Efficiency comparison between tracking and optimally fixed flat solar collectors

Abstract

Abstract We investigate the optimal orientation for a fixed flat plate solar collector using the clear sky model. The ground reflection component of irradiation that hits the collector’s surface is ignored due to its relatively small magnitude when compared to the direct beam and sky diffusive components. Analytical calculations demonstrate that regardless of the collector’s latitude, the most effective azimuthal angle, $$\gamma ^*$$ γ ∗ , is 0, which generally corresponds to a North–South direction. However, the optimal tilt angle, $$\beta ^*$$ β ∗ , is dependent on both the Day of Year (DoY) and the collector’s local latitude. For latitudes typical of mid-altitude climate zones, we can calculate the optimal tilt angle and the maximum energy that the collector can harvest during each DoY. We compare the maximum daily received energy—which is the sum of the direct beam and sky diffusive energies—associated with this optimal orientation to their corresponding values when the flat plate tracks the Sun. The relative increase in total energy due to Sun tracking depends critically on the DoY, with a minimum value of about $$17\%$$ 17 % in early winter and a maximum value of $$40\%$$ 40 % over a large interval.