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Use explicit finite difference instead of scipy.misc.derivative in pvsyst_temperature_coeff #1674

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Merged
merged 3 commits into from
Feb 27, 2023
Merged

Use explicit finite difference instead of scipy.misc.derivative in pvsyst_temperature_coeff #1674

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use explicit finite difference instead of scipy.misc.derivative
kandersolar Feb 26, 2023
6293d80
whatsnew
kandersolar Feb 26, 2023
ec8903a
private function in tools.py
kandersolar Feb 27, 2023
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2 changes: 2 additions & 0 deletions docs/sphinx/source/whatsnew/v0.9.5.rst
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Expand Up @@ -32,6 +32,8 @@ Bug fixes
* When using ``utc_time_range`` with :py:func:`pvlib.iotools.read_ecmwf_macc`,
the time index subset is now selected with ``nearest`` instead of ``before``
and ``after`` for consistency with ``cftime>=1.6.0``. (:issue:`1609`, :pull:`1656`)
* :py:func:`~pvlib.ivtools.sdm.pvsyst_temperature_coeff` no longer raises
a scipy deprecation warning (and is slightly more accurate) (:issue:`1644`, :pull:`1674`)


Testing
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9 changes: 7 additions & 2 deletions pvlib/ivtools/sdm.py
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Expand Up @@ -11,7 +11,6 @@
from scipy import constants
from scipy import optimize
from scipy.special import lambertw
from scipy.misc import derivative

from pvlib.pvsystem import calcparams_pvsyst, singlediode, v_from_i
from pvlib.singlediode import bishop88_mpp
Expand Down Expand Up @@ -1344,5 +1343,11 @@ def maxp(temp_cell, irrad_ref, alpha_sc, gamma_ref, mu_gamma, I_L_ref,
I_o_ref, R_sh_ref, R_sh_0, R_s, cells_in_series, R_sh_exp, EgRef,
temp_ref)
pmp = maxp(temp_ref, *args)
gamma_pdc = derivative(maxp, temp_ref, args=args)

# first order centered difference at temp_ref
dx = 1e-3
x0 = temp_ref
dy = maxp(x0+dx, *args) - maxp(x0-dx, *args)
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Since bishop88 is vectorized it shouldn't cost any more to compute 4 values than 2. Why not x = [x0-2dx, x0-dx, x0+dx, x0+2dx], pmp = maxp(x, ...) and use the fourth order formula?

gamma_pdc = np.array([1, -8, 8, -1]) * pmp / (12 * dx)

https://www.dam.brown.edu/people/alcyew/handouts/numdiff.pdf

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I didn't hit the button to submit this comment. No action required here, archiving the comment in case the issue arises.

gamma_pdc = dy / (2*dx)

return gamma_pdc / pmp