## 4 Classification and Features of Smartphone Apps for Solar PV Energy
### Education and Learning of PV Systems  
The last topic of solar PV apps is education and learning. Table 9 lists the corresponding apps and their developer/company, platform, price, and main functions. The apps in this category show the principles or conceptual diagram of a general PV system rather than a manual only for a specific product. Apps that deliver solar news were excluded. The apps in this category mainly show the structure or operating principles of PV systems, explain the connection method for various types of system, or provide a PV-related DB. Most investigated apps were free, but one was 4.00 USD. As they provide relatively simple functions, the role of built-in sensors was difficult to define.  
Several apps can show image-based solar PV wiring diagrams for educational purposes [112; 113; 114; 115; 116; 117]. They provide a simple visual representation of the physical connections and layout of an electrical system or circuit. They show how the electrical wires are interconnected and where fixtures and components can be connected to the system for grid-connected or off-grid PV systems. Conversely, the Solar PV Technology Mobile Course app [118] provides a flexible learning course with quizzes for practicing electricians who have basic skills in electrical, mechanical, or electronics field (Figure 7). This educational app emphasizes the development of practical and theoretical knowledge in basic solar PV technology, products, and systems. It covers various topics such as electrical concepts, PV modules, battery, charge controller, system sizing, and system maintenance.  
A couple of DB-type apps were also observed, and they allow users to retrieve specific data. The PV Local Laws and Regulation app [119] can be used to easily search information on national or regional laws related to solar PV energy in Republic of Korea. It covers legal information such as permission to develop activities (i.e., guidelines for permits, city planning ordinances), permission for power facility development, basic energy ordinance, low-carbon green growth ordinance, PV promotion ordinance, autonomous law, and solar construction bidding. For instance, it clarifies that the separation distance between residential areas or roads and a PV system to be installed is different for each region within a province. The SolarDanawa app [120] provides a DB of manufacturers of PV system equipment such as solar modules, solar inverters, connect boards, and PV system monitoring in Republic of Korea. Through these apps, solar vendors, government officials, and researchers responsible for solar projects can easily and quickly find useful information.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Name of App** & **Developer/Company** & **Platform** & **Price \({}^{*}\)** & **Function** & **Reference** \\ \hline Full Solar Wiring Diagram & Devdroid79 & Android & Free & [112] \\ Solar Panel Wiring Diagram & BTSudio & Android & Free & [113] \\ Solar Panel Diagram Wiring Free & Florentinus WD & Android & Free & [114] \\ Solar Wiring Diagram Free & Wiring Diagram & Android & Free & [115] \\ Solar Wiring Diagram Best & Electrical Studio & Android & Free & References & [116] \\ Solar Energy Systems & The JAMBRONG & Android & Free & [117] \\ Solar PV Technology Mobile Course & Ishan Talks Apps & Android & Free & [118] \\ PV Local Laws and Regulation & Mal-eum & Both & \$4.00 & [119] \\ SolarDanawa & Bitmoa & Android & Free & [120] \\ \hline \hline \end{tabular}  
* Price in USD.  
\end{table}
Table 9: Summary of smartphone applications for education and learning purposes of PV system.