From a5f58af47a8a5d4ea59777f31ca79977905099d3 Mon Sep 17 00:00:00 2001
From: Will Vining <wfvining@gmail.com>
Date: Tue, 25 Aug 2020 15:32:14 -0600
Subject: [PATCH 01/14] Identify surface orientation from AC power and clearsky
 irradiance

Implements method for identifying tilt and azimuth given ac power,
clearsky irradiance, and solar position.
---
 pvanalytics/system.py                         | 158 ++++++++++++++++++
 pvanalytics/tests/conftest.py                 |  20 ++-
 .../tests/features/test_orientation.py        |  20 +--
 pvanalytics/tests/test_system.py              |  97 ++++++++++-
 4 files changed, 268 insertions(+), 27 deletions(-)

diff --git a/pvanalytics/system.py b/pvanalytics/system.py
index b3e2ccf3..efdfa10c 100644
--- a/pvanalytics/system.py
+++ b/pvanalytics/system.py
@@ -2,8 +2,10 @@
 import enum
 import warnings
 import numpy as np
+import scipy
 import pandas as pd
 import pvlib
+from pvlib.temperature import TEMPERATURE_MODEL_PARAMETERS
 from pvanalytics.util import _fit, _group
 
 
@@ -401,3 +403,159 @@ def infer_orientation_daily_peak(power_or_poa, sunny, tilts,
                 best_azimuth = azimuth
                 best_tilt = tilt
     return best_azimuth, best_tilt
+
+
+def _power_residuals_from_clearsky(system_params,
+                                   ghi, dhi, dni,
+                                   solar_zenith, solar_azimuth,
+                                   power_ac, temperature,
+                                   wind_speed,
+                                   temperature_coefficient,
+                                   temperature_model_parameters):
+    # Return the residuals between a system with parameters given in `params`
+    # and the data in `power_ac`.
+    #
+    # Parameters
+    # ----------
+    # system_params : array-like
+    #     array of four floats: tilt, azimuth, DC capacity, and inverter
+    #     DC input limit.
+    # ghi : Series
+    #     Clear sky GHI
+    # dhi : Series
+    #     Clear sky DHI
+    # dni : Series
+    #     Clear sky DNI
+    # solar_zenith : Series
+    #     Solar zenith at the same times as data in `power_ac`
+    # solar_azimuth : Series
+    #     Solar azimuth at the same times as data in `power_ac`
+    # power_ac : Series
+    #     Measured AC power under clear sky conditions.
+    # temperature : float or Series
+    #     Air temperature at which to model the hypothetical system. If a
+    #     float then a constant temperature is used. If a Series, must have
+    #     the same index as `power_ac`. [C]
+    # wind_speed : float or Series
+    #     Wind speed. If a float then a constant wind speed is used. If a
+    #     Series, must have the same index as `power_ac`. [m/s]
+    # temperature_model_parameters : dict
+    #     Parameters fot the cell temperature model.
+    #
+    # Returns
+    # -------
+    # Series
+    #     Difference between `power_ac` and the PVWatts output with the
+    #     given parameters.
+    tilt = system_params[0]
+    azimuth = system_params[1]
+    dc_capacity = system_params[2]
+    dc_limit = system_params[3]
+    poa = pvlib.irradiance.get_total_irradiance(
+        tilt, azimuth,
+        solar_zenith,
+        solar_azimuth,
+        dni, ghi, dhi
+    )
+    temp_cell = pvlib.temperature.sapm_cell(
+        poa['poa_global'],
+        temperature,
+        wind_speed,
+        **temperature_model_parameters
+    )
+    pdc = pvlib.pvsystem.pvwatts_dc(
+        poa['poa_global'],
+        temp_cell,
+        dc_capacity,
+        temperature_coefficient
+    )
+    return power_ac - pvlib.inverter.pvwatts(pdc, dc_limit)
+
+
+def _rsquared(data, residuals):
+    # Calculate the coefficient of determination from `residuals`
+    model = data + residuals
+    _, _, r, _, _ = scipy.stats.linregress(model, data)
+    return r*r
+
+
+def orientation_fit_pvwatts(power_ac, ghi, dhi, dni,
+                            solar_zenith, solar_azimuth,
+                            temperature=25, wind_speed=0,
+                            temperature_coefficient=-0.002,
+                            temperature_model_parameters=None):
+    """Get the tilt and azimuth that give pvwatts output that most closely
+    fits the data in `power_ac`.
+
+    Uses non-linear least squares to optimize over four free variables
+    to find the values that result in the best fit between power modeled
+    using PVWatts and `power_ac`. The four free variables are
+    - surface tilt
+    - surface azimuth
+    - the DC capacity of the system
+    - the DC input limit of the inverter.
+
+    Parameters
+    ----------
+    power_ac : Series
+        AC power from the system in clear sky conditions.
+    ghi : Series
+        Clear sky GHI at the same times as `power_ac`
+    dhi : Series
+        Clear sky DHI.
+    dni : Series
+        Clear sky DNI.
+    solar_zenith : Series
+        Solar zenith. [degrees]
+    solar_azimuth : Series
+        Solar azimuth. [degrees]
+    temperature : float or Series, default 25
+        Air temperature at which to model the hypothetical system. If a
+        float then a constant temperature is used. If a Series, must have
+        the same index as `power_ac`. [C]
+    wind_speed : float or Series, default 0
+        Wind speed. If a float then a constant wind speed is used. If a
+        Series, must have the same index as `power_ac`. [m/s]
+    temperature_model_parameters : dict, optional
+        Parameters fot the cell temperature model. If not specified
+        ``pvlib.temperature.TEMPERATURE_MODEL_PARAMETERS['sapm'][
+        'open_rack_glass_glass'] is used. See
+        :py:func`pvlib.temperature.sapm_cell` for more information.
+
+    Returns
+    -------
+    surface_tilt : float
+        Tilt of the array. [degrees]
+    surface_azimuth : float
+        Azimuth of the array. [degrees]
+    r_squared : float
+        :math:`r^2` value for the fit at the returned orientation.
+
+    """
+    if temperature_model_parameters is None:
+        temperature_model_parameters = \
+            TEMPERATURE_MODEL_PARAMETERS['sapm']['open_rack_glass_glass']
+    initial_tilt = 45
+    initial_azimuth = 180
+    initial_dc_capacity = power_ac.max()
+    initial_dc_limit = power_ac.max() * 1.5
+    fit_result = scipy.optimize.least_squares(
+        _power_residuals_from_clearsky,
+        [initial_tilt, initial_azimuth, initial_dc_capacity, initial_dc_limit],
+        bounds=([0, 0, power_ac.max()*0.5, power_ac.max()*0.5],
+                [90, 360, power_ac.max()*2, power_ac.max()*3]),
+        kwargs={
+            'ghi': ghi,
+            'dhi': dhi,
+            'dni': dni,
+            'solar_zenith': solar_zenith,
+            'solar_azimuth': solar_azimuth,
+            'power_ac': power_ac,
+            'temperature': temperature,
+            'temperature_coefficient': temperature_coefficient,
+            'wind_speed': wind_speed,
+            'temperature_model_parameters': temperature_model_parameters
+        }
+    )
+    r_squared = _rsquared(power_ac, fit_result.fun)
+    return fit_result.x[0], fit_result.x[1], r_squared
diff --git a/pvanalytics/tests/conftest.py b/pvanalytics/tests/conftest.py
index c13c5ba0..fe2841e9 100644
--- a/pvanalytics/tests/conftest.py
+++ b/pvanalytics/tests/conftest.py
@@ -2,7 +2,8 @@
 import pytest
 import numpy as np
 import pandas as pd
-from pvlib import location
+from pvlib import location, pvsystem
+from pvlib.temperature import TEMPERATURE_MODEL_PARAMETERS
 
