1. School of Computing and Mathematical Sciences, Birkbeck, University of London, London WC1E 7HX, UK
2. Centrica Energy, Skelagervej 1, 9000 Aalborg, Denmark
3. Department of Applied Mathematics and Statistics, Johns Hopkins University, Baltimore, MD 21218, USA
4. Ralph O’Connor Sustainable Energy Institute (ROSEI), Johns Hopkins University, Baltimore, MD 21211, USA
5. Business School, University of Inland, Vormstuguvegen 2, 2624 Lillehammer, Norway