## 4 Discussion  
The cooling capacity calculated from the thermal energy supplied to the absorption chiller and its EER can serve as a basis for an economic study by evaluating its cost when generated by an electric vapor compression chiller. In the case of a solar collector surface of 122.5 m\({}^{2}\) (49 solar collectors), a driving temperature of 75 \({}^{\circ}\)C and a specific storage volume of 15 L/m\({}^{2}\), 31,466 kWh of thermal energy are sent to the absorption chiller from the hot water storage tank during the summer season (June-September). Considering an EER of 0.722 corresponding to the 75 \({}^{\circ}\)C driving temperature (Table 2), the absorption chiller would provide a cooling capacity of 22,718 kWh. If this cooling capacity were produced by an electric compression chiller with an EER of 3, and considering an electricity price of 0.2 euros per kWh, the absorption chiller would suppose a saving of 1515 euros (per year if it only operates in the summer season). This saving should compensate for the difference between the higher cost of the solar cooling system compared to that of a vapor compression chiller. However, given the cost of the solar air conditioning system, the economic study is meaningless. The selling price of the absorption chiller (Yazaki WFC-SC10) in Spain (on 29 April 2019) was of 39,620 euros (without taxes). There is only one company that imports this brand of absorption machines in Spain. The cost of the absorption chiller represents only a fraction between 30 and 35% of the solar cooling system total cost (solar collector field, storage tank, cooling tower, water treatment system, etc.) according to the experience of the authors [10]. This means that the total cost of the 35 kW solar cooling facility would be approximately of 105,000 euros (3000 euros per kW of cooling capacity). The solar cooling system total cost of 3000 euros per kW of cooling capacity is the approximate cost of the facility that the authors designed and built at the Miguel Hernandez University of Elche. This cost coincides with that provided by [PERSON] and [PERSON] [4] of 2675 euros per kW of cooling capacity. In the case of the Miguel Hernandez University facility, the cost of the 17.6 kW cooling capacity Yazaki WFC-SC5 absorption machine was of 24,391 euros (without taxes and with a special discount). At this facility, an open cooling tower was chosen because it was three times cheaper than a closed one. From the point of view of the absorption chiller maintenance it is much more convenient to use a closed cooling tower, even more so considering that the absorption chiller represents a high percentage of the total cost of the solar cooling system. The economic analysis could be even worse if we took into account the parasitic electrical consumption of the solar energy cooling system. According to the data recorded in the Miguel Hernandez University facility, the cooling capacity of the absorption machine was just 1.7 times higher than the electrical consumption associated with pumps, cooling tower fan and control systems. The above mentioned price for the absorption chiller includes only one year guarantee. The company that imports the absorption chiller is also the only company that carries out its maintenance in Spain. The maintenance and the initial cost make this system incapable of competing with other air conditioning systems, being therefore limited to demonstration facilities. [PERSON] et al. [18] describe a method to estimate the upper bound of the cooling energy yield by a solar-cooling facility. It can be applied by hand to get a reference value. Although the details can be found there, here we show its comparison to our practical results. The method assumes that the absorption machine is directly coupled to the collector field and takes into account the thermodynamic performance of both: the solar collectors and the absorption cooling machine. The tables used by the method must be prepared in advance, based on those parameters.