1. Postgraduate Researcher Department of Mathematics and Statistics, University of Reading, Whiteknights, P.O. Box 220, Berkshire RG6 6AX, UK e-mail:
2. Doctor, Lecturer in Renewable Energy Department of Construction Management and Engineering, University of Reading, Whiteknights, P.O. Box 220, Berkshire RG6 6AY, UK e-mail:
3. Professor of Applied Mathematics Department of Mathematics and Statistics, University of Reading, Whiteknights, P.O. Box 220, Berkshire RG6 6AX, UK e-mail:
4. Doctor, Senior Lecturer in Mathematical Engineering School of Systems Engineering, University of Reading, Whiteknights, P.O. Box 220, Berkshire RG6 6AY, UK e-mail: