## 5 Progress of Data Transmission Protocols for Wireless Communication in Solar PV Monitoring Systems
### Wi-Fi-Based Module  
Wi-Fi technology is based on the 802.11 family standard which is implemented to develop a wireless local area network (WLAN) [98]. The Wi-Fi-based monitoring system depends on a Wi-Fi module commonly using ESP8266 for data transmission. This tool can read current changes up to 5A with an error reading of 2.5% in the ammeter and voltages up to 30 V with an error reading of 0.073% in the voltmeter. The range of the Wi-Fi module can reach up to 100 m with the data rate between 11 Mb/s and 54 Mb/s. However, the Wi-Fi module consumes more power in transmitting data than other data transmission modules. [PERSON] et al. [99] introduced a method to monitor and protect the solar PV system with low power communication using an ESP 8266 Wi-Fi module. A total of three nodes consisting of a 12 V DC motor, LED lights, and LED lamps were observed with an average error of 2.4% for the current sensor and 0.073% for the voltage sensor recorded. The proposed work needs further improvements to elevate the efficiency as well as to decrease the transmission time of the data. [PERSON] and [PERSON] [42] proposed a method based on an ESP32 module to monitor the electrical parameters of the solar panel and battery. The designed system used low-cost sensors, an ESP32 Wi-Fi module, and an SD-card reader. A total of 12 solar modules each at 130 W was tested. The work consisted of low power applications which could be improved comprehensively for high power applications such as 1 kW. In addition to the above methodology, environmental parameters should be considered for future works in terms of panel conditions. Moreover, the presented technology proves insufficient for supporting any intelligent decisions or notifications. [PERSON] et al. [100] designed a low-cost monitoring system utilizing a Wi-Fi module ESP8266 for maximum power point tracking (MPPT) in a solar PV plant. The system consisted of two electronic boards, a data acquisition sensing board, and a DC-DC boost converter. Besides, a website was also designed to store and display the monitored data in real-time. The block diagram of the proposed monitoring system is displayed in Figure 13[100]. Further improvements related to fault detection as well as remote sensing could be implemented with the integration of a failure system to send the information related to sensor failure. [PERSON] et al. [101] proposed a Wi-Fi-based solar PV monitoring system using a Wi-Fi module for data transmission to monitor solar panel parameters such as voltage, current, and temperature. The monitoring of the parameters was completed in real-time. The results showed that the average errors of voltage and current were 0.96% and 5.6%, respectively. The methodology observed is simple and could be comprehensively improved for a wide range of applications such as fault detection, measurement of efficiency, as well as panel condition. [PERSON] and [PERSON] [102] proposed an open source SCADA architecture to develop an efficient monitoring system and a robust supervisory control system. The developed structure consisted of various components such as sensors, ESP32 Thing Micro-Controller (RTU), a Thinger.IO local server IoT platform, a Raspberry PiMicro-Controller and a local Wi-Fi Router. The ESP32 Thing Micro-Controller (RTU) is used to collect the electrical data from various sensors and then transfers the obtained sensor data to the Thinger.IO local server IoT platform through a Wi-Fi network for data storage, remote control, and real-time monitoring. The proposed SCADA system was tested using 260 W and a 12 V Solar PV System to monitor the voltage, current, and power remotely. Some issues relating to monitoring using Wi-Fi are as follows:  
* The deployment of unauthorized devices without undergoing security review possesses could result in a threat for the insertion attack;
* Bypassing access points by clients makes them prone to external threats as well as threats against each other;
* Interception and monitoring of traffic across a LAN.