Create plot_ghi_transposition.py example

docs/examples/plot_ghi_transposition.py

@@ -0,0 +1,83 @@
+"""
+GHI to POA Transposition
+=========================
+
+Example of generating clearsky GHI and POA irradiance.
+"""
+
+# %%
+# This example shows how to use the
+# :py:meth:`pvlib.location.Location.get_clearsky` method to generate clearsky
+# GHI data as well as how to use the
+# :py:meth:`pvlib.irradiance.get_total_irradiance` function to transpose
+# GHI data to Plane of Array (POA) irradiance.
+
+from pvlib import location
+from pvlib import irradiance
+import pandas as pd
+from matplotlib import pyplot as plt
+
+# For this example, we will be using Golden, Colorado
+tz = 'MST'
+lat, lon = 39.755, -105.221
+
+# Create location object to store lat, lon, timezone
+site = location.Location(lat, lon, tz=tz)
+
+
+# Calculate clear-sky GHI and transpose to plane of array
+# Define a function so that we can re-use the sequence of operations with
+# different locations
+def get_irradiance(site_location, date, tilt, surface_azimuth):
+    # Creates one day's worth of 10 min intervals
+    times = pd.date_range(date, freq='10min', periods=6*24,
+                          tz=site_location.tz)
+    # Generate clearsky data using the Ineichen model, which is the default
+    # The get_clearsky method returns a dataframe with values for GHI, DNI,
+    # and DHI
+    clearsky = site_location.get_clearsky(times)
+    # Get solar azimuth and zenith to pass to the transposition function
+    solar_position = site_location.get_solarposition(times=times)
+    # Use the get_total_irradiance function to transpose the GHI to POA
+    POA_irradiance = irradiance.get_total_irradiance(
+        surface_tilt=tilt,
+        surface_azimuth=surface_azimuth,
+        dni=clearsky['dni'],
+        ghi=clearsky['ghi'],
+        dhi=clearsky['dhi'],
+        solar_zenith=solar_position['apparent_zenith'],
+        solar_azimuth=solar_position['azimuth'])
+    # Return DataFrame with only GHI and POA
+    return pd.DataFrame({'GHI': clearsky['ghi'],
+                         'POA': POA_irradiance['poa_global']})
+
+
+# Get irradiance data for summer and winter solstice, assuming 25 degree tilt
+# and a south facing array
+summer_irradiance = get_irradiance(site, '06-20-2020', 25, 180)
+winter_irradiance = get_irradiance(site, '12-21-2020', 25, 180)
+
+# Convert Dataframe Indexes to Hour:Minute format to make plotting easier
+summer_irradiance.index = summer_irradiance.index.strftime("%H:%M")
+winter_irradiance.index = winter_irradiance.index.strftime("%H:%M")
+
+# Plot GHI vs. POA for winter and summer
+fig, (ax1, ax2) = plt.subplots(1, 2, sharey=True)
+summer_irradiance['GHI'].plot(ax=ax1, label='GHI')
+summer_irradiance['POA'].plot(ax=ax1, label='POA')
+winter_irradiance['GHI'].plot(ax=ax2, label='GHI')
+winter_irradiance['POA'].plot(ax=ax2, label='POA')
+ax1.set_xlabel('Time of day (Summer)')
+ax2.set_xlabel('Time of day (Winter)')
+ax1.set_ylabel('Irradiance ($W/m^2$)')
+ax1.legend()
+ax2.legend()
+plt.show()
+
+# %%
+# Note that in Summer, there is not much gain when comparing POA irradiance to
+# GHI. In the winter, however, POA irradiance is significantly higher than
+# GHI. This is because, in winter, the sun is much lower in the sky, so a
+# tilted array will be at a more optimal angle compared to a flat array.
+# In summer, the sun gets much higher in the sky, and there is very little
+# gain for a tilted array compared to a flat array.

docs/sphinx/source/whatsnew/v0.7.2.rst

@@ -67,6 +67,7 @@ Documentation
 * Add example of IV curve generation. (:pull:`872`)
 * Add section about gallery examples to Contributing guide. (:pull:`905`)
 * Add section with link to Code of Conduct in Contributing guide. (:pull:`922`)
+* Add example of GHI to POA transposition (:pull:`933`)
 
 Requirements
 ~~~~~~~~~~~~
@@ -81,3 +82,4 @@ Contributors
 * Kevin Anderson (:ghuser:`kanderso-nrel`)
 * Karthikeyan Singaravelan (:ghuser:`tirkarthi`)
 * Siyan (Veronica) Guo (:ghuser:`veronicaguo`)
+* Eric Fitch (:ghuser:`ericf900`)