Performance evaluation of a solar water heating system with glass-covered parabolic trough concentrators, under different system tracking modes

The thermal performance of a new type of solar water heater system consists of an array of parabolic trough collectors was studied. In CFD simulation of the system, a practical mathematical model was proposed that the realistic non-uniform solar flux distribution obtained by optical analysis is implemented in thermal modeling of the system. The system performance was investigated in three different tracking modes, stationary south-face, tilted N–S axis with daily tilt adjustment, and full tracking mode under the complexity of non-uniform solar flux distribution on the outer surface of the water pipe. The system was studied experimentally in Isfahan, Iran, with latitude and longitude of 32.6539° N, 51.6660° E, respectively. In experiments, the inlet water mass rate in the range of 0.005–0.15 kg s−1, and inlet temperature in the range of 20–40 °C was investigated. The system’s average daily thermal efficiency at full tracking mode is greater than 60%, and at optimal conditions, the efficiency of more than 70% is also achievable. For the N–S axis with daily tilt adjusted equal to noontime zenith angle, its performance is greater than 45% and for the system at stationary mode with a tilt angle equal to local latitude is less than 40%. Results indicate that the system performance is severely affected by tracking errors, and the effect of these errors in tilt adjustment is more significant than surface azimuth adjustment. At full tracking mode, an accuracy error of 6° in tilt adjustment leads to a reduction of 10% in the system thermal efficiency, while the accuracy error up to 20° in azimuth adjustment has no significant effect on its performance.