## 3 Materials and Methods
### Development of Meteorological DAS  
The meteorological data acquisition is carried out to offer additional data to PV array and also assists to address the desires of the PV power plant for long-standing, high accuracy, well preserved and standard systems in variable weather conditions. The measuring parameters are pyranometer for solar radiation, relative humidity probe for both ambient temperature and relative humidity as well as  
Figure 4: Schematic view of the meteorological and electrical parameters with sensors for the DAS.  
wind monitor for wind speed. These devices are all mounted at the roof-top of the commercial building at SolarWatt park, to experimentally measure metrological parameters at different positions of the sun.  
The solar radiation measurements comprise a SOLYS 2 sun tracker, which contains two pyranometers, Pyrhelometer and pyrgeometer. The sun tracker is a fitted device capable of measuring global, direct and diffuse components of the sun as well as other meteorological parameters. It is an automatic two-axis instrument used for both vertical and horizontal solar radiation with a team of measuring devices such as the time, date, longitude, latitude and altitude of this location to calculate and track the position of the sun at all the time. Hence, the image of the sun tracker is presented in Figure 5.  
However, as shown in Figure 6, Kipp & Zonen CMP 11 pyranometers were used to monitor the global horizontal irradiance (GHI) and global irradiance on a tilted surface. The tilted pyranometer (extreme right) is on the same slope (12\({}^{\circ}\)) as the roof of the commercial building, thus, measuring the same amount of solar radiation subjected to the PV array. CMP 11 pyranometer is made up of a 32-junction thermopile as a sensing element. The thermopile involves thermocouple junction with sets that were in series connection.  
The measurement (hot) junction of one of the thermocouple absorbs thermal radiation, increasing its temperature. The difference between the measurement and a fixed temperature reference (cold) junction produces a voltage directly proportional to the differential temperature created due to the thermoelectric effect [22]. The sensitivity of the CMP 11 used in this study is 8 \(\mu\)V/m\({}^{-2}\) with a spectral range of 285 to 2800 nm. Its response time is less than 1.7 s (63%) and 5 s (95%) [23]. The weather station was elevated by 1 m above the roof, providing unobstructed solar radiation for the radiometers. The weather station was also strategically located such that it does not cast a shadow on the PV array.  
Furthermore, the 6-plate natural aspirated radiation shield in the middle of the weather station, house the temperature and relative humidity probe. The white painted radiation shield allows it to reflect solar radiation, whereas, allows the natural free flow of air through the louvers. This mechanism keeps the probe close as possible to the ambient air temperature (eliminating solar effect) and water vapour [24]. The HMP60 temperature and relative humidity probe measure the outdoor air temperature, and relative humidity using a platinum resistance temperature (PRT) detector to measure air temperature [25] and a capacitive relative humidity sensor to measure relative humidity [26]. The measurement specifications of HMP60 probe temperature and relative humidity sensor are given in Table 1[24].  
Figure 5: The Sun tracker comprising pyrheliometer, pyranometers and pyrgeometer with the black balls shading the horizontal instruments.  
All sensors were connected to a CR1000 were they are scanned in 10 min interval and data store every 30 min. Meanwhile, a 12 Volt DC power supply was used to power the CR1000. The power supply was complemented with a 12 Volt rechargeable battery and an uninterruptable power supply system.