calculating spectral modifiers have been moved to :py:mod:`pvlib.spectrum`:
+  ``pvlib.atmosphere.first_solar_spectral_correction`` is now
+  :py:func:`pvlib.spectrum.first_solar_spectral_correction` and
+  ``pvlib.pvsystem.sapm_spectral_loss`` is now
+  :py:func:`pvlib.spectrum.sapm_spectral_correction`. (:pull:`1628`)
 
 
 Enhancements

pvlib/__init__.py

@@ -1,6 +1,9 @@
 from pvlib.version import __version__  # noqa: F401
 
 from pvlib import (  # noqa: F401
+    # list spectrum first so it's available for atmosphere & pvsystem (GH 1628)
+    spectrum,
+
     atmosphere,
     bifacial,
     clearsky,
@@ -20,7 +23,6 @@
     soiling,
     solarposition,
     spa,
-    spectrum,
     temperature,
     tools,
     tracking,

pvlib/atmosphere.py

@@ -3,11 +3,11 @@
 absolute airmass and to determine pressure from altitude or vice versa.
 """
 
-from warnings import warn
-
 import numpy as np
 import pandas as pd
+import pvlib
 
+from pvlib._deprecation import deprecated
 
 APPARENT_ZENITH_MODELS = ('simple', 'kasten1966', 'kastenyoung1989',
                           'gueymard1993', 'pickering2002')
@@ -321,175 +321,10 @@ def gueymard94_pw(temp_air, relative_humidity):
     return pw
 
