## 4 Classification and Features of Smartphone Apps for Solar PV Energy
### PV Site Evaluation  
The third topic of the solar PV apps is site investigation and evaluation of PV system. Table 5 lists those apps and their developer/company, platform, price, and main functions. The apps in this category measure or calculate the tilt and orientation of a building roof or PV module by using built-in sensors, or they measure solar irradiation by attaching an external sensor to the smartphone. In addition, some apps are mainly used to evaluate PV sites based on Google satellite images, extract roof characteristics (e.g., area, tilt, and orientation), or combine insolation and shadow analysis. Despite providing various features, all the investigated apps were free. Some apps can also be utilized as a solar compass or pyranometer. Solar Compass [48] is an Android app that can be used to find directions in the field using the position of the sun in the sky. When the user rotates it toward the sun, the app automatically rotates to point to the desired direction based on the value obtained from the built-in magnetometer sensor. Solar Measurement--Pyranometer app [49] is a gadget that enables the measurement of on-site solar radiation by attaching external solar radiation sensors to the smartphone. As the field of view of smartphone cameras only have \(\pm\)30\({}^{\circ}\), they cannot easily perform the pyranometer function. With this app, the user can download the diffusor which is printable and attachable to the smartphone camera lens. The diffusor enables the lens to achieve 180\({}^{\circ}\) field of view to fully encompass the sky, thus enabling the measurement of solar radiation. The app is calibrated and measures the solar radiation (in W/m\({}^{2}\)) when the user pushes a button with the camera facing the sun. The measurement deviation of the app is approximately \(\pm\)30%; thus, its accuracy is not high. Professional measurement of solar radiation should be performed by highly accurate thermopile pyranometers. Nevertheless, this app can be used for educational purposes of irradiance measurements in weather, climate, solar energy, agriculture, and other related fields. Figure 2: Representative smartphone applications for the module optimization. (**a**) Calculation of optimal module tilt (Seasonal PV Tilt Angles app), (**b**) PV system configuration and report by electrical load (Solar Calculator app). \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Name of App** & **Developer/Company** & **Platform** & **Price** & **Function** & **Remarks** & **Reference** \\ \hline Solar Compass & [PERSON] & Android & Free & Measurement & Azimuth measurement of sun position & [48] \\ Solar Measurement/Pyrammeter-App & Hulseflow Thermal Sensors & iOS & Free & & Irradiance measurement & [49] \\ \hline Solar Calculation Tips & Green Engineering Tips & Android & Free & & & [50] \\ Optimal Tilt Angle for PV System & NRG Labs & Android & Free & & [51] \\ Simply-solar & [PERSON] & iOS & Free & + Calculation & & [52] \\ SOLARF Pro & PV Photovoltaic & SOLARPE SOFT & Android & Free & & [53] \\ Solar Energy & & & & & & [54] \\ SOLARPE & PV Photovoltaic & SOLARPE SOFT & Android & Free & & [54] \\ Solar Energy & & & & & & \\ \hline Solar Consult & [PERSON] & iOS & Free & Measurement & For roof and rooftop & [55] \\ \hline RoofSnoop & iRenewables Limited & iOS & Free & & & For roof & [56] \\ Solar Survey & [PERSON] & Android & Free & Analysis \& Simulation & Augmented railty (AR) visualization & [57] \\ SolarEdge Site Mapper & SolarEdge Technologies & Both & Free & & PV module layout design & [58] \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Summary of smartphone applications for site evaluation of PV systems. Several apps have been proposed not only to measure tilt angle and orientation of PV modules, but also to calculate their optimal values to maximize power generation [50; 51; 52; 53; 54]. The apps in this category are different from the apps in the category of PV system optimal settings [42; 43; 44; 45; 46] because they can provide functions of on-site measurement as well as calculations.