Rshunt and Rserie

[EngineerSolar]

Hi dear engineers,

I am running simulation for a solar farm using the pan file from a client. However, I found in the pan file, the Rshunt and Rserie are defined irregularly high which led to a gain at the irradiance level. Knowing your method of calculating defaults are as below:

-Rshunt = Vmp / (0.2 * (Isc-Imp)). The 0.2 coefficient may be different for other technologies (0.33 for amorphous).

-Rserie is determined according to the low-light performance resulting from the model, in order to obtain a relative efficiency of -3% at 200 W/m2.

I'm wondering if you have any recommendation for a range of Rshunt and Rserie values in the simulation?

Thank you in advance for helping!

[Lazare Fesnien]

Hi,

Five parameters not defined from the datasheets are used in the one-diode model (as modified by PVsyst): Rserie, Rshunt, RshExp, Rsh(0) and Gamma (diode ideality factor).

The main modification of PVsyst to the standard model is the exponential behaviour of the Rshunt value acc. to the irradiance.

PVsyst fixes some default values:

RshExp = -5.5 seems a very stable parameter, established on our long-term measured data at sun (direct measurement of the Rshunt as the slope of the I/V curve around V = 0), valid for any technology.

Rhsunt = "reasonable hypothesis" of PVsyst, established acc. to Imp/Isc at Vmpp. This doesn't have a high impact with crystalline modules.

RSh(0) = 12 * Rshunt for most technologies, was diminished for crystalline but seems indeed to be of the order of 10. This ratio is also fixed for default values.

Now remains Rserie, and the closely related Gamma value. This is determined according to the low-light efficiency curve at 25°C.

If we avail of IEC 61853 measurements, the value is set for matching these measurements.

If not, we fix a low-light relative efficiency = -3% @ 200 W/m2.

Sometimes this value cannot be reached by the model. In these case we increase the RShunt value, which allows higher Rseries and therefore higher low-light efficiencies.