## 4 Classification and Features of Smartphone Apps for Solar PV Energy
### Environmental and Economic Assessment of PV Systems  
The fifth topic of solar PV apps is environmental or economic assessment of PV systems. The layout design function of the PV system is also included in some apps. Table 7 lists smartphone apps in this category and their developer/company, platform, price, and main functions. Unlike conventional power generation approaches (e.g., thermal steam or nuclear), renewable energy resources, including PV, have environmental advantages but also economic limitations due to their high costs. Therefore, most PV projects often estimate not only the potential power generation, but also the environmental benefits and economic profitability. Some apps in this category can also measure the optimal tilt and orientation of PV modules [74; 75; 76; 77], which were already discussed in detail in the previous subsection. PV power generation is commonly an indispensable input factor to assess environmental benefits (e.g., CO\({}_{2}\) emissions reduction) or economic profitability (e.g., expected profit, payback period, internal rate of return) of a PV system. Therefore, some apps in this category cover not only environmental and economic evaluation, but also estimation of PV power generation. Conversely, a couple of apps simply assess the environmental or economic benefit by inputting the PV power output. Accordingly, the apps were divided into three groups: only economic assessment, potential and economic assessment, and all three aspects assessment (potential, environmental, and economic). A couple of apps can only assess the economic profit of PV systems by entering several input values [78; 79; 80]. These apps estimate revenues for various conditions and situations considering the balance of system (BoS). The Sunny Solar Panel Calculator [79] allows users to input various parameters, such as amount of panels, panel capacity, panel tilt, power price, based on which it estimates the average yearly profit. The PV Profit Calculator [80] estimates the potential profit of a PV system in a spot market more accurately by entering various parameters such as installation type, capacity of power plant with sunshine hour (automatically retrieved by selecting a date and region in the app) or power generation, system marginal price (SMP), price, and weight of renewable energy certificate (REC; subsidy) (recent DB provided). Several apps can evaluate both PV potential and economic profitability [74; 75; 81; 82; 83; 84; 85]. These apps estimate PV potential by setting of options and parameters, and the economic profit is assessed based on the estimated PV potential. Most of these apps provide a cash flow diagram for the PV plant (the net amount of cash and cash-equivalents transferred in and out of a PV business) to clarify the costs and benefits considering compound interest over time. The expected yearly profit and payback period for different scenarios are then analyzed. However, the accuracy of the financial analysis is not high as the assumptions and parameters provided are not close to actual values in PV businesses. Numerous apps can assess power generation, environment benefits, and economic profits of PV systems [76; 77; 86; 87; 88; 89; 90]. The environmental and economic assessments are performed after estimating the power generation. The processes and accuracies of the economic and energy production results were similar to those of the above apps. However, many of these apps also express the amount of CO\({}_{2}\) emissions reduced through PV power generation, or the corresponding effect in various kinds of values such as miles not driven, gasoline not used, coal not burned, crude oil not used, mature trees grown, or recycled garbage. The apps provide various additional functions in addition to these three main features. The Photovoltaic Estimation & IR app [85], for example, provides a feasibility study that shows the economic advantages of using PV insulation glass for canopy or walkway of buildings.