 
-def first_solar_spectral_correction(pw, airmass_absolute,
-                                    module_type=None, coefficients=None,
-                                    min_pw=0.1, max_pw=8):
-    r"""
-    Spectral mismatch modifier based on precipitable water and absolute
-    (pressure-adjusted) airmass.
-
-    Estimates a spectral mismatch modifier :math:`M` representing the effect on
-    module short circuit current of variation in the spectral
-    irradiance. :math:`M`  is estimated from absolute (pressure currected) air
-    mass, :math:`AM_a`, and precipitable water, :math:`Pw`, using the following
-    function:
-
-    .. math::
-
-        M = c_1 + c_2 AM_a  + c_3 Pw  + c_4 AM_a^{0.5}
-            + c_5 Pw^{0.5} + c_6 \frac{AM_a} {Pw^{0.5}}
-
-    Default coefficients are determined for several cell types with
-    known quantum efficiency curves, by using the Simple Model of the
-    Atmospheric Radiative Transfer of Sunshine (SMARTS) [1]_. Using
-    SMARTS, spectrums are simulated with all combinations of AMa and
-    Pw where:
-
-       * :math:`0.5 \textrm{cm} <= Pw <= 5 \textrm{cm}`
-       * :math:`1.0 <= AM_a <= 5.0`
-       * Spectral range is limited to that of CMP11 (280 nm to 2800 nm)
-       * spectrum simulated on a plane normal to the sun
-       * All other parameters fixed at G173 standard
-
-    From these simulated spectra, M is calculated using the known
-    quantum efficiency curves. Multiple linear regression is then
-    applied to fit Eq. 1 to determine the coefficients for each module.
-
-    Based on the PVLIB Matlab function ``pvl_FSspeccorr`` by Mitchell
-    Lee and Alex Panchula of First Solar, 2016 [2]_.
-
-    Parameters
-    ----------
-    pw : array-like
-        atmospheric precipitable water. [cm]
-
-    airmass_absolute : array-like
-        absolute (pressure-adjusted) airmass. [unitless]
-
-    min_pw : float, default 0.1
-        minimum atmospheric precipitable water. Any pw value lower than min_pw
-        is set to min_pw to avoid model divergence. [cm]
-
-    max_pw : float, default 8
-        maximum atmospheric precipitable water. Any pw value higher than max_pw
-        is set to NaN to avoid model divergence. [cm]
-
-    module_type : None or string, default None
-        a string specifying a cell type. Values of 'cdte', 'monosi', 'xsi',
-        'multisi', and 'polysi' (can be lower or upper case). If provided,
-        module_type selects default coefficients for the following modules:
-
-            * 'cdte' - First Solar Series 4-2 CdTe module.
-            * 'monosi', 'xsi' - First Solar TetraSun module.
-            * 'multisi', 'polysi' - anonymous multi-crystalline silicon module.
-            * 'cigs' - anonymous copper indium gallium selenide module.
-            * 'asi' - anonymous amorphous silicon module.
-
-        The module used to calculate the spectral correction
-        coefficients corresponds to the Multi-crystalline silicon
-        Manufacturer 2 Model C from [3]_. The spectral response (SR) of CIGS
-        and a-Si modules used to derive coefficients can be found in [4]_
-
-    coefficients : None or array-like, default None
-        Allows for entry of user-defined spectral correction
-        coefficients. Coefficients must be of length 6. Derivation of
-        coefficients requires use of SMARTS and PV module quantum
-        efficiency curve. Useful for modeling PV module types which are
-        not included as defaults, or to fine tune the spectral
-        correction to a particular PV module. Note that the parameters for
-        modules with very similar quantum efficiency should be similar,
-        in most cases limiting the need for module specific coefficients.
-
-    Returns
-    -------
-    modifier: array-like
-        spectral mismatch factor (unitless) which is can be 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] Gueymard, Christian. SMARTS2: a simple model of the atmospheric
-       radiative transfer of sunshine: algorithms and performance
-       assessment. Cocoa, FL: Florida Solar Energy Center, 1995.
-    .. [2] Lee, Mitchell, and Panchula, Alex. "Spectral Correction for
-       Photovoltaic Module Performance Based on Air Mass and Precipitable
-       Water." IEEE Photovoltaic Specialists Conference, Portland, 2016
-    .. [3] Marion, William F., et al. User's Manual for Data for Validating
-       Models for PV Module Performance. National Renewable Energy
-       Laboratory, 2014. http://www.nrel.gov/docs/fy14osti/61610.pdf
-    .. [4] Schweiger, M. and Hermann, W, Influence of Spectral Effects
-       on Energy Yield of Different PV Modules: Comparison of Pwat and
-       MMF Approach, TUV Rheinland Energy GmbH report 21237296.003,
-       January 2017
-    """
-
-    # --- Screen Input Data ---
-
-    # *** Pw ***
-    # Replace Pw Values below 0.1 cm with 0.1 cm to prevent model from
-    # diverging"
-    pw = np.atleast_1d(pw)
-    pw = pw.astype('float64')
-    if np.min(pw) < min_pw:
-        pw = np.maximum(pw, min_pw)
-        warn(f'Exceptionally low pw values replaced with {min_pw} cm to '
-             'prevent model divergence')
-
-    # Warn user about Pw data that is exceptionally high
-    if np.max(pw) > max_pw:
-        pw[pw > max_pw] = np.nan
-        warn('Exceptionally high pw values replaced by np.nan: '
-             'check input data.')
-
-    # *** AMa ***
-    # Replace Extremely High AM with AM 10 to prevent model divergence
-    # AM > 10 will only occur very close to sunset
-    if np.max(airmass_absolute) > 10:
-        airmass_absolute = np.minimum(airmass_absolute, 10)
-
-    # Warn user about AMa data that is exceptionally low
-    if np.min(airmass_absolute) < 0.58:
-        warn('Exceptionally low air mass: ' +
-             'model not intended for extra-terrestrial use')
-        # pvl_absoluteairmass(1,pvl_alt2pres(4340)) = 0.58 Elevation of
-        # Mina Pirquita, Argentian = 4340 m. Highest elevation city with
-        # population over 50,000.
-
-    _coefficients = {}
-    _coefficients['cdte'] = (
-        0.86273, -0.038948, -0.012506, 0.098871, 0.084658, -0.0042948)
-    _coefficients['monosi'] = (
-        0.85914, -0.020880, -0.0058853, 0.12029, 0.026814, -0.0017810)
-    _coefficients['xsi'] = _coefficients['monosi']
-    _coefficients['polysi'] = (
-        0.84090, -0.027539, -0.0079224, 0.13570, 0.038024, -0.0021218)
-    _coefficients['multisi'] = _coefficients['polysi']
-    _coefficients['cigs'] = (
-        0.85252, -0.022314, -0.0047216, 0.13666, 0.013342, -0.0008945)
-    _coefficients['asi'] = (
-        1.12094, -0.047620, -0.0083627, -0.10443, 0.098382, -0.0033818)
-
-    if module_type is not None and coefficients is None:
-        coefficients = _coefficients[module_type.lower()]
-    elif module_type is None and coefficients is not None:
-        pass
-    elif module_type is None and coefficients is None:
-        raise TypeError('No valid input provided, both module_type and ' +
-                        'coefficients are None')
-    else:
-        raise TypeError('Cannot resolve input, must supply only one of ' +
-                        'module_type and coefficients')
-
-    # Evaluate Spectral Shift
-    coeff = coefficients
-    ama = airmass_absolute
-    modifier = (
-        coeff[0] + coeff[1]*ama + coeff[2]*pw + coeff[3]*np.sqrt(ama) +
-        coeff[4]*np.sqrt(pw) + coeff[5]*ama/np.sqrt(pw))
-
-    return modifier
+first_solar_spectral_correction = deprecated(
+    since='0.9.5',
+    alternative='pvlib.spectrum.first_solar_spectral_correction'
+)(pvlib.spectrum.first_solar_spectral_correction)
 
 
 def bird_hulstrom80_aod_bb(aod380, aod500):

pvlib/pvsystem.py

@@ -19,7 +19,7 @@
 from pvlib._deprecation import deprecated
 
 from pvlib import (atmosphere, iam, inverter, irradiance,
-                   singlediode as _singlediode, temperature)
+                   singlediode as _singlediode, spectrum, temperature)
 from pvlib.tools import _build_kwargs, _build_args
 
