## 5 Progress of Data Transmission Protocols for Wireless Communication in Solar PV Monitoring Systems
### LoRa-Based Module
Large SFs are implemented more than small SFs for long-distance communication resulting in a low transfer rate and a high Packet Error Rate (PER) [130]. The time on-air utilized by data (bytes) to be transmitted and received with different SFs is shown in Table 3. For example, if 10 bytes of data were sent with SF = 7, it would take around 0.1 s, whereas if the SF is increased to 11, it would take 0.5 s for the same byte of data to be transferred. The comparison of the specifications for data transmission protocols used in solar PV monitoring systems is presented in Table 4. Bluetooth, Wi-Fi, and ZigBee constitute short range data transmission modules whereas GSM and LoRa comprise long-range data transmission modules. A comprehensive comparative study for the different data processing modules and the data transmission protocols for solar PV monitoring systems is tabulated in Table 5. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Module** & \multirow{2}{*}{**Range**} & \multirow{2}{*}{**Power**} & \multirow{2}{*}{**Topology**} & \multirow{2}{*}{**Data**} & \multirow{2}{*}{**Sampling Rate**} \\
**Implemented** & & & & & **Transmission Rate** & \\ \hline Bluetooth & Short range & 100 m & 10–500 mW & Point to point & 1 Mbps & 44.1 kHz \\ Wi-Fi & \multirow{2}{*}{Short range} & 150 m & 1 W & Star & 11 Mbps & 20 MHz \\ ZigBee & \multirow{2}{*}{modules} & 300 m & 1 mW & Mesh & 250 kbps & 8 MHz \\ GSM & Long Range & 10–30 km & 1–5 W & Star & 270.8 kbps & 8 kHz \\ LoRa & module & 10–30 km & 25 mW & Star, Mesh & 5469–293 bps & 500 kHz \\ \hline \hline \end{tabular}  
* The data transmission rate for Wi-Fi is variable and depends on protocols and frequency utilized. The value of 11 Mbps here refers to 802.11b protocol with 2.4 GHz frequency.  
\end{table} 
Table 4: Comparison of various specifications of data transmission modules. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**MAC Payload Size** & \multirow{2}{*}{**SF = 7**} & \multirow{2}{*}{**SF = 9**} & \multirow{2}{*}{**SF = 8**} & \multirow{2}{*}{**SF = 10**} & \multirow{2}{*}{**SF = 11**} & \multirow{2}{*}{**SF = 12**} \\
**(in Bytes)** & & & & & & \\ \hline
10 & 0.1 & 0.1 & 0.1 & 0.25 & 0.5 & 1 \\
20 & 0.1 & 0.1 & 0.18 & 0.3 & 0.7 & 1.4 \\
30 & 0.2 & 0.1 & 0.3 & 0.48 & 0.8 & 1.5 \\
40 & 0.2 & 0.1 & 0.35 & 0.51 & 1 & 1.8 \\
50 & 0.22 & 0.2 & 0.39 & 0.6 & 1.2 & 2.2 \\ \hline \hline \end{tabular}  
* The comparison of the specifications for data transmission protocols used in solar PV monitoring systems is presented in Table 4. Bluetooth, Wi-Fi, and ZigBee constitute short range data transmission modules whereas GSM and LoRa comprise long-range data transmission modules.  
\end{table} 
Table 3: Time on air utilized by data packets at different SFs. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Data Processing Modules**} & \multicolumn{4}{c}{**Data**} & \multicolumn{4}{c}{**Measured Parameters**} & \multicolumn{4}{c}{**Softward**} & \multirow{2}{*}{**Monitoring**} & \multicolumn{4}{c}{**Peak Power of**} & \multirow{2}{*}{**Achievements**} & \multirow{2}{*}{**Related Reference**} \\  & **Transmission** & & & & & & & & & & & & & & & & **Language Used** & **Platform** & **Multiplier/Plants** & \\ \cline{2-19}  & **Proposed** & & &  
Based on the abovementioned reviews, some guidelines need to be taken into consideration to select an appropriate technology for solar PV monitoring systems. The guidelines are presented in Table 6.  
Therefore, the information discussed above will act as guidelines in selecting an appropriate solar PV monitoring system.