 
 def pytest_addoption(parser):
@@ -99,3 +100,20 @@ def clearsky_year(one_year_hourly, albuquerque):
 def solarposition_year(one_year_hourly, albuquerque):
     """One year of solar position data in albuquerque"""
     return albuquerque.get_solarposition(one_year_hourly)
+
+
+@pytest.fixture(scope='module')
+def system_parameters():
+    """System parameters for generating simulated power data."""
+    sandia_modules = pvsystem.retrieve_sam('SandiaMod')
+    sapm_inverters = pvsystem.retrieve_sam('cecinverter')
+    module = sandia_modules['Canadian_Solar_CS5P_220M___2009_']
+    inverter = sapm_inverters['ABB__MICRO_0_25_I_OUTD_US_208__208V_']
+    temperature_model_parameters = (
+        TEMPERATURE_MODEL_PARAMETERS['sapm']['open_rack_glass_glass']
+    )
+    return {
+        'module_parameters': module,
+        'inverter_parameters': inverter,
+        'temperature_model_parameters': temperature_model_parameters
+    }
diff --git a/pvanalytics/tests/features/test_orientation.py b/pvanalytics/tests/features/test_orientation.py
index b85d19a3..dd80564d 100644
--- a/pvanalytics/tests/features/test_orientation.py
+++ b/pvanalytics/tests/features/test_orientation.py
@@ -1,28 +1,10 @@
 import pytest
 from pandas.util.testing import assert_series_equal
 import pandas as pd
-from pvlib import pvsystem, tracking, modelchain, irradiance
-from pvlib.temperature import TEMPERATURE_MODEL_PARAMETERS
+from pvlib import tracking, modelchain, irradiance
 from pvanalytics.features import orientation
 
 
-@pytest.fixture(scope='module')
-def system_parameters():
-    """System parameters for generating simulated power data."""
-    sandia_modules = pvsystem.retrieve_sam('SandiaMod')
-    sapm_inverters = pvsystem.retrieve_sam('cecinverter')
-    module = sandia_modules['Canadian_Solar_CS5P_220M___2009_']
-    inverter = sapm_inverters['ABB__MICRO_0_25_I_OUTD_US_208__208V_']
-    temperature_model_parameters = (
-        TEMPERATURE_MODEL_PARAMETERS['sapm']['open_rack_glass_glass']
-    )
-    return {
-        'module_parameters': module,
-        'inverter_parameters': inverter,
-        'temperature_model_parameters': temperature_model_parameters
-    }
-
-
 def test_clearsky_ghi_fixed(clearsky, solarposition):
     """Identify every day as fixed, since clearsky GHI is sunny."""
     assert orientation.fixed_nrel(
diff --git a/pvanalytics/tests/test_system.py b/pvanalytics/tests/test_system.py
index 33d07364..b3ee3651 100644
--- a/pvanalytics/tests/test_system.py
+++ b/pvanalytics/tests/test_system.py
@@ -1,8 +1,9 @@
-"""Tests for funcitons that identify system characteristics."""
+"""Tests for system parameter identification functions."""
 import pytest
-import numpy as np
 import pandas as pd
-from pvlib import pvsystem, tracking, modelchain, irradiance
+import numpy as np
+import pvlib
+from pvlib import location, pvsystem, tracking, modelchain, irradiance
 from pvlib.temperature import TEMPERATURE_MODEL_PARAMETERS
 from pvanalytics import system
 
@@ -51,9 +52,9 @@ def summer_ghi(summer_clearsky):
 @pytest.fixture
 def summer_power_fixed(summer_clearsky, albuquerque, system_parameters):
     """Simulated power from a FIXED PVSystem in Albuquerque, NM."""
-    system = pvsystem.PVSystem(**system_parameters)
+    pv_system = pvsystem.PVSystem(**system_parameters)
     mc = modelchain.ModelChain(
-        system,
+        pv_system,
         albuquerque,
         orientation_strategy='south_at_latitude_tilt'
     )
@@ -64,9 +65,9 @@ def summer_power_fixed(summer_clearsky, albuquerque, system_parameters):
 @pytest.fixture
 def summer_power_tracking(summer_clearsky, albuquerque, system_parameters):
     """Simulated power for a pvlib SingleAxisTracker PVSystem in Albuquerque"""
-    system = tracking.SingleAxisTracker(**system_parameters)
+    pv_system = tracking.SingleAxisTracker(**system_parameters)
     mc = modelchain.ModelChain(
-        system,
+        pv_system,
         albuquerque,
         orientation_strategy='south_at_latitude_tilt'
     )
@@ -406,3 +407,85 @@ def test_orientation_with_gaps(clearsky_year, solarposition_year):
     )
     assert azimuth == 180
     assert tilt == 15
+
+
+@pytest.fixture(scope='module')
+def naive_times():
+    """One year at 1-hour intervals"""
+    return pd.date_range(
+        start='2020',
+        end='2021',
+        freq='H'
+    )
+
+
+@pytest.fixture(scope='module',
+                params=[(35, -106, 'Etc/GMT+7'),
+                        (50, 10, 'Etc/GMT-1'),
+                        (-37, 144, 'Etc/GMT-10')],
+                ids=['Albuquerque', 'Berlin', 'Melbourne'])
+def system_location(request):
+    """Location of the system."""
+    return location.Location(
+        request.param[0], request.param[1], tz=request.param[2]
+    )
+
+
+@pytest.fixture(scope='module',
+                params=[(0, 180), (30, 180), (30, 90), (30, 270), (30, 0)],
+                ids=['South-0', 'South-30', 'East-30', 'West-30', 'North-30'])
+def system_power(request, system_location, naive_times):
+    tilt = request.param[0]
+    azimuth = request.param[1]
+    local_time = naive_times.tz_localize(system_location.tz)
+    clearsky = system_location.get_clearsky(
+        local_time, model='simplified_solis'
+    )
+    solar_position = system_location.get_solarposition(local_time)
+    poa = irradiance.get_total_irradiance(
+        tilt, azimuth,
+        solar_position['zenith'],
+        solar_position['azimuth'],
+        **clearsky
+    )
+    temp_cell = pvlib.temperature.sapm_cell(
+        poa['poa_global'],
+        25, 0,
+        **pvlib.temperature.TEMPERATURE_MODEL_PARAMETERS[
+            'sapm'
+        ][
+            'open_rack_glass_glass'
+        ]
+    )
+    pdc = pvsystem.pvwatts_dc(poa['poa_global'], temp_cell, 100, -0.002)
+    pac = pvsystem.inverter.pvwatts(pdc, 120)
+    return {
+        'location': system_location,
+        'tilt': tilt,
+        'azimuth': azimuth,
+        'clearsky': clearsky,
+        'solar_position': solar_position,
+        'ac': pac
+    }
+
+
+@pytest.mark.slow
+def test_orientation_fit_pvwatts(system_power):
+    day_mask = system_power['ac'] > 0
+    tilt, azimuth, rsquared = system.orientation_fit_pvwatts(
+        system_power['ac'][day_mask],
+        solar_zenith=system_power['solar_position']['zenith'][day_mask],
+        solar_azimuth=system_power['solar_position']['azimuth'][day_mask],
+        **system_power['clearsky'][day_mask]
+    )
+    assert rsquared > 0.9
+    assert tilt == pytest.approx(system_power['tilt'], abs=10)
+    if system_power['tilt'] == 0:
+        # Any azimuth will give the same results at tilt 0.
+        return
+    if system_power['azimuth'] == 0:
+        # 0 degrees equals 360 degrees.
+        assert (azimuth == pytest.approx(0, abs=10)
+                or azimuth == pytest.approx(360, abs=10))
+    else:
+        assert azimuth == pytest.approx(system_power['azimuth'], abs=10)

