To store energy is necessary for both the power grid and the future of electric cars.

The regulation of renewable energy

A gyroscope demonstrates the principle of motion conservation.

As energy sources with unequal power are increasingly exploited, such as wind power, the need for regulating this power becomes increasingly important.

The fact that wind power is dependent on wind conditions means there are sometimes surpluses and sometimes deficits.

For example, if wind power is at a deficit, energy can be taken from hydropower, whose reservoirs filled up when wind was at a surplus.

But hydropower, nuclear and other energy sources that have a smoother power output have a limited capacity to handle uneven production. Both hydro and nuclear power have, for political reasons, been subject to restrictions that make it unrealistic to continuously improve their capacities.

It may therefore be necessary to seek new solutions for energy storage during times when production is high, and then use this energy when production is lower.

Energy storage for a green vehicle fleet

Effective methods for energy storage are not just necessary to facilitate frequency regulation in the electricity grid. Even higher demands are imposed on mobile storage devices for use in, for example electric cars. The ability to store a large amount of energy with as little loss of energy as possible is crucial to increase the electric car’s range and make it competitive with gasoline and diesel cars.

Flywheels can be the solution

To store energy by using flywheels may be a potential solution to the two problems mentioned above. The principle of flywheels: the more energy that enters the system the faster it rotates. And when energy is extracted, the rotational speed decreases.

The most advanced systems have blades made of composite materials and magnetic bearings that rotate at speeds of 20,000 to 50,000 revolutions per minute. Such systems can be maximally charged in a few minutes and have an energy efficiency of up to 90 percent. Energy efficiency is the ratio of energy that can be taken out of the system in relation to the energy supplied to the system.

Flywheels in cars and fusion reactors

Flywheel technology can be used in various scales.

For example, the Tokamak reactor at the JET fusion facility in England uses two flywheels that weigh 775 tons each and can rotate up to 225 revolutions per minute. Minutes before full-scale experiments are carried out at JET, power from the grid is used to accelerate the flywheels. This large amount of energy is then released in a short amount of time to carry out the experiments.

Flywheels can also be used on a smaller scale to store energy in cars for example. Their long lifetime, short charge time and high efficiency are what makes flywheels beneficial.

Pros and cons

Flywheels are potentially very environmentally friendly and enable the efficient storage of energy. In addition, they can be built with harmless materials and without hazardous chemicals. Energy efficiency is important in an energy system where there is still a deficit of renewable energy sources.

One disadvantage is the potential safety risks that arise if a flywheel is loaded up with more energy than its components can handle. Such a scenario could result in an almost explosion-like event, which requires security walls thus increasing the weight of the unit.

There are also continuing challenges to minimize energy losses due to friction. Classic ball bearings have proved relatively ineffective, while magnetic bearings in a vacuum have been shown to meet the challenge better.

Another challenge is to avoid a destructive gyro effect when the flywheel is placed in a vehicle. They should be mounted on the moving axes in the vehicle to minimize the gyro affect on the vehicle’s handling.

Flywheel technology can be used both as an energy storage system and as a frequency regulator in large grids. We will certainly be hearing more about flywheels in the future.

The article was published in November 2011