ALKAFF, A. MONTHLY AVERAGE DAILY INSOLATION AND OPTIMUM TILT ANGLE OF SOLAR COLLECTOR IN P.D.R. YEMEN Periodica Polytechnica Mechanical Engineering, [S. l.], v. 35, n. 3, p. 183–198, 1991. Disponível em: https://www.pp.bme.hu/me/article/view/5597. Acesso em: 12 may. 2025.