From ead8058b69bca9345c5791acaaefd3bba9221774 Mon Sep 17 00:00:00 2001
From: Will Vining <wfvining@gmail.com>
Date: Mon, 5 Oct 2020 15:33:17 -0600
Subject: [PATCH 02/14] Add to API documentation

Add entry to the list of functions for orientation inference in api.rst and fix minor issues in the docstring.
---
 docs/api.rst          |  1 +
 pvanalytics/system.py | 11 ++++++-----
 2 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/docs/api.rst b/docs/api.rst
index abdf0377..f5aeaf4f 100644
--- a/docs/api.rst
+++ b/docs/api.rst
@@ -241,6 +241,7 @@ power or plane of array irradiance measurements.
    :toctree: generated/
 
    system.infer_orientation_daily_peak
+   system.orientation_fit_pvwatts
 
 Metrics
 =======
diff --git a/pvanalytics/system.py b/pvanalytics/system.py
index efdfa10c..cd134e08 100644
--- a/pvanalytics/system.py
+++ b/pvanalytics/system.py
@@ -490,6 +490,7 @@ def orientation_fit_pvwatts(power_ac, ghi, dhi, dni,
     Uses non-linear least squares to optimize over four free variables
     to find the values that result in the best fit between power modeled
     using PVWatts and `power_ac`. The four free variables are
+
     - surface tilt
     - surface azimuth
     - the DC capacity of the system
@@ -500,11 +501,11 @@ def orientation_fit_pvwatts(power_ac, ghi, dhi, dni,
     power_ac : Series
         AC power from the system in clear sky conditions.
     ghi : Series
-        Clear sky GHI at the same times as `power_ac`
+        Clear sky GHI with same index as `power_ac`.
     dhi : Series
-        Clear sky DHI.
+        Clear sky DHI with same index as `power_ac`.
     dni : Series
-        Clear sky DNI.
+        Clear sky DNI with same index as `power_ac`.
     solar_zenith : Series
         Solar zenith. [degrees]
     solar_azimuth : Series
@@ -519,8 +520,8 @@ def orientation_fit_pvwatts(power_ac, ghi, dhi, dni,
     temperature_model_parameters : dict, optional
         Parameters fot the cell temperature model. If not specified
         ``pvlib.temperature.TEMPERATURE_MODEL_PARAMETERS['sapm'][
-        'open_rack_glass_glass'] is used. See
-        :py:func`pvlib.temperature.sapm_cell` for more information.
+        'open_rack_glass_glass']`` is used. See
+        :py:func:`pvlib.temperature.sapm_cell` for more information.
 
     Returns
     -------

From a9c780bb731c1e12b289c655146cf36ab7dbc6a5 Mon Sep 17 00:00:00 2001
From: Will Vining <wfvining@gmail.com>
Date: Tue, 20 Oct 2020 10:10:20 -0600
Subject: [PATCH 03/14] Additional tests for system.orientation_fit_pvwatts()

Test with missing data and with Series for temperature and wind_speed
parameters.
---
 pvanalytics/system.py            | 12 +++++
 pvanalytics/tests/test_system.py | 87 ++++++++++++++++++++++++++++++++
 2 files changed, 99 insertions(+)

diff --git a/pvanalytics/system.py b/pvanalytics/system.py
index cd134e08..28703243 100644
--- a/pvanalytics/system.py
+++ b/pvanalytics/system.py
@@ -496,6 +496,8 @@ def orientation_fit_pvwatts(power_ac, ghi, dhi, dni,
     - the DC capacity of the system
     - the DC input limit of the inverter.
 
+    All parameters passed as a Series must have the same index.
+
     Parameters
     ----------
     power_ac : Series
@@ -533,6 +535,16 @@ def orientation_fit_pvwatts(power_ac, ghi, dhi, dni,
         :math:`r^2` value for the fit at the returned orientation.
 
