pvcell _VocSTC() and Voc() methods

[lp74]

Hi @mikofski,

this is a great library, thank you very much for your effort.
I've got a question about the open circuit voltage as computed in pvcell.py:

C = self.Aph * self.Isc + self.Isat1 + self.Isat2
delta = self.Isat2 ** 2. + 4. * self.Isat1 * C
return self.Vt * np.log(((-self.Isat2 + np.sqrt(delta)) / 2. / self.Isat1) ** 2.)

May you give some references (article) for this estimation? I am a little bit lost here.

[lp74]

I've understood.

It is very simple: you solve a second order equation in x = sqrt(Voc/Vt).

Thank you anyway.

[mikofski]

You beat me to it! Yes you just consider an ideal cell with Rs=0 and Rsh=Inf, then solve. I was going to say it's similar to the 1- diode equivalent explained in pvlib single diode section on Bishop's method, except for 2 diodes. Sorry I don't know a reference, but it's a common solar trick