Recently, application and control technology of battery energy storage systems (BESS) in the power systems have made remarkable progress due to advance in the storage battery technology and rapid penetration of the variable renewable energy sources, such as photovoltaic generations and wind turbines. As a countermeasure to the issues caused by high penetration of variable renewable energy sources, a considerable number of demonstration projects on BESS for the power systems have been conducted domestically and overseas. In these projects, the results have been steadily achieved, and some have already been utilized for the power system operation. In this context, the application of BESS in the power system is considered to shift from the trial to the practical phase and is expected to increase in the near future. Hence in this paper, the background of the installation and the application purpose of BESS to the power system and the trends of applied technology to the power system are overviewed.

The installation of renewable energy (RE) power plants, such as photovoltaic power and wind power, is rapidly increased in recent years. The following problems are assumed because the power output fluctuates enormously by a change in weather. One is a problem of short period fluctuation that it is difficult to keep frequency constant, because the output fluctuation of RE increases, on the other hand, the load frequency control (LFC) plants decrease. The other is a problem of long period fluctuation that the surplus electric power occurs in the daytime by the increase of PV. Tohoku Electric Power Company began to operate a large scale battery system (BESS) in Nishi-Sendai substation in February, 2015, and is working on the verification project which inspects the expansion effect of the frequency coordination by the BESS as a frequency fluctuation measure. This paper describes the outline of frequency control and the control effect by the BESS.

This paper presents the operation and planning method of Battery Energy Storage System (BESS) for leveling of the distribution transformer load. The proposed method makes an operation schedule of BESS considering next day's forecast data of PV output and load, and operate the BESS based on the planned schedule. Furthermore, in order to compensate the forecast error of PV output and load, the proposed method revises the operation schedule of BESS considering accumulated forecast error of distribution substation load. The validity of proposed method is shown by numerical simulation analysis and experimental results.

Recently, the introduction of photovoltaic generations has greatly increased. The fluctuation of PV output has a large influence on power flow followed by voltage fluctuation. In order to overcome this situation, we introduced a battery system which has ability to control active and reactive power outputs. This battery system is installed into distribution system to reduce short-term voltage fluctuation. This research confirmed effectiveness of the battery system and evaluated battery life cycle. Also, this battery system was installed to Shimoze distribution substation, where 1,000kW PV plant and household PVs are connected. This paper is a summary of this research which covers the result of field test of the battery system and battery life cycle estimation.

In Kyushu area, renewable energy, mainly consists of PV, has been introduced rapidly. Therefore, as for dispatching operation, a risk that renewable energy should be suppressed because of restrictions of thermal plants' minimum operation is growing faster than ever especially during light demand daytime. To avoid this risk, in March 2016 we constructed Buzen Battery Substation and installed a large scale battery system (output: 50MW × 6 hours, capacity: 300MWh) featured NAS batteries. We implemented verification study by operating NAS battery system's function similar to a pumped storage plants aiming to avoid maximally 300MWh suppression of renewable energy per day by establishing its operation method to improve the energy balance. As a result, we verified that NAS battery system has ability to charge/discharge 300MWh energy safely and to control the grid voltage by changing reactive power output.

High penetration of intermittent renewable energy such as photovoltaic (PV) and wind power could cause shortage of power system flexibility. Demand response is expected to help supply ancillary service instead of the conventional power plant. Commercial air conditioners are a promising responsive load for demand response because they account for a large proportion of power consumption in the power system. We calculate a system operation cost and hourly operation pattern of each power plant by using the optimal power generation model considering flexibility supply from controlling commercial air conditioner. We obtained the following results as an effect of commercial air conditioner control. (1) The power generation of oil-fired power plants decreases at peak time and annual fuel cost of oil-fired plant is reduced by approximately 30% at most in Kanto area. (2) The percentage of rated operation mode of LNG combined cycle plants increases. (3) Curtailed energy rate of PV decreases because a power storage amount by pumped hydro power generation increases. (4) Required battery capacity to reduce PV curtailed amount decreased by combining battery energy storage system in case of high penetration of PV.

Recently, the penetration of the renewable energy has been increasing. Especially, the wind power generation has focused as the technology to solve environmental problems. However, the high penetration of wind farm (WF) may have a bad influence on the power system, caused by the fluctuating power outputs. This paper proposes the scheduling operation method of WF to deal with ramp events in order to dispatch power stably and deliberately, using a battery energy storage system (BESS). And the evaluation of the BESS capacity clarifies the required BESS capacity for this method.