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Merged
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Jul 9, 2018
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Implement calcparams_pvsyst and tests #486

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e20a079
initial version of calcparams_pvsyst and test
Jun 20, 2018
e93cd8a
fix argument list in tests
Jun 20, 2018
846c913
Fix typo in test argument R_sh_0
Jun 20, 2018
f457370
remove EgRef from PVSystem.test_calcparams_pvsyst
Jun 20, 2018
691a9a7
add documentation for mugamma, fix typo
Jun 20, 2018
36d5941
edits and fix to test error
Jun 20, 2018
131ff75
Fix argument list and expected result
Jun 20, 2018
9d5d55e
Fix error in calculation of nNsVth
Jun 20, 2018
d1be467
Add note to whatsnew.rst
Jun 20, 2018
8d79f3d
Add line to api.rst
Jun 20, 2018
34390a9
Edits to function signatures, variable names
Jun 21, 2018
95bfde9
Change mugamma to mu_gamma, add issue to whatsnew text
Jun 23, 2018
75e89f0
Change to mu_gamma in tests
Jun 27, 2018
046a386
remove **kwargs from method calcparams_pvsyst signature, add irrad_re…
Jul 5, 2018
632ff87
fix typo in Boltzmann constant J/K
Jul 6, 2018
1295bcf
Remove scope=session from pvsyst fixture
Jul 6, 2018
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1 change: 1 addition & 0 deletions docs/sphinx/source/api.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -202,6 +202,7 @@ Functions relevant for the single diode model.
:toctree: generated/

pvsystem.calcparams_desoto
pvsystem.calcparams_pvsyst
pvsystem.i_from_v
pvsystem.singlediode
pvsystem.v_from_i
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1 change: 1 addition & 0 deletions docs/sphinx/source/whatsnew/v0.6.0.rst
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Expand Up @@ -13,6 +13,7 @@ Enhancements
* Add sea surface albedo in irradiance.py (:issue:`458`)
* Implement first_solar_spectral_loss in modelchain.py (:issue:`359`)
* Clarify arguments Egref and dEgdT for calcparams_desoto (:issue:`462`)
* Add pvsystem.calcparams_pvsyst to compute values for the single diode equation using the PVsyst v6 model (:issue:'470')
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@mikofski mikofski Aug 3, 2018 •
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please change single spaces around issue #470 to backticks, and also surround pvsystem.calcparams_pvsyst with backticks - @wholmgren or @cwhanse , can you do this directly in master, thx

Add `pvsystem.calcparams_pvsyst` to compute values for the single diode equation using the PVsyst v6 model (:issue:`470`)



Bug fixes
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225 changes: 191 additions & 34 deletions pvlib/pvsystem.py
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Expand Up @@ -302,11 +302,40 @@ def calcparams_desoto(self, effective_irradiance, temp_cell, **kwargs):
"""

kwargs = _build_kwargs(['a_ref', 'I_L_ref', 'I_o_ref', 'R_sh_ref',
'R_s', 'alpha_sc', 'EgRef', 'dEgdT'],
'R_s', 'alpha_sc', 'EgRef', 'dEgdT',
'irrad_ref', 'temp_ref'],
self.module_parameters)

return calcparams_desoto(effective_irradiance, temp_cell, **kwargs)

def calcparams_pvsyst(self, effective_irradiance, temp_cell):
"""
Use the :py:func:`calcparams_pvsyst` function, the input
parameters and ``self.module_parameters`` to calculate the
module currents and resistances.

Parameters
----------
effective_irradiance : numeric
The irradiance (W/m2) that is converted to photocurrent.

temp_cell : float or Series
The average cell temperature of cells within a module in C.

Returns
-------
See pvsystem.calcparams_pvsyst for details
"""

kwargs = _build_kwargs(['gamma_ref', 'mu_gamma', 'I_L_ref', 'I_o_ref',
'R_sh_ref', 'R_sh_0', 'R_sh_exp',
'R_s', 'alpha_sc', 'EgRef',
'irrad_ref', 'temp_ref',
'cells_in_series'],
self.module_parameters)

return calcparams_pvsyst(effective_irradiance, temp_cell, **kwargs)
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This could be done in a separate issue (see #476), but I think the PVSystem methods should scale the outputs to the modules_per_string and strings_per_inverter.