 
@@ -672,8 +672,8 @@ def sapm_celltemp(self, poa_global, temp_air, wind_speed):
     @_unwrap_single_value
     def sapm_spectral_loss(self, airmass_absolute):
         """
-        Use the :py:func:`sapm_spectral_loss` function, the input
-        parameters, and ``self.module_parameters`` to calculate F1.
+        Use the :py:func:`pvlib.spectrum.sapm_spectral_correction` function,
+        the input parameters, and ``self.module_parameters`` to calculate F1.
 
         Parameters
         ----------
@@ -686,7 +686,8 @@ def sapm_spectral_loss(self, airmass_absolute):
             The SAPM spectral loss coefficient.
         """
         return tuple(
-            sapm_spectral_loss(airmass_absolute, array.module_parameters)
+            spectrum.sapm_spectral_correction(airmass_absolute,
+                                              array.module_parameters)
             for array in self.arrays
         )
 
@@ -884,7 +885,7 @@ def noct_sam_celltemp(self, poa_global, temp_air, wind_speed,
     @_unwrap_single_value
     def first_solar_spectral_loss(self, pw, airmass_absolute):
         """
-        Use :py:func:`pvlib.atmosphere.first_solar_spectral_correction` to
+        Use :py:func:`pvlib.spectrum.first_solar_spectral_correction` to
         calculate the spectral loss modifier. The model coefficients are
         specific to the module's cell type, and are determined by searching
         for one of the following keys in self.module_parameters (in order):
@@ -925,7 +926,7 @@ def _spectral_correction(array, pw):
                 module_type = array._infer_cell_type()
                 coefficients = None
 
-            return atmosphere.first_solar_spectral_correction(
+            return spectrum.first_solar_spectral_correction(
                 pw, airmass_absolute,
                 module_type, coefficients
             )
@@ -2598,43 +2599,10 @@ def sapm(effective_irradiance, temp_cell, module):
     return out
 
 
-def sapm_spectral_loss(airmass_absolute, module):
-    """
-    Calculates the SAPM spectral loss coefficient, F1.
-
-    Parameters
-    ----------
-    airmass_absolute : numeric
-        Absolute airmass
-
-    module : dict-like
-        A dict, Series, or DataFrame defining the SAPM performance
-        parameters. See the :py:func:`sapm` notes section for more
-        details.
-
-    Returns
-    -------
-    F1 : numeric
-        The SAPM spectral loss coefficient.
-
-    Notes
-    -----
-    nan airmass values will result in 0 output.
-    """
-
-    am_coeff = [module['A4'], module['A3'], module['A2'], module['A1'],
-                module['A0']]
-
-    spectral_loss = np.polyval(am_coeff, airmass_absolute)
-
-    spectral_loss = np.where(np.isnan(spectral_loss), 0, spectral_loss)
-
-    spectral_loss = np.maximum(0, spectral_loss)
-
-    if isinstance(airmass_absolute, pd.Series):
-        spectral_loss = pd.Series(spectral_loss, airmass_absolute.index)
-
-    return spectral_loss
+sapm_spectral_loss = deprecated(
+    since='0.9.5',
+    alternative='pvlib.spectrum.sapm_spectral_correction'
+)(spectrum.sapm_spectral_correction)
 
 
 def sapm_effective_irradiance(poa_direct, poa_diffuse, airmass_absolute, aoi,
@@ -2694,11 +2662,11 @@ def sapm_effective_irradiance(poa_direct, poa_diffuse, airmass_absolute, aoi,
     See also
     --------
     pvlib.iam.sapm
-    pvlib.pvsystem.sapm_spectral_loss
+    pvlib.spectrum.sapm_spectral_correction
     pvlib.pvsystem.sapm
     """
 
-    F1 = sapm_spectral_loss(airmass_absolute, module)
+    F1 = spectrum.sapm_spectral_correction(airmass_absolute, module)
     F2 = iam.sapm(aoi, module)
 
     Ee = F1 * (poa_direct * F2 + module['FD'] * poa_diffuse)

pvlib/spectrum/__init__.py

@@ -1,3 +1,8 @@
 from pvlib.spectrum.spectrl2 import spectrl2  # noqa: F401
-from pvlib.spectrum.mismatch import (get_example_spectral_response, get_am15g,
-                                     calc_spectral_mismatch_field)
+from pvlib.spectrum.mismatch import (  # noqa: F401
+    calc_spectral_mismatch_field,
+    first_solar_spectral_correction,
+    get_am15g,
+    get_example_spectral_response,
+    sapm_spectral_correction,
+)