## 4 Classification and Features of Smartphone Apps for Solar PV Energy
### PV Site Evaluation
This is a feature available only on smartphone apps, not on desktop software. The measurement of tilt angle and orientation of PV module is possible because of the built-in magnetometer and accelerometer sensors in smartphones, respectively. The on-site measurement of tilt angle of PV modules enables users to obtain the input value for energy simulation or to optimally adjust the tilt angle of the PV module. Some apps [50] can calculate solar factors, such as local time meridian, equation of time, declination angle, zenith angle, and elevation angle. A couple of apps [53; 54] can calculate the distance between PV modules to avoid shadows. The SOLARPE Pro app [53] includes all the above-mentioned features, and it connects with the National Aeronautics and Space Administration (NASA) DB to check parameters for the installation place, as shown in Figure 3a. For roof or rooftop PV power generation, some apps can measure or analyze the characteristics of the roof or rooftop. The Solar Consult app [55] not only measures the tilt and orientation of the roof, but also analyzes the number and size of PV modules considering roof characteristics, such as shape (i.e., flat or pitched), area, tilt angle, and orientation. Figure 3b shows screenshots of PV designs according to the roof type in the Solar Consult app, which can measure the tilt angle of the roof and has an orientation meter that works like a compass to display the deviation from the South. The app can identify if the roof is suitable for a PV module system, according to the amount of sunlight, obtained through an address or by displaying the location. The app calculates multiple types of PV modules for maximum output according to the type of roof (i.e., flat or pitched). In case of a flat roof, the length of the shadow behind a row of PV module can be calculated. On the contrary, the RoofSnoop app [56] can extract characteristic information of the roof (e.g., location, area, slope, orientation, and shape) via satellite images and street view of Google Maps (Figure 3c). This function enables remote-roof surveys before visiting the site to confirm roof dimensions and angles. The user can easily identify the roof to be measured, determine the outlines of the roof, and obtain the roof width, ridge-to-gutter distance, azimuth, and surface area in the map. The main advantage of this app is that it analyzes the roof characteristics via satellite images from anywhere, rather than by using the smartphone's built-in sensors in the field. The Solar Survey app [57] is a PV site evaluation tool based on AR technology. It can estimate the solar resources in a location based on Typical Meteorological Year 3 (TMY3) data from the internet and measure the potential shading obstacles using an AR display via the camera. Therefore, it can provide more accurate weather information than other apps. Moreover, shading information can be given in a format available for input into other PV simulation software. The SolarEdge Site Mapper app [58] allows to streamline the registration of PV array by mapping its physical layout intuitively.