Solar Concentrator Consisting of Multiple Aspheric Reflectors

Abstract

This paper presents an off-axis-focused solar concentrator system consisting of 190 aspheric reflectors, where the aperture radius of each reflector is 10 cm, and vertices of all reflectors are orderly arranged in the same plane. The aspheric parameters controlling the curvature of the reflectors are determined using coordinate transformations and the particle swarm optimization (PSO) algorithm. Based on these aspheric parameters, the light distribution of focal plane was calculated by the ray tracing method. The analyses show that the designed concentrator system has a spot radius of less than 1 cm and the concentration ratio over 3300:1 is achieved using only one reflection. The design results have been verified with the optical design software Zemax.Most of the important developments of solar concentrators have been done in the solar thermal and PV systems. In the solar thermal system, the most common method is to increase focusing stages and reflectors. Rodriguez-Sanchez et al. (2015) employed secondary devices to optimize the focusing position and the incidence angle of sunlight [17]. Balaji et al. (2016) employed the combination of multi-stage focusing and multiple reflectors to increase the concentration ratio and also to improve the flux distribution over the circumference of the absorber [18]. Benyakhlef et al. (2016) used multiple rotating curved heliostats instead of flat ones to reflect the sun-rays onto the linear receiver at a fixed position. Primary focusing heliostats were arranged in rows whereas the secondary reflector was only one reflector. Interestingly, the curvature allowed the heliostats to be more precise than in flat ones and offered a higher concentration capacity [19]. Sharma et al. (2015) utilized the line Fresnel reflector (LFR) field consisting of parallel rows of collectors in which each collector-row was composed of parallel rows of reflectors that direct the sun-rays toward linear receivers [20]. Qin et al. (2013) raised the concentration ratio of a trough concentrator to 285:1 in case of off-axis focus by adopting reflective aspheric surfaces [14]. Recently, a prototype of two-stage non-imaging solar concentrator showed a higher concentration ratio at the receiver plane [21]. However, improving the spatial uniformity can efficiently increase the concentration ratio. A new concept of high-flux non-coaxial concentrating solar simulator was introduced to the typical ellipsoidal reflectors [22]. In some cases, multiple reflectors were used to focus the solar beam on the same small area in order to increase the temperature of the focus area [23][24][25][26]. Loni et al. (2016) used parabolic dish concentrators to focus the sun-rays on the receiver for obtaining a high temperature of work fluid. Furthermore, they designed a cylindrical closed-tube open-cavity solar receiver in such a way to absorb the solar energy to the maximum extent [27]. Other methods have also been applied to achieve high concentration ratio. Liang et al. (2015) investigated solar concentrator based on the off-ax...