Title: Photovoltaic devices methods of linear dependence and linearity measurements
Scope: 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-linearity’s of PV device electrical parameters. Typical device parameters are the short-circuit current ISC, the open-circuit voltage VOC and the maximum power Pmax. 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 ISC from the ideal linear dependence on irradiance (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.