     """
+    power_ac = power_ac.dropna()
+    ghi = ghi.dropna()
+    dhi = dhi.dropna()
+    dni = dni.dropna()
+    solar_azimuth = solar_azimuth.dropna()
+    solar_zenith = solar_zenith.dropna()
+    if isinstance(temperature, pd.Series):
+        temperature = temperature.dropna()
+    if isinstance(wind_speed, pd.Series):
+        wind_speed = wind_speed.dropna()
     if temperature_model_parameters is None:
         temperature_model_parameters = \
             TEMPERATURE_MODEL_PARAMETERS['sapm']['open_rack_glass_glass']
diff --git a/pvanalytics/tests/test_system.py b/pvanalytics/tests/test_system.py
index b3ee3651..f26ca3cb 100644
--- a/pvanalytics/tests/test_system.py
+++ b/pvanalytics/tests/test_system.py
@@ -489,3 +489,90 @@ def test_orientation_fit_pvwatts(system_power):
                 or azimuth == pytest.approx(360, abs=10))
     else:
         assert azimuth == pytest.approx(system_power['azimuth'], abs=10)
+
+
+def test_orientation_fit_pvwatts_missing_data(naive_times):
+    tilt = 30
+    azimuth = 100
+    system_location = location.Location(35, -106)
+    local_time = naive_times.tz_localize('MST')
+    clearsky = system_location.get_clearsky(
+        local_time, model='simplified_solis'
+    )
+    clearsky.loc['3/1/2020':'3/15/2020'] = np.nan
+    solar_position = system_location.get_solarposition(clearsky.index)
+    solar_position.loc['3/1/2020':'3/15/2020'] = np.nan
+    poa = irradiance.get_total_irradiance(
+        tilt, azimuth,
+        solar_position['zenith'],
+        solar_position['azimuth'],
+        **clearsky
+    )
+    temp_cell = pvlib.temperature.sapm_cell(
+        poa['poa_global'],
+        25, 0,
+        **pvlib.temperature.TEMPERATURE_MODEL_PARAMETERS[
+            'sapm'
+        ][
+            'open_rack_glass_glass'
+        ]
+    )
+    pdc = pvsystem.pvwatts_dc(poa['poa_global'], temp_cell, 100, -0.002)
+    pac = pvsystem.inverter.pvwatts(pdc, 120)
+    tilt_out, azimuth_out, rsquared = system.orientation_fit_pvwatts(
+        pac, **clearsky,
+        solar_zenith=solar_position['zenith'],
+        solar_azimuth=solar_position['azimuth']
+    )
+    assert rsquared > 0.9
+    assert tilt_out == pytest.approx(tilt, abs=10)
+    assert azimuth_out == pytest.approx(azimuth, abs=10)
+    clearsky.dropna(inplace=True)
+    pac.dropna(inplace=True)
+    solar_position.dropna(inplace=True)
+    tilt_out, azimuth_out, rsquared = system.orientation_fit_pvwatts(
+        pac, **clearsky,
+        solar_zenith=solar_position['zenith'],
+        solar_azimuth=solar_position['azimuth']
+    )
+    assert rsquared > 0.9
+    assert tilt_out == pytest.approx(tilt, abs=10)
+    assert azimuth_out == pytest.approx(azimuth, abs=10)
+
+
+def test_orientation_fit_pvwatts_temp_wind_as_series(naive_times):
+    tilt = 30
+    azimuth = 100
+    system_location = location.Location(35, -106)
+    local_time = naive_times.tz_localize('MST')
+    clearsky = system_location.get_clearsky(
+        local_time, model='simplified_solis'
+    )
+    solar_position = system_location.get_solarposition(clearsky.index)
+    poa = irradiance.get_total_irradiance(
+        tilt, azimuth,
+        solar_position['zenith'],
+        solar_position['azimuth'],
+        **clearsky
+    )
+    temp_cell = pvlib.temperature.sapm_cell(
+        poa['poa_global'],
+        25, 1,
+        **pvlib.temperature.TEMPERATURE_MODEL_PARAMETERS[
+            'sapm'
+        ][
+            'open_rack_glass_glass'
+        ]
+    )
+    pdc = pvsystem.pvwatts_dc(poa['poa_global'], temp_cell, 100, -0.002)
+    pac = pvsystem.inverter.pvwatts(pdc, 120)
+    tilt_out, azimuth_out, rsquared = system.orientation_fit_pvwatts(
+        pac, **clearsky,
+        solar_zenith=solar_position['zenith'],
+        solar_azimuth=solar_position['azimuth'],
+        temperature=pd.Series(25, index=clearsky.index),
+        wind_speed=pd.Series(1, index=clearsky.index)
+    )
+    assert rsquared > 0.9
+    assert tilt_out == pytest.approx(tilt, abs=10)
+    assert azimuth_out == pytest.approx(azimuth, abs=10)

From 63865ef069fbfb68676c0a9f402906bbf4be0e1e Mon Sep 17 00:00:00 2001
From: Will Vining <wfvining@gmail.com>
Date: Tue, 20 Oct 2020 15:20:34 -0600
Subject: [PATCH 04/14] Require input with no missing values

---
 pvanalytics/system.py            | 26 +++++++-----
 pvanalytics/tests/test_system.py | 72 ++++++++++++++++++++++++++------
 2 files changed, 74 insertions(+), 24 deletions(-)

diff --git a/pvanalytics/system.py b/pvanalytics/system.py
index 28703243..702a7773 100644
--- a/pvanalytics/system.py
+++ b/pvanalytics/system.py
@@ -496,7 +496,9 @@ def orientation_fit_pvwatts(power_ac, ghi, dhi, dni,
     - the DC capacity of the system
     - the DC input limit of the inverter.
 
-    All parameters passed as a Series must have the same index.
+    All parameters passed as a Series must have the same index and must not
+    contain any undefined values (i.e. NaNs). If any input contains NaNs a
+    ValueError is raised.
 
     Parameters
     ----------
@@ -534,17 +536,19 @@ def orientation_fit_pvwatts(power_ac, ghi, dhi, dni,
     r_squared : float
         :math:`r^2` value for the fit at the returned orientation.
 
