## 5 Progress of Data Transmission Protocols for Wireless Communication in Solar PV Monitoring Systems
### Bluetooth-Based Module  
Bluetooth is a wireless technology for exchanging data over short distances. Bluetooth functions are executed using an IEEE standard of 802.15.4 and Low-Rate Wireless Personal Area Networks (LRWPANs). It is an emerging platform and one of the most popular modes of transmission for sending data from one device to another [103]. Radio interference is removed in Bluetooth technology and replaced by a Speed Frequency Hopping (SFH) technique which allows devices to make complete access of the radio spectrum. Users have access to data transfer among various devices by forming an ad hoc network [104]. The transmitting power can be increased for sending the data up to 100 m in Bluetooth technology [105].  
[PERSON] et al. [106] designed a portable solar PV system for measuring the data of the generated PV power using Bluetooth communication protocols. The INA219 sensor was used to monitor the current, voltage, and power as well as execute the 12C communication protocol. The 12C protocol consists of two communication cables: serial data (SDA) and serial clock (SCA), which allows up to 127 slave devices to be connected. The latencies generated by masters of many slaves during the transmission of data from each slave can be taken into consideration. [PERSON] [105] presented a solar PV monitoring system based  
Figure 13: Schematic diagram of the monitoring scheme using an ESP8266 module.  
on Bluetooth technology for a photovoltaics substation. The proposed monitoring system was combined with an older automation system to develop a new system for a solar PV substation. The presented methodology could be improved by integrating the proposed algorithm with the safety and economics of the substation which could lead to an increase in the overall efficiency of the system. [PERSON] et al. [38] proposed a Bluetooth-based solar PV monitoring, evaluation, and fault detection system. The proposed system was designed to monitor the voltage, current, temperature, and irradiance of the solar panel. The results were displayed in MATLAB/Simulink platform. The experimental test was performed on a 1 kWp solar panel with a sampling time of 1 min. A fault detection parameter was proposed by observing the readings of the simulated results and then comparing them with the theoretical data obtained from the panels. All data visualization, simulation, and fault detection were completed on a common platform of MATLAB Simulink. [PERSON] et al. [107] introduced a solar PV monitoring system using Bluetooth module HC-05 to transmit data. The data were monitored by the user through the Bluetooth Terminal Application. The paper also focused on the distribution of power using a relay. The relay was switched ON/OFF by the control signal from the Arduino Uno to distribute the power properly. As per the review of the methodology, the complexity of the system could be minimized by utilizing some of the advanced microcontrollers (AVR and ARM architectures) in conjunction with the Wi-Fi transmission protocols which would provide a higher transmission range.  
Bluetooth offers various advantages but also comes with several disadvantages, including factors such as authorization, encryption, and authentication [104]. One of the main concerns about the security of Bluetooth is the pairing process [108]. Attackers can imitate users, end connections between the devices, and modify data [109]. Furthermore, it has a limited operational range of up to 100 m. Moreover, it suffers from high power requirements and exhibits slow data transmission compared to other monitoring technologies [110]. In the case of monitoring environmental parameters, transmitting a large amount of data at short intervals would require a multi-hop routing protocol which could access larger areas by using other nodes in the network as relays to reach the destination node [111].