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Flywheel Energy Storage Basics

Mark Robinson

For several years, I worked as a consultant for Beacon Power System. Their model involved using flywheels buried in residential lawns to store energy from solar systems and use it as a battery. They also promoted flywheel storage at remote locations such as cell phone towers.

One of the more exciting applications was in Subway systems and roller coasters. As the vehicle was breaking, the breaking energy would be used to wind the flywheel, which could then be used to accelerate.



Flywheel energy storage (FES) is a technology that stores kinetic energy through rotational motion. The stored energy can be used to generate electricity when needed. Flywheels have been used for centuries, but modern FES systems use advanced materials and design techniques to achieve higher efficiency, longer life, and lower maintenance costs. This paper will discuss the basics of FES, its advantages and disadvantages, and its applications in various fields.

Principle of Flywheel Energy Storage: A flywheel is a rotating disk or cylinder that stores kinetic energy. When energy is input into the flywheel, it starts spinning, and the kinetic energy is stored in the form of rotational motion. The amount of energy stored in the flywheel is proportional to the mass and the square of the flywheel’s rotational speed. The formula for calculating the kinetic energy of a flywheel is as follows:

KE = 1/2 * I * w^2

KE is the kinetic energy, I am the moment of inertia, and w is the angular velocity.

Advantages of Flywheel Energy Storage:

  1. High Power Density: FES has a very high power density, meaning it can quickly deliver much energy. This makes it suitable for applications that require high power output in a short time, such as uninterruptible power supply (UPS) systems and electric vehicles.
  2. Long Life: FES systems have a long lifespan because no chemicals are involved, unlike batteries. The mechanical components of a flywheel are designed to withstand high stresses and can last for many years.
  3. Low Maintenance: FES systems require minimal maintenance compared to other energy storage technologies. No chemicals are involved, so there is no need for periodic replacement or disposal of hazardous materials.
  4. Environmentally Friendly: FES is a clean technology that does not emit pollutants or greenhouse gases during operation. It is a sustainable and environmentally friendly way of storing energy.

Disadvantages of Flywheel Energy Storage:

  1. High Cost: Manufacturing and maintaining FES systems is relatively high compared to other energy storage technologies.
  2. Limited Energy Storage Capacity: FES systems have a limited energy storage capacity compared to other energy storage technologies. They are best suited for applications that require short-term energy storage and quick power delivery.
  3. High Energy Losses: FES systems have high energy losses due to friction and air resistance, which can reduce the system’s overall efficiency.

Applications of Flywheel Energy Storage:

  1. Uninterruptible Power Supply (UPS) Systems: FES can be a backup power source in case of a power outage. The high power density of FES makes it suitable for providing emergency power to critical facilities such as hospitals and data centers.
  2. Electric Vehicles: FES can be used as a storage device in electric vehicles. FES’s high power density and fast charging capabilities make it an ideal candidate for providing quick bursts of power to electric cars.
  3. Renewable Energy Integration: FES can integrate renewable energy sources into the grid. The variable nature of renewable energy sources can be balanced by using FES as a buffer to store excess energy during periods of low demand and release it during periods of high demand.
  4. Spacecraft: FES has been used in spacecraft for attitude control and stabilization. The high energy density and low maintenance requirements make it an attractive energy storage option for spacecraft.

Conclusion: Flywheel energy storage is a promising technology with many advantages over other technologies. It is a clean, sustainable, and environmentally friendly energy storage method. Although FES has some disadvantages, such as high cost and limited energy storage capacity, its high power density and long lifespan make it an attractive option for


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