Honda Uses 100MWh NAS Battery for Grid Stabilization (2)
Continued from Honda Uses 100MWh NAS Battery for Grid Stabilization (1)
Incorporates gas engines and VOC generator for optimum control
The center incorporates a cogeneration system using gas engines and a volatile organic compound (VOC) generator, in addition to solar power generation systems and NAS batteries.
It took about 10 years for the company to thoroughly understand the issues on actual use of NAS batteries on site, which even manufacturers do not notice, according to the company (Fig. 5).
When the NAS batteries are fully discharged during peak power consumption hours in summer, the output has to be limited for several hours immediately after discharge because of the batteries heating. The center has been searching for a solution regarding what should be done to optimize the use of the batteries in collaboration with other power sources at the center while considering the risk of excessive demand.
Because NAS batteries are operated at a high temperature of 300°C, consideration should be given to the loss due to electric heaters. In terms of the environmental value, the loss is the factor that increases the power cost and carbon dioxide (CO2).
In consideration of this factor, the company expects that the NAS batteries can be used for absorption and leveling of excess power as measures against output control such as the one implemented in the Kyushu region, in combination with solar power generation systems.
Maintenance of the NAS battery system includes inspection of inverters and cleaning of filters. Maintenance is performed in the seasons when the demand for power is low because the operation needs to be stopped in the meantime. The batteries are divided into three blocks with 4MW of output each, and operation of the blocks is stopped one by one for precise inspection, etc. The NAS battery system is operated under a 15-year lease contract.
The company uses four gas engine cogeneration units (Fig. 6). The outputs are 7MW, 1.252MW, 550kW and 55kW, respectively. The systems are introduced under a 15-year energy service contract with Tokyo Gas Engineering Solutions Corp (TGES) of Minato-ku, Tokyo, and the power and steam are purchased. The systems contribute significantly to CO2 reduction because the waste heat can also be used.
In gas cogeneration, the efficiency is the highest when the engine continues to turn at the maximum output, contributing to reducing environmental loads. For this reason, the systems are operated on weekdays from Monday to Friday at the maximum output by weekly start-stop (WSS) continuous operation, and the operation is stopped on weekends and consecutive holidays.
Gas engine generators need to be stopped for about one month every several tens of thousands of hours for a full overhaul, in addition to the need for routine oil replacement and plug replacement. Because the output is high, the power received from the TEPCO group increases than usual during the inspection. Periodic inspections are performed by arranging them in advance to avoid consumption of power exceeding the amount agreed with TEPCO.
The VOC generator features an output of 300kW and uses waste gasoline as the fuel (Fig. 7). The VOC generator and the solar power generation systems are owned by the company. The basic design of the VOC generator was prepared by the Japan Aerospace Exploration Agency (JAXA), and the generator was manufactured by IHI Power Systems Co Ltd. It was introduced in 2003 and is currently in operation.
The power consumed at the center is purchased and supplied from the four power generation and storage systems, as well as the TEPCO power grid.
The on-site smart grid is constructed via the Community Energy Management System (CEMS), which combines the systems and optimally controls and manages them. High-efficiency and stable energy consumption is realized by the CEMS (Fig. 8).
All electricity at the center is centrally controlled, starting from power generation to storage in batteries and reception of power from the grid. The energy consumed by each of 10,000 to 20,000 lights and power supplies to the equipment in all buildings is measured.
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.