+    Raises
+    ------
+    ValueError
+        If any input passed as a Series contains undefined values (i.e. NaNs).
     """
-    power_ac = power_ac.dropna()
-    ghi = ghi.dropna()
-    dhi = dhi.dropna()
-    dni = dni.dropna()
-    solar_azimuth = solar_azimuth.dropna()
-    solar_zenith = solar_zenith.dropna()
-    if isinstance(temperature, pd.Series):
-        temperature = temperature.dropna()
-    if isinstance(wind_speed, pd.Series):
-        wind_speed = wind_speed.dropna()
+    if power_ac.hasnans:
+        raise ValueError("power_ac must not contain undefined values")
+    if ghi.hasnans or dhi.hasnans or dni.hasnans:
+        raise ValueError("ghi, dhi, and dni must not contain undefined values")
+    if isinstance(temperature, pd.Series) and temperature.hasnans:
+        raise ValueError("temperature must not contain undefined values")
+    if isinstance(wind_speed, pd.Series) and wind_speed.hasnans:
+        raise ValueError("wind_speed must not contain undefined values")
     if temperature_model_parameters is None:
         temperature_model_parameters = \
             TEMPERATURE_MODEL_PARAMETERS['sapm']['open_rack_glass_glass']
diff --git a/pvanalytics/tests/test_system.py b/pvanalytics/tests/test_system.py
index f26ca3cb..79ca33ee 100644
--- a/pvanalytics/tests/test_system.py
+++ b/pvanalytics/tests/test_system.py
@@ -519,17 +519,23 @@ def test_orientation_fit_pvwatts_missing_data(naive_times):
     )
     pdc = pvsystem.pvwatts_dc(poa['poa_global'], temp_cell, 100, -0.002)
     pac = pvsystem.inverter.pvwatts(pdc, 120)
-    tilt_out, azimuth_out, rsquared = system.orientation_fit_pvwatts(
-        pac, **clearsky,
-        solar_zenith=solar_position['zenith'],
-        solar_azimuth=solar_position['azimuth']
-    )
-    assert rsquared > 0.9
-    assert tilt_out == pytest.approx(tilt, abs=10)
-    assert azimuth_out == pytest.approx(azimuth, abs=10)
-    clearsky.dropna(inplace=True)
-    pac.dropna(inplace=True)
     solar_position.dropna(inplace=True)
+    with pytest.raises(ValueError,
+                       match=".* must not contain undefined values"):
+        system.orientation_fit_pvwatts(
+            pac, **clearsky,
+            solar_zenith=solar_position['zenith'],
+            solar_azimuth=solar_position['azimuth']
+        )
+    pac.dropna(inplace=True)
+    with pytest.raises(ValueError,
+                       match=".* must not contain undefined values"):
+        system.orientation_fit_pvwatts(
+            pac, **clearsky,
+            solar_zenith=solar_position['zenith'],
+            solar_azimuth=solar_position['azimuth']
+        )
+    clearsky.dropna(inplace=True)
     tilt_out, azimuth_out, rsquared = system.orientation_fit_pvwatts(
         pac, **clearsky,
         solar_zenith=solar_position['zenith'],
@@ -564,14 +570,54 @@ def test_orientation_fit_pvwatts_temp_wind_as_series(naive_times):
             'open_rack_glass_glass'
         ]
     )
+    temperature = pd.Series(25, index=clearsky.index)
+    wind_speed = pd.Series(1, index=clearsky.index)
+    temperature_missing = temperature.copy()
+    temperature_missing.loc['4/5/2020':'4/10/2020'] = np.nan
+    wind_speed_missing = wind_speed.copy()
+    wind_speed_missing.loc['5/5/2020':'5/15/2020'] = np.nan
     pdc = pvsystem.pvwatts_dc(poa['poa_global'], temp_cell, 100, -0.002)
     pac = pvsystem.inverter.pvwatts(pdc, 120)
+    with pytest.raises(ValueError,
+                       match=".* must not contain undefined values"):
+        system.orientation_fit_pvwatts(
+            pac, **clearsky,
+            solar_zenith=solar_position['zenith'],
+            solar_azimuth=solar_position['azimuth'],
+            temperature=temperature_missing,
+            wind_speed=wind_speed_missing
+        )
+    with pytest.raises(ValueError,
+                       match="temperature must not contain undefined values"):
+        system.orientation_fit_pvwatts(
+            pac, **clearsky,
+            solar_zenith=solar_position['zenith'],
+            solar_azimuth=solar_position['azimuth'],
+            temperature=temperature_missing,
+            wind_speed=wind_speed
+        )
+    with pytest.raises(ValueError,
+                       match="wind_speed must not contain undefined values"):
+        system.orientation_fit_pvwatts(
+            pac, **clearsky,
+            solar_zenith=solar_position['zenith'],
+            solar_azimuth=solar_position['azimuth'],
+            temperature=temperature,
+            wind_speed=wind_speed_missing
+        )
+    # ValueError if indices don't match
+    with pytest.raises(ValueError):
+        system.orientation_fit_pvwatts(
+            pac, **clearsky,
+            solar_zenith=solar_position['zenith'],
+            solar_azimuth=solar_position['azimuth'],
+            temperature=temperature_missing.dropna(),
+            wind_speed=wind_speed_missing.dropna()
+        )
     tilt_out, azimuth_out, rsquared = system.orientation_fit_pvwatts(
         pac, **clearsky,
-        solar_zenith=solar_position['zenith'],
         solar_azimuth=solar_position['azimuth'],
-        temperature=pd.Series(25, index=clearsky.index),
-        wind_speed=pd.Series(1, index=clearsky.index)
+        solar_zenith=solar_position['zenith']
     )
     assert rsquared > 0.9
     assert tilt_out == pytest.approx(tilt, abs=10)

From 092f51170603638858ef45c6d5f2e8ac5230718d Mon Sep 17 00:00:00 2001
From: Will Vining <wfvining@gmail.com>
Date: Tue, 20 Oct 2020 15:22:13 -0600
Subject: [PATCH 05/14] Require pvlib>=0.8

Need this for pvlib.inverter.pvwatts()
---
 requirements.txt | 2 +-
 setup.py         | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/requirements.txt b/requirements.txt
index 8b8e54a0..6981aca0 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,4 +1,4 @@
 numpy>=1.16.0
 pandas>=0.25.0,<1.1.0
-pvlib>=0.7.0
+pvlib>=0.8.0
 scipy>=1.3.0
diff --git a/setup.py b/setup.py
index 7bf1af55..36417b84 100644
--- a/setup.py
+++ b/setup.py
@@ -33,7 +33,7 @@
 INSTALL_REQUIRES = [
     'numpy >= 1.16.0',
     'pandas >= 0.25.1',
-    'pvlib >= 0.7.0',
+    'pvlib >= 0.8.0',
     'scipy >= 1.3.0'
 ]
 

From f9aef5f7585731f1c8b0a9461399247b127c8a11 Mon Sep 17 00:00:00 2001
From: Will Vining <wfvining@gmail.com>
Date: Tue, 20 Oct 2020 15:34:39 -0600
Subject: [PATCH 06/14] Use larger default for `temperature_coefficient`

---
 pvanalytics/system.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pvanalytics/system.py b/pvanalytics/system.py
index 702a7773..7ae9e95a 100644
--- a/pvanalytics/system.py
+++ b/pvanalytics/system.py
@@ -482,7 +482,7 @@ def _rsquared(data, residuals):
 def orientation_fit_pvwatts(power_ac, ghi, dhi, dni,
                             solar_zenith, solar_azimuth,
                             temperature=25, wind_speed=0,
-                            temperature_coefficient=-0.002,
+                            temperature_coefficient=-0.004,
                             temperature_model_parameters=None):
     """Get the tilt and azimuth that give pvwatts output that most closely
     fits the data in `power_ac`.

