###### Abstract  
Compound parabolic concentrator (CPC) solar collectors are widely used for solar energy systems in industry; however, CPC collectors for residential applications have not been fully investigated. In this work, the thermal performance of non-tracking, small-size and low-cost CPC collectors with an absorber with and without segmented fins was studied experimentally and by means of a proposed numerical methodology that included ray tracing simulation and a coupled heat transfer finite element method (FEM)-computational fluid dynamics (CFD) simulation, which was validated with experimental data. The experimental results showed that the CPC with a finned absorber has better thermal performance than that of the CPC with absorber without fins, which was attributed to the increase in thermal energy on the absorber surface. The numerical results showed that ray tracing simulation can be used to estimate the heat flux on the absorber surface and the FEM-CFD simulation can be used to estimate the heat transfer from the absorber to the water running through the pipe along with its temperature. The numerical results showed that mass flow rate is an important parameter for the design of the CPC collectors. The numerical methodology developed in this work was capable of describing the thermal performance of the CPC collectors and can be used for the modeling of the thermal behavior of other CPCs solar systems. compound parabolic concentrator (CPC); solar energy; ray tracing simulation; computational fluid dynamics (CFD); finite element method (FEM); coupled FEM-CFD simulation; fin; thermal performance; incidence angle modifier (IAM) +
Footnote †: journal: Applied Sciences  
can be flat or tubular [8]. The absorber heat is transferred, by conduction, to a heating pipe. If the absorber is a pipe, the absorber heat is transferred directly, by convection, to the circulating working fluid. The first CPC collector was designed by [PERSON] [9; 10]; since then, several improvements to the original design have been developed including the optimization of the geometry of the reflective surface to attain a maximum concentration ratio [11] (defined as the ratio of the aperture area to the absorber area), the improvement of the absorber by using evacuated tubes to surround the surface of the absorber to reduce heat loss [7] and the use of fins in the absorber to increase solar radiation absorption [12; 13]. CPC collectors can be classified for low temperature (<100 \({}^{\circ}\)C), medium temperature (100-250 \({}^{\circ}\)C) and high temperature applications (>500 \({}^{\circ}\)C) [14]. Low temperature CPCs are used for residential applications including water and space heating. CPCs for residential applications have been widely studied [5]; however, many of the studied residential CPCs are large and heavy and include technological features to achieve higher temperatures and thermal efficiency. These features, such as evacuated tubes and tracking systems, increase the manufacturing and maintenance cost, which could be a problem for the use of CPCs in low income and remote areas. Research on low cost and small size CPC collectors for residential applications is limited. [PERSON] et al. [15] developed a methodology to manufacture inexpensive CPC solar collectors, which produced CPC reflective surfaces with an accuracy of 94% with respect to the ideal CPC surface shape. This methodology was then used by [PERSON] et al. [16] to design and build a small size CPC solar collector with a tubular absorber and concentration ratio of 1.41, for residential applications, using low cost materials; they obtained an average thermal efficiency of \(\sim\)43% using a fixed tilt angle of 21\({}^{\circ}\) on a winter day. [PERSON] et al. [17] reported a simplified low-tech design of a CPC collector with a concentration ratio of 1 and found that a reduction in the manufacturing cost is feasible, while obtaining an increase of 79 \({}^{\circ}\)C in the receiver stagnation temperature.