1. Energy and Environment Laboratory, Department of Physics, Faculty of Science, University of Yaounde I, Yaounde P.O. Box 812, Cameroon
2. LISIE, University Institute of Technology Fotso Victor of Bandjoun (IUT-FV), University of Dschang, Bandjoun P.O. Box 134, Cameroon
3. Department of Physics, University of Ndjamena, N’djamena P.O. Box 1117, Chad
4. Carnot Energy Laboratory (CEL), Department of Physics, Faculty of Science, University of Bangui, Bangui P.O. Box 1450, Central African Republic