Add hsu soiling model gallery example.

docs/examples/plot_fig3A_hsu_soiling_example.py

@@ -0,0 +1,75 @@
+"""
+Hsu Soiling Model Example
+====================
+
+Example of soiling using the Hsu model.
+"""
+
+# %%
+# This example shows basic usage of pvlib's Hsu Soiling model [1]_ with
+# :py:func:`pvlib.soiling.hsu`.
+#
+# References
+# -----------
+# .. [1] M. Coello and L. Boyle, "Simple Model For Predicting Time Series
+#    Soiling of Photovoltaic Panels," in IEEE Journal of Photovoltaics.
+#    doi: 10.1109/JPHOTOV.2019.2919628
+#
+# This example recreates figure 3A in [1]_ for the Fixed Settling
+# Velocity case.
+# Rainfall data comes from Imperial County, CA TMY3 file
+# PM2.5 and PM10 data come from the EPA.
+
+
+
+import pathlib
+from matplotlib import pyplot as plt
+import matplotlib.image as mpimg
+from pvlib.soiling import hsu
+import pvlib
+import pandas as pd
+
+
+# get full path to the data directory
+DATA_DIR = pathlib.Path(pvlib.__file__).parent / 'data'
+
+# read rainfall, PM2.5, and PM10 data from file
+imperial_county = pd.read_csv(DATA_DIR / 'soiling_hsu_example_inputs.csv',
+                              index_col=0, parse_dates=True)
+rainfall = imperial_county['rain']
+depo_veloc = {'2_5': 0.0009, '10': 0.004}  # defaults
+rain_accum_period = pd.Timedelta('1h')     # default
+cleaning_threshold = 0.5
+tilt = 30
+pm2_5 = imperial_county['PM2_5'].values
+pm10 = imperial_county['PM10'].values
+# run the hsu soiling model
+soiling_ratio = hsu(rainfall, cleaning_threshold, tilt, pm2_5, pm10,
+                    depo_veloc=None, rain_accum_period=rain_accum_period)
+
+# plot daily soiling ratios and compare with Coello and Boyle Fig 3A.
+daily_soiling_ratio = soiling_ratio.resample('d').mean()
+fig, ax1 = plt.subplots(figsize=(12, 3))
+ax1.plot(daily_soiling_ratio.index, daily_soiling_ratio, marker='.',
+         c='r', label='hsu function output')
+ax1.set_ylabel('Daily Soiling Ratio')
+ax1.set_ylim(0.79, 1.01)
+ax1.set_title('Imperial County TMY')
+ax1.legend(loc='center left')
+
+daily_rain = rainfall.resample('d').sum()
+ax2 = ax1.twinx()
+ax2.plot(daily_rain.index, daily_rain, marker='.',
+         c='c', label='daily rainfall')
+ax2.set_ylabel('Daily Rain (mm)')
+ax2.set_ylim(-10, 210)
+ax2.legend(loc='center right')
+fig.tight_layout()
+fig.show()
+
+# show the original plot for comparison
+fig2, ax = plt.subplots(figsize=(18, 5))
+img = mpimg.imread(DATA_DIR / 'Coello_Boyle_2019_Fig3.png')
+ax.imshow(img, interpolation='nearest')
+fig2.tight_layout()
+fig2.show()

docs/sphinx/source/whatsnew/v0.8.0.rst

@@ -29,6 +29,7 @@ Documentation
 * Clarify units for heat loss factors in
   :py:func:`pvlib.temperature.pvsyst_cell` and
   :py:func:`pvlib.temperature.faiman`. (:pull:`960`)
+* Added hsu soiling model example to the gallery.  (:pull:`990`)
 
 Requirements
 ~~~~~~~~~~~~