This part of IEC 60904 describes the procedures used to measure the dependence of any electrical parameter ( Y) of a photovoltaic (PV) device with respect to a test parameter ( X) and to determine the degree at which this dependence is close to an ideal linear (straight-line) function. It also gives guidance on how to consider deviations from the ideal linear dependence and in general on how to deal with non-linearities of PV device electrical parameters. Typical device parameters are the short-circuit current I , the open-circuit SC . Typical test parameters are the temperature T and the irradiance G. However, the same principles described in this document can be applied to any other test parameter with proper adjustment of the procedure used to vary the parameter itself.
Performance evaluations of PV modules and systems, as well as performance translations from one set of temperature and irradiance to another, frequently rely on the use of linear equations (see for example IEC 60891, IEC 61853-1, IEC 61829 and IEC 61724-1). This document lays down the requirements for linear dependence test methods, data analysis and acceptance limits of results to ensure that these linear equations will give satisfactory results. Such requirements prescribe also the range of the temperature and irradiance over which the linear equations may be used. This document gives also a procedure on how to correct for deviations of the short-circuit current I from the ideal linear dependence on irradiance SC (linearity) for PV devices, regardless of whether they are classified linear or non-linear according to the limits set in 9.7. The impact of spectral irradiance distribution and spectral mismatch is considered for measurements using solar simulators as well as under natural sunlight.
The measurement methods described herein apply to all PV devices, with some caution to be used for multi-junction PV devices, and are intended to be carried out on a device, or in some cases on an equivalent device of identical technology, that is stable according to the criteria set in the relevant part of IEC 61215. These measurements are meant to be performed prior to all measurements and correction procedures that require a linear device or that prescribe restrictions for non-linear devices.
