## 1 Introduction  
Reducing greenhouse gas emissions is an urgent issue as a measure against global warming [1]. To solve the problem, it is indispensable to introduce a large amount of renewable energy such as solar power generation and wind power generation [2, 3, 4]. However, the mass introduction of renewable energy makes it difficult to balance the power system. It has also been pointed out that restrictions on the power system are becoming apparent, such as surplus power generated during the interim period when power demand is low. Energy management that includes time shifts, such as dispersion of power demand in consideration of the balance between power supply and demand is required [5; 6]. [PERSON] et al. [2] analyzed how to use solar energy efficiently. In the future, it is necessary to analyze the optimal operation method for technical and economics. [PERSON] et al. [5] analyzed the demand-side management (DSM) overview and provided the optimal solution. [PERSON] et al. [3; 6] examined renewable energy optimal operation such as wind power and photovoltaic (PV) in Denmark, and proposed optimal systems for efficient energy supply. These previous studies have not examined the introduction of a heat storage system. In the future, the introduction of power storage systems and heat storage systems is expected [7; 8; 9]. The introduction of a power storage system is considered to be an effective solution, but there are still many problems in terms of installation cost and energy loss [10; 11]. Under these circumstances, attention to heat storage systems is regaining attention. Until now, heat storage systems have aimed to save costs by storing cold and hot heat for air conditioning with inexpensive electricity at night and using it in the daytime. In the future, the surplus electricity in the daytime will be used to store cold and hot heat for air conditioning and will be used during cloudy hours and at night when sufficient electricity from sunlight cannot be obtained [12; 13]. Therefore, it is expected to work as an adjustment device that shifts the time of power supply and demand [14]. Water thermal energy storage (WTES) systems are the most widespread and serve the function of adjusting electric power [15]. The WTES system has been introduced to reduce power consumption during peak hours in the daytime by using it as a daily heat storage system that stores heat at night and dissipates heat in the daytime [16]. In addition, since the heat source machine can be operated at full load operation at night and heat can be stored in a short time, the efficiency of the heat source equipment can be improved and the operating time of the heat source primary pump can be reduced. In some cases, energy saving can be achieved [17]. On the other hand, aquifer thermal energy storage (ATES) systems that store heat in strata surrounded by groundwater such as sand layers, which have relatively high permeability in the ground, are beginning to spread mainly in Europe and the United States [18; 19; 20]. Similar to the conventional WTES system, this system stores cold and hot water at night and performs heat utilization operations in the daytime. In addition, it stores hot heat in summer and uses it in winter. It is also possible to directly use the groundwater in the aquifer. The ATES system and the WTES system also use water as a heat source. In the WTES system, a tank is installed in the underground space of the building to store heat and dissipate heat. The ATES system performs heat storage and heat utilization operation for underground strata. The ATES system has a larger capacity than the WTES system and has the advantage of using geothermal heat. Disadvantages include heat loss due to groundwater and the presence or absence of an aquifer. The ATES system can be expected as a measure against the heat island. However, it is important to manage the groundwater because it uses the groundwater directly.