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add marion's adjustment to pvwatts_dc (#2569)
* add marion's adjustment * linting * Update pvlib/pvsystem.py Co-authored-by: Cliff Hansen <[email protected]> * Update pvlib/pvsystem.py Co-authored-by: Cliff Hansen <[email protected]> * Update pvlib/pvsystem.py Co-authored-by: Cliff Hansen <[email protected]> * Update pvlib/pvsystem.py Co-authored-by: Cliff Hansen <[email protected]> * Update pvlib/pvsystem.py Co-authored-by: Cliff Hansen <[email protected]> * more suggested changes * Update pvlib/pvsystem.py doi sphinx Co-authored-by: RDaxini <[email protected]> * Update pvlib/pvsystem.py Co-authored-by: RDaxini <[email protected]> * Update pvlib/pvsystem.py Co-authored-by: RDaxini <[email protected]> * cleaning up docs * Update pvlib/pvsystem.py Co-authored-by: Will Holmgren <[email protected]> * prevent negative power * fix typo in error eqn * fix the right typo this time... * reorder err eqns * add more detail on `cap_adjustment` * return same object type that was input * fix issue with scalars * another fix * add tests * increase test coverage * more test coverage * fix shallow copy issue * Update pvlib/pvsystem.py Co-authored-by: RDaxini <[email protected]> * Update pvlib/pvsystem.py Co-authored-by: RDaxini <[email protected]> * Update pvlib/pvsystem.py Co-authored-by: RDaxini <[email protected]> * update whatsnew * reorganize to clean it up * single comp path on numpy array * added some comments * unit formatting * call keyword arguments as keyword arguments * quick fix * a few more missed keyword args * simplify with_k_and_cap_adjustmen * Update pvlib/pvsystem.py Co-authored-by: Cliff Hansen <[email protected]> * Update pvlib/pvsystem.py Co-authored-by: Cliff Hansen <[email protected]> * Update pvlib/pvsystem.py Co-authored-by: Cliff Hansen <[email protected]> * doc formatting/linting --------- Co-authored-by: Cliff Hansen <[email protected]> Co-authored-by: RDaxini <[email protected]> Co-authored-by: Will Holmgren <[email protected]>
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‎docs/sphinx/source/whatsnew/v0.13.2.rst‎

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@@ -37,12 +37,13 @@ Enhancements
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:py:func:`~pvlib.singlediode.bishop88_mpp`,
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:py:func:`~pvlib.singlediode.bishop88_v_from_i`, and
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:py:func:`~pvlib.singlediode.bishop88_i_from_v`. (:issue:`2497`, :pull:`2498`)
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* Add Marion 2008 non-linear irradiance adjustment factor to
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:py:func:`pvlib.pvsystem.pvwatts_dc`. (:issue:`2566`, :pull:`2569`)
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* Accelerate :py:func:`~pvlib.pvsystem.singlediode` when scipy>=1.15 is
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installed. (:issue:`2497`, :pull:`2571`)
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* Add :py:func:`~pvlib.iotools.get_era5`, a function for accessing
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ERA5 reanalysis data. (:pull:`2573`)
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Documentation
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~~~~~~~~~~~~~
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* Provide an overview of single-diode modeling functionality in :ref:`singlediode`. (:pull:`2565`)
@@ -66,4 +67,5 @@ Maintenance
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Contributors
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~~~~~~~~~~~~
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* Will Hobbs (:ghuser:`williamhobbs`)
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* Cliff Hansen (:ghuser:`cwhanse`)

