Abstract
Power temperature coefficients delta (TCo) measured indoor at standard test conditions (STC) (as given on products datasheet) always present a negative sign; an increase in temperature leads to a reduced power output. Interestingly, the magnitude of the TCo is not always confirmed outdoor with significant differences between technologies with even change in signs in some cases (e. g., a-Si). It is important to investigate if the reported outdoor behavior is a true effect or if it is the result of a choice of nonhomogeneous sets of data (e. g., either irradiance sensor or modules shaded). In this work, the importance of filtering procedures is discussed in order to work with a reliable set of data and to establish a method that allows comparison with indoor data.