Modern flywheel energy storage technology uses composite materials with high tensile strength, which can withstand the centrifugal force generated by high-speed (tens of thousands to hundreds of thousands of revolutions per minute) rotation, and realize energy storage and release through electrical control of the speed. High-efficiency motor/generator design, contact bearing with extremely low friction coefficient or non-contact magnetic bearing can ensure that the storage efficiency of the flywheel body is higher than 85%.
The safe failure mode of flywheels is one of the future concerns. Technological progress has been very rapid in the past ten years. Foreign institutions that conduct flywheel energy storage technology research mainly include NASA Glenn Research Center in the United States, Active Power Company, Argonne National Laboratory, Beacon Power Company, The University of Texas at Austin, US-flywheel Co., etc., and Canada’s Flywheel Energy System Inc. ., Urenco inc., Flywheel Energy Storage for Wind Power Generation in Europe, FLYWIP and The New Energy and Technology Research Organization in Japan, Chinese research institutions mainly include Institute of Electrical Engineering, Chinese Academy of Sciences, Tsinghua University, North China Electric Power University, Beihang University, Nanjing University of Aeronautics and Astronautics, Hefei University of Technology, Huazhong University of Science and Technology, Northwest Nonferrous Metal Research Institute and Southeast University and other units.
Argonne National Laboratory in the United States and Edison Power Company cooperated in the flywheel energy storage experiment of SMB (Superconducting Magnetic Bearing). When the flywheel rotor weighs 0.32kg, the friction coefficient of SMB is only 3×10-7, setting a world record. The Lawrence Livermore National Laboratory (LLNL) in the United States is committed to the research of ultra-high-speed flywheels, and has developed a small vehicle-mounted flywheel module of 1kW·h for electric vehicles and a large flywheel module of 2~25kW·h for stationary power stations.
There are also Ashman Technology Corporation, AVCON, Power R&.D, Rocketdyne/Rockwell, Trinity Flywheels and American Flywheel Systems Inc. Based on the current technological status, the integrated ultra-high-speed flywheel system can achieve a specific energy of 10-150W·h/kg and a specific power of 2-10kW/kg. The ultra-high-speed flywheel (rotor diameter 20cm, height 30cm) developed by LLNL has a maximum speed of 60,000 r/min, an energy storage of 1kW·h, and a maximum output power of 100kW.
At the University of Texas Research Center (UT-CEM) in Austin, a composite flywheel (Table 1) was used on a city bus with non-contact magnetic bearings. The flywheel mechanism has the characteristics of small mass and high performance. The structure of the hybrid drive system used in the car is shown in Figure 1. After using the flywheel, fuel can be saved by 30%.
At present, FIAT has started to evaluate the practical performance of ultra-high-speed flywheels. The specific method is to install a hybrid energy source system using an ultra-high-speed flywheel as an auxiliary energy source for a lead-acid battery on an electric vehicle, and conduct experimental tests. The simulation results show that using this system can save 20% of energy. Further development of flywheel batteries focuses on optimizing the overall mass, volume and cost of the flywheel to the level of application in electric vehicles. But in any case, there is still a long way to go to apply ultra-high-speed flywheels to electric vehicles due to two major problems, namely gyro torque and prevention of failure.
Canadian FESI (Flywheel Energy Systen Inc.), established in 1993, is committed to commercializing flywheel technology, engaging in the design, manufacture, assembly and testing of flywheel components and components, and has developed a 50kW flywheel system for hybrid drive vehicles .
In the early 1980s, the Swiss engineering company Oerlikon successfully developed the first bus powered entirely by flywheels. The diameter of the flywheel is 1.63m, the weight is 1.5t, and the speed reaches 3000r/min. The car can carry 70 passengers and has a travel distance of about 0.8km. It is charged by the grid when parking at each station, and the flywheel needs to be charged for 2 minutes. The ultra-high-speed flywheel can be used for fixed energy storage systems (25kW·h capacity and 130kw power output) for electric power Vehicle charging. The reason is that the high power output capability of the flywheel reduces the peak power output of the power system and facilitates fast charging of the battery system. As a new type of fixed energy storage system, ultra-high-speed flywheels have attracted extensive attention for fast charging of electric vehicles, which are easier to implement than those used in on-board energy storage systems.
German experts Bornemann and others made an experimental prototype in 1994, and in 1997 they proposed the conceptual design of a 5M·.h/100MW superconducting flywheel energy storage power station. The power station consists of 10 flywheel modules, each module has energy storage of 0.5MW·h, a power of 10MW, a weight of 30t, a diameter of 3.5m, and a height of 6.5m. A synchronous motor/generator is used for power input and output.
In the early 1990s, Japan’s Institute of Superconducting Engineering reported an experiment in which a 100W light bulb was lit using the electrical energy stored in a superconducting magnetic levitation flywheel. Since then, Japan has expanded the energy storage scale of superconducting flywheels year by year, and has determined a corresponding research plan for the commercialization of superconducting flywheel energy storage devices. In 1993, Japan’s Shikoku Research Institute completed the basic design of a vertical flywheel energy storage power generation system using high-temperature superconducting magnetic bearings. The storage energy of this device is 8MW·h.
Figure 2 is part of a car that uses flywheel technology.
Read more: Detailed explanation of the structure and principle of the flywheel energy storage device