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Apr 5, 2019
Merged

fix erbs near zenith=90 #683

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9bcc9b7
fix erbs near zenith=90
wholmgren Mar 29, 2019
1baefd9
document return type change
wholmgren Mar 29, 2019
c347ba2
fix copy/paste in test
wholmgren Mar 29, 2019
f3779bc
fix docs
wholmgren Apr 4, 2019
830603c
revert accidental changes to test_clearsky
wholmgren Apr 4, 2019
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1 change: 1 addition & 0 deletions docs/sphinx/source/whatsnew.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,7 @@ What's New

These are new features and improvements of note in each release.

.. include:: whatsnew/v0.6.2.rst
.. include:: whatsnew/v0.6.1.rst
.. include:: whatsnew/v0.6.0.rst
.. include:: whatsnew/v0.5.2.rst
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25 changes: 18 additions & 7 deletions docs/sphinx/source/whatsnew/v0.6.2.rst
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Expand Up @@ -14,20 +14,31 @@ date will require Python 3. (:issue:`501`)

API Changes
~~~~~~~~~~~

* :py:func:`~pvlib.irradiance.erbs` *doy* argument changed to
*datetime_or_doy* to be consistent with allowed types and similar
functions (:py:func:`~pvlib.irradiance.disc`,
:py:func:`~pvlib.irradiance.get_extra_radiation`).
* :py:func:`~pvlib.irradiance.erbs` DataFrame vs. OrderedDict return
behavior now determined by type of *datetime_or_doy* instead of
*ghi* or *zenith*.
* Added *min_cos_zenith* and *max_zenith* keyword arguments to
:py:func:`~pvlib.irradiance.erbs`. (:issue:`681`)

Enhancements
~~~~~~~~~~~~
* Add US CRN data reader to `pvlib.iotools`.
* Add SOLRAD data reader to `pvlib.iotools`.
* Add EPW data reader to `pvlib.iotools`. (:issue:`591`)
* Add US CRN data reader to :ref:`iotools`.
* Add SOLRAD data reader to :ref:`iotools`.
* Add EPW data reader to :ref:`iotools`. (:issue:`591`)

