The applicability of renewable energy sources is expected to increase, such that these are considered main power sources. Photovoltaic (PV) power generation has emerged as an especially attractive renewable energy technology for households. However, it is difficult to supply stable electric power and store energy by using PV alone because PV power generation depends on weather. Therefore, the use of PV in combination with other energy resources such as storage batteries (BT), fuel cells (FC), and heat pump water heaters (HPWH) has been attracting attention. The introduction of these energy resources into households makes it possible to satisfy household electricity demand via power generation in each household; therefore, this energy system is called a distributed energy system. In addition, the number of households that will face the termination of the electricity sales period of the Feed-in Tariff system (FIT system) after 2019, and it is necessary to develop a control method of optimizing distributed energy systems to operate it more efficiently, such as operation method after the termination of the FIT system (No FIT), in addition to the operation method when using the FIT system. Herein we proposed various control methods using PV, BT, and FC, such that PV is the main power source. We also proposed a control method for optimizing the start/stop times of FC to operate the three energy resources more efficiently. We simulated the annual energy production/ consumption in a house by using this proposed method. Optimization of FC’s start/stop times improves various aspects of a co-operative system combining FC, PV and BT. Results of this case study showed the possibility of combining three energy resources efficiently by optimizing FC’s start/stop times.

When water in a pot is heated on a gas stove, heat transfer on the side of the pot was theoretically analyzed assuming that the convective heat transfer coefficient and the representative temperature of the combustion gas were known. The calculated pan side temperatures were in good agreement with the measured values. The amount of heat transferred by convection to the outer surface of the side of the pot is partly dissipated into the room by radiation, but most of it flows into the pot. Some of the incoming heat is transferred to the steam at the top of the pot, but most of it is transferred to the water. The amount of heat transferred depends on the water level in the pot. In addition, the heating power of the stove, the dimensions of the pot (diameter, height, and thickness), and the material and structure of the pot are factors governing the heat transfer performance of the pot. The results of a theoretical analysis incorporating these factors make accurately predict the heat transfer on the side of a pot heated on a stove.