# pvl_est_Rs_Swanson

PVL_EST_RS_SWANSON Estimate Rs using the method of Swanson.

## Contents

- Syntax
- Description:
- Inputs:
- Outputs:
- Example
- References:
- See also

## Syntax

- `[Rs, errest] = pvl_est_Rs_Swanson(V1, I1, V2, I2, delI)`
- `[Rs, errest] = pvl_est_Rs_Swanson(V1, I1, V2, I2, delI, Rsh1, Rsh2, nNsVth, Io)`

## Description:

The method of Swanson (see [1]) estimates series resistance using points from two IV curves at unequal but similar irradiance, e.g., at 950 W/m2 and 1000 W/m2. The cell temperature is assumed to be the same for both IV curves. A point is selected on each IV curve where the current is less than Isc by the input delI. If optional arguments are provided, the difference between the returned Rs value and the Rs parameter for the single diode equation is estimated, see [2].

## Inputs:

- `V1` - a vector of voltage for the first IV curve, in V.
- `I1` - a vector of current for the first IV curve, in A.
- `V2` - a vector of voltage for the second IV curve, in V.
- `I2` - a vector of current for the second IV curve, in A.
- `delI` - offset from short circuit at which to choose IV curve points.
- `Rsh1` - (optional) shunt resistance, in ohms, for the first IV curve.
- `Rsh2` - (optional) shunt resistance, in ohms, for the second IV curve.
- `nNsVth` - (optional) the product n (diode factor) x Ns (cells in series) x Vth (thermal voltage per cell) for both IV curves.
- `Io` - (optional) the dark current, in A, for both IV curves.

## Outputs:

- `Rs` - the series resistance value in ohms.
- `errest` - the estimated difference between Rs and the series resistance parameter for the single diode equation.

## Example

    clearvars

    % Set up parameters for a representative 60 cell cSi module using the Desoto model
    Const.q = 1.60218E-19;
    Const.k = 1.38066E-23;
    Const.E0 = 1000;
    Const.T0 = 25;

    param.aIsc = 0.0008;  % A/C
    param.bVoc = -0.1900; % V/C

    param.Rs_ref = 0.2;
    param.Rsh_ref = 1000;
    param.IL_ref = 8.0;
    param.I0_ref = 5e-10;

    param.a_ref = 1.05 * 60 * Const.k/Const.q * (273.15 + Const.T0);

    EgRef = 1.121;
    dEgdT = -0.0002677;

    % Calculate first IV curve
    Ee = 1000;
    Tc = 25;
    nPts = 100;
    [IL, I0, Rs, Rsh1, nNsVth] = pvl_calcparams_desoto(Ee, Tc, param.aIsc, param, EgRef, dEgdT);
    IVcurve1 = pvl_singlediode(IL, I0, Rs, Rsh1, nNsVth, nPts);

    % Calculate second IV curve
    Ee = 950;
    [IL, I0, Rs, Rsh2, nNsVth] = pvl_calcparams_desoto(Ee, Tc, param.aIsc, param, EgRef, dEgdT);
    IVcurve2 = pvl_singlediode(IL, I0, Rs, Rsh2, nNsVth, nPts);

    % Current differential
    delI = 0.95*(IVcurve1.Isc - IVcurve1.Imp);

    % Estimate Rs
    Rs = pvl_est_Rs_Swanson(IVcurve1.V, IVcurve1.I, IVcurve2.V, IVcurve2.I, delI)

    Rs =

        0.2117

## References:

- [1] D. Pysch, A. Mette, S. W. Glunz, “A review and comparison of different methods to determine the series resistance of solar cells", Solar. Energy Materials and Cells 91, pp. 1698-1706, 2007.

- [2] C. Hansen and B. King, "Determining series resistance for equivalent circuit models of a PV module", in 45th IEEE Photovoltaic Specialist Conference, Waikoloa, HI, 2018.

## See also

`pvl_est_Rs_Bowden` , `pvl_est_Rs_sunsVoc` , `pvl_est_Rs_Pysch` , `pvl_est_Rs_IEC60891_1` , `pvl_est_Rs_IEC60891_2`

Copyright 2018 Sandia National Laboratories