1. National Renewable Energy Laboratory Golden CO 80401 USA
2. DTU Fotonik Frederiksborgvej 399, Building 130 Roskilde 4000 Denmark
3. Renewable Energy Research Center National Institute of Advanced Industrial Science and Technology (AIST) Fukushima 963‐0298 Japan
4. Faculty of Electrical Engineering University of Ljubljana Tržaška cesta 25 Ljubljana SI‐1000 Slovenia