Irradiance Losses

[Miriam]

Dear All

I would like to know what is the meaning of Irradiance losses and which is the meaning when these have positive values.

Thanks.

[Michel Villoz]

Hi Miriam,

read the help content which gives details on these losses. To make it short, it is essentially the shunt resistance which limits the efficiency at low light level.

Brgds,

Michel

[André Mermoud]

In PVsyst, the evaluation of the "Losses" of a PV array (as for the definition of the normalised performance ratios in Europe, see Help), takes as starting point the energy which would be produced if the system worked always at STC conditions (1000 W/m², 25°C, AM1.5).

The first loss evaluated in the simulation process and the loss diagram is the "Irradiance loss", which is the difference between the STC efficiency and the effective efficiency under the instantaneous irradiance, at 25°C (see "How is evaluated the "Low-light" efficiency ?".

Low-light efficiencies over STC may be obtained, mainly by the choice of the Rserie value.

Values obtained by official flash-tests measurements for crystalline modules usually don't overcome 0.3 to 0.5%. Higher values in the model should be suspected of manipulation of the Rserie parameter.

These efficiency performances measured outdoor are lower by 0.5 to 1%, probably due to the diffuse contents of the incident irradiance, which suffers of IAM loss effect.

You can also obtain slightly positive irradiance loss in very sunny situations, when the system mainly operates above 400 to 600 W/m2.