IEC 60904-5:2011 describes the preferred method for determining the equivalent cell temperature (ECT) of PV devices (cells, modules and arrays of one type of module), for the purposes of comparing their thermal characteristics, determining NOCT (nominal operating cell temperature) and translating measured I-V characteristics to other temperatures. The main technical changes with regard to the previous edition are as follows: - added method on how to extract the input parameters; - rewritten method on how to calculate ECT; - reworked formulae to be in line with IEC 60891.