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We've chosen not to scale inside dc_model functions to offer flexibility, e.g., model a system with strings of different lengths, to implement module-to-module mismatch models, etc. Granted some of these capabilities are not presently in pvlib.


def sapm(self, effective_irradiance, temp_cell, **kwargs):
"""
Use the :py:func:`sapm` function, the input parameters,
Expand Down Expand Up @@ -462,7 +491,7 @@ def first_solar_spectral_loss(self, pw, airmass_absolute):
coefficients = None

return atmosphere.first_solar_spectral_correction(pw,
airmass_absolute,
airmass_absolute,
module_type,
coefficients)

Expand Down Expand Up @@ -946,12 +975,12 @@ def physicaliam(aoi, n=1.526, K=4., L=0.002):


def calcparams_desoto(effective_irradiance, temp_cell,
alpha_sc, a_ref, I_L_ref, I_o_ref, R_sh_ref, R_s,
alpha_sc, a_ref, I_L_ref, I_o_ref, R_sh_ref, R_s,
EgRef=1.121, dEgdT=-0.0002677,
irrad_ref=1000, temp_ref=25):
'''
Calculates five parameter values for the single diode equation at
effective irradiance and cell temperature using the De Soto et al.
Calculates five parameter values for the single diode equation at
effective irradiance and cell temperature using the De Soto et al.
model described in [1]. The five values returned by calcparams_desoto
can be used by singlediode to calculate an IV curve.

Expand All @@ -968,34 +997,34 @@ def calcparams_desoto(effective_irradiance, temp_cell,
module in units of A/C.

a_ref : float
The product of the usual diode ideality factor (n, unitless),
The product of the usual diode ideality factor (n, unitless),
number of cells in series (Ns), and cell thermal voltage at reference
conditions, in units of V.

I_L_ref : float
The light-generated current (or photocurrent) at reference conditions,
in amperes.

I_o_ref : float
The dark or diode reverse saturation current at reference conditions,
in amperes.

R_sh_ref : float
The shunt resistance at reference conditions, in ohms.

R_s : float
The series resistance at reference conditions, in ohms.

EgRef : float
The energy bandgap at reference temperature in units of eV.
1.121 eV for crystalline silicon. EgRef must be >0. For parameters
1.121 eV for crystalline silicon. EgRef must be >0. For parameters
from the SAM CEC module database, EgRef=1.121 is implicit for all
cell types in the parameter estimation algorithm used by NREL.

dEgdT : float
The temperature dependence of the energy bandgap at reference
conditions in units of 1/K. May be either a scalar value
(e.g. -0.0002677 as in [1]) or a DataFrame (this may be useful if
conditions in units of 1/K. May be either a scalar value
(e.g. -0.0002677 as in [1]) or a DataFrame (this may be useful if
dEgdT is a modeled as a function of temperature). For parameters from
the SAM CEC module database, dEgdT=-0.0002677 is implicit for all cell
types in the parameter estimation algorithm used by NREL.
Expand All @@ -1011,28 +1040,21 @@ def calcparams_desoto(effective_irradiance, temp_cell,
Tuple of the following results:

photocurrent : numeric
Light-generated current in amperes at irradiance=S and
cell temperature=Tcell.
Light-generated current in amperes

saturation_current : numeric
Diode saturation curent in amperes at irradiance
S and cell temperature Tcell.
Diode saturation curent in amperes

resistance_series : float
Series resistance in ohms at irradiance S and cell temperature
Tcell.
Series resistance in ohms
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While passing through this territory, seems like this should be changed to "numeric" from "float".

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Cut and paste inheritance? I don't think there is a difference here. numeric would admit long, complex and int types as well as float. Probably should change to float unless there's a reason otherwise.

