Used for load leveling and as measures against instantaneous voltage drop, tested for DR and VPP
The NAS battery system in the on-site grid has been used to level the loads and to avoid the impacts of instantaneous voltage drop.
For load leveling (Fig. 9), the NAS batteries are operated according to the schedule in high-efficiency operation patterns and according to the schedule depending on the season, and the batteries are linked to other power sources at the center. The batteries also contribute to the improvement in the use rate of the gas power generation equipment and the effective use of the solar power generation systems.
As measures against instantaneous voltage drop, the impact on important research equipment that requires stability in power quality is minimized by using the instantaneous voltage drop compensation function of the NAS batteries (Fig. 10). The power supply to important equipment is switched from the grid power supply to the storage battery discharge power supply in a short time. Voltage drop in the important equipment at the center is reduced to about 6ms, responding to instantaneous voltage drop (that continues for about 70 ms) in the power grid.
Instantaneous voltage drop leads to incomplete test data and decline in test quality, requiring retesting in some cases. The purpose of the measures is to prevent such problems.
The company has also been conducting validation tests of VPP (virtual power plant) and DR (demand response) using NAS batteries and in collaboration with the TEPCO group.
For example, the company and the TEPCO group have been participating in the advanced control-type DR validation project since 2016. In fiscal 2016, the high-speed DR operation was successfully controlled with high accuracy at a rate reaching 92%, by automatic output increase control responding to commands from the closed communication network to NAS batteries 10 minutes in advance (Fig. 11).
The average error against the estimated DR output based on the standard value was maintained within ±5% by controlling fluctuations in load after DR operation by the NAS batteries.
NAS batteries have a certain level of discharge margin against the rated discharge pattern. The possibility of providing supply/demand adjustment capacity and reserve capacity to power transmission/distribution companies was proved by effective use of the discharge margin, according to the company.
During very cold weather from the end of January to early February in 2018, the output was actually increased by automatic remote DR command responding to the request of TEPCO to make adjustments (Fig. 12).
The supply/demand situation in areas covered by TEPCO was tight during this period. Responding to a request from TEPCO, the aggregator, remote DR commands were transmitted targeting six hours in total, three hours in the morning and three hours in the evening when the demand for power for heating increases, contributing to the improvement in the supply/demand in the areas covered by TEPCO by full automatic operation. The requests continued day after day, but the company could respond to them quickly, realizing speedy and reliable DR operations, according to the company.
As an operation model in the future, there is an effort to connect multiple nearby plants by a network (Fig. 13).
The off-grid "Kiyohara Smart Energy Center," where Tokyo Gas Co Ltd supplies electricity and heat to seven plants of three companies in the Kiyohara Industrial Park in Utsunomiya City, using five cogeneration systems of 6MW class, etc, is one of the examples. It is believed that moves toward networking multiple companies and plants for off-grid systems where only in-house power is used will be accelerated.