## 4 Experimental Results and Discussion
### Efficiency Comparison between Concentrating and Nonconcentrating PV Systems  
In this section, the results obtained above will be applied to compare the \(NCPV\) system and the \(CPV\) system. The following assumptions were considered in order to compare the two systems:  
1. The available roof area of the building was considered to be the same for both technologies. Specifically, the flat roof has a width of 786.88 (mm) and a length of 658 (mm). 2. According to Figures 20-22, the electrical efficiency varies with incident solar irradiance, ambient temperature, and wind speed. Figure 11 shows how the ambient temperature varies as a function of the time of day at each location under study. Therefore, the electrical efficiency can take a large number of values. The electrical efficiency of \(PV\) cells was considered to be the same for both technologies, i.e., 0.18. The operating temperature of the \(PV\) cells was also assumed to be the same. It can be considered that the losses \(Q_{convPV}\) and \(Q_{radPV}\) remain constant if the solar irradiance remains constant. 3. The \(NCPV\) system has a southern orientation and an optimal tilt angle, as determined by the procedure used in [62]. 4. The method proposed by [60] was used to determine solar irradiance for both technologies. Table 6 shows the optimum tilt angle and the annual solar irradiation incident on the \(PV\) cells of the \(NCPV\) system at each location under study. Figure 22: Electrical efficiency for an ambient temperature of 40 (\({}^{\circ}\)). Figure 16 shows the solar irradiation gain incident on the \(PV\) cells according to the following equation:  
\[HG=\frac{H_{NCPV}-H_{CPV}}{H_{NCPV}}\cdot 100 \tag{17}\]  
where \(H_{NCPV}\) is the solar irradiation incident on the \(PV\) cells in the \(NCPV\) system (kWh), and \(H_{CPV}\) is the solar irradiation incident on the \(PV\) cells in the \(CPV\) system (kWh). As with all \(NCPV\) systems, all three solar irradiance components are incident on the \(PV\) cells, and the incident solar irradiance will be much higher than in the case of \(CPV\) systems, which only use the beam component of the solar irradiance. As shown in Figure 23, the studied configuration always shows better results than the base configuration. With respect to the base configuration (\(\beta_{M}=0\) (\({}^{\circ}\)) and \(\beta_{S}=0\) (\({}^{\circ}\))), the solar irradiation gain is higher than 60%, whereas it is higher than 45% for the longitudinal tilt configuration. The total useful energy in the \(NCPV\) system is only electrical energy. In contrast, the total useful energy in the \(CPV\) system is the sum of electrical energy and thermal energy. To compare the two technologies, the total useful energy gain must be used:  
\[EG=\frac{E_{NCPV}-E_{CPV}}{E_{NCPV}}\cdot 100 \tag{18}\]  
where \(E_{NCPV}\) is the total useful energy in the \(NCPV\) system (kWh), and \(E_{CPV}\) is the total useful energy in the \(CPV\) system (kWh). If \(EG\) is positive, \(NCPV\) systems prove to perform better; however, \(CPV\) systems are considered higher-performing if \(EG\) is negative. Figure 24 shows the total useful energy gain for the base configuration (\(\beta_{M}=0\) (\({}^{\circ}\)) and \(\beta_{S}=0\) (\({}^{\circ}\))) and for the studied configuration. The total useful energy gain at the lowest latitude location (Medellin) in the absence of wind (see Figure 24a) is in favour of \(NCPV\) systems. In contrast, this energy gain is in favour of \(CPV\) systems for higher latitudes. As in the rest of the work, the studied configuration shows better results than the base configuration. It is worth noting that this gain is 70% higher at the highest latitude location (Almeria) in the case of \(CPV\) systems. Figure 24b shows the effect of wind on the useful energy gain. If the wind speed