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Jul 22, 2016
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add optional ivcurve calculation to singlediode #223

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d162786
add optional ivcurve calculation to singlediode
wholmgren Jul 20, 2016
37c4785
only include i v keys if needed
wholmgren Jul 21, 2016
a6db2b8
update test for singlediode p_mp fix
wholmgren Jul 22, 2016
9cf9f6c
add a moderate point test sd series
wholmgren Jul 22, 2016
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2 changes: 2 additions & 0 deletions docs/sphinx/source/whatsnew/v0.4.0.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -51,6 +51,8 @@ Enhancements
* Add solarposition.nrel_earthsun_distance function and option to
calculate extraterrestrial radiation using the NREL solar position
algorithm. (:issue:`211`, :issue:`215`)
* pvsystem.singlediode can now calculate IV curves if a user supplies
an ivcurve_pnts keyword argument. (:issue:`83`)
* Includes SAM data files in the distribution. (:issue:`52`)


Expand Down
118 changes: 64 additions & 54 deletions pvlib/pvsystem.py
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Original file line number Diff line number Diff line change
Expand Up @@ -413,7 +413,8 @@ def sapm_effective_irradiance(self, poa_direct, poa_diffuse,
self.module_parameters, reference_irradiance=reference_irradiance)

def singlediode(self, photocurrent, saturation_current,
resistance_series, resistance_shunt, nNsVth):
resistance_series, resistance_shunt, nNsVth,
ivcurve_pnts=None):
"""Wrapper around the :py:func:`singlediode` function.

Parameters
Expand All @@ -425,7 +426,8 @@ def singlediode(self, photocurrent, saturation_current,
See pvsystem.singlediode for details
"""
return singlediode(photocurrent, saturation_current,
resistance_series, resistance_shunt, nNsVth)
resistance_series, resistance_shunt, nNsVth,
ivcurve_pnts=ivcurve_pnts)

def i_from_v(self, resistance_shunt, resistance_series, nNsVth, voltage,
saturation_current, photocurrent):
Expand Down Expand Up @@ -1533,7 +1535,7 @@ def sapm_effective_irradiance(poa_direct, poa_diffuse, airmass_absolute, aoi,


def singlediode(photocurrent, saturation_current, resistance_series,
resistance_shunt, nNsVth):
resistance_shunt, nNsVth, ivcurve_pnts=None):
r'''
Solve the single-diode model to obtain a photovoltaic IV curve.

Expand All @@ -1555,23 +1557,23 @@ def singlediode(photocurrent, saturation_current, resistance_series,

Parameters
----------
photocurrent : float or Series
photocurrent : numeric
Light-generated current (photocurrent) in amperes under desired
IV curve conditions. Often abbreviated ``I_L``.

saturation_current : float or Series
saturation_current : numeric
Diode saturation current in amperes under desired IV curve
conditions. Often abbreviated ``I_0``.

resistance_series : float or Series
resistance_series : numeric
Series resistance in ohms under desired IV curve conditions.
Often abbreviated ``Rs``.

resistance_shunt : float or Series
resistance_shunt : numeric
Shunt resistance in ohms under desired IV curve conditions.
Often abbreviated ``Rsh``.

nNsVth : float or Series
nNsVth : numeric
The product of three components. 1) The usual diode ideal factor
(n), 2) the number of cells in series (Ns), and 3) the cell
thermal voltage under the desired IV curve conditions (Vth). The
Expand All @@ -1580,21 +1582,35 @@ def singlediode(photocurrent, saturation_current, resistance_series,
temp_cell is the temperature of the p-n junction in Kelvin, and
q is the charge of an electron (coulombs).

ivcurve_pnts : None or int
Number of points in the desired IV curve. If None or 0, no
IV curves will be produced.

