1. Graduate Research Assistant, Division of Applied Mechanics and Energy Conversion, Univ. of Leuven (K.U. Leuven), Celestijnenlaan 300A, B-3001 Leuven, Belgium. E-mail: erik.delarue@mech.kuleuven.be
2. Energy and Environmental Markets, Fortis Bank, Warandeberg 3, B-1000 Brussels, Belgium. E-mail: kris.voorspools@fortis.com
3. Professor, Division of Applied Mechanics and Energy Conversion, Univ. of Leuven (K.U. Leuven), Celestijnenlaan 300A, B-3001 Leuven, Belgium (corresponding author). E-mail: william.dhaeseleer@mech.kuleuven.be