From 608b2558fdc65209cedf112a630f3e8c4db274e9 Mon Sep 17 00:00:00 2001
From: Will Vining <wfvining@gmail.com>
Date: Tue, 20 Oct 2020 15:38:58 -0600
Subject: [PATCH 07/14] Change block comment to docstring

---
 pvanalytics/system.py | 71 ++++++++++++++++++++++---------------------
 1 file changed, 36 insertions(+), 35 deletions(-)

diff --git a/pvanalytics/system.py b/pvanalytics/system.py
index 7ae9e95a..16a871e8 100644
--- a/pvanalytics/system.py
+++ b/pvanalytics/system.py
@@ -412,41 +412,42 @@ def _power_residuals_from_clearsky(system_params,
                                    wind_speed,
                                    temperature_coefficient,
                                    temperature_model_parameters):
-    # Return the residuals between a system with parameters given in `params`
-    # and the data in `power_ac`.
-    #
-    # Parameters
-    # ----------
-    # system_params : array-like
-    #     array of four floats: tilt, azimuth, DC capacity, and inverter
-    #     DC input limit.
-    # ghi : Series
-    #     Clear sky GHI
-    # dhi : Series
-    #     Clear sky DHI
-    # dni : Series
-    #     Clear sky DNI
-    # solar_zenith : Series
-    #     Solar zenith at the same times as data in `power_ac`
-    # solar_azimuth : Series
-    #     Solar azimuth at the same times as data in `power_ac`
-    # power_ac : Series
-    #     Measured AC power under clear sky conditions.
-    # temperature : float or Series
-    #     Air temperature at which to model the hypothetical system. If a
-    #     float then a constant temperature is used. If a Series, must have
-    #     the same index as `power_ac`. [C]
-    # wind_speed : float or Series
-    #     Wind speed. If a float then a constant wind speed is used. If a
-    #     Series, must have the same index as `power_ac`. [m/s]
-    # temperature_model_parameters : dict
-    #     Parameters fot the cell temperature model.
-    #
-    # Returns
-    # -------
-    # Series
-    #     Difference between `power_ac` and the PVWatts output with the
-    #     given parameters.
+    """Return the residuals between a system with parameters given in `params`
+    and the data in `power_ac`.
+
+    Parameters
+    ----------
+    system_params : array-like
+        array of four floats: tilt, azimuth, DC capacity, and inverter
+        DC input limit.
+    ghi : Series
+        Clear sky GHI
+    dhi : Series
+        Clear sky DHI
+    dni : Series
+        Clear sky DNI
+    solar_zenith : Series
+        Solar zenith at the same times as data in `power_ac`
+    solar_azimuth : Series
+        Solar azimuth at the same times as data in `power_ac`
+    power_ac : Series
+        Measured AC power under clear sky conditions.
+    temperature : float or Series
+        Air temperature at which to model the hypothetical system. If a
+        float then a constant temperature is used. If a Series, must have
+        the same index as `power_ac`. [C]
+    wind_speed : float or Series
+        Wind speed. If a float then a constant wind speed is used. If a
+        Series, must have the same index as `power_ac`. [m/s]
+    temperature_model_parameters : dict
+        Parameters fot the cell temperature model.
+
+    Returns
+    -------
+    Series
+        Difference between `power_ac` and the PVWatts output with the
+        given parameters.
+    """
     tilt = system_params[0]
     azimuth = system_params[1]
     dc_capacity = system_params[2]

From 332b02a600c60a30f8f6e75feaac3d00aeede448 Mon Sep 17 00:00:00 2001
From: Will Vining <wfvining@gmail.com>
Date: Tue, 20 Oct 2020 15:40:23 -0600
Subject: [PATCH 08/14] Rename dc_limit to dc_inverter_limit

---
 pvanalytics/system.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/pvanalytics/system.py b/pvanalytics/system.py
index 16a871e8..8a58728b 100644
--- a/pvanalytics/system.py
+++ b/pvanalytics/system.py
@@ -451,7 +451,7 @@ def _power_residuals_from_clearsky(system_params,
     tilt = system_params[0]
     azimuth = system_params[1]
     dc_capacity = system_params[2]
-    dc_limit = system_params[3]
+    dc_inverter_limit = system_params[3]
     poa = pvlib.irradiance.get_total_irradiance(
         tilt, azimuth,
         solar_zenith,
@@ -470,7 +470,7 @@ def _power_residuals_from_clearsky(system_params,
         dc_capacity,
         temperature_coefficient
     )
-    return power_ac - pvlib.inverter.pvwatts(pdc, dc_limit)
+    return power_ac - pvlib.inverter.pvwatts(pdc, dc_inverter_limit)
 
 
 def _rsquared(data, residuals):

From 086210e6fd2bb0520d2648ce4f4208f170ce51f1 Mon Sep 17 00:00:00 2001
From: Will Vining <wfvining@gmail.com>
Date: Fri, 23 Oct 2020 07:34:13 -0600
Subject: [PATCH 09/14] Rename orientation_fit_pvwatts() to
 infer_orientation_fit_pvwatts()

Keeps the names consistent within the system module.
---
 pvanalytics/system.py            | 10 +++---
 pvanalytics/tests/test_system.py | 61 ++++++++++++++++++--------------
 2 files changed, 39 insertions(+), 32 deletions(-)

diff --git a/pvanalytics/system.py b/pvanalytics/system.py
index 8a58728b..e05023bc 100644
--- a/pvanalytics/system.py
+++ b/pvanalytics/system.py
@@ -480,11 +480,11 @@ def _rsquared(data, residuals):
     return r*r
 
 
-def orientation_fit_pvwatts(power_ac, ghi, dhi, dni,
-                            solar_zenith, solar_azimuth,
-                            temperature=25, wind_speed=0,
-                            temperature_coefficient=-0.004,
-                            temperature_model_parameters=None):
+def infer_orientation_fit_pvwatts(power_ac, ghi, dhi, dni,
+                                  solar_zenith, solar_azimuth,
+                                  temperature=25, wind_speed=0,
+                                  temperature_coefficient=-0.004,
+                                  temperature_model_parameters=None):
     """Get the tilt and azimuth that give pvwatts output that most closely
     fits the data in `power_ac`.
 
