1. RealTek, Norwegian University of Life Sciences, Ås 1430, Norway
2. The Norwegian Public Service Pension Fund, Oslo 0212, Norway
3. Department of Solar Energy, Institute of Energy Technology, Kjeller 2007, Norway
4. Department of Technology Systems, University of Oslo, Oslo 0371, Norway
5. Department of Physics, Wesleyan University, Middletown, Connecticut 06459-0155, USA