WIP: PVSystem attributes as iterables

docs/sphinx/source/api.rst

@@ -236,7 +236,10 @@ PV temperature models
    temperature.pvsyst_cell
    temperature.faiman
    temperature.fuentes
+   temperature.ross
    pvsystem.PVSystem.sapm_celltemp
+   pvsystem.PVSystem.pvsyst_celltemp
+   pvsystem.PVSystem.faiman_celltemp
 
 Temperature Model Parameters
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^

docs/sphinx/source/whatsnew/v0.8.1.rst

@@ -13,6 +13,8 @@ Deprecations
 
 Enhancements
 ~~~~~~~~~~~~
+* Added :py:func:`pvlib.temperature.ross` for cell temperature modeling using
+  only NOCT. (:pull:`1045`)
 
 
 Bug fixes
@@ -35,3 +37,5 @@ Requirements
 Contributors
 ~~~~~~~~~~~~
 * Kevin Anderson (:ghuser:`kanderso-nrel`)
+* Will Holmgren (:ghuser:`wholmgren`)
+* Cliff Hansen (:ghuser:`cwhanse`)

pvlib/pvsystem.py

@@ -245,9 +245,16 @@ def get_aoi(self, solar_zenith, solar_azimuth):
             The angle of incidence
         """
 
-        aoi = irradiance.aoi(self.surface_tilt, self.surface_azimuth,
-                             solar_zenith, solar_azimuth)
-        return aoi
+        try:
+            aoi = [irradiance.aoi(t, a, solar_zenith, solar_azimuth)
+                   for t, a in zip(self.surface_tilt, self.surface_azimuth)]
+            if isinstance(self.surface_tilt, np.ndarray):
+                aoi = np.asarray(aoi)
+            return aoi
+        except TypeError:
+            return irradiance.aoi(self.surface_tilt, self.surface_azimuth,
+                                  solar_zenith, solar_azimuth)
+
 
     def get_irradiance(self, solar_zenith, solar_azimuth, dni, ghi, dhi,
                        dni_extra=None, airmass=None, model='haydavies',
@@ -293,15 +300,20 @@ def get_irradiance(self, solar_zenith, solar_azimuth, dni, ghi, dhi,
         if airmass is None:
             airmass = atmosphere.get_relative_airmass(solar_zenith)
 
-        return irradiance.get_total_irradiance(self.surface_tilt,
-                                               self.surface_azimuth,
-                                               solar_zenith, solar_azimuth,
-                                               dni, ghi, dhi,
-                                               dni_extra=dni_extra,
-                                               airmass=airmass,
-                                               model=model,
-                                               albedo=self.albedo,
-                                               **kwargs)
+        try:
+            poa = [irradiance.get_total_irradiance(
+                t, a, solar_zenith, solar_azimuth, dni, ghi, dhi,
+                dni_extra=dni_extra, airmass=airmass, model=model,
+                albedo=self.albedo, **kwargs)
+                for t, a in zip(self.surface_tilt, self.surface_azimuth)]
+            if isinstance(self.surface_tilt, np.ndarray):
+                poa = np.asarray(poa)
+            return poa
+        except TypeError:
+            return irradiance.get_total_irradiance(
+                self.surface_tilt, self.surface_azimuth, solar_zenith,
+                solar_azimuth, dni, ghi, dhi, dni_extra=dni_extra,
+                airmass=airmass, model=model, albedo=self.albedo, **kwargs)
 
     def get_iam(self, aoi, iam_model='physical'):
         """
@@ -370,7 +382,9 @@ def calcparams_desoto(self, effective_irradiance, temp_cell, **kwargs):
                                 'R_s', 'alpha_sc', 'EgRef', 'dEgdT',
                                 'irrad_ref', 'temp_ref'],
                                self.module_parameters)
-
+        if isinstance(effective_irradiance, list):
+            return [calcparams_desoto(ee, tc, **kwargs)
+                    for ee, tc in zip(effective_irradiance, temp_cell)]
         return calcparams_desoto(effective_irradiance, temp_cell, **kwargs)
 
     def calcparams_cec(self, effective_irradiance, temp_cell, **kwargs):
@@ -524,7 +538,7 @@ def sapm_spectral_loss(self, airmass_absolute):
         """
         return sapm_spectral_loss(airmass_absolute, self.module_parameters)
 
-    def sapm_effective_irradiance(self, poa_direct, poa_diffuse,
+    def sapm_effective_irradiance(self, total_irrad,
                                   airmass_absolute, aoi,
                                   reference_irradiance=1000):
         """
@@ -534,11 +548,10 @@ def sapm_effective_irradiance(self, poa_direct, poa_diffuse,
 
