[1] Energy Modelling Group, General Energy Research Department, Paul Scherrer Institute, Villigen CH-5232, Switzerland
[2] Department of Electrical Engineering, Natl. Technical University of Athens, Zografou Campus, 9 Iroon Politechniou Str., GR-157 73, Athens, Greece
[3] Environmentally Compatible Ener. S., Intl. Inst. for Appl. Syst. Analysis, A-2361, Laxenburg, Austria
[4] Swiss Fed. Institute of Technology, Zürich, Switzerland
[5] Swiss Fed. Institute of Technology, Lausanne, Switzerland
[6] ENSAE, University of Dauphine, Paris, France
[7] University Pierre et Marie Curie, Paris, France