diff --git a/pvanalytics/tests/test_system.py b/pvanalytics/tests/test_system.py
index 79ca33ee..2a7cad2e 100644
--- a/pvanalytics/tests/test_system.py
+++ b/pvanalytics/tests/test_system.py
@@ -472,12 +472,11 @@ def system_power(request, system_location, naive_times):
 @pytest.mark.slow
 def test_orientation_fit_pvwatts(system_power):
     day_mask = system_power['ac'] > 0
-    tilt, azimuth, rsquared = system.orientation_fit_pvwatts(
+    tilt, azimuth, rsquared = system.infer_orientation_fit_pvwatts(
         system_power['ac'][day_mask],
         solar_zenith=system_power['solar_position']['zenith'][day_mask],
         solar_azimuth=system_power['solar_position']['azimuth'][day_mask],
-        **system_power['clearsky'][day_mask]
-    )
+        **system_power['clearsky'][day_mask])
     assert rsquared > 0.9
     assert tilt == pytest.approx(system_power['tilt'], abs=10)
     if system_power['tilt'] == 0:
@@ -522,24 +521,27 @@ def test_orientation_fit_pvwatts_missing_data(naive_times):
     solar_position.dropna(inplace=True)
     with pytest.raises(ValueError,
                        match=".* must not contain undefined values"):
-        system.orientation_fit_pvwatts(
-            pac, **clearsky,
+        system.infer_orientation_fit_pvwatts(
+            pac,
             solar_zenith=solar_position['zenith'],
-            solar_azimuth=solar_position['azimuth']
+            solar_azimuth=solar_position['azimuth'],
+            **clearsky
         )
     pac.dropna(inplace=True)
     with pytest.raises(ValueError,
                        match=".* must not contain undefined values"):
-        system.orientation_fit_pvwatts(
-            pac, **clearsky,
+        system.infer_orientation_fit_pvwatts(
+            pac,
             solar_zenith=solar_position['zenith'],
-            solar_azimuth=solar_position['azimuth']
+            solar_azimuth=solar_position['azimuth'],
+            **clearsky
         )
     clearsky.dropna(inplace=True)
-    tilt_out, azimuth_out, rsquared = system.orientation_fit_pvwatts(
-        pac, **clearsky,
+    tilt_out, azimuth_out, rsquared = system.infer_orientation_fit_pvwatts(
+        pac,
         solar_zenith=solar_position['zenith'],
-        solar_azimuth=solar_position['azimuth']
+        solar_azimuth=solar_position['azimuth'],
+        **clearsky
     )
     assert rsquared > 0.9
     assert tilt_out == pytest.approx(tilt, abs=10)
@@ -580,44 +582,49 @@ def test_orientation_fit_pvwatts_temp_wind_as_series(naive_times):
     pac = pvsystem.inverter.pvwatts(pdc, 120)
     with pytest.raises(ValueError,
                        match=".* must not contain undefined values"):
-        system.orientation_fit_pvwatts(
-            pac, **clearsky,
+        system.infer_orientation_fit_pvwatts(
+            pac,
             solar_zenith=solar_position['zenith'],
             solar_azimuth=solar_position['azimuth'],
             temperature=temperature_missing,
-            wind_speed=wind_speed_missing
+            wind_speed=wind_speed_missing,
+            **clearsky
         )
     with pytest.raises(ValueError,
                        match="temperature must not contain undefined values"):
-        system.orientation_fit_pvwatts(
-            pac, **clearsky,
+        system.infer_orientation_fit_pvwatts(
+            pac,
             solar_zenith=solar_position['zenith'],
             solar_azimuth=solar_position['azimuth'],
             temperature=temperature_missing,
-            wind_speed=wind_speed
+            wind_speed=wind_speed,
+            **clearsky
         )
     with pytest.raises(ValueError,
                        match="wind_speed must not contain undefined values"):
-        system.orientation_fit_pvwatts(
-            pac, **clearsky,
+        system.infer_orientation_fit_pvwatts(
+            pac,
             solar_zenith=solar_position['zenith'],
             solar_azimuth=solar_position['azimuth'],
             temperature=temperature,
-            wind_speed=wind_speed_missing
+            wind_speed=wind_speed_missing,
+            **clearsky
         )
     # ValueError if indices don't match
     with pytest.raises(ValueError):
-        system.orientation_fit_pvwatts(
-            pac, **clearsky,
+        system.infer_orientation_fit_pvwatts(
+            pac,
             solar_zenith=solar_position['zenith'],
             solar_azimuth=solar_position['azimuth'],
             temperature=temperature_missing.dropna(),
-            wind_speed=wind_speed_missing.dropna()
+            wind_speed=wind_speed_missing.dropna(),
+            **clearsky
         )
-    tilt_out, azimuth_out, rsquared = system.orientation_fit_pvwatts(
-        pac, **clearsky,
+    tilt_out, azimuth_out, rsquared = system.infer_orientation_fit_pvwatts(
+        pac,
+        solar_zenith=solar_position['zenith'],
         solar_azimuth=solar_position['azimuth'],
-        solar_zenith=solar_position['zenith']
+        **clearsky
     )
     assert rsquared > 0.9
     assert tilt_out == pytest.approx(tilt, abs=10)

From 8c5f38cf6127306bd88ddf0af8fd12d9e3f0b49c Mon Sep 17 00:00:00 2001
From: Will Vining <wfvining@gmail.com>
Date: Fri, 23 Oct 2020 12:11:12 -0600
Subject: [PATCH 10/14] Improve documentation

Co-authored-by: Cliff Hansen <cwhanse@sandia.gov>
---
 pvanalytics/system.py | 23 +++++++++++++++++------
 1 file changed, 17 insertions(+), 6 deletions(-)

diff --git a/pvanalytics/system.py b/pvanalytics/system.py
index e05023bc..a2c6a7b4 100644
--- a/pvanalytics/system.py
+++ b/pvanalytics/system.py
@@ -412,7 +412,7 @@ def _power_residuals_from_clearsky(system_params,
                                    wind_speed,
                                    temperature_coefficient,
                                    temperature_model_parameters):
-    """Return the residuals between a system with parameters given in `params`
+    """Return the residuals between a system with parameters given in `system_params`
     and the data in `power_ac`.
 
     Parameters
@@ -439,14 +439,22 @@ def _power_residuals_from_clearsky(system_params,
     wind_speed : float or Series
         Wind speed. If a float then a constant wind speed is used. If a
         Series, must have the same index as `power_ac`. [m/s]
+    temperature_coefficient : float
+        Temperature coefficient of DC power. [1/C]
     temperature_model_parameters : dict
-        Parameters fot the cell temperature model.
+        Parameters for the cell temperature model.
 
     Returns
     -------
     Series
         Difference between `power_ac` and the PVWatts output with the
         given parameters.
+    
+    Notes
+    ------
+    Uses the defaults in `pvlib.irradiance.get_total_irradiance` to calculated plane-of-array
+    irradiance, i.e., the isotropic model for sky diffuse irradiance, and the Perez irradiance
+    transposition model.
     """
     tilt = system_params[0]
     azimuth = system_params[1]
@@ -485,9 +493,12 @@ def infer_orientation_fit_pvwatts(power_ac, ghi, dhi, dni,
                                   temperature=25, wind_speed=0,
                                   temperature_coefficient=-0.004,
                                   temperature_model_parameters=None):
-    """Get the tilt and azimuth that give pvwatts output that most closely
+    """Get the tilt and azimuth that give PVWatts output that most closely
     fits the data in `power_ac`.
 
