Isat2fix (#64)

* Added temperature dependance for Isat2, i.e. Isat2(Tcell)

* test for wide range of Tcell values - added after implementing Isat2 as a function of Tcell

* generated new iv curve

* Isat2 to Isat2_T0

* Update example.py

Isat2 => Isat2_T0

* Update test_diode.py

* Deleting the old IV curve

* updated IV curve test file

* fixed isat2 typos caused by replace

* use entire iec matrix

pvmismatch/contrib/gen_coeffs/__init__.py

@@ -6,7 +6,7 @@
 import numpy as np
 from scipy import optimize
 from pvmismatch.contrib.gen_coeffs import diode, two_diode
-from pvmismatch.pvmismatch_lib.pvcell import ISAT1_T0, ISAT2, RS, RSH
+from pvmismatch.pvmismatch_lib.pvcell import ISAT1_T0, ISAT2_T0, RS, RSH
 
 # IEC 61853 test matrix
 TC_C = [15.0, 25.0, 50.0, 75.0]
@@ -37,7 +37,7 @@ def gen_two_diode(isc, voc, imp, vmp, nseries, nparallel,
     vmp_cell = vmp / nseries
     if x0 is None:
         isat1 = ISAT1_T0  # [A]
-        isat2 = ISAT2
+        isat2 = ISAT2_T0
         rs = RS  # [ohms]
         rsh = RSH  # [ohms]
     else:

pvmismatch/contrib/gen_coeffs/example.py

@@ -23,16 +23,16 @@
 iec61853 = gen_coeffs.gen_iec_61853_from_sapm(gen_coeffs.PVMODULES[PROD_NAME])
 iec61853['i_mp'] = iec61853['p_mp'] / iec61853['v_mp']
 #isc0, alpha_isc = gen_coeffs.gen_sapm(iec61853)
-x, sol = gen_coeffs.gen_two_diode(ISC0, VOC0, IMP0, VMP0, NS, NP, T0)
-#x, sol = gen_coeffs.gen_two_diode(
-#    iec61853['i_sc'], iec61853['v_oc'], iec61853['i_mp'],
-#    iec61853['v_mp'], NS, NP, tc=TC, method='lm',
-#    x0=(2.25e-11, 1.5e-6, 0.004, 10.0)
-#)
+#x, sol = gen_coeffs.gen_two_diode(ISC0, VOC0, IMP0, VMP0, NS, NP, T0)
+x, sol = gen_coeffs.gen_two_diode(
+    iec61853['i_sc'], iec61853['v_oc'], iec61853['i_mp'],
+    iec61853['v_mp'], NS, NP, tc=TC, method='lm',
+    x0=(2.25e-11, 1.5e-6, 0.004, 10.0)
+)
 isat1, isat2, rs, rsh = x
 
 pvc = pvcell.PVcell(
-    Rs=rs, Rsh=rsh, Isat1_T0=isat1, Isat2=isat2,
+    Rs=rs, Rsh=rsh, Isat1_T0=isat1, Isat2_T0=isat2,
     Isc0_T0=ISC0/NP, alpha_Isc=AISC
 )
 f1 = plt.figure()

pvmismatch/contrib/gen_coeffs/tests/test_diode.py

@@ -3,7 +3,7 @@
 """
 
 from pvmismatch.pvmismatch_lib.pvcell import (
-    RS as RS_2, RSH as RSH_2, ISAT1_T0 as ISAT1_2, ISAT2 as ISAT2_2
+    RS as RS_2, RSH as RSH_2, ISAT1_T0 as ISAT1_2, ISAT2_T0 as ISAT2_2
 )
 from pvmismatch.contrib.gen_coeffs import diode
 from pvmismatch.contrib.gen_coeffs import PVMODULES

pvmismatch/pvmismatch_lib/pvcell.py

@@ -16,7 +16,7 @@
 RS = 0.004267236774264931  # [ohm] series resistance
 RSH = 10.01226369025448  # [ohm] shunt resistance
 ISAT1_T0 = 2.286188161253440E-11  # [A] diode one saturation current
-ISAT2 = 1.117455042372326E-6  # [A] diode two saturation current
+ISAT2_T0 = 1.117455042372326E-6  # [A] diode two saturation current
 ISC0_T0 = 6.3056  # [A] reference short circuit current
 TCELL = 298.15  # [K] cell temperature
 ARBD = 1.036748445065697E-4  # reverse breakdown coefficient 1
@@ -50,15 +50,15 @@ class PVcell(object):
 
