1. Institute for Renewable Energy, Eurac Research, Viale Druso 1, 39100 Bolzano, Italy
2. Department of Civil, Environmental and Mechanical Engineering, University of Trento, via Mesiano 77, 38123 Trento, Italy
3. Department of Electric and Electronic Engineering, Imperial College London, Exhibition Rd., South Kensington, London SW7 2AZ, UK