## 4 Results
The analysis of thermal efficiency and useful heat is presented in Figure 7. It shows the behavior of thermal efficiency for the stable section, for which the maximum value calculated was 16.95%, this value is the average efficiency for a 10 min period. The useful heat behavior varied from 2.9 kW to 5.2 kW, the \(G_{b}\) was registered between 700.1 W/m\({}^{2}\) to 832 W/m\({}^{2}\). In this case, the exergy efficiency varied between 7.4 and 11.7. Figure 8 shows the temperature profiles in the storage tank, and at the inlet and outlet from the solar collector's field as a function of the solar irradiance (Gb) registered in Cuernavaca in 5 December. The solar radiation presents a normal profile; however, some clouds appeared during the day as it can be seen in the plot, the maximum \(G_{b}\) was 859 W/m\({}^{2}\). The period of evaluation was considered from 9:30 a.m. to 15:00 p.m. For this day the stable section was in a range from 12:00 p.m. to 14:00 p.m. The behavior of the storage tank temperature profile was held constant for two hours. The average temperature held in the storage tank was 96.8 \({}^{\circ}\)C, the maximum outlet temperature HTF was 101.7 \({}^{\circ}\)C.  
Figure 8: Behavior \(G_{b}\) and outlet, inlet and storage tank temperatures, 5 December 2017. Figure 7: Thermal efficiency, exergy efficiency, and useful heat, 29 November 2017. The thermal efficiency and useful heat were analyzed for the stable section and are presented in Figure 9. In this day the values of efficiency were lower than other tests, the \(G_{b}\) was registered in a range from 668.6 to 853 W/m\({}^{2}\), as a result of a cloudy day, the maximum value calculated was 14.82% and the minimum was 6.27%. The data was average of efficiency every 10 min. However, the useful heat was between 1.9 to 4.9 kW when the \(G_{b}\) was around 853 W/m\({}^{2}\). The minimum exergy efficiency was around 4.2 at 14:00 while the maximum value was 11.1 at 12:09. The Figure 10, corresponding to 11 December, shows the solar radiation behavior and the temperature profiles for the inlet, outlet, and storage tank during the day. The Gaussian profile presents a maximum \(G_{b}\) was 987 W/m\({}^{2}\) in Cuernavaca city, this value is the highest value registered with respect to the reported previously. The evaluation was carried out for 5.5 h (9:30 a.m.-15:00 p.m.). In the stable section was presented between 12:17 p.m. to 14:45 p.m. It is very interesting the behavior of the storage tank temperature, because it was kept constant during 5.5 h. The average storage tank temperature was 96.0 \({}^{\circ}\)C and the maximum outlet temperature of HTF was 102.6 \({}^{\circ}\)C.  
Figure 10: Behavior \(G_{b}\) and outlet, inlet and storage tank temperatures, 11 December 2017. Figure 5.0 Thermal efficiency, exergy efficiency, and useful heat, 5 December 2017. The analysis of thermal efficiency and useful heat are presented in Figure 5.1 It shows the behavior of thermal efficiency for the stable section (9:30 a.m.-15:00 p.m.), for which the maximum value calculated was 15.80% and the minimum was 8.05%. The useful heat behavior varied in a range from 2.95 kW to 5.98 kW, the \(G_{b}\) was registered between 981 W/m\({}^{2}\) and 954 W/m\({}^{2}\). The decreasing trend in the useful energy is associated with the proximity of this temperature to the boiling temperature in the city of Cuernavaca. The exergy efficiency follows the same trend than others parameters, varying from 7.8 to 15%. According to the results of the evaluation of solar collectors, the outlet temperature data was used as inlet data of absorption cycle, the inlet temperature was in a range from 85 to 95 \({}^{\circ}\)C, according to the results of PTCs. The useful heat was considered to be supplied to the generator in a range from 1.9 to 6.5 kW. In Figure 12, a comparison of the theoretical and experimental useful heat for the collectors' field is presented for one typical day. The figure shows a variation of Qu as a function of the test time.