# Investigation of the Automatic Monitoring System of a Solar Power Plant with Flexible PV Modules
## 3 Results and Discussion
To collect data from digital wattmeters, the first stage of the operational data monitoring system (also called the MCU module) was designed and manufactured. This stage is based on the PIC24 FV32 KA302. Microcontrollers of this series are characterized by high work reliability and are widely used in digital electronic devices and systems, e.g., in medical equipment. The electrical circuit of the first stage is presented in Figure 4. This stage consists of a connector to which a programmer is connected to program the microcontroller. DC/DC converters are used for matching the level of the digital signal. A special module is used, the purpose of which is the conversion of protocols from RS232 to TCP. This is necessary in order to be able to transfer information to the industrial PLC module. Therefore, the communication between the MCU module and the PLC is ensured with the help of an RS232/TCP converter. As can be seen from the electrical circuit, separate inputs for the information transmitted by digital wattmeters are designed in the MCU module. This information consists of electric current and voltage values from which the power value is found. The inputs of the digital wattmeters are connected to the corresponding logic inputs of the microcontroller and the information is transmitted in digital form. The monitoring data of the power values of solar panels, charge controllers and receivers allow one to understand whether the overall working process of the solar power plant is optimal and suitable. Also, monitoring the charging and feeding power of individual receivers allows one to see whether the required charging and feeding process is ensured and whether there are no work problems in the entire system. Figure 3: Electrical diagram of power measurement. In order for any (in this case, monitoring) system to be implemented and function optimally, it is necessary to properly design and manufacture the printed circuit boards (PCBs) where all electronic components will be installed. PCB design is a certain stage of research because it is necessary to ensure an optimal design and to select the transitions and length of the optimally conductive paths, so that, e.g., additional noises are avoided and the dimensions and price of the device are ensured to be as small as possible. During this study, two PCB variants were designed, one of which is intended for the realization of a digital wattmeter (Figure 5a) and the other PCB is intended for the realization of an MCU module (Figure 5b). The basis of the PCB consists of copper tracks covered with solder and a special layer resistant to environmental effects, which protects the metal tracks from oxidation and other negative processes. The protective layer is a dielectric to prevent accidental exposure to electric current. In addition to the microcontroller, the printed circuit board has designed spaces for active SMD elements such as capacitors and diodes. A partial optimization of the PCB board was performed; the track length was kept as small as possible so that impedance mismatches would not affect the data transfer rate. The fastest signal using USB Full Speed has a rise time of 4 ns, so using the 10% signal edge travel limit, tracks should be no longer than 60.96 mm. Using Python 9 and HTML programming languages, a software code was created for a virtual interface between a MySQL database and a computer application, where instantaneous data reflecting the real-time operation of the solar power plant are displayed. This interface is more suitable for the public demonstration of monitoring related to system operation and data display. The image of the PC application is presented in Figure 6. As we can see in the main window, the electrical values (voltage, current and power) of individual solar panels can be monitored. In this application, the system maintenance operator can make certain changes and evaluate whether the solar electric monitoring system is working properly. Figure 4: Electrical diagram of the first stage of the monitoring system.