‎pvlib/pvsystem.py‎

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@@ -2886,53 +2886,118 @@ def scale_voltage_current_power(data, voltage=1, current=1):
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@renamed_kwarg_warning(
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"0.13.0", "g_poa_effective", "effective_irradiance")
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def pvwatts_dc(effective_irradiance, temp_cell, pdc0, gamma_pdc, temp_ref=25.):
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def pvwatts_dc(effective_irradiance, temp_cell, pdc0, gamma_pdc, temp_ref=25.,
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k=None, cap_adjustment=False):
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r"""
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Implements NREL's PVWatts DC power model. The PVWatts DC model [1]_ is:
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.. math::
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P_{dc} = \frac{G_{poa eff}}{1000} P_{dc0} ( 1 + \gamma_{pdc} (T_{cell} - T_{ref}))
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Note that ``pdc0`` is also used as a symbol in
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:py:func:`pvlib.inverter.pvwatts`. ``pdc0`` in this function refers to the DC
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power of the modules at reference conditions. ``pdc0`` in
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:py:func:`pvlib.inverter.pvwatts` refers to the DC power input limit of
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the inverter.
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Implement NREL's PVWatts (Version 5) DC power model.
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Parameters
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----------
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effective_irradiance: numeric
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Irradiance transmitted to the PV cells. To be
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fully consistent with PVWatts, the user must have already
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applied angle of incidence losses, but not soiling, spectral,
2909-
etc. [W/m^2]
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Irradiance transmitted to the PV cells. To be fully consistent with
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PVWatts, the user must have already applied angle of incidence losses,
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but not soiling, spectral, etc. [Wm⁻²]
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temp_cell: numeric
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Cell temperature [C].
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pdc0: numeric
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Power of the modules at 1000 W/m^2 and cell reference temperature. [W]
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Power of the modules at 1000 Wm⁻² and cell reference temperature. [W]
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gamma_pdc: numeric
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The temperature coefficient of power. Typically -0.002 to
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-0.005 per degree C. [1/C]
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The temperature coefficient of power. Typically -0.002 to -0.005 per
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degree C. [1/°C]
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temp_ref: numeric, default 25.0
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Cell reference temperature. PVWatts defines it to be 25 C and
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is included here for flexibility. [C]
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Cell reference temperature. PVWatts defines it to be 25 °C and is
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included here for flexibility. [°C]
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k: numeric, optional
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Irradiance correction factor, defined in [2]_. Typically positive.
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[unitless]
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cap_adjustment: Boolean, default False
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If True, only apply the optional adjustment at and below 1000 Wm⁻²
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29212916
Returns
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-------
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pdc: numeric
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DC power. [W]
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Notes
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-----
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The PVWatts Version 5 DC model [1]_ is:
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.. math::
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P_{dc} = \frac{G_{poa eff}}{1000} P_{dc0} ( 1 + \gamma_{pdc} (T_{cell} - T_{ref}))
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This model has also been referred to as the power temperature coefficient
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model.
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An optional adjustment can be applied to :math:`P_{dc}` as described in
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[2]_. The adjustment accounts for the variation in module efficiency with
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irradiance. The piece-wise adjustment to power is parameterized by `k`,
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where `k` is the reduction in actual power at 200 Wm⁻² relative to power
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calculated at 200 Wm⁻² as 0.2*`pdc0`. For example, a module that is rated
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at 500 W at STC but produces 95 W at 200 Wm⁻² (a 5% relative reduction in
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efficiency) would have a value of `k` = 0.01.
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.. math::
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k=\frac{0.2P_{dc0}-P_{200}}{P_{dc0}}
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For positive `k` values, and `k` is typically positive, this adjustment
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would also increase relative efficiency when irradiance is above 1000 Wm⁻².
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This may not be desired, as modules with nonlinear irradiance response
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often have peak efficiency near 1000 Wm⁻², and it is either flat or
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declining at higher irradiance. An optional parameter, `cap_adjustment`,
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can address this by modifying the adjustment from [2]_ to only apply below
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1000 Wm⁻².
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Note that ``pdc0`` is also used as a symbol in
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:py:func:`pvlib.inverter.pvwatts`. ``pdc0`` in this function refers to the
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DC power of the modules at reference conditions. ``pdc0`` in
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:py:func:`pvlib.inverter.pvwatts` refers to the DC power input limit of
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the inverter.
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References
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----------
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.. [1] A. P. Dobos, "PVWatts Version 5 Manual"
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http://pvwatts.nrel.gov/downloads/pvwattsv5.pdf
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(2014).
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.. [2] B. Marion, "Comparison of Predictive Models for
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Photovoltaic Module Performance,"
2965+
:doi:`10.1109/PVSC.2008.4922586`,
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https://docs.nrel.gov/docs/fy08osti/42511.pdf
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(2008).
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""" # noqa: E501
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pdc = (effective_irradiance * 0.001 * pdc0 *
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(1 + gamma_pdc * (temp_cell - temp_ref)))
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# apply Marion's correction if k is provided
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if k is not None:
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# preserve input types
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index = pdc.index if isinstance(pdc, pd.Series) else None
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is_scalar = np.isscalar(pdc)
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2980+
# calculate error adjustments
2981+
err_1 = k * (1 - (1 - effective_irradiance / 200)**4)
2982+
err_2 = k * (1000 - effective_irradiance) / (1000 - 200)
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err = np.where(effective_irradiance <= 200, err_1, err_2)
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# cap adjustment, if needed
2986+
if cap_adjustment:
2987+
err = np.where(effective_irradiance >= 1000, 0, err)
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# make error adjustment
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pdc = pdc - pdc0 * err
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# set negative power to zero
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pdc = np.where(pdc < 0, 0, pdc)
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# preserve input types
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if index is not None:
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pdc = pd.Series(pdc, index=index)
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elif is_scalar:
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pdc = float(pdc)
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return pdc
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‎tests/test_pvsystem.py‎

