Abstract: This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the Editor-in-Chief and the authors. The article duplicates significant parts of a paper that had already appeared in Energy 32 (2007) 1634 – 1646, http://dx.doi.org/10.1016/j.energy.2006.12.007. An investigation by the National Taiwan University has concluded that the co-authors Falin Chen, Eric Wang and Kuo-Tung Tseng were not aware of this submission of the corresponding author. One of the conditions of submission of a paper for publication is that authors declare explicitly that the paper is not under consideration for publication elsewhere. Re-use of any data should be appropriately cited. As such this article represents a severe abuse of the scientific publishing system. The scientific community takes a very strong view on this matter and apologies are offered to readers of the journal that this was not detected during the submission process.