+    Input data `power_ac`, `ghi`, `dhi`, `dni` should reflect clear-sky
+    conditions.
+    
     Uses non-linear least squares to optimize over four free variables
     to find the values that result in the best fit between power modeled
     using PVWatts and `power_ac`. The four free variables are
@@ -506,11 +517,11 @@ def infer_orientation_fit_pvwatts(power_ac, ghi, dhi, dni,
     power_ac : Series
         AC power from the system in clear sky conditions.
     ghi : Series
-        Clear sky GHI with same index as `power_ac`.
+        Clear sky GHI with same index as `power_ac`. [W/m^2]
     dhi : Series
-        Clear sky DHI with same index as `power_ac`.
+        Clear sky DHI with same index as `power_ac`. [W/m^2]
     dni : Series
-        Clear sky DNI with same index as `power_ac`.
+        Clear sky DNI with same index as `power_ac`. [W/m^2]
     solar_zenith : Series
         Solar zenith. [degrees]
     solar_azimuth : Series

From af636cd41169b9965ceb55da815e7ec6e6aedf98 Mon Sep 17 00:00:00 2001
From: Will Vining <wfvining@gmail.com>
Date: Fri, 23 Oct 2020 12:23:04 -0600
Subject: [PATCH 11/14] Add notes on returned values and operating on clipped
 data

---
 pvanalytics/system.py | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/pvanalytics/system.py b/pvanalytics/system.py
index a2c6a7b4..6bc1cca0 100644
--- a/pvanalytics/system.py
+++ b/pvanalytics/system.py
@@ -508,6 +508,12 @@ def infer_orientation_fit_pvwatts(power_ac, ghi, dhi, dni,
     - the DC capacity of the system
     - the DC input limit of the inverter.
 
+    Of these four parameters, only tilt and azimuth are returned. While, DC
+    capacity and the DC input limit are calculated, their values may not be
+    accurate. While its value is not returned, because the DC input limit is
+    used as a free variable for the optimization process, this function
+    can operate on `power_ac` data that includes inverter clipping.
+
     All parameters passed as a Series must have the same index and must not
     contain any undefined values (i.e. NaNs). If any input contains NaNs a
     ValueError is raised.

From eebea089f89cc3baaa78c59f76a66e70fafbaa99 Mon Sep 17 00:00:00 2001
From: Will Vining <wfvining@gmail.com>
Date: Fri, 23 Oct 2020 12:30:20 -0600
Subject: [PATCH 12/14] Reorder parameters to _power_residuals_from_clearsky()

---
 pvanalytics/system.py | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/pvanalytics/system.py b/pvanalytics/system.py
index 6bc1cca0..a79ba065 100644
--- a/pvanalytics/system.py
+++ b/pvanalytics/system.py
@@ -407,8 +407,9 @@ def infer_orientation_daily_peak(power_or_poa, sunny, tilts,
 
 def _power_residuals_from_clearsky(system_params,
                                    ghi, dhi, dni,
+                                   power_ac,
                                    solar_zenith, solar_azimuth,
-                                   power_ac, temperature,
+                                   temperature,
                                    wind_speed,
                                    temperature_coefficient,
                                    temperature_model_parameters):
@@ -426,12 +427,12 @@ def _power_residuals_from_clearsky(system_params,
         Clear sky DHI
     dni : Series
         Clear sky DNI
+    power_ac : Series
+        Measured AC power under clear sky conditions.
     solar_zenith : Series
         Solar zenith at the same times as data in `power_ac`
     solar_azimuth : Series
         Solar azimuth at the same times as data in `power_ac`
-    power_ac : Series
-        Measured AC power under clear sky conditions.
     temperature : float or Series
         Air temperature at which to model the hypothetical system. If a
         float then a constant temperature is used. If a Series, must have

From 930dfe593b056a8174fcbe98161cbcf2dae5c395 Mon Sep 17 00:00:00 2001
From: Will Vining <wfvining@gmail.com>
Date: Fri, 23 Oct 2020 12:31:54 -0600
Subject: [PATCH 13/14] Clean up whitespace

---
 pvanalytics/system.py | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/pvanalytics/system.py b/pvanalytics/system.py
index a79ba065..94b83a6d 100644
--- a/pvanalytics/system.py
+++ b/pvanalytics/system.py
@@ -413,8 +413,8 @@ def _power_residuals_from_clearsky(system_params,
                                    wind_speed,
                                    temperature_coefficient,
                                    temperature_model_parameters):
-    """Return the residuals between a system with parameters given in `system_params`
-    and the data in `power_ac`.
+    """Return the residuals between a system with parameters given in
+    `system_params` and the data in `power_ac`.
 
     Parameters
     ----------
@@ -450,12 +450,12 @@ def _power_residuals_from_clearsky(system_params,
     Series
         Difference between `power_ac` and the PVWatts output with the
         given parameters.
-    
+
     Notes
     ------
-    Uses the defaults in `pvlib.irradiance.get_total_irradiance` to calculated plane-of-array
-    irradiance, i.e., the isotropic model for sky diffuse irradiance, and the Perez irradiance
-    transposition model.
+    Uses the defaults in :py:func:`pvlib.irradiance.get_total_irradiance` to
+    calculated plane-of-array irradiance, i.e., the isotropic model for sky
+    diffuse irradiance, and the Perez irradiance transposition model.
     """
     tilt = system_params[0]
     azimuth = system_params[1]
@@ -499,7 +499,7 @@ def infer_orientation_fit_pvwatts(power_ac, ghi, dhi, dni,
 
     Input data `power_ac`, `ghi`, `dhi`, `dni` should reflect clear-sky
     conditions.
-    
+
     Uses non-linear least squares to optimize over four free variables
     to find the values that result in the best fit between power modeled
     using PVWatts and `power_ac`. The four free variables are

From 843346173879f7dc5587ddf3584bc4633485543c Mon Sep 17 00:00:00 2001
From: Will Vining <wfvining@gmail.com>
Date: Fri, 23 Oct 2020 13:29:53 -0600
Subject: [PATCH 14/14] Change function name in api.rst

---
 docs/api.rst | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/docs/api.rst b/docs/api.rst
index f5aeaf4f..3d0ed60c 100644
--- a/docs/api.rst
+++ b/docs/api.rst
@@ -241,7 +241,7 @@ power or plane of array irradiance measurements.
    :toctree: generated/
 
    system.infer_orientation_daily_peak
-   system.orientation_fit_pvwatts
+   system.infer_orientation_fit_pvwatts
 
 Metrics
 =======