## 4 Conclusions  
In this work, the thermal performance of a small size CPC collector with an absorber with and without fins was assessed experimentally and by using a numerical methodology in Merida, Mexico (21.02\({}^{\circ}\) N, 89.63\({}^{\circ}\) W). The following conclusions can be drawn from this study:  
* Using a small-size, low-temperature CPC collector with an aperture area of \(\sim\)0.18 m\({}^{2}\) for water heating in residential applications is feasible; however, the design of the CPC should be optimized to obtain higher temperatures.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \begin{tabular}{c} **CPC Collector** \\ **without Fins** \\ \end{tabular} & \begin{tabular}{c} **CPC Collector with** \\ **Segmented Fins** \\ \end{tabular} & \
\begin{tabular}{c} **Flat Plate** \\ **Collector** \\ \end{tabular} &
\begin{tabular}{c} **Evacuated Tube** \\ **Collector** \\ \end{tabular} \\ \hline Copper tube, fins, fittings & \$23 & \$47 & \$65 & - \\ Steel sheet and supports & \$11 & \$11 & \$15 & - \\ Aluminum sheet & \$20 & \$20 & - & - \\ Aluminum frame & - & - & \$15 & - \\ Thermal insulation & \$6 & \$6 & \$10 & - \\ Glass cover & \$5 & \$5 & \$20 & - \\ Total cost & \$65 & \$89 & \$125 & \$300 1 \\ \hline \hline \end{tabular} \({}^{1}\)Retail price.  
\end{table}
Table 3: Estimated fabrication cost for the proposed CPC collectors and flat plate collector (all costs are in USD).  
* The proposed numerical methodology, which included ray tracing simulations to map the heat flux on the absorber surface of the FEM model, which was coupled with a CFD model to estimate the temperature of the water, was capable of describing the thermal performance of the CPC collector.
* Mass flow rate is an important parameter that should be determined and optimized to obtain the maximum temperature difference between inlet and outlet temperatures and the optimal thermal efficiency while at the same time providing enough hot water.
* The best thermal performance of the CPC collectors in winter was observed when absorbers with fins were used, due to the increase in surface area.
* The use of copper fins in the absorber could also result in an increase in the cost of the fabrication of the CPC collector. Therefore, a comprehensive techno-economic analysis is needed to complement the thermal performance study.  
Conceptualization, J.E.B.-D., J.G.C. and E.A.F.-J.; methodology, J.E.B.-D., J.G.C., E.A.F.-J., D.G.C.-C., J.F.K.-D., L.D.P.-L. and A.B.; software, J.E.B.-D. and D.G.C.-C.; validation, [PERSON]-D., [PERSON]-C., [PERSON]-D. and E.A.F.-J.; formal analysis, [PERSON]-D.; investigation, [PERSON]-D.; resources, J.G.C. and E.A.F.-J.; data curation, [PERSON]-D., D.G.C.-C. and E.A.F.-J.; writing--original draft preparation, [PERSON]-D., J.G.C. and E.A.F.-J.; writing--review and editing, [PERSON]-C., [PERSON]-D., L.D.P.-L., A.B.; visualization, [PERSON]-D., D.G.C.-C. and E.A.F.-J.; supervision, J.G.C., [PERSON], [PERSON] and A.B.; project administration, J.G.C.; funding acquisition, J.G.C. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Consejo Nacional de Ciencia y Tecnologia de Mexico (CONACYT) through the project SENER-CONACYT S0019-2014-01, grant number 254667. The author [PERSON] was supported by CONACYT scholarship (No. 250809).  
Not applicable.  
The data presented in this study are available on request from the corresponding author.  
The authors thank [PERSON] for helping with the ray tracing simulations.  
The authors declare no conflict of interest.