correct noct function, adjust tests, add comments

Author: cwhanse

pvlib/temp_bright_sun_dev.py

@@ -0,0 +1,24 @@
+# -*- coding: utf-8 -*-
+"""
+Created on Wed Feb  3 13:45:02 2021
+
+@author: cliff
+"""
+
+import pandas as pd
+import pytz
+from pvlib import solarposition
+
+tz = pytz.timezone('Etc/GMT+7')
+dt = pd.date_range(start='02-01-2021 00:00:00', end='02-27-2021 00:00:00',
+                   freq='1H', tz=tz)
+
+rs_spa = solarposition.sun_rise_set_transit_spa(dt, 35, -116)
+
+rs_pyephem = solarposition.sun_rise_set_transit_ephem(dt, 35, -116)
+
+both = pd.DataFrame(index=dt)
+both['rise_spa'] = rs_spa['sunrise']
+both['rise_ephem'] = rs_pyephem['sunrise']
+both['set_spa'] = rs_spa['sunset']
+both['set_ephem'] = rs_pyephem['sunset']

pvlib/temperature.py

@@ -708,19 +708,23 @@ def fuentes(poa_global, temp_air, wind_speed, noct_installed, module_height=5,
     return pd.Series(tmod_array - 273.15, index=poa_global.index, name='tmod')
 
 
-def _adj_noct(x):
-    return np.piecewise(x, [x < 0.5, (x >= 0.5) & (x < 1.5),
-                            (x >= 1.5) & (x < 2.5), (x >= 2.5) & (x < 3.5),
-                            x >= 3.5], [18., 11., 6., 2., 0.])
+def _adj_for_mounting_standoff(x):
+    # supports noct cell temperature model.
+    # the exact division of the range of x into intervals is not specified
+    # in the SAM code, except for the last interval x > 3.5.
+    return np.piecewise(x, [x <= 0, (x > 0) & (x < 0.5),
+                            (x >= 0.5) & (x < 1.5), (x >= 1.5) & (x < 2.5),
+                            (x >= 2.5) & (x <= 3.5), x > 3.5],
+                        [0., 18., 11., 6., 2., 0.])
 
 
 def noct(poa_global, temp_air, wind_speed, noct, eta_m_ref,
          effective_irradiance=None, transmittance_absorbtance=0.9,
-         array_height=1, mount_standoff=3.5):
+         array_height=1, mount_standoff=4):
     '''
     Cell temperature model from the System Advisor Model (SAM).
 
-    The model is described in [1], Section 10.6.
+    The model is described in [1]_, Section 10.6.
 
     Parameters
     ----------
@@ -756,7 +760,7 @@ def noct(poa_global, temp_air, wind_speed, noct, eta_m_ref,
         be either 1 or 2. For systems elevated less than one story, use 1.
         If system is elevated more than two stories, use 2.
 
-    mount_standoff : numeric, default 3.5
+    mount_standoff : numeric, default 4
         Distance between array mounting and mounting surface. Use default
         if system is ground-mounted. [inches]
 
@@ -790,10 +794,12 @@ def noct(poa_global, temp_air, wind_speed, noct, eta_m_ref,
         raise ValueError(
             f'array_height must be 1 or 2, {array_height} was given')
 
-    noct_adj = noct + _adj_noct(mount_standoff)
+    noct_adj = noct + _adj_for_mounting_standoff(mount_standoff)
     tau_alpha = transmittance_absorbtance * irr_ratio
 
-    cell_temp_init = ross(poa_global, temp_air, noct_adj)
+    # [1] Eq. 10.37 isn't clear on exactly what "G" is. SAM SSC code uses
+    # poa_global where G appears
+    cell_temp_init = poa_global / 800. * (noct_adj - 20.)
     heat_loss = 1 - eta_m_ref / tau_alpha
     wind_loss = 9.5 / (5.7 + 3.8 * wind_adj)
-    return cell_temp_init * heat_loss * wind_loss
+    return temp_air + cell_temp_init * heat_loss * wind_loss

pvlib/tests/test_temperature.py

@@ -217,15 +217,15 @@ def test_fuentes_timezone(tz):
 def test_noct():
     poa_global, temp_air, wind_speed, noct, eta_m_ref = (1000., 25., 1., 45.,
                                                          0.2)
-    expected = 54.41542289
+    expected = 54.151119403
     result = temperature.noct(poa_global, temp_air, wind_speed, noct,
                               eta_m_ref)
-    assert np.isclose(result, expected)
+    assert assert_allclose(result, expected)
     # test with different types
     result = temperature.noct(np.array(poa_global), np.array(temp_air),
                               np.array(wind_speed), np.array(noct),
                               np.array(eta_m_ref))
-    assert np.isclose(result, expected)
+    assert assert_allclose(result, expected)
     dr = pd.date_range(start='2020-01-01 12:00:00', end='2020-01-01 13:00:00',
                        freq='1H')
     result = temperature.noct(pd.Series(index=dr, data=poa_global),
@@ -247,8 +247,8 @@ def test_noct_options():
                               eta_m_ref, effective_irradiance,
                               transmittance_absorbtance, array_height,
                               mount_standoff)
-    expected = 58.36654459
-    assert np.isclose(result, expected)
+    expected = 60.477703576
+    assert_allclose(result, expected)
 
 
 def test_noct_errors():