Experimental Assessment Of The Tilt Angle Influence On The Solar Thermal Collectors Performance

Solar thermal collectors are usually installed at a fixed tilt angle. In the design stage of the solar thermal systems, the optimal value of the tilt angle is numerically evaluated according to the latitude and the climate of the location, aiming to maximize the yearly received solar energy and thus the yearly thermal energy output. To experimentally evaluate the influence of the tilt angle on the thermal energy output of the solar thermal collectors, a complex research infrastructure was developed in the Renewable Energy Systems and Recycling (RESREC) Research Centre of the Transilvania University of Brasov, Romania, consisting of nine solar thermal systems with flat plate and evacuated tubes solar thermal collectors. The solar thermal collectors were installed at tilt angles ranging between 0 degrees and 90 degrees on the rooftops of nine buildings in the R&D Institute to evaluate in the same time their performances under the continental temperate climate conditions of Brasov city (45.65 degrees N, 25.59 degrees E). The experimental results obtained in three types of days (sunny, intermediate and cloudy) are comparatively presented in the paper. The influence of the tilt angle on the thermal energy output of each type of solar thermal collector is discussed during the three types of days. Thus, the maximum thermal energy output was obtained in the case of the solar collectors tilted at 40 degrees. Differences up to 10 degrees... 15 degrees of this angle did not significantly affect the output, only the extreme values of the tilt angle (0 degrees and 90 degrees) showed negative influence.