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I'm good with float instead of numeric, because that seems to be most accurate.


resistance_shunt : numeric
Shunt resistance in ohms at irradiance S and cell temperature
Tcell.
Shunt resistance in ohms

nNsVth : numeric
Modified diode ideality factor at irradiance S and cell
temperature Tcell. Note that in source [1] nNsVth = a (equation
2). nNsVth is the product of the usual diode ideality factor
(n), the number of series-connected cells in the module (Ns),
and the thermal voltage of a cell in the module (Vth) at a cell
temperature of Tcell.
The product of the usual diode ideality factor (n, unitless),
number of cells in series (Ns), and cell thermal voltage at
specified effective irradiance and cell temperature.

References
----------
Expand All @@ -1051,8 +1073,6 @@ def calcparams_desoto(effective_irradiance, temp_cell,

See Also
--------
sapm
sapm_celltemp
singlediode
retrieve_sam

Expand Down Expand Up @@ -1143,7 +1163,7 @@ def calcparams_desoto(effective_irradiance, temp_cell,

# Boltzmann constant in eV/K
k = 8.617332478e-05

# reference temperature
Tref_K = temp_ref + 273.15
Tcell_K = temp_cell + 273.15
Expand All @@ -1152,9 +1172,9 @@ def calcparams_desoto(effective_irradiance, temp_cell,

nNsVth = a_ref * (Tcell_K / Tref_K)

# In the equation for IL, the single factor effective_irradiance is
# used, in place of the product S*M in [1]. effective_irradiance is
# equivalent to the product of S (irradiance reaching a module's cells) *
# In the equation for IL, the single factor effective_irradiance is
# used, in place of the product S*M in [1]. effective_irradiance is
# equivalent to the product of S (irradiance reaching a module's cells) *
# M (spectral adjustment factor) as described in [1].
IL = effective_irradiance / irrad_ref * \
(I_L_ref + alpha_sc * (Tcell_K - Tref_K))
Expand All @@ -1164,14 +1184,151 @@ def calcparams_desoto(effective_irradiance, temp_cell,
# Rsh = Rsh_ref * (S_ref / S) where S is broadband irradiance reaching
# the module's cells. If desired this model behavior can be duplicated
# by applying reflection and soiling losses to broadband plane of array
# irradiance and not applying a spectral loss modifier, i.e.,
# irradiance and not applying a spectral loss modifier, i.e.,
# spectral_modifier = 1.0.
Rsh = R_sh_ref * (irrad_ref / effective_irradiance)
Rs = R_s

return IL, I0, Rs, Rsh, nNsVth


def calcparams_pvsyst(effective_irradiance, temp_cell,
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=5.5,
EgRef=1.121,
irrad_ref=1000, temp_ref=25):
'''
Calculates five parameter values for the single diode equation at
effective irradiance and cell temperature using the PVsyst v6
model described in [1,2,3]. The five values returned by calcparams_pvsyst
can be used by singlediode to calculate an IV curve.

Parameters
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What is the difference between numeric and float?

Should a user NOT expect this function to be vectorized over the "float" parameters?

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I'm pretty sure the function will work on array or Series inputs. Is the issue the type description float implies a singleton?

We aren't using numeric or float consistently in the comments. For me to fix that, requires that I learn the distinction. New issue, I think.

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I've used numeric for input that can be scalar, np.array, or pd.Series. float is specific to scalar. Whether or not this is a good idea could be discussed in a separate issue, if necessary.

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for more context, note that some functions require "array-like" (np.array or pd.Series) and others require pd.Series.

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So, numeric unless there's a reason to specify a scalar float?

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or unless there's a reason to specify array-like or Series.

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I looked at both calcparams_desoto and calcparams_pvsyst and I'm going to leave the docstrings as is for now. The typical use of either function is to pass model parameters for one module and a list of conditions (irradiance and temperature). That use is reflected in the docstring's use of numeric and float, where each model parameter is a single value for a module. The functions are more flexible that this use case.

If we want to overhaul the docstrings, let's open a new issue for it.

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I think an issue is wise in order to define what we mean to ourselves/users and make everything consistent.

