Up to about 800 DC-powered LED lights are installed in places where people often enter and exit, which is probably the first in the world" (Tian Lu He Xing, Director of the Department of Environmental Science, Graduate School of Tohoku University, Japan).
DC emergency switch panel
The Department of Environmental Science, Graduate School of Tohoku University, Japan, aims to achieve energy conservation in real estate and power generation during disasters. In this school building, a combination of solar cells, batteries and DC power supply technology was introduced. Hybrid control system" Note 1). The system has been in operation since the end of November 2012 (Figure 1).
Figure 1: 60kW solar module and DC-powered LED lighting
Tohoku University of Japan is equipped with a 60kW solar cell module (a) on the roof of the manufacturing building. In the future, it is planned to install pipes for water-cooling of solar cells during the summer. 800 DC-powered LED lights (b) are installed in the main building and the teaching building.
The system is mainly composed of a 60kW solar cell module and a 57.6kWh large-scale power storage system. It also includes an AC/DC hybrid control system that can supply 300V DC (DC) and 100V or 200V AC (AC), as well as the entire system. Implementation of the management of "EMS (Energy Management System)" and so on.
The power generated by the solar cell is not sold, but is directly used for the battery to be consumed by the home. In addition, it aims to quickly charge an electric vehicle (EV) with the goal of energy movement in an emergency. The solar cells are placed on the roof, and the battery and AC/DC hybrid control system are placed on the main building. DC power is supplied to the 6-story main building and the teaching building, and about 800 LED lights supporting DC 300V are introduced.
Equipped with approximately 10,000 battery cells
Solar cell modules, high-voltage DC power systems, and LED lighting that supports DC power are handled by Taiwan Electronics Corporation of Delta Electronics. LED lighting is used after stepping down from 300V to 24V through an internal DC-DC converter. The opening and closing operations prevent the risk of electric shock by controlling the low voltage portion of the DC-DC converter instead of the power line with a switch.
Large power storage systems were developed by Sony (Figure 2). The system consists of eight 7.2kWh power storage units. The power storage unit consists of a control unit that controls the power storage unit, an 8kW AC-DC converter, a 10kW DC-DC converter with MPPT for solar cells, a battery management system that monitors the battery unit, and six 1.2kWh power storage units. Module composition.
Figure 2: Setting up a 57.6 kWh power storage unit
Eight power storage units are installed on the first floor of the main building. Each unit is 7.2kWh. The power storage unit is equipped with six 1.2kWh power storage modules.
The characteristics of the power storage system are that the power storage units can be independently controlled one by one, and the entire system does not need to be stopped during maintenance and addition. It is equipped with approximately 10,000 cylindrical battery cells with a diameter of 28mm. The positive electrode material uses lithium iron phosphate (LiFePO4) which is excellent in safety.
The AC/DC hybrid control system also improves redundancy in case of an emergency (Figure 3). An emergency switcher including a power switch (DTMC) and an electromagnetic contactor (MC) for switching power in an emergency. In addition to the ability to input the power of the solar cell, AC current can be input from single-phase and three-phase commercial power sources, and DC-driven LED illumination can be used for AC input, and an emergency AC-DC converter is provided. The construction of the control system and various wirings are handled by Japan Systema.
Figure 3: AC/DC hybrid control system supporting both AC and DC
The solar cell is directly connected to the battery in a direct current manner. It can supply 300V DC to the LED lighting at the load end and supply 100V AC (a) to the common socket. Power supply (b) can be supplied from a commercial power source using a power switch and an electromagnetic contactor in an emergency.
EMS was developed by NTT and NTT COMWARE. The EMS is composed of an "adaptive function unit" that collects data from various devices, an "optimal control function unit" that performs device control and device monitoring, and a "visualization function unit" that "predicts the generation of predicted data and visualizes energy". In terms of visualization, it is planned to switch from the current display to a new display device using a digital signage and a space recognition interface, and the power storage unit disposed on the arc will be used as a screen.
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