Since the use of photovoltaics in the domestic and industrial sector is increasing, the reliability and safety of photovoltaic systems is becoming more and more important. One of the crucial issues for safety is the formation of a hot-spot, which can reach several hundred degrees Celsius in less than thirty minutes. For this reason, a fire may occur under prolonged exposure. However, a method for hot-spot detection during operation, based solely on current-voltage characteristics, has not yet been established because the detailed formation mechanism of these hot-spots is different for every sample. We have proposed electro-thermal coupled model to reproduce the temperature distribution in a solar cell with a hot-spot that is caused by a reverse bias voltage due to a local partial shade. This time, we propose an improved model using current FB (feedback).

The development of a stable supply system for electricity with 100% renewable energy is needed by low-carbon societies working toward attaining the targets of the Paris Agreement. The purpose of this study was to evaluate the stable electricity supply systems in Japan supplied with 100% variable renewable energy (VRE) resources with a secondary battery system (SBS) or a hydrogen storage system (HSS) using a practical tool. For that purpose, the authors developed a practical tool based on a spread sheet to evaluate the stable electricity supply system without curtailment of VREs. Using the tool with actual time patterns of outputs of VREs in eastern Japan, the authors obtained the following results. The optimal capacity ratio of solar to wind is 3.3 with SBS and 4.4 with HSS. However, the system cost of stable electricity via SBS is over 100 JPY/kWh because of the high cost of batteries. The cost of a system with an HSS, at approximately 29 JPY/kWh, can be much lower than an SBS, because the energy storage cost of an HSS is much lower than that of an SBS.