Comparing Flywheel and Thermal Energy Storage Solutions

November 03, 2022

Flywheel vs Thermal Energy Storage Solutions

As more renewable energy sources like wind and solar power are integrated into our power grids, the need for energy storage solutions becomes increasingly important. Energy storage solutions allow us to store excess energy and release it when there is high demand, resulting in a more efficient and stable grid. Two popular energy storage solutions are flywheel and thermal energy storage. In this blog, we'll provide a factual unbiased comparison between these two solutions.

Flywheel Energy Storage

Flywheel energy storage uses the principles of kinetic energy to store and release energy. The system consists of a spinning rotor in a vacuum enclosure that is connected to a motor-generator. When energy is input into the system, the motor-generator spins the rotor at high speeds, storing the energy in the form of rotational motion. When energy is needed, the motor-generator slows down the rotor, converting the rotational motion back into electrical energy.

One major advantage of flywheel energy storage is its fast response time. Since there is no chemical reaction taking place, the input and output of energy can occur in a matter of seconds, making it an ideal solution for balancing the grid during short-term fluctuations in demand. It also has a longer lifespan compared to batteries, with an estimated 20-30 years of service.

However, one major downside of flywheel energy storage is its high cost. The vacuum enclosure and high-speed rotor require high-tech materials and manufacturing, making flywheel energy storage considerably more expensive than other options.

Thermal Energy Storage

Thermal energy storage, on the other hand, uses heat to store and release energy. The system consists of a storage tank filled with a heat transfer fluid, such as molten salt or water, that is heated or cooled during times of excess or low energy demand. When energy is needed, the hot (or cold) fluid is pumped through a heat exchanger, which transfers the thermal energy to a power cycle to generate electricity.

One major advantage of thermal energy storage is its low cost, as the materials required to build the storage tanks and heat exchangers are relatively inexpensive. It can also store large amounts of energy for longer periods of time than flywheels, making it an ideal solution for longer fluctuations in demand.

However, thermal energy storage does have a slower response time than flywheels due to the time required to heat or cool the storage fluid. It also has a shorter lifespan, with an estimated 10-20 years of service.

A head-to-head comparison

Feature Flywheel Energy Storage Thermal Energy Storage
Response time Fast, in seconds Slow, in hours
Lifespan 20-30 years 10-20 years
Capital cost High Low
Ongoing costs Low Low
Efficiency 85-90% 75-80%


In conclusion, both flywheel and thermal energy storage solutions have their advantages and disadvantages. Flywheel energy storage is best suited for short-term fluctuations in demand, while thermal energy storage is better for longer fluctuations. Flywheels have a longer lifespan, but thermal energy storage is less expensive. Ultimately, the choice between these two solutions will depend on the specific needs and constraints of each application.


  1. Energy Storage Association
  2. U.S. Department of Energy

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