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@@ -2181,6 +2181,54 @@ def test_pvwatts_dc_series():
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assert_series_equal(expected, out)
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def test_pvwatts_dc_scalars_with_k():
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expected = 8.9125
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out = pvsystem.pvwatts_dc(100, 30, 100, -0.003, k=0.01)
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assert_allclose(out, expected)
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def test_pvwatts_dc_arrays_with_k():
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irrad_trans = np.array([np.nan, 100, 1200])
2192+
temp_cell = np.array([30, np.nan, 30])
2193+
irrad_trans, temp_cell = np.meshgrid(irrad_trans, temp_cell)
2194+
expected = np.array([[nan, 8.9125, 118.45],
2195+
[nan, nan, nan],
2196+
[nan, 8.9125, 118.45]])
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out = pvsystem.pvwatts_dc(irrad_trans, temp_cell, 100, -0.003, k=0.01)
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assert_allclose(out, expected, equal_nan=True)
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2200+
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def test_pvwatts_dc_series_with_k():
2202+
irrad_trans = pd.Series([np.nan, 100, 100, 1200])
2203+
temp_cell = pd.Series([30, np.nan, 30, 30])
2204+
expected = pd.Series(np.array([ nan, nan, 8.9125, 118.45]))
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out = pvsystem.pvwatts_dc(irrad_trans, temp_cell, 100, -0.003, k=0.01)
2206+
assert_series_equal(expected, out)
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2208+
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def test_pvwatts_dc_with_k_and_cap_adjustment():
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irrad_trans = [100, 1200]
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temp_cell = 25
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out = []
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expected = [0, 120.0]
2214+
for irrad in irrad_trans:
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out.append(pvsystem.pvwatts_dc(irrad, temp_cell, 100, -0.003, k=0.15,
2216+
cap_adjustment=True))
2217+
assert_allclose(out, expected)
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2219+
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def test_pvwatts_dc_arrays_with_k_and_cap_adjustment():
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irrad_trans = np.array([np.nan, 100, 1200])
2222+
temp_cell = np.array([30, np.nan, 30])
2223+
irrad_trans, temp_cell = np.meshgrid(irrad_trans, temp_cell)
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expected = np.array([[nan, 8.9125, 118.2],
2225+
[nan, nan, nan],
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[nan, 8.9125, 118.2]])
2227+
out = pvsystem.pvwatts_dc(irrad_trans, temp_cell, 100, -0.003, k=0.01,
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cap_adjustment=True)
2229+
assert_allclose(out, expected, equal_nan=True)
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2231+
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def test_pvwatts_losses_default():
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expected = 14.075660688264469
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out = pvsystem.pvwatts_losses()

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