Na’man, Salahaldin, Haval Y. Yacoob, and Omar S. Omar. 2013. “Optimum Tilt Angle for South Facing Flat Solar Collectors in Duhok City”. Science Journal of University of Zakho 1 (1):405-13. https://sjuoz.uoz.edu.krd/index.php/sjuoz/article/view/98.