# pvl_est_Rs_sunsVoc

PVL_EST_RS_SUNSVOC Estimate Rs using the suns-Voc method.

## Contents

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

## Syntax

- `[Rs, errest] = pvl_est_Rs_sunsVoc(sunsV, sunsI, Isc, Vmp, Imp)`
- `[Rs, errest] = pvl_est_Rs_sunsVoc(sunsV, sunsI, Isc, Vmp, Imp, Rsh1, Rsh2, nNsVth, Io, Isc2)`

## Description:

The suns-Voc method estimates series resistance using the suns-Voc curve and a measured IV curve. It is assumed that both the suns-Voc and measured IV curves are at cell temperature of 25C. The suns-Voc curve is expressed as a pair of vectors (sunsV, sunsI) where sunsV is a vector of Voc at irradiance levels E, and sunsI = Isc0 - Isc(E) where Isc0 is the short circuit current at STC (1000 W/m2 and 25C). A point is selected on the (sunsV, sunsI) curve where the pseudo-current sunsI is equal to the measured Imp.

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]. For this estimate, shunt resistance and short circuit current are required for the IV curve at irradiance E = (1 - Imp / Isc0)*1000 W/m2.

## Inputs:

- `sunsV` - a vector of voltage for suns-Voc curve.
- `sunsI` - a vector of pseudo-current in amps for the suns-Voc curve.
- `Isc` - short circuit current in amps for the measured IV curve.
- `Vmp` - voltage at the maximum power point for the measured IV curve.
- `Imp` - current at the maximum power point for the measured IV curve.
- `Rsh1` - (optional) shunt resistance, in ohms, for the measured IV curve.
- `Rsh2` - (optional) shunt resistance, in ohms, for the IV curve at irradiance E = (1 - Imp / Isc0) * 1000 W/m2 where Isc0 is short circuit current in amps at STC.
- `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.
- `Isc2` - (optional) short circuit current, in amps, for the IV curve at irradiance E = (1 - Imp / Isc0) * 1000 W/m2 where Isc0 is short circuit current in amps at STC.

## 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 IV curve at STC
    Ee = 1000;
    Tc = 25;
    nPts = 100;
    [IL, I0, Rs, Rshf, nNsVth] = pvl_calcparams_desoto(Ee, Tc, param.aIsc, param, EgRef, dEgdT);
    IVcurve_STC = pvl_singlediode(IL, I0, Rs, Rshf, nNsVth, nPts);

    % simulate suns-Voc curve
    suns = 10:10:1000; suns = suns(:);
    sunsTc = ones(size(suns)).*25;
    sunsIsc0 = IVcurve_STC.Isc;
    sunsIsc = suns./1000.*sunsIsc0;

    [IL, I0, Rs, Rsh, nNsVth] = pvl_calcparams_desoto(suns, sunsTc, param.aIsc, param, EgRef, dEgdT);
    res = pvl_singlediode(IL, I0, Rs, Rsh, nNsVth, nPts);
    sunsVoc.V = [res(:).Voc];
    sunsVoc.I = (1 - suns(:)/1000)*sunsIsc0;

    % Estimate Rs
    Rs = pvl_est_Rs_sunsVoc(sunsVoc.V, sunsVoc.I, IVcurve_STC.Isc, IVcurve_STC.Vmp, IVcurve_STC.Imp)

    Rs =

        0.2144

## 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_Swanson` , `pvl_est_Rs_Pysch` , `pvl_est_Rs_IEC60891_1` , `pvl_est_Rs_IEC60891_2`

Copyright 2018 Sandia National Laboratories