## 3 Experimental Setup
### Test Conditions
#### 3.6.1 Longitudinal Tilt Angle  
In order to generate a broad image of the energy analysis presented in this study, six cities were selected according to the following criteria:  
1. The cities are located in the Northern Hemisphere. There are several reasons for focusing this study on this hemisphere: (a) Ninety percent of the world's population is concentrated in the Northern Hemisphere [51]. (b) The Northern Hemisphere has  
\begin{table}
\begin{tabular}{l c} \hline \hline
**Parameter** & **Parameter Uncertainty (\%)** \\ \hline Wind speed & 0.7\% \\ Ambient temperature & 0.5\% \\ Flow rate & 2\% \\ Water temperature & 0.5\% \\ Electrical power & 1\% \\ \hline \hline \end{tabular}
\end{table}
Table 3: Computed uncertainty of performance parameter.  
Figure 9: Photographs of the measuring instruments.  
the largest building roof area, which is the ideal location for energy production in cities. In the European Union, there is a total roof area of residential buildings of about 19 billion (m\({}^{2}\)) [52].
2. There is high beam incident solar irradiance in the chosen city. This is one of the conditions that had to be met for this type of technology to be cost-effective. The SolarGis software [53] uses data from 19 high-precision satellites for its simulations and provides maps with a rigorous, systematic approach of different parts of the world. Figure 10 shows a map of the direct normal solar irradiation all over world.
3. There are different climate zones with quite different latitudes. In [24], they propose the choice of study locations with a difference of about 6 (\({}^{\circ}\)) latitude starting at latitudes of 36 (\({}^{\circ}\)) up to 60 (\({}^{\circ}\)). In our study, locations higher than 40 (\({}^{\circ}\)) latitude are not considered due to the value of the incident direct solar irradiance.  
Table 4 shows the geographic characteristics of the cities under study.  
Figure 11 shows some environmental conditions at the locations under study. This figure shows the daily mean temperature and daily normal irradiance with solar tracking for the month of June. The highest solar irradiance values occur in this month. The values shown in Figure 11 are obtained from the PVG  
\begin{table}
\begin{tabular}{c c c c c} \hline  & **Cities** & **Latitude** & **Longitude** & **Altitude** \\ \hline
1 & Medellin (Colombia) & 06\({}^{\circ}\)14\({}^{\prime}\)38\({}^{\prime\prime}\) N & 75\({}^{\circ}\)34\({}^{\prime}\)04\({}^{\prime\prime}\) W & 1469 (m) \\
2 & Bangkok (Thailand) & 13\({}^{\circ}\)45\({}^{\prime}\)14\({}^{\prime\prime}\) N & 100\({}^{\circ}\)29\({}^{\prime}\)34\({}^{\prime\prime}\) E & 9 (m) \\
3 & Morelia (Mexico) & 19\({}^{\circ}\)42\({}^{\prime}\)10\({}^{\prime\prime}\) N & 10\({}^{\circ}\)11\({}^{\prime}\)24\({}^{\prime\prime}\) W & 1921 (m) \\
4 & Karachi (Pakistan) & 24\({}^{\circ}\)52\({}^{\prime}\)01\({}^{\prime\prime}\) N & 6\({}^{\circ}\)01\({}^{\prime}\)51\({}^{\prime\prime}\) E & 14 (m) \\
5 & Cairo (Egypt) & 30\({}^{\circ}\)29\({}^{\prime}\)24\({}^{\prime\prime}\) N & 31\({}^{\circ}\)14\({}^{\prime}\)38\({}^{\prime\prime}\) W & 41 (m) \\
6 & Almeria (Spain) & 36\({}^{\circ}\)50\({}^{\prime}\)07\({}^{\prime\prime}\) N & 02\({}^{\circ}\)24\({}^{\prime}\)08\({}^{\prime\prime}\) W & 22 (m) \\ \hline \end{tabular}
\end{table}
Table 4: Cities under study.  
Figure 10: Direct normal irradiation map all over world [53].  
4. The optimal longitudinal tilt angle of the secondary system demonstrated in [24] is used to define the longitudinal tilt angle at each chosen location. This angle coincides with the latitude of the location.