## 1 Introduction  
After experiencing the first oil crisis in 1973 and other energy crises, Japan promoted the diversification of energy sources to create a society that does not rely heavily on fossil fuels. After the first oil crisis, dependence on fossil fuels decreased from 94% to 81.2% in 2010. However, owing to the shutdown of all nuclear power plants after the Great East Japan Earthquake in 2011, the operation of thermal power plants increased, and dependence on fossil fuels rose again to 87.4% in FY2017 (statistics by the government were made by fiscal year) [1]. Based on these events, the Japanese energy industry must solve three problems: the depletion of fossil fuels, global warming, and safe and stable energy supply. Expectations regarding renewable energy solving this problem are increasing. Renewable energy refers to energy that can be used repeatedly by utilizing phenomena that occur naturally on Earth, such as sunlight, wind power, and geothermal heat, rather than the energy generated from fossil fuels, such as oil, coal, and natural gas. Specifically, renewable energy includes photovoltaic, solar thermal, wind, geothermal, and hydraulic power generation. The share of power generation from renewable energy increased, and photovoltaic power generation is increasing. The rapid spread of solar power generation is due to the feed-in tariff (FIT) system for renewable energy introduced in 2012 and the following excellent features of solar power generation. 1. Inexhaustible energy source  
A solar cell directly converts light energy from the sun into electrical energy via the photoelectric effect of a semiconductor. If we could convert 100% of the solar energy that hits the Earth, the amount of energy would be so large that it would cover the world's annual energy consumption in just one hour and never run out. 2. Maintenance, automation, and uncrewed operations are easy. Unlike thermal power plants, there are no rotating machines or high-temperature, high-pressure parts; therefore, no mechanical wear occurs, and no lubricating oil is required. The operation and maintenance are simple, and the system can easily be automated or can be operated unmanned. 3. Installation locations are not limited. Because it can be installed in unused spaces, such as roofs and walls, there is no need to prepare new land for installation. 4. Because of its modular structure, it is suitable for mass production and has a considerable scale advantage. Because solar cells are manufactured with a compact module structure, they are highly mass-producible. Line manufacturing is complex because other equipment require large parts. In recent years, owing to global warming caused by the depletion of fossil fuels and rising greenhouse gases, renewable energy sources, such as solar, hydroelectric, wind, and geothermal power, have attracted attention. Among these, photovoltaic power generation is desirable because it has fewer location restrictions than other methods [2; 3; 4; 5; 6; 7; 8]. Advances in solar cell technology require rapid and detailed performance measurement methods [9; 10]. Solar cells can be used outdoors by covering multiple PV cells with fillers, glass, and backsheets. However, once a module has been processed, it cannot be disassembled. A typical method for measuring and evaluating solar cell performance involves examining the \(I\)-\(V\) characteristics of a PV module. However, after processing the module, it is only possible to measure and evaluate the performance of the PV module as a whole [11; 12; 13; 14; 15]. Detailed performance measurements and performance evaluations after processing are necessary to further improve the quality of the PV modules. Infrared thermography, electroluminescence (EL) inspection, and photoluminescence (PL) inspection are visible performance measurement/evaluation methods other than \(I\)-\(V\) measurement techniques. Infrared thermography identifies defects such as hot spots inside PV modules by examining the heat dissipation distribution of PV modules.