         Parameters
         ----------
-        poa_direct : numeric
-            The direct irradiance incident upon the module.  [W/m2]
-
-        poa_diffuse : numeric
-            The diffuse irradiance incident on module.  [W/m2]
+        total_irrad : Dataframe
+            Contains 'poa_direct', the direct irradiance incident upon the
+            module [W/m2], and 'poa_diffuse', the diffuse irradiance incident
+            on the module [W/m2].
 
         airmass_absolute : numeric
             Absolute airmass. [unitless]
@@ -551,9 +564,16 @@ def sapm_effective_irradiance(self, poa_direct, poa_diffuse,
         effective_irradiance : numeric
             The SAPM effective irradiance. [W/m2]
         """
-        return sapm_effective_irradiance(
-            poa_direct, poa_diffuse, airmass_absolute, aoi,
-            self.module_parameters)
+        try:
+            ee = [sapm_effective_irradiance(
+                  df['poa_direct'], df['poa_diffuse'], airmass_absolute, aoi,
+                  self.module_parameters)
+                  for df, aoi in zip(total_irrad, aoi)]
+            return ee
+        except TypeError:
+            return sapm_effective_irradiance(
+                total_irrad['poa_direct'], total_irrad['poa_diffuse'],
+                airmass_absolute, aoi, self.module_parameters)
 
     def pvsyst_celltemp(self, poa_global, temp_air, wind_speed=1.0):
         """Uses :py:func:`temperature.pvsyst_cell` to calculate cell

pvlib/temperature.py

@@ -377,9 +377,10 @@ def pvsyst_cell(poa_global, temp_air, wind_speed=1.0, u_c=29.0, u_v=0.0,
 
 def faiman(poa_global, temp_air, wind_speed=1.0, u0=25.0, u1=6.84):
     r'''
-    Calculate cell or module temperature using the Faiman model.  The Faiman
-    model uses an empirical heat loss factor model [1]_ and is adopted in the
-    IEC 61853 standards [2]_ and [3]_.
+    Calculate cell or module temperature using the Faiman model.
+
+    The Faiman model uses an empirical heat loss factor model [1]_ and is
+    adopted in the IEC 61853 standards [2]_ and [3]_.
 
     Usage of this model in the IEC 61853 standard does not distinguish
     between cell and module temperature.
@@ -443,6 +444,53 @@ def faiman(poa_global, temp_air, wind_speed=1.0, u0=25.0, u1=6.84):
     return temp_air + temp_difference
 
 
+def ross(poa_global, temp_air, noct):
+    r'''
+    Calculate cell temperature using the Ross model.
+
+    The Ross model [1]_ assumes the difference between cell temperature
+    and ambient temperature is proportional to the plane of array irradiance,
+    and ignores the effects of wind. The model implicitly assumes steady or
+    slowly changing irradiance conditions.
+
+    Parameters
+    ----------
+    poa_global : numeric
+        Total incident irradiance. [W/m^2]
+
+    temp_air : numeric
+        Ambient dry bulb temperature. [C]
+
+    noct : numeric
+        Nominal operating cell temperature [C], determined at conditions of
+        800 W/m^2 irradiance, 20 C ambient air temperature and 1 m/s wind.
+
+    Returns
+    -------
+    cell_temperature : numeric
+        Cell temperature. [C]
+
+    Notes
+    -----
+    The Ross model for cell temperature :math:`T_{C}` is given in [1]_ as
+
+    .. math::
+
+        T_{C} = T_{a} + \frac{NOCT - 20}{80} S
+
+    where :math:`S` is the plane of array irradiance in :math:`mW/{cm}^2`.
+    This function expects irradiance in :math:`W/m^2`.
+
+    References
+    ----------
+    .. [1] Ross, R. G. Jr., (1981). "Design Techniques for Flat-Plate
+       Photovoltaic Arrays". 15th IEEE Photovoltaic Specialist Conference,
+       Orlando, FL.
+    '''
+    # factor of 0.1 converts irradiance from W/m2 to mW/cm2
+    return temp_air + (noct - 20.) / 80. * poa_global * 0.1
+
+
 def _fuentes_hconv(tave, windmod, tinoct, temp_delta, xlen, tilt,
                    check_reynold):
     # Calculate the convective coefficient as in Fuentes 1987 -- a mixture of

pvlib/tests/test_temperature.py

@@ -124,6 +124,14 @@ def test_faiman_ndarray():
     assert_allclose(expected, result, 3)
 
 
+def test_ross():
+    result = temperature.ross(np.array([1000., 600., 1000.]),
+                              np.array([20., 40., 60.]),
+                              np.array([40., 100., 20.]))
+    expected = np.array([45., 100., 60.])
+    assert_allclose(expected, result)
+
+
 def test_faiman_series():
     times = pd.date_range(start="2015-01-01", end="2015-01-02", freq="12H")
     temps = pd.Series([0, 10, 5], index=times)