Returns
-------
If ``photocurrent`` is a Series, a DataFrame with the following
columns. All columns have the same number of rows as the largest
input DataFrame.
OrderedDict or DataFrame

The returned dict-like object always contains the keys/columns:

* i_sc - short circuit current in amperes.
* v_oc - open circuit voltage in volts.
* i_mp - current at maximum power point in amperes.
* v_mp - voltage at maximum power point in volts.
* p_mp - power at maximum power point in watts.
* i_x - current, in amperes, at ``v = 0.5*v_oc``.
* i_xx - current, in amperes, at ``V = 0.5*(v_oc+v_mp)``.

If ivcurve_pnts is greater than 0, the output dictionary will also
include the keys:

If ``photocurrent`` is a scalar, a dict with the following keys.
* i - IV curve current in amperes.
* v - IV curve voltage in volts.

* i_sc - short circuit current in amperes.
* v_oc - open circuit voltage in volts.
* i_mp - current at maximum power point in amperes.
* v_mp - voltage at maximum power point in volts.
* p_mp - power at maximum power point in watts.
* i_x - current, in amperes, at ``v = 0.5*v_oc``.
* i_xx - current, in amperes, at ``V = 0.5*(v_oc+v_mp)``.
The output will be an OrderedDict if photocurrent is a scalar,
array, or ivcurve_pnts is not None.

The output will be a DataFrame if photocurrent is a Series and
ivcurve_pnts is None.

Notes
-----
Expand Down Expand Up @@ -1648,37 +1664,29 @@ def singlediode(photocurrent, saturation_current, resistance_series,
i_xx = i_from_v(resistance_shunt, resistance_series, nNsVth,
0.5*(v_oc+v_mp), saturation_current, photocurrent)

# @wholmgren: need to move this stuff to a different function
# If the user says they want a curve of with number of points equal to
# NumPoints (must be >=2), then create a voltage array where voltage is
# zero in the first column, and Voc in the last column. Number of columns
# must equal NumPoints. Each row represents the voltage for one IV curve.
# Then create a current array where current is Isc in the first column, and
# zero in the last column, and each row represents the current in one IV
# curve. Thus the nth (V,I) point of curve m would be found as follows:
# (Result.V(m,n),Result.I(m,n)).
# if NumPoints >= 2
# s = ones(1,NumPoints); # shaping DataFrame to shape the column
# # DataFrame parameters into 2-D matrices
# Result.V = (Voc)*(0:1/(NumPoints-1):1);
# Result.I = I_from_V(Rsh*s, Rs*s, nNsVth*s, Result.V, I0*s, IL*s);
# end

dfout = {}
dfout['i_sc'] = i_sc
dfout['i_mp'] = i_mp
dfout['v_oc'] = v_oc
dfout['v_mp'] = v_mp
dfout['p_mp'] = p_mp
dfout['i_x'] = i_x
dfout['i_xx'] = i_xx

try:
dfout = pd.DataFrame(dfout, index=photocurrent.index)
except AttributeError:
pass
out = OrderedDict()
out['i_sc'] = i_sc
out['v_oc'] = v_oc
out['i_mp'] = i_mp
out['v_mp'] = v_mp
out['p_mp'] = p_mp
out['i_x'] = i_x
out['i_xx'] = i_xx

# create ivcurve
if ivcurve_pnts:
ivcurve_v = (np.asarray(v_oc)[..., np.newaxis] *
np.linspace(0, 1, ivcurve_pnts))
ivcurve_i = i_from_v(
resistance_shunt, resistance_series, nNsVth, ivcurve_v.T,
saturation_current, photocurrent).T
out['v'] = ivcurve_v
out['i'] = ivcurve_i

if isinstance(photocurrent, pd.Series) and not ivcurve_pnts:
out = pd.DataFrame(out, index=photocurrent.index)

return dfout
return out


# Created April,2014
Expand Down Expand Up @@ -1879,11 +1887,13 @@ def i_from_v(resistance_shunt, resistance_series, nNsVth, voltage,
except ImportError:
raise ImportError('This function requires scipy')

