## 4 Classification and Features of Smartphone Apps for Solar PV Energy
### Potential Assessment of PV Systems  
The fourth topic of solar PV apps is the potential assessment (power output estimation) of PV systems. Table 6 lists the corresponding apps and their developer/company, platform, price, and main functions. The fundamental feature of these apps is the analysis or simulation of PV potential energy yield under various conditions and environments [59; 60; 61; 62; 63; 64; 65; 66; 67; 68; 69; 70; 71; 72; 73]. The respective high-level calculations consider variables and options for various scenarios compared to the aforementioned simple calculations. In addition to the potential assessment, apps that also assess environmental benefits or economic profitability are summarized in the next section. The prices for apps in this category ranged within 0-14.99 USD. Figure 3: Representative smartphone applications for site evaluation. (**a**) Measurement of tilt and orientation of module, (**b**) Efficiency of solar irradiation according to the module orientation, (**c**) Roof characteristics, and (**d**) Roof PV design using Solar Consult app. In general, local weather data, site characteristics, and performance of PV modules and inverters are essential to predict PV power generation. Local weather data include GHI, direct normal irradiance (DNI), diffuse horizontal irradiance (DHI), ambient temperature, wind speed, wind direction, pressure, albedo, and other parameters. Site characteristics include area, shading, inclination, separation distance, and other conditions. Performance of PV system includes capacity, efficiency, miscellaneous loss, and other electrical characteristics of module and inverters. The more data is considered, the higher the accuracy of potential power generation. The factors considered vary depending on the purpose for which the app was developed and their accuracy also vary. As summarized in Table 6, apps in this category can be divided into hourly [65; 66; 72; 73], daily [61; 62], monthly [63; 64; 68; 69; 70; 71], and yearly [60; 67] estimations. Originally, this distinction is associated with the temporal resolution of weather data that can be provided or entered into the app. The app that predicts hourly power generation can obtain hourly weather data (i.e., irradiance value) by connecting to a worldwide irradiance DB link via wireless communication and/or measuring solar irradiance via external sensor. Similarly, the apps that estimate monthly power generation utilize a DB with average monthly irradiance data. However, instead of considering actual irradiance data, several apps allow the users to simply determine the options and values to analyze or simulate PV power output. In addition to PV energy yield, many apps in this category also include additional features mentioned in earlier sections such as visualization of sun path [65; 73], calculation of power consumption (electric load) for comparison with potential power generation [61; 62; 64; 66], determination of optimal tilt and orientation of PV module based on geographic coordinates [60; 67; 70; 71; 72], or on-site measurement of solar irradiance, tilt, and orientation of module or roof [67; 72; 73]. These functions can help maximize power generation and enhance the understanding of the power output calculation process. SolarTester Pro [73] is a representative app that includes various of the aforementioned features. This app makes hourly performance predictions for grid-connected PV projects based on system design parameters specified by the user. The user can simulate the sun path, perform shading modeling, and obtain the optimal TOF as well as measure tilt and orientation of module and roof. The app recognizes the user's location and automatically loads the irradiance data of the region using an internal worldwide irradiance DB by NASA.