Abstract
One major barrier for the installation of PV modules in the built environment concerns their aesthetic appearance. This is especially true for building-integrated PV (BIPV), in which the PV modules form an integral part of the building skin. In order to tackle this issue, several PV manufacturers offer coloured PV modules, which allow for easier integration within the building design. In addition to the colour, the surface finish of the front glass (matt, glossy, satinated, structured...) is also crucial for the overall visual impression [1,2]. Apart from inherent transmission losses, there are also some reliability concerns for coloured PV modules, regarding both power and appearance degradation. Optical degradation can be triggered by material incompatibilities with adjacent layers or degradation effects of the colourant induced by environmental stress. While measurements of yellowness index, etc have been used for backsheet and encapsulant degradation, the presence of inherent colouration may introduce additional error sources to established measurement methodologies. Generally speaking, all colour measurements involve a light source (either broadband or spectrally modulated), optics to gather the reflected or transmitted light from a specific sample, and a spectrometer (or for modulated sources a simple optical sensor) to acquire a signal. Equipment varies significantly regarding what incidence angle a sample is illuminated under, and how the light is collected. Often measurement equipment, which has not been designed for glazed surfaces is used, which can lead to measurement errors due to light scattered within the superstrate glass in PV modules [3]. In addition to mismatch between measurement equipment, also the sample design and parameters chosen for the measurement process can play a large role: Measurements can either be carried out on PV mini-modules or samples of coloured glass prior to lamination on a variety of backgrounds. In addition, measurements can be performed on the coated or uncoated side, potentially leading to different results. Also, a potential impact of the surface finishing of the glass has to be taken into account for colour measurements. Preliminary measurement results indicate, that results may be comparable in hue angle, even when colour coordinates differ significantly, however this is not true for all methodologies. Within the framework of IEA PVPS Task 15, a round-robin comparison of colour measurements at different laboratories is currently being planned and will be carried out in the coming months. The results will be present at the conference.