----------
effective_irradiance : numeric
The irradiance (W/m2) that is converted to photocurrent.

temp_cell : numeric
The average cell temperature of cells within a module in C.

alpha_sc : float
The short-circuit current temperature coefficient of the
module in units of A/C.

gamma_ref : float
The diode ideality factor

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missing mugamma documentation here. mugamma or mu_gamma?

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added. changed to mu_gamma

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it appears that the change was not applied here.

mu_gamma : float
The temperature coefficient for the diode ideality factor, 1/K

I_L_ref : float
The light-generated current (or photocurrent) at reference conditions,
in amperes.

I_o_ref : float
The dark or diode reverse saturation current at reference conditions,
in amperes.

R_sh_ref : float
The shunt resistance at reference conditions, in ohms.

R_sh_0 : float
The shunt resistance at zero irradiance conditions, in ohms.

R_s : float
The series resistance at reference conditions, in ohms.

cells_in_series : integer
The number of cells connected in series.

R_sh_exp : float
The exponent in the equation for shunt resistance, unitless. Defaults
to 5.5.

EgRef : float
The energy bandgap at reference temperature in units of eV.
1.121 eV for crystalline silicon. EgRef must be >0.

irrad_ref : float (optional, default=1000)
Reference irradiance in W/m^2.

temp_ref : float (optional, default=25)
Reference cell temperature in C.

Returns
-------
Tuple of the following results:

photocurrent : numeric
Light-generated current in amperes

saturation_current : numeric
Diode saturation current in amperes

resistance_series : float
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Seems like this should be "numeric" too.

Series resistance in ohms

resistance_shunt : numeric
Shunt resistance in ohms

nNsVth : numeric
The product of the usual diode ideality factor (n, unitless),
number of cells in series (Ns), and cell thermal voltage at
specified effective irradiance and cell temperature.

References
----------
[1] K. Sauer, T. Roessler, C. W. Hansen, Modeling the Irradiance and
Temperature Dependence of Photovoltaic Modules in PVsyst,
IEEE Journal of Photovoltaics v5(1), January 2015.

[2] A. Mermoud, PV modules modelling, Presentation at the 2nd PV
Performance Modeling Workshop, Santa Clara, CA, May 2013

[3] A. Mermoud, T. Lejeune, Performance Assessment of a Simulation Model
for PV modules of any available technology, 25th European Photovoltaic
Solar Energy Conference, Valencia, Spain, Sept. 2010

See Also
--------
calcparams_desoto
singlediode

'''

# Boltzmann constant in J/K
k = 1.38064852e-23

# elementary charge in coulomb
q = 1.6021766e-19

# reference temperature
Tref_K = temp_ref + 273.15
Tcell_K = temp_cell + 273.15

gamma = gamma_ref + mu_gamma * (Tcell_K - Tref_K)
nNsVth = gamma * k / q * cells_in_series * Tcell_K

IL = effective_irradiance / irrad_ref * \
(I_L_ref + alpha_sc * (Tcell_K - Tref_K))
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Optimization possibility: Tcell_K - Tref_K is computed twice.


I0 = I_o_ref * ((Tcell_K / Tref_K) ** 3) * \
(np.exp((q * EgRef) / (k * gamma) * (1 / Tref_K - 1 / Tcell_K)))

Rsh_tmp = (R_sh_ref - R_sh_0 * np.exp(-R_sh_exp)) / (1.0 - np.exp(-R_sh_exp))
Rsh_base = np.maximum(0.0, Rsh_tmp)
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In looking over http://files.pvsyst.com/help/pvmodule_rshexp.htm, it is not clear to me why Rsh_base is not simply R_sh_ref. What am I missing?

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You're not, PVsyst documentation is missing that definition of Rsh_base. Ken Sauer and Thomas Roessler are my sources, they got it verbally from PVsyst.


Rsh = Rsh_base + (R_sh_0 - Rsh_base) * \
np.exp(-R_sh_exp * effective_irradiance / irrad_ref)
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Optimization possibility: effective_irradiance / irrad_ref is computed twice.


Rs = R_s

return IL, I0, Rs, Rsh, nNsVth


def retrieve_sam(name=None, path=None):
'''
Retrieve latest module and inverter info from a local file or the
Expand Down
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