Dynamic concentration factor: A novel parameter for the rigorous evaluation of solar compound parabolic collectors

Abstract

Solar-driven photoactivated processes have proven to be effective technologies for removing pathogens and chemical contaminants from water. Reflector systems are commonly used to concentrate the sunlight and improve their efficiency. Among them, compound parabolic collectors (CPC) are the most widely used, being the concentration factor (CF), their main design parameter, calculated directly from the geometry. This work presents the development of a novel parameter, called dynamic concentration factor (DCF), to assess the efficiency of a CPC as a function of the solar vector (the beam angle depends on location, season of the year and time of the day) and the reflective properties of the material. The DCF is defined as the ratio between the incident radiation reaching the receiver with and without the collector. DCF of CPC with different acceptance angles have been calculated with a ray-tracing tool and validated with experimental data from actinometry reactions. Analysis of the results has been done by plotting the dependence of the DCF versus the beam angle for increasing reflectivity indexes. This facilitates the estimation of the total radiation available to conduct a photoactivated process, whose reaction rate is proportional to the incident photons in the receiver. Global worldwide results using time-varying local solar irradiation data showed that, although the CPC with an acceptance angle of 90° (CF = 1) is commonly assumed as an optimal configuration due to its ability to concentrate diffuse radiation, the use of CPC with different acceptance angles could be more suitable in some regions of the planet.