     _calc_now = False  #: if True ``calcCells()`` is called in ``__setattr__``
 
-    def __init__(self, Rs=RS, Rsh=RSH, Isat1_T0=ISAT1_T0, Isat2=ISAT2,
+    def __init__(self, Rs=RS, Rsh=RSH, Isat1_T0=ISAT1_T0, Isat2_T0=ISAT2_T0,
                  Isc0_T0=ISC0_T0, aRBD=ARBD, bRBD=BRBD, VRBD=VRBD_,
                  nRBD=NRBD, Eg=EG, alpha_Isc=ALPHA_ISC,
                  Tcell=TCELL, Ee=1., pvconst=PVconstants()):
         # user inputs
         self.Rs = Rs  #: [ohm] series resistance
         self.Rsh = Rsh  #: [ohm] shunt resistance
         self.Isat1_T0 = Isat1_T0  #: [A] diode one sat. current at T0
-        self.Isat2 = Isat2  #: [A] diode two saturation current
+        self.Isat2_T0 = Isat2_T0  #: [A] diode two saturation current
         self.Isc0_T0 = Isc0_T0  #: [A] short circuit current at T0
         self.aRBD = aRBD  #: reverse breakdown coefficient 1
         self.bRBD = bRBD  #: reverse breakdown coefficient 2
@@ -142,6 +142,18 @@ def Isat1(self):
         )
         return self.Isat1_T0 * _Tstar * _expTstar  # [A] Isat1(Tcell)
 
+    @property
+    def Isat2(self):
+        """
+        Diode two saturation current at Tcell in amps.
+        """
+        _Tstar = self.Tcell ** 3. / self.pvconst.T0 ** 3.  # scaled temperature
+        _inv_delta_T = 1. / self.pvconst.T0 - 1. / self.Tcell  # [1/K]
+        _expTstar = np.exp(
+            self.Eg * self.pvconst.q / (2.0 * self.pvconst.k) * _inv_delta_T
+        )
+        return self.Isat2_T0 * _Tstar * _expTstar  # [A] Isat2(Tcell)
+
     @property
     def Isc0(self):
         """

pvmismatch/tests/test_settemps.py

@@ -7,6 +7,7 @@
 import numpy as np
 from nose.tools import ok_
 from pvmismatch.pvmismatch_lib.pvsystem import PVsystem
+from pvmismatch.pvmismatch_lib.pvcell import PVcell
 import logging
 
 logging.basicConfig(level=logging.DEBUG)
@@ -150,3 +151,27 @@ def test_settemp():
     assert pvsys.pvstrs[2].pvmods[4].pvcells[5].Tcell == 310
     assert pvsys.pvstrs[2].pvmods[4].pvcells[3] == pvsys.pvstrs[2].pvmods[4].pvcells[5]
     assert pvsys.pvstrs[1].pvmods[0] == pvsys.pvstrs[1].pvmods[2]
+
+def test_settemp_cell():
+    """
+    Test setTemp method for a wide range of temperatures. 
+    Test added after implementing Isat2 as Isat2(Tcell)
+    """
+    pvc = PVcell()
+    Pmp_arr = []
+    Vmp_arr = []
+    Voc_arr = []
+    Isc_arr = []
+
+    temps = [-85, -60, -40, -25, 0, 25, 40, 60, 85]
+    for t in temps:
+        pvc.Tcell = float(t) + 273.15
+        Pmp_arr.append(pvc.Pcell.max())
+        Vmp_arr.append(pvc.Vcell[pvc.Pcell.argmax()])
+        Voc_arr.append(pvc.calcVcell(0))
+        Isc_arr.append(pvc.Isc)
+
+    assert(np.all(np.gradient(np.squeeze(Vmp_arr)) < 0))
+    assert(np.all(np.gradient(np.squeeze(Voc_arr)) < 0))
+    assert(np.all(np.gradient(Isc_arr) > 0))
+