Illumination homogeneity of bifacial systems : outdoor measurements with systematically varied installation conditions : visual

The optimum mounting condition for bifacial modules is a trade-off maximizing the performance of the front and backside output obtained for the given installation conditions. At the backside of bifacial PV modules there are more complex conditions concerning the illumination intensity and illumination homogeneity, compared to the frontside. In extended PV plants, with parallel rows of bifacial modules, there are additional factors, such as reduced ground albedo due to shading by adjacent rows, which have to be considered. At the ZHAW, we implemented an outdoor test system to analyse the performance of bifacial arrays at differing mounting conditions by a new methodical measurement approach. The tilt angle is adjusted periodically between 0° and 90° in twelve positions within a one minute interval. In this paper we focus on outdoor measurement results concerning the illumination homogeneity at the front and backside and its impact on the total output. Not only the module data itself is analysed, but also a set of multiple small light sensors is attached at the rim of the bifacial centre module in order to reveal the illumination homogeneity in more detail. This setup enables a detailed analysis of the sensitivity at different tilt angles as well as more general yield results from long-term measurements