Implement irradiance.complete_irradiance with component sum equations

docs/sphinx/source/reference/irradiance.rst

@@ -28,6 +28,7 @@ Decomposing and combining irradiance
    irradiance.poa_components
    irradiance.get_ground_diffuse
    irradiance.dni
+   irradiance.complete_irradiance
 
 Transposition models
 --------------------

docs/sphinx/source/whatsnew/v0.9.4.rst

@@ -10,14 +10,17 @@ Deprecations
 Enhancements
 ~~~~~~~~~~~~
 * Multiple code style issues fixed that were reported by LGTM analysis. (:issue:`1275`, :pull:`1559`)
+* Added a function to calculate one of GHI, DHI, and DNI from values of the other two.
+  :py:func:`~pvlib.irradiance.complete_irradiance`
+  (:issue:`1565`, :pull:`1567`)
 * Add optional ``return_components`` parameter to :py:func:`pvlib.irradiance.haydavies` to return
   individual diffuse irradiance components (:issue:`1553`, :pull:`1568`)
 
+
 Bug fixes
 ~~~~~~~~~
 
 
-
 Testing
 ~~~~~~~
 * Corrected a flawed test for :py:func:`~pvlib.irradiance.get_ground_diffuse` (:issue:`1569`, :pull:`1575`)
@@ -36,6 +39,7 @@ Requirements
 
 Contributors
 ~~~~~~~~~~~~
+* Kirsten Perry (:ghuser:`kperrynrel`)
 * Christian Orner (:ghuser:`chrisorner`)
 * Saurabh Aneja (:ghuser:`spaneja`)
 * Marcus Boumans (:ghuser:`bowie2211`)

pvlib/irradiance.py

@@ -12,6 +12,7 @@
 import pandas as pd
 
 from pvlib import atmosphere, solarposition, tools
+import pvlib  # used to avoid dni name collision in complete_irradiance
 
 
 # see References section of get_ground_diffuse function
@@ -2948,3 +2949,67 @@ def dni(ghi, dhi, zenith, clearsky_dni=None, clearsky_tolerance=1.1,
             (zenith < zenith_threshold_for_zero_dni) &
             (dni > max_dni)] = max_dni
     return dni
+
+
+def complete_irradiance(solar_zenith,
+                        ghi=None,
+                        dhi=None,
+                        dni=None,
+                        dni_clear=None):
+    r"""
+    Use the component sum equations to calculate the missing series, using
+    the other available time series. One of the three parameters (ghi, dhi,
+    dni) is passed as None, and the other associated series passed are used to
+    calculate the missing series value.
+
+    The "component sum" or "closure" equation relates the three
+    primary irradiance components as follows:
+
+    .. math::
+
+       GHI = DHI + DNI \cos(\theta_z)
+
+    Parameters
+    ----------
+    solar_zenith : Series
+        Zenith angles in decimal degrees, with datetime index.
+        Angles must be >=0 and <=180. Must have the same datetime index
+        as ghi, dhi, and dni series, when available.
+    ghi : Series, optional
+        Pandas series of dni data, with datetime index. Must have the same
+        datetime index as dni, dhi, and zenith series, when available.
+    dhi : Series, optional
+        Pandas series of dni data, with datetime index. Must have the same
+        datetime index as ghi, dni, and zenith series, when available.
+    dni : Series, optional
+        Pandas series of dni data, with datetime index. Must have the same
+        datetime index as ghi, dhi, and zenith series, when available.
+    dni_clear : Series, optional
+        Pandas series of clearsky dni data. Must have the same datetime index
+        as ghi, dhi, dni, and zenith series, when available. See
+        :py:func:`dni` for details.
+
+    Returns
+    -------
+    component_sum_df : Dataframe
+        Pandas series of 'ghi', 'dhi', and 'dni' columns with datetime index
+    """
+    if ghi is not None and dhi is not None and dni is None:
+        dni = pvlib.irradiance.dni(ghi, dhi, solar_zenith,
+                                   clearsky_dni=dni_clear,
+                                   clearsky_tolerance=1.1)
+    elif dni is not None and dhi is not None and ghi is None:
+        ghi = (dhi + dni * tools.cosd(solar_zenith))
+    elif dni is not None and ghi is not None and dhi is None:
+        dhi = (ghi - dni * tools.cosd(solar_zenith))
+    else:
+        raise ValueError(
+            "Please check that exactly one of ghi, dhi and dni parameters "
+            "is set to None"
+        )
+    # Merge the outputs into a master dataframe containing 'ghi', 'dhi',
+    # and 'dni' columns
+    component_sum_df = pd.DataFrame({'ghi': ghi,
+                                     'dhi': dhi,
+                                     'dni': dni})
+    return component_sum_df

pvlib/modelchain.py

@@ -1289,13 +1289,13 @@ def complete_irradiance(self, weather):
         self._assign_times()
         self.results.solar_position = self.location.get_solarposition(
             self.results.times, method=self.solar_position_method)
-
+        # Calculate the irradiance using the component sum equations,
+        # if needed
         if isinstance(weather, tuple):
             for w in self.results.weather:
                 self._complete_irradiance(w)
         else:
             self._complete_irradiance(self.results.weather)
-
         return self
 
     def _complete_irradiance(self, weather):
@@ -1304,26 +1304,32 @@ def _complete_irradiance(self, weather):
                    "Results can be too high or negative.\n" +
                    "Help to improve this function on github:\n" +
                    "https://github.com/pvlib/pvlib-python \n")
-
         if {'ghi', 'dhi'} <= icolumns and 'dni' not in icolumns:
             clearsky = self.location.get_clearsky(
                 weather.index, solar_position=self.results.solar_position)
-            weather.loc[:, 'dni'] = pvlib.irradiance.dni(
-                weather.loc[:, 'ghi'], weather.loc[:, 'dhi'],
-                self.results.solar_position.zenith,
-                clearsky_dni=clearsky['dni'],
-                clearsky_tolerance=1.1)
+            complete_irrad_df = pvlib.irradiance.complete_irradiance(
+                solar_zenith=self.results.solar_position.zenith,
+                ghi=weather.ghi,
+                dhi=weather.dhi,
+                dni=None,
+                dni_clear=clearsky.dni)
+            weather.loc[:, 'dni'] = complete_irrad_df.dni
         elif {'dni', 'dhi'} <= icolumns and 'ghi' not in icolumns:
             warnings.warn(wrn_txt, UserWarning)
-            weather.loc[:, 'ghi'] = (
-                weather.dhi + weather.dni *
-                tools.cosd(self.results.solar_position.zenith)
-            )
+            complete_irrad_df = pvlib.irradiance.complete_irradiance(
+                solar_zenith=self.results.solar_position.zenith,
+                ghi=None,
+                dhi=weather.dhi,
+                dni=weather.dni)
+            weather.loc[:, 'ghi'] = complete_irrad_df.ghi
         elif {'dni', 'ghi'} <= icolumns and 'dhi' not in icolumns:
             warnings.warn(wrn_txt, UserWarning)
-            weather.loc[:, 'dhi'] = (
-                weather.ghi - weather.dni *
-                tools.cosd(self.results.solar_position.zenith))
+            complete_irrad_df = pvlib.irradiance.complete_irradiance(
+                solar_zenith=self.results.solar_position.zenith,
+                ghi=weather.ghi,
+                dhi=None,
+                dni=weather.dni)
+            weather.loc[:, 'dhi'] = complete_irrad_df.dhi
 
     def _prep_inputs_solar_pos(self, weather):
         """