Project design > Array and system losses

The Module quality loss is a parameter that should express your own confidence to the real module's performance, with respect to the manufacturer's specifications.

It is at your entire disposal: you can put it at any value (for example for keeping some reserve on the production warranty, etc).

Default value

By default, PVsyst initializes the "Module Quality Loss" according to the PV module manufacturer's tolerance specification.

PVsyst will choose a quarter of the difference between these values. For example, with -3...+3%, it will be 1.5%, and with positive sorting 0..+3%, it will be -0.75% (i.e. a negative loss value, representing a gain).

NB: This value of a quarter between low and high tolerance is the PVsyst choice. We usually consider a conservative option (i.e. the modules will never be better than announced). It doesn't have any other background reasons.

During the simulation, this factor will induce a loss on the Array Pmpp production, constant (in percentage) over all operating conditions.

In the past, it was well-known that most of PV modules series didn't match the manufacturer nominal specifications. The real behavior of modules with respect to the specifications was one of the greater uncertainties in the PV system performance evaluation.

Now, with "guaranteed" power assertions and increasing availability of independent certifications, the situation seems going toward some clarification.

At the output of the factory, each PV module is flashed, and put is the power series corresponding to this measured STC power. This is the basis of the "tolerance" definition.

Now we have to know:

- According to the flash-test manufacturers, the flash-test measurements cannot be guaranteed to a better accuracy than +/- 3% (except for high quality laboratory instruments).

- During the first days of operation, the crystalline PV modules (only p-type wafers) may be subject to a LID degradation, of the order of 1 to 3%, depending mainly on the crystal manufacturing quality (oxygen traces). The LID is now explicitly specified as loss in PVsyst.

You can find some references about values reported by different authors in Thevenard (2010), p.19.