## 3 Results
### Solar Collector for Hybrid Chiller  
Before performing the simulation of the solar collector, the hot temperature of the solar collector was measured. The values of radiation and temperatures measured for a typical day in Mexico City are shown in Figure 6. The measurements were made with a type K thermocouple and a direct radiation meter TM-206 MCA TENMARS. The accuracy of the thermocouple and pyrometer are, respectively, \(\pm\)0.75% and \(\pm\) 10 W/m\({}^{2}\) (or 5%, whichever is greater in sunlight). Measurements were made every 30 min. The value of each variable was saved when data were stable for at least 30 s. From the figure, it can be seen that the ambient temperature and radiation, respectively, were between 21 and 28 \({}^{\circ}\)C and 600 and 1200 W/m\({}^{2}\) during the day. With these radiation and ambient temperature values, it was possible to measure temperature values in the hot spot of approximately 200 to 400 \({}^{\circ}\)C. In the figure, the value of radiation at 14:00 is lower because the instrument used measures instantaneous radiation. In this case, the meter display was obstructed by a cloud. This was not an obstacle for the temperature at that time to remain at the maximum value of 400 \({}^{\circ}\)C approximately. The results of the low-capacity solar concentrator modeled in Section 2.2 are shown in this section. Figure 7 shows the area and diameter of the solar absorber obtained as a function of the concentration ratio, \(C\), varying from 5 to 100. It can be seen that the area and diameter of the absorber decrease at a rate of 2.5% and 1.66%, respectively, for each concentration unit between the values of \(C\) = 20 and \(C\) = 40. For higher values of the concentration ratio, the decrease ratio is 1.1% and 1.0% for the area and the diameter, respectively. For concentration ratios lower than 10, the area and the diameter decrease at a rate of 10.66% and 5.8%, respectively, for each unit of concentration ratio increment. These results suggest that, with concentration ratios greater than 20, the diameter of the absorber will be less than 30 cm. This can contribute to the radiation in the hot source being distributed over a larger area, reaching medium temperatures, rather than high temperatures, which contributes to improving the efficiency of the solar concentrator, as shown below. Figure 6: Radiation and temperature values measured in the solar concentrator during a typical day in Mexico City. Heat supplied to the hybrid system and cooling power produced by both cooling systems are shown in Figure 8, for a temperature in the solar collector of 200 \({}^{\circ}\)C and 40% of the heat produced supplied to the absorption cooling system, \(x_{g}=0.4\). In the same figure, with \(I=1000\) W/m\({}^{2}\), it can be seen that the cooling produced by the absorption cooling system is approximately 11% less than the heat supplied to the generator. However, the compression system can produce 1, and up to 2 and 3 times more cooling than the heat supplied to the Stirling engine hot source, with efficiencies in this thermal engine of 0.1, 0.2 and 0.3, respectively. The efficiency of the solar concentrator, shown in Figure 9, was evaluated at temperatures in the hot spot, \(T_{h}\), of 200, 300 and 400 \({}^{\circ}\)C. From the figure it can be seen that, in the radiation range from 200 to 1000 W/m\({}^{2}\) and \(C=30\), the efficiency decreases faster when the temperature of the hot spot is 400 \({}^{\circ}\)C than when it is 200 \({}^{\circ}\)C.  
Figure 8: Thermal power produced by the solar concentrator and by absorption/compression refrigeration systems, with respect to solar radiation. Figure 7: Area and diameter of the solar absorber in relation to the concentration ratio. To show the relationship between the performances of the different systems that compose the solar hybrid chiller, Figure 10 shows the efficiency of the solar concentrator, together with the COP of the two cooling systems, as a function of the solar radiation.