Rsh = resistance_shunt
Rs = resistance_series
I0 = saturation_current
IL = photocurrent
V = voltage
# asarray turns Series into arrays so that we don't have to worry
# about multidimensional broadcasting failing
Rsh = np.asarray(resistance_shunt)
Rs = np.asarray(resistance_series)
I0 = np.asarray(saturation_current)
IL = np.asarray(photocurrent)
V = np.asarray(voltage)

argW = (Rs*I0*Rsh *
np.exp(Rsh*(Rs*(IL+I0)+V) / (nNsVth*(Rs+Rsh))) /
Expand Down
96 changes: 66 additions & 30 deletions pvlib/test/test_pvsystem.py
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Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,7 @@
from collections import OrderedDict

import numpy as np
from numpy import nan
from numpy import nan, array
import pandas as pd

import pytest
Expand Down Expand Up @@ -150,6 +150,14 @@ def sapm_module_params(sam_data):
return module_parameters


@pytest.fixture(scope="session")
def cec_module_params(sam_data):
modules = sam_data['cecmod']
module = 'Example_Module'
module_parameters = modules[module]
return module_parameters


def test_sapm(sapm_module_params):

times = pd.DatetimeIndex(start='2015-01-01', periods=5, freq='12H')
Expand Down Expand Up @@ -307,17 +315,15 @@ def test_PVSystem_sapm_effective_irradiance(sapm_module_params):
aoi, reference_irradiance=reference_irradiance)


def test_calcparams_desoto(sam_data):
module = 'Example_Module'
module_parameters = sam_data['cecmod'][module]
def test_calcparams_desoto(cec_module_params):
times = pd.DatetimeIndex(start='2015-01-01', periods=2, freq='12H')
poa_data = pd.Series([0, 800], index=times)

IL, I0, Rs, Rsh, nNsVth = pvsystem.calcparams_desoto(
poa_data,
temp_cell=25,
alpha_isc=module_parameters['alpha_sc'],
module_parameters=module_parameters,
alpha_isc=cec_module_params['alpha_sc'],
module_parameters=cec_module_params,
EgRef=1.121,
dEgdT=-0.0002677)

Expand All @@ -328,13 +334,11 @@ def test_calcparams_desoto(sam_data):
assert_allclose(nNsVth, 0.473)


def test_PVSystem_calcparams_desoto(sam_data):
module = 'Example_Module'
module_parameters = sam_data['cecmod'][module].copy()
def test_PVSystem_calcparams_desoto(cec_module_params):
module_parameters = cec_module_params.copy()
module_parameters['EgRef'] = 1.121
module_parameters['dEgdT'] = -0.0002677
system = pvsystem.PVSystem(module=module,
module_parameters=module_parameters)
system = pvsystem.PVSystem(module_parameters=module_parameters)
times = pd.DatetimeIndex(start='2015-01-01', periods=2, freq='12H')
poa_data = pd.Series([0, 800], index=times)
temp_cell = 25
Expand Down Expand Up @@ -367,26 +371,21 @@ def test_i_from_v():


@requires_scipy
def test_PVSystem_i_from_v(sam_data):
module = 'Example_Module'
module_parameters = sam_data['cecmod'][module]
system = pvsystem.PVSystem(module=module,
module_parameters=module_parameters)
def test_PVSystem_i_from_v():
system = pvsystem.PVSystem()
output = system.i_from_v(20, .1, .5, 40, 6e-7, 7)
assert_allclose(-299.746389916, output, 5)


