R. Georgiev, K. Peychev

Abstract. The purpose of this paper is to study the thermal efficiency of a laboratory solar thermal module at different mounting angles. Mounting angles are 20˚, 30˚ and 40˚, with due allowance for the annual calendar time and latitude of Bulgaria. The solar thermal module is based on vacuum tubes of the “Heat pipe” type. These are 5 pipes of active length and diameter respectively 1,450 mm and 35 mm. For the indicated annual period the highest extent of efficiency is obtained at mounting angle 40˚. The extent of efficiency at the other mounting angles 30˚ and 20˚ decreases by 11% and 21% on average when temperature of the heat agent rises to 65 ÷ 70˚ C. Mounting angle significantly affects heat production and the extent of efficiency of the solar thermal module. Appropriate values for this angle are respectively 30˚ – for June and July and 40˚ – for May, August and September for the territory of Bulgaria