Bug fixes
~~~~~~~~~
* Compatibility with pandas 0.24 deprecations. (:issue:`659`)
* pvwatts_ac raised ZeroDivisionError when called with scalar pdc=0
and a RuntimeWarning for array(0) input. Now correctly returns 0s
of the appropriate type. (:issue:`675`)
* :py:func:`~pvlib.pvsystem.pvwatts_ac` raised ``ZeroDivisionError``
when called with scalar ``pdc=0``
and a ``RuntimeWarning`` for ``array(0)`` input. Now correctly returns
0s of the appropriate type. (:issue:`675`)
* Fixed :py:func:`~pvlib.irradiance.erbs` behavior when zenith is
near 90 degrees. (:issue:`681`)


Testing
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3 changes: 1 addition & 2 deletions pvlib/iotools/epw.py
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Expand Up @@ -70,8 +70,7 @@ def read_epw(filename, coerce_year=None):
longitude Float site longitude
TZ Float UTC offset
altitude Float site elevation
=============== ====== ========================================

=============== ====== =========================================


============================= ==============================================================================================================================================================
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31 changes: 19 additions & 12 deletions pvlib/irradiance.py
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Expand Up @@ -2152,7 +2152,7 @@ def _gti_dirint_gte_90_kt_prime(aoi, solar_zenith, solar_azimuth, times,
return kt_prime_gte_90


def erbs(ghi, zenith, doy):
def erbs(ghi, zenith, datetime_or_doy, min_cos_zenith=0.065, max_zenith=87):
r"""
Estimate DNI and DHI from GHI using the Erbs model.

Expand All @@ -2179,8 +2179,15 @@ def erbs(ghi, zenith, doy):
Global horizontal irradiance in W/m^2.
zenith: numeric
True (not refraction-corrected) zenith angles in decimal degrees.
doy: scalar, array or DatetimeIndex
The day of the year.
datetime_or_doy : int, float, array, pd.DatetimeIndex
Day of year or array of days of year e.g.
pd.DatetimeIndex.dayofyear, or pd.DatetimeIndex.
min_cos_zenith : numeric, default 0.065
Minimum value of cos(zenith) to allow when calculating global
clearness index `kt`. Equivalent to zenith = 86.273 degrees.
max_zenith : numeric, default 87
Maximum value of zenith to allow in DNI calculation. DNI will be
set to 0 for times with zenith values greater than `max_zenith`.

Returns
-------
Expand All @@ -2205,14 +2212,10 @@ def erbs(ghi, zenith, doy):
disc
"""

dni_extra = get_extra_radiation(doy)
dni_extra = get_extra_radiation(datetime_or_doy)

# This Z needs to be the true Zenith angle, not apparent,
# to get extraterrestrial horizontal radiation)
i0_h = dni_extra * tools.cosd(zenith)

kt = ghi / i0_h
kt = np.maximum(kt, 0)
kt = clearness_index(ghi, zenith, dni_extra, min_cos_zenith=min_cos_zenith,
max_clearness_index=1)
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nice 🚀


# For Kt <= 0.22, set the diffuse fraction
df = 1 - 0.09*kt
Expand All @@ -2229,14 +2232,18 @@ def erbs(ghi, zenith, doy):
dhi = df * ghi

dni = (ghi - dhi) / tools.cosd(zenith)
bad_values = (zenith > max_zenith) | (ghi < 0) | (dni < 0)
dni = np.where(bad_values, 0, dni)
# ensure that closure relationship remains valid
dhi = np.where(bad_values, ghi, dhi)
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very nice! 🚀


data = OrderedDict()
data['dni'] = dni
data['dhi'] = dhi
data['kt'] = kt

if isinstance(dni, pd.Series):
data = pd.DataFrame(data)
if isinstance(datetime_or_doy, pd.DatetimeIndex):
data = pd.DataFrame(data, index=datetime_or_doy)

return data

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58 changes: 48 additions & 10 deletions pvlib/test/test_irradiance.py
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Expand Up @@ -620,21 +620,59 @@ def test_gti_dirint():


def test_erbs():
ghi = pd.Series([0, 50, 1000, 1000])
zenith = pd.Series([120, 85, 10, 10])
doy = pd.Series([1, 1, 1, 180])
expected = pd.DataFrame(np.
array([[ -0.00000000e+00, 0.00000000e+00, -0.00000000e+00],
[ 9.67127061e+01, 4.15709323e+01, 4.05715990e-01],
[ 7.94187742e+02, 2.17877755e+02, 7.18119416e-01],
[ 8.42358014e+02, 1.70439297e+02, 7.68919470e-01]]),
columns=['dni', 'dhi', 'kt'])
index = pd.DatetimeIndex(['20190101']*3 + ['20190620'])
ghi = pd.Series([0, 50, 1000, 1000], index=index)
zenith = pd.Series([120, 85, 10, 10], index=index)
expected = pd.DataFrame(np.array(
[[0.00000000e+00, 0.00000000e+00, 0.00000000e+00],
[9.67192672e+01, 4.15703604e+01, 4.05723511e-01],
[7.94205651e+02, 2.17860117e+02, 7.18132729e-01],
[8.42001578e+02, 1.70790318e+02, 7.68214312e-01]]),
columns=['dni', 'dhi', 'kt'], index=index)

out = irradiance.erbs(ghi, zenith, doy)
out = irradiance.erbs(ghi, zenith, index)

assert_frame_equal(np.round(out, 0), np.round(expected, 0))


def test_erbs_min_cos_zenith_max_zenith():
# map out behavior under difficult conditions with various
# limiting kwargs settings
columns = ['dni', 'dhi', 'kt']
times = pd.DatetimeIndex(['2016-07-19 06:11:00'], tz='America/Phoenix')

# max_zenith keeps these results reasonable
out = irradiance.erbs(ghi=1.0, zenith=89.99999,
datetime_or_doy=times, min_cos_zenith=0)
expected = pd.DataFrame(np.array(
[[0., 1., 1.]]),
columns=columns, index=times)
assert_frame_equal(out, expected)

# 4-5 9s will produce bad behavior without max_zenith limit
out = irradiance.erbs(ghi=1.0, zenith=89.99999,
datetime_or_doy=times, max_zenith=100)
expected = pd.DataFrame(np.array(
[[6.00115286e+03, 9.98952601e-01, 1.16377640e-02]]),
columns=columns, index=times)
assert_frame_equal(out, expected)

# 1-2 9s will produce bad behavior without either limit
out = irradiance.erbs(ghi=1.0, zenith=89.99, datetime_or_doy=times,
min_cos_zenith=0, max_zenith=100)
expected = pd.DataFrame(np.array(
[[4.78419761e+03, 1.65000000e-01, 1.00000000e+00]]),
columns=columns, index=times)
assert_frame_equal(out, expected)

# check default behavior under hardest condition
out = irradiance.erbs(ghi=1.0, zenith=90, datetime_or_doy=times)
expected = pd.DataFrame(np.array(
[[0., 1., 0.01163776]]),
columns=columns, index=times)
assert_frame_equal(out, expected)


def test_erbs_all_scalar():
ghi = 1000
zenith = 10
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