## 3 Methodology
### Study Under Real Operating Conditions  
For this section, the solar irradiance on a horizontal surface was determined in real operating conditions of the \(PV\) module mounting systems. In order to evaluate the \(PV\) module mounting systems under study from the point of view of the incident solar irradiance on the \(PV\) field, an experimental setup was needed to recreate real operating conditions. The experimental setup consisted of an annual fixed tilt angle system and a horizontal single-axis tracker. The experimental setup is shown in Figure 5:  
The characteristics of the experimental setup were as follows:  
1. Location of the experimental setup. In order to be able to compare both \(PV\) module mounting systems, it was necessary that the installation location was the same. The experimental setup was installed at the Department of Electrical Engineering of the University of Oviedo (Gijon, Spain) (latitude 43\({}^{\circ}\)31\({}^{\prime}\)27\({}^{\prime\prime}\) N, longitude 05\({}^{\circ}\)43\({}^{\prime}\)07\({}^{\prime\prime}\) W, elevation 28 (m) above sea level). Gijon is characterised by a temperate oceanic climate typical of Spain's Atlantic coast, with cool summers and wet and mostly mild winters. The code assigned to Gijon under the Koppen climate classification is \(C_{fb}\). 2. The ground-mounted \(PV\) power plant. This type of \(PV\) power plant is composed of fixed tilt angle systems (see Figure 5a). The following considerations were taken into account in the design of this \(PV\) plant: (1) the configuration was \(2 Vx2\); (2) the fixed tilt angle system was south-facing; (3) the \(PV\) field had a tilt angle of 33.5(\({}^{\circ}\)); this angle is the optimum angle according to the Jacobson equation [18]; (4) the longitudinal spacing for maintenance was 4 (m); (5) the transversal installation distance was 0.30 (m); (6) the transverse and longitudinal installation distance between the \(PV\) modules  
Figure 5: Images of the experimental setup. was 0.025 (m), due to the clamps; (7) the \(PV\) module used was the CanadianSolar CS3U-355 PB-FG, 355 (Wp). 3. The single-axis tracking \(PV\) power plant. This type of \(PV\) power plant is composed of horizontal single-axis trackers (see Figure 5b). The following considerations were taken into account in the design of this \(PV\) plant: (1) the configuration was \(1 Vx8\); (2) the pitch was 6.5 (m); (3) the limit of movement was \(\pm 60(^{\circ})\); (4) the transversal installation distance was 0.30 (m); (5) the transverse and longitudinal installation distance between the \(PV\) modules was 0.025 (m), due to the clamps; (6) the \(PV\) module used was the CanadianSolar CS3U-355 PB-FG, 355 (Wp). 4. Measuring instruments (see Figure 5c). The measurement system consisted of three pyranometers. The experimental measurements taken were global horizontal solar irradiance (Pyranometer 1), diffuse horizontal solar irradiance (Pyranometer 2), and reflected solar irradiance (Pyranometer 3). Its characteristics were as follows: (a) the same type of pyranometer was used; (b) the pyranometer used was the \(CMP11\) model manufactured by Kipp & Zonen; (c) the accuracy class was Class A (secondary standard); (d) the pyranometer's measurement range was 0-4000 \((W/\text{m}^{2})\); (e) the expected daily accuracy was less than 2%. Several sources of error can be associated with any experimental process, such as calibration, precision, methodology of experiments, etc. [54]. These sources of error affect the experimental results [54]. In this study, solar irradiances were measured directly; therefore, the uncertainty of the measurements was defined by the accuracy of the pyranometers [55]. As the uncertainty of the pyranometers was less than 3%, the experimental data can be considered to be highly accurate [55]. 5. Duration of the test campaign. The test campaign was carried out in 2022. The pyranometers measured solar irradiance every second, calculating the average every minute. Data were recorded for one year.