@requires_scipy
def test_singlediode_series(sam_data):
module = 'Example_Module'
module_parameters = sam_data['cecmod'][module]
def test_singlediode_series(cec_module_params):
times = pd.DatetimeIndex(start='2015-01-01', periods=2, freq='12H')
poa_data = pd.Series([0, 800], index=times)
IL, I0, Rs, Rsh, nNsVth = pvsystem.calcparams_desoto(
poa_data,
temp_cell=25,
alpha_isc=module_parameters['alpha_sc'],
module_parameters=module_parameters,
alpha_isc=cec_module_params['alpha_sc'],
module_parameters=cec_module_params,
EgRef=1.121,
dEgdT=-0.0002677)
out = pvsystem.singlediode(IL, I0, Rs, Rsh, nNsVth)
Expand Down Expand Up @@ -424,31 +423,68 @@ def test_singlediode_floats(sam_data):
'p_mp': 38.194165464983037,
'i_x': 6.7556075876880621,
'i_sc': 6.9646747613963198,
'v_mp': 6.221535886625464}
'v_mp': 6.221535886625464,
'i': None,
'v': None}
assert isinstance(out, dict)
for k, v in out.items():
assert_allclose(expected[k], v, atol=3)
if k in ['i', 'v']:
assert v is None
else:
assert_allclose(expected[k], v, atol=3)


@requires_scipy
def test_PVSystem_singlediode_floats(sam_data):
module = 'Example_Module'
module_parameters = sam_data['cecmod'][module]
system = pvsystem.PVSystem(module=module,
module_parameters=module_parameters)
out = system.singlediode(7, 6e-7, .1, 20, .5)
def test_singlediode_floats_ivcurve():
out = pvsystem.singlediode(7, 6e-7, .1, 20, .5, ivcurve_pnts=3)
expected = {'i_xx': 4.2685798754011426,
'i_mp': 6.1390251797935704,
'v_oc': 8.1063001465863085,
'p_mp': 38.194165464983037,
'i_x': 6.7556075876880621,
'i_sc': 6.9646747613963198,
'v_mp': 6.221535886625464}
'v_mp': 6.221535886625464,
'i': np.array([6.965172e+00, 6.755882e+00, 2.575717e-14]),
'v': np.array([0. , 4.05315, 8.1063])}
assert isinstance(out, dict)
for k, v in out.items():
assert_allclose(expected[k], v, atol=3)


@requires_scipy
def test_singlediode_series_ivcurve(cec_module_params):
times = pd.DatetimeIndex(start='2015-06-01', periods=3, freq='6H')
poa_data = pd.Series([0, 400, 800], index=times)
IL, I0, Rs, Rsh, nNsVth = pvsystem.calcparams_desoto(
poa_data,
temp_cell=25,
alpha_isc=cec_module_params['alpha_sc'],
module_parameters=cec_module_params,
EgRef=1.121,
dEgdT=-0.0002677)

out = pvsystem.singlediode(IL, I0, Rs, Rsh, nNsVth, ivcurve_pnts=3)

expected = OrderedDict([('i_sc', array([ nan, 3.01054475, 6.00675648])),
('v_oc', array([ nan, 9.96886962, 10.29530483])),
('i_mp', array([ nan, 2.65191983, 5.28594672])),
('v_mp', array([ nan, 8.33392491, 8.4159707 ])),
('p_mp', array([ nan, 22.10090078, 44.48637274])),
('i_x', array([ nan, 2.88414114, 5.74622046])),
('i_xx', array([ nan, 2.04340914, 3.90007956])),
('v',
array([[ nan, nan, nan],
[ 0. , 4.98443481, 9.96886962],
[ 0. , 5.14765242, 10.29530483]])),
('i',
array([[ nan, nan, nan],
[ 3.01079860e+00, 2.88414114e+00, 3.10862447e-14],
[ 6.00726296e+00, 5.74622046e+00, 0.00000000e+00]]))])

for k, v in out.items():
assert_allclose(expected[k], v, atol=1e-2)


def test_scale_voltage_current_power(sam_data):
data = pd.DataFrame(
np.array([[2, 1.5, 10, 8, 12, 0.5, 1.5]]),
Expand Down