Flywheel energy storage, an innovative mechanical energy storage method, will hold a significant position in the future energy storage field due to its unique energy conversion principles and wide application prospects.
What is Flywheel Energy Storage?
Flywheel energy storage technology uses reversible bidirectional motors (electric motor/generator) to facilitate the conversion between electrical energy and the mechanical energy of a high-speed rotating flywheel. The system stores kinetic energy through the flywheel’s rapid rotation and converts kinetic energy into electrical energy through an electric generator coaxially aligned with the flywheel.
Please read this article for a simple explanation of the Flywheel Energy Storage.
Principles of Flywheel Energy Storage
Energy Storage Phase: During the storage phase, the flywheel accelerates through an electric motor or other means, converting electrical energy into mechanical energy that is stored in the flywheel. The higher the flywheel’s rotation speed, the greater the amount of energy stored.
Energy Transfer Phase: When energy release is needed, the flywheel begins to decelerate and converts the stored mechanical energy back into electrical energy. In this phase, the mechanical energy within the flywheel is transformed into electrical energy through the generator and is supplied to the grid.
Control Phase: During the operation of the flywheel energy storage system, precise control of the flywheel’s acceleration and deceleration is necessary. The control system monitors the differences between the electrical grid’s load and supply, adjusting the flywheel’s rotation speed to maintain the stability and balance of the grid.
Advantages of Flywheel Energy Storage
Currently, flywheel energy storage is considered a new technology in the energy storage industry, demonstrating unique advantages in many areas, making it one of the most promising short-term high-power energy storage technologies:
| High Energy Density and Instantaneous Power: Flywheel energy storage technology has a very high energy density, approximately 100–130 W·h/kg, or 360–500 kJ/kg.
| Long Lifecycle: Throughout its entire lifecycle, overcharging or over-discharging does not affect the energy density and lifespan, and the flywheel is not subject to damage.
| High Energy Conversion Efficiency: The efficiency generally reaches around 90%, meaning more usable energy and less heat dissipation, higher than that of chemical batteries.
Components of a Flywheel Energy Storage Device
A flywheel energy storage device mainly consists of the following core components:
| Flywheel Body: The core component of the storage system, usually made of high-strength carbon fiber composites to increase the ultimate angular velocity and reduce weight, maximally storing energy.
| Bearing System: The role of the bearing system is to support the flywheel rotor, reducing frictional resistance and ensuring efficient and reliable operation. Common types of bearings include magnetic bearings, which can significantly reduce mechanical losses.
| Electric Motor/Generator: Integrated as a single component, it is responsible for the conversion between electrical energy and mechanical energy. In storage mode, the motor drives the flywheel to accelerate its rotation, converting electrical energy to mechanical energy for storage; in release mode, the motor operates as a generator, converting the stored mechanical energy back into electrical energy for external loads.
| Power Conversion Device: This device enhances the system’s flexibility and controllability, processing the output electrical energy from the flywheel energy storage system into frequency conversion, rectification, or constant voltage to meet different load requirements.
| Vacuum Chamber: The vacuum chamber primarily provides a vacuum environment to reduce aerodynamic losses when the motor operates, thereby improving the overall system efficiency.
Role of Magnetic Bearings in Flywheel Energy Storage Devices
Types of Magnetic Bearings
| Passive Magnetic Bearings: Permanent magnetic bearings are a type of passive magnetic bearing that uses permanent magnets to suspend two or more magnetic rings axially or radially. With the ongoing development of permanent magnets in recent years, their load capacity has significantly increased, leading to broader applications.
| Active Magnetic Bearings: Also known as electromagnetic bearings, these control magnetic field changes by altering the on/off state and magnitude of current in the control circuit, utilizing real-time feedback position signals and output current signals to adjust control currents quickly, allowing stable suspension between the stator and rotor.
Requirements for Permanent Magnets
| High Magnetic Energy Product: Magnets are required to have a high magnetic energy product to achieve sufficient magnetic field strength and force in limited space.
| Thermal Stability: Since the rotation of the flywheel generates heat, magnets need to maintain stable magnetic properties in high-temperature environments to prevent demagnetization or performance degradation.
| Mechanical Strength: Magnets must possess sufficient mechanical strength to withstand potential mechanical forces during installation and operation.
The commonly used permanent magnet materials in flywheel energy storage magnetic bearings mainly include neodymium-iron-boron (NdFeB) magnets. This material is well-suited for use in magnetic bearings within flywheel energy storage systems due to its high energy density and excellent magnetic performance.
Applications of Flywheel Energy Storage
Due to its advantages of high power density, high efficiency, long lifespan, and pollution-free operation, flywheel energy storage is now widely applied in high-power, fast-response, and frequent-use scenarios.
| Energy-saving Equipment for Rail Transit: The high power density and efficiency of flywheel energy storage perfectly align with rail transit systems, substantially exceeding the energy-saving effects of other energy-saving equipment. In urban rail transit operations, electricity accounts for about 40% of operational costs, with train traction power constituting 45%-60% of total electricity costs.
Of this, 17% is recoverable regenerative braking energy. However, the regenerative energy recovery in current urban rail systems is generally dissipated using resistive methods, which results in resource waste and impacts the grid. Utilizing flywheel energy storage devices can achieve a 15% reduction in traction energy consumption.
| Uninterruptible Power Supply (UPS): In power systems, there are many users with high-quality energy demands, such as semiconductor manufacturing, banking computer systems, and communication systems. To ensure a continuous and reliable power supply for these users when external grids are disconnected or the power quality is abnormal, flywheel energy storage UPS systems can be equipped.
| Balancing and Regulation of Renewable Energy: Renewable energies such as wind and solar are often unstable due to their dependence on natural environmental conditions. Flywheel energy storage can quickly respond to these fluctuations, balancing power output in a short time and enhancing the reliability of integrating renewable energy into the grid.
Magnetic Bearings Provider
At Tengye, we’re thrilled to be early participants in your new projects and new research. Our passion for magnets extends from material selection and design optimization to providing magnetic solutions. We hope to bring our knowledge and experience to the forefront by actively engaging in your upcoming projects. Work with our magnet experts to get the right magnet solution.
Image Source: Greyviews & Ieso & Researchgate & VYCON & Waukbearing
