TBC solar cell simulation problem

[ygrf0816]

I am currently working on a simulation project involving TBC type solar cells, specifically focusing on shading effects. I have been using the PVmismatch library for these simulations, but I have encountered a discrepancy between the simulated IV curves and the actual measured results.

To provide more context, I have defined an 8 modules series system and have been progressively shading one component from one cell up to six cells. In my simulations, when I completely shade one cell on one component, the IV curve exhibits a "step-like" bending characteristic, which is not observed in the actual measurements. It is only when I increase the shading to six cells that the simulated results align with the actual measurements.

Case1-3: single cell full shading

Case2-2: Three cells in a column full shading

Case2-5: Six cells in a column full shading

I suspect that this discrepancy might be due to the natural formation of Shunt Diodes between the interdigitated back-contact electrodes in TBC cells.To address this, I attempted to modify the calcCell function within the PVCell class by incorporating a Shunt Diode. Additionally, I increased the Vbypass value for each sub-string of cells to -5V, but the simulation results remained unchanged.

def calcCell(self):
        """
        Calculate cell I-V curves.
        Returns (Icell, Vcell, Pcell) : tuple of numpy.ndarray of float
        """
        Vreverse = self.VRBD * self.pvconst.negpts
        Vff = self.Voc
        delta_Voc = self.VocSTC - self.Voc
        # to make sure that the max voltage is always in the 4th quadrant, add
        # a third set of points log spaced with decreasing density, from Voc to
        # Voc @ STC unless Voc *is* Voc @ STC, then use an arbitrary voltage at
        # 80% of Voc as an estimate of Vmp assuming a fill factor of 80% and
        # Isc close to Imp, or if Voc > Voc @ STC, then use Voc as the max
        if delta_Voc == 0:
            Vff = 0.8 * self.Voc
            delta_Voc = 0.2 * self.Voc
        elif delta_Voc < 0:
            Vff = self.VocSTC
            delta_Voc = -delta_Voc
        Vquad4 = Vff + delta_Voc * np.flipud(self.pvconst.negpts)
        Vforward = Vff * self.pvconst.pts
        Vdiode = np.concatenate((Vreverse, Vforward, Vquad4), axis=0)
        Idiode1 = self.Isat1 * (np.exp(Vdiode / self.Vt) - 1.)
        Idiode2 = self.Isat2 * (np.exp(Vdiode / 2. / self.Vt) - 1.)
        Ishunt = Vdiode / self.Rsh
        fRBD = 1. - Vdiode / self.VRBD
        # use epsilon = 2.2204460492503131e-16 to avoid "divide by zero"
        fRBD[fRBD == 0] = EPS
        Vdiode_norm = Vdiode / self.Rsh / self.Isc0_T0
        fRBD = self.Isc0_T0 * fRBD ** (-self.nRBD)
        IRBD = (self.aRBD * Vdiode_norm + self.bRBD * Vdiode_norm ** 2) * fRBD 
        #2024.11.14 add dark current IShuntDiode from shunt diode
        IShuntDiode = 1e-12 * (np.exp(0.0527 / self.Vt) - 1.)
        Icell = self.Igen - Idiode1 - Idiode2 - Ishunt - IRBD + IShuntDiode
        Icell_p = self.Igen - Idiode1 - Idiode2 - Ishunt - IRBD
        # Vcell = Vdiode - Icell * self.Rs
        Vcell = Vdiode - Icell_p * self.Rs
        Pcell = Icell * Vcell
        return Icell, Vcell, Pcell

    # 2024/11/14 new diode model
    #  *-->--*--->---*--Rs--*-->-Icell--+
    #  ^     |       |      ^         ^
    #  |     |       |      |            |
    # Igen  Idiode  Ishunt IDS         Vcell
    #  |     |       |      |            |
    #  |     v       v      |           |
    #  *--<--*---<---*--<---*-----------=

Given these challenges, I would like to inquire whether the current version of the PVmismatch library supports shading simulation for BC (Back-Contact) structure solar cells. If not, there are any potential modifications or alternative approaches that might achieve more accurate simulation results?