add Boyle/Coello (Humboldt State Univ) soiling model

docs/sphinx/source/api.rst

@@ -298,7 +298,7 @@ PVWatts model
    pvsystem.pvwatts_ac
    pvsystem.pvwatts_losses
 
-Functions for fitting PV models
+Functions for fitting diode models
 -------------------------------
 .. autosummary::
    :toctree: generated/
@@ -307,6 +307,14 @@ Functions for fitting PV models
     ivtools.fit_sdm_cec_sam
     ivtools.fit_sdm_desoto
 
+Losses
+------
+.. autosummary::
+   :toctree: generated/
+
+   losses.soiling_hsu
+
+
 Other
 -----
 

docs/sphinx/source/whatsnew/v0.7.1.rst

@@ -17,6 +17,9 @@ Enhancements
 * Added :py:func:`~pvlib.iotools.get_pvgis_tmy` to get PVGIS TMY datasets.
 * Added :py:func:`~pvlib.iotools.parse_epw` to parse a file-like buffer
   containing weather data in the EPW format.
+* Added a new module `pvlib.losses` for various loss models.
+* Added the Humboldt State University soiling model
+  :py:func:`~pvlib.losses.soiling_hsu`. (:issue:`739`)
 
 Bug fixes
 ~~~~~~~~~
@@ -39,3 +42,4 @@ Contributors
 ~~~~~~~~~~~~
 * Kevin Anderson (:ghuser:`kanderso-nrel`)
 * Mark Mikofski (:ghuser:`mikofski`)
+* Valliappan CA (:ghuser:`nappaillav`)

pvlib/__init__.py

@@ -14,3 +14,4 @@
 from pvlib import modelchain  # noqa: F401
 from pvlib import singlediode  # noqa: F401
 from pvlib import bifacial  # noqa: F401
+from pvlib import losses  # noqa: F401

pvlib/losses.py

@@ -0,0 +1,87 @@
+# -*- coding: utf-8 -*-
+"""
+This module contains functions for losses of various types: soiling, mismatch,
+snow cover, etc.
+"""
+
+import numpy as np
+import pandas as pd
+from pvlib.tools import cosd
+
+
+def soiling_hsu(rainfall, cleaning_threshold, tilt, pm2_5, pm10,
+                depo_veloc={'2_5': 0.004, '10': 0.0009},
+                rain_accum_period=pd.Timedelta('1h')):
+    """
+    Calculates soiling ratio given particulate and rain data using the model
+    from Humboldt State University [1]_.
+
+    Parameters
+    ----------
+
+    rainfall : Series
+        Rain accumulated in each time period. [mm]
+
+    cleaning_threshold : float
+        Amount of rain in an accumulation period needed to clean the PV
+        modules. [mm]
+
+    tilt : float
+        Tilt of the PV panels from horizontal. [degree]
+
+    pm2_5 : numeric
+        Concentration of airborne particulate matter (PM) with
+        aerodynamic diameter less than 2.5 microns. [g/m^3]
+
+    pm10 : numeric
+        Concentration of airborne particulate matter (PM) with
+        aerodynamicdiameter less than 10 microns. [g/m^3]
+
+    depo_veloc : dict, default {'2_5': 0.4, '10': 0.09}
+        Deposition or settling velocity of particulates. [m/s]
+
+    rain_accum_period : Timedelta, default 1 hour
+        Period for accumulating rainfall to check against `cleaning_threshold`
+        It is recommended that `rain_accum_period` be between 1 hour and
+        24 hours.
+
+    Returns
+    -------
+    soiling_ratio : Series
+        Values between 0 and 1. Equal to 1 - transmission loss.
+
+    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
+    .. [2] Atmospheric Chemistry and Physics: From Air Pollution to Climate
+       Change. J. Seinfeld and S. Pandis. Wiley and Sons 2001.
+
+    """
+    try:
+        from scipy.special import erf
+    except ImportError:
+        raise ImportError("The soiling_hsu function requires scipy.")
+
+    # accumulate rainfall into periods for comparison with threshold
+    accum_rain = rainfall.rolling(rain_accum_period, closed='right').sum()
+    # cleaning is True for intervals with rainfall greater than threshold
+    cleaning_times = accum_rain.index[accum_rain >= cleaning_threshold]
+
+    horiz_mass_rate = pm2_5 * depo_veloc['2_5']\
+        + np.maximum(pm10 - pm2_5, 0.) * depo_veloc['10']
+    tilted_mass_rate = horiz_mass_rate * cosd(tilt)  # assuming no rain
+
+    # tms -> tilt_mass_rate
+    tms_cumsum = np.cumsum(tilted_mass_rate * np.ones(rainfall.shape))
+
+    mass_no_cleaning = pd.Series(index=rainfall.index, data=tms_cumsum)
+    mass_removed = pd.Series(index=rainfall.index)
+    mass_removed[0] = 0.
+    mass_removed[cleaning_times] = mass_no_cleaning[cleaning_times]
+    accum_mass = mass_no_cleaning - mass_removed.ffill()
+
+    soiling_ratio = 1 - 0.3437 * erf(0.17 * accum_mass**0.8473)
+
+    return soiling_ratio

