public static IVTrace CalcSweep(CellSpec cell, double insolationW, double tempC)
{
double voc = cell.CalcVoc(insolationW, tempC);
double isc = cell.CalcIsc(insolationW, tempC);
int n = 100;
double[] vecv = new double[n + 1];
for (int i = 0; i <= n; i++) {
vecv[i] = voc * (double)i / n;
}
double[] veci = CalcIV(cell, vecv, insolationW, tempC);
//Debug.Assert(Math.Abs(veci[0] - isc) < 0.001);
//Debug.Assert(Math.Abs(veci[n]) < 0.001);
double pmp = 0.0;
double imp = 0.0, vmp = 0.0;
for (int i = 0; i < n; i++) {
double p = veci[i] * vecv[i];
if (p > pmp) {
pmp = p;
vmp = vecv[i];
imp = veci[i];
}
}
IVTrace trace = new IVTrace();
trace.I = veci;
trace.V = vecv;
trace.Isc = isc;
trace.Voc = voc;
trace.Imp = imp;
trace.Vmp = vmp;
return trace;
}
/// <summary>
/// Computes an IV curve.
/// </summary>
public static double[] CalcIV(CellSpec cell, double[] vecv, double insolationW, double tempC)
{
double[] veci = new double[vecv.Length];
double i0 = cell.CalcI0(insolationW, tempC);
double isc = cell.CalcIsc(insolationW, tempC);
double t = tempC + Constants.C_IN_KELVIN;
double k = Constants.BOLTZMANN_K;
double q = Constants.ELECTRON_CHARGE_Q;
double ni = cell.NIdeal;
double rs = cell.SeriesR;
double epsilon = 0.000001;
bool invalid = false;
for (int i = 0; i < vecv.Length; i++) {
double v = vecv[i];
// iterate to convergence
double iprev = 0.0, icurr = 0.0;
for (int j = 0; j < 2000; j++) {
double vdrop = iprev * rs;
double idark = i0 * (Math.Exp((q * (v + vdrop)) / (ni * k * t)) - 1.0);
icurr = isc - idark;
if (Math.Abs(icurr - iprev) < 1e-6) {
//Debug.WriteLine("converged in " + j);
break;
}
iprev = 0.95 * iprev + 0.05 * icurr;
}
// check for invalid results (the simulation didn't converge)
if (icurr < -epsilon || (i > 0 && icurr > veci[i - 1])){
invalid = true;
}
veci[i] = Math.Max(icurr, 0.0);
}
if (invalid)
{
Debug.WriteLine("Warning: the IV trace didn't converge, returning zero currents");
return new double[vecv.Length];
}
return veci;
}
private void Recalculate()
{
// recalc
CellSpec spec = new CellSpec();
UpdateSpec(spec);
// show sanity checks
double i0 = spec.CalcI0(wattsIn, tempC);
double isc = spec.CalcIsc(wattsIn, tempC);
double voc = spec.CalcVoc(wattsIn, tempC);
IVTrace sweep = CellSimulator.CalcSweep(spec, wattsIn, tempC);
labelMaxPower.Text = string.Format(
"Isc={0:0.000}A Voc={1:0.000}V @{2:0.00}C\n" +
"Imp={3:0.000}A Vmp={4:0.000}V Pmp={5:0.000}W\n" +
"Rev. sat. current {6:0.000}A, fill factor {7:0.0}%",
isc, voc, tempC,
sweep.Imp, sweep.Vmp, sweep.Pmp,
i0, sweep.FillFactor * 100.0);
// show an iv plot
chartIV.X = sweep.V;
chartIV.Y = sweep.I;
}