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fix pvwatts_ac exception and return value when called with pdc=0s #676

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Merged
merged 2 commits into from
Mar 20, 2019
Merged

fix pvwatts_ac exception and return value when called with pdc=0s #676

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e1cc8a7
assert what the pvwatts_ac(0) output should be
wholmgren Mar 19, 2019
83201ca
fix it
wholmgren Mar 19, 2019
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3 changes: 3 additions & 0 deletions docs/sphinx/source/whatsnew/v0.6.2.rst
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Expand Up @@ -24,6 +24,9 @@ Enhancements
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`)


Testing
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9 changes: 8 additions & 1 deletion pvlib/pvsystem.py
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Expand Up @@ -2967,8 +2967,15 @@ def pvwatts_ac(pdc, pdc0, eta_inv_nom=0.96, eta_inv_ref=0.9637):
pac0 = eta_inv_nom * pdc0
zeta = pdc / pdc0

# arrays to help avoid divide by 0 for scalar and array
eta = np.zeros_like(pdc, dtype=float)
pdc_neq_0 = ~np.equal(pdc, 0)

# eta < 0 if zeta < 0.006. pac is forced to be >= 0 below. GH 541
eta = eta_inv_nom / eta_inv_ref * (-0.0162*zeta - 0.0059/zeta + 0.9858)
eta = eta_inv_nom / eta_inv_ref * (
- 0.0162*zeta
- np.divide(0.0059, zeta, out=eta, where=pdc_neq_0)
+ 0.9858)

pac = eta * pdc
pac = np.minimum(pac0, pac)
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11 changes: 8 additions & 3 deletions pvlib/test/test_pvsystem.py
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Expand Up @@ -1366,6 +1366,10 @@ def test_pvwatts_ac_scalars():
expected = 85.58556604752516
out = pvsystem.pvwatts_ac(90, 100, 0.95)
assert_allclose(out, expected)
# GH 675
expected = 0.
out = pvsystem.pvwatts_ac(0., 100)
assert_allclose(out, expected)


def test_pvwatts_ac_possible_negative():
Expand All @@ -1378,19 +1382,20 @@ def test_pvwatts_ac_possible_negative():

@needs_numpy_1_10
def test_pvwatts_ac_arrays():
pdc = np.array([[np.nan], [50], [100]])
pdc = np.array([[np.nan], [0], [50], [100]])
pdc0 = 100
expected = np.array([[nan],
[0.],
[47.60843624],
[95.]])
out = pvsystem.pvwatts_ac(pdc, pdc0, 0.95)
assert_allclose(out, expected, equal_nan=True)


def test_pvwatts_ac_series():
pdc = pd.Series([np.nan, 50, 100])
pdc = pd.Series([np.nan, 0, 50, 100])
pdc0 = 100
expected = pd.Series(np.array([ nan, 47.608436, 95. ]))
expected = pd.Series(np.array([nan, 0., 47.608436, 95.]))
out = pvsystem.pvwatts_ac(pdc, pdc0, 0.95)
assert_series_equal(expected, out)

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