pvlib/tests/test_losses.py

@@ -0,0 +1,92 @@
+import pandas as pd
+from pandas.util.testing import assert_series_equal
+from pvlib.losses import soiling_hsu
+from conftest import requires_scipy
+import pytest
+
+
+@pytest.fixture
+def expected_output():
+    # Sample output (calculated manually)
+    dt = pd.date_range(start=pd.datetime(2019, 1, 1, 0, 0, 0),
+                       end=pd.datetime(2019, 1, 1, 23, 59, 0), freq='1h')
+
+    expected_no_cleaning = pd.Series(
+        data=[0.884980357535360, 0.806308930084762, 0.749974647038078,
+              0.711804155175089, 0.687489866078621, 0.672927554408964,
+              0.664714899337491, 0.660345851212099, 0.658149551658860,
+              0.657104593968981, 0.656633344364056, 0.656431630729954,
+              0.656349579062171, 0.656317825078228, 0.656306121502393,
+              0.656302009396500, 0.656300630853678, 0.656300189543417,
+              0.656300054532516, 0.656300015031680, 0.656300003971846,
+              0.656300001006533, 0.656300000244750, 0.656300000057132],
+        index=dt)
+
+    return expected_no_cleaning
+
+
+@pytest.fixture
+def expected_output_2(expected_output):
+    # Sample output (calculated manually)
+    dt = pd.date_range(start=pd.datetime(2019, 1, 1, 0, 0, 0),
+                       end=pd.datetime(2019, 1, 1, 23, 59, 0), freq='1h')
+
+    expected_no_cleaning = expected_output
+
+    expected = pd.Series(index=dt)
+    expected[dt[:4]] = expected_no_cleaning[dt[:4]]
+    expected[dt[4:7]] = 1.
+    expected[dt[7]] = expected_no_cleaning[dt[0]]
+    expected[dt[8:12]] = 1.
+    expected[dt[12:17]] = expected_no_cleaning[dt[:5]]
+    expected[dt[17:21]] = 1.
+    expected[dt[21:]] = expected_no_cleaning[:3]
+
+    return expected
+
+
+@pytest.fixture
+def rainfall_input():
+
+    dt = pd.date_range(start=pd.datetime(2019, 1, 1, 0, 0, 0),
+                       end=pd.datetime(2019, 1, 1, 23, 59, 0), freq='1h')
+    rainfall = pd.Series(
+        data=[0., 0., 0., 0., 1., 0., 0., 0., 0.5, 0.5, 0., 0., 0., 0., 0.,
+              0., 0.3, 0.3, 0.3, 0.3, 0., 0., 0., 0.], index=dt)
+    return rainfall
+
+
+@requires_scipy
+def test_soiling_hsu_no_cleaning(rainfall_input, expected_output):
+    """Test Soiling HSU function"""
+
+    rainfall = rainfall_input
+    pm2_5 = 1.0
+    pm10 = 2.0
+    depo_veloc = {'2_5': 1.0, '10': 1.0}
+    tilt = 0.
+    expected_no_cleaning = expected_output
+
+    result = soiling_hsu(rainfall=rainfall, cleaning_threshold=10., tilt=tilt,
+                         pm2_5=pm2_5, pm10=pm10, depo_veloc=depo_veloc,
+                         rain_accum_period=pd.Timedelta('1h'))
+    assert_series_equal(result, expected_no_cleaning)
+
+
+@requires_scipy
+def test_soiling_hsu(rainfall_input, expected_output_2):
+    """Test Soiling HSU function"""
+
+    rainfall = rainfall_input
+    pm2_5 = 1.0
+    pm10 = 2.0
+    depo_veloc = {'2_5': 1.0, '10': 1.0}
+    tilt = 0.
+    expected = expected_output_2
+
+    # three cleaning events at 4:00-6:00, 8:00-11:00, and 17:00-20:00
+    result = soiling_hsu(rainfall=rainfall, cleaning_threshold=0.5, tilt=tilt,
+                         pm2_5=pm2_5, pm10=pm10, depo_veloc=depo_veloc,
+                         rain_accum_period=pd.Timedelta('3h'))
+
+    assert_series_equal(result, expected)