Better magnets will help to store fluctuating energy from solar cells and wind turbines in flywheels. The process may help to remove one of the major barriers to further increasing the deployment of renewable energy.

Energy storage is one of the 21st century’s biggest challenges, and it is a precondition for being able to exploit the full potential of renewable energy in the energy supply system. One solution could be to store energy from sources such as wind turbines and solar cells as kinetic energy in flywheels. This will mean that electricity is available when the sun is not shining and there is no wind.

Aarhus University researchers and a number of private companies have now joined forces to optimise and further develop the technology.

“The project works using the principle behind a flywheel, whereby we keep a heavy cylinder floating in a vacuum-filled container by means of a magnetic field. Electrical energy from a wind turbine, for example, can be used to set the flywheel in motion. As long as the flywheel is rotating, it will store the energy that initially started it,” says Associate Professor Søren Peder Madsen.

The kinetic energy can later be converted into electrical energy when it is needed, and the flywheel can function as a storage facility for the fluctuating solar and wind energy.

The company WattsUp Power has designed the flywheels, so that they hover on magnetic bearings with no air resistance. This reduces the energy loss in the storage technology to an absolute minimum.

Compact and environmentally friendly
Research circles call the flywheel technology Flywheel Energy Storage (FES), and it has been well known for many years. In fact, it is already being used at some locations in the US: among other things to even out fluctuations in the power supply in New York.

The advantage of the technology is that the flywheels can “charge up” very quickly and then release large quantities of energy very rapidly. The researchers expect that, in the future, they’ll be able to get the flywheels to last for far longer than the batteries available today.

Furthermore, the materials in the flywheel have less impact on the environment and, in principle, they can be recycled infinitely. They don’t take up a great deal of space: a 30 kWh installation, corresponding to the consumption of a detached house with solar cells on the roof, is approximately the size of a small refrigerator.

However, Søren Peder Madsen stresses that there is still one significant obstacle to overcome before the technology can make a significant contribution to meeting our storage needs.

“At the moment the flywheels lose energy too quickly to be useful storage. They self-discharge far too much, but we’re working on the problem, and we’re aiming at making them a real alternative to modern batteries.”

Small magnets with a difficult job
Researchers in the project want to improve the technology by holding the flywheel’s floating cylinder in the air with new nanomagnets, all the dimensions of which, from atomic structure level up to millimetre scale, have to be controlled with great precision. Researchers expect that this will enable them to generate storage potential for up to two days.

“We hope that we can crack the code to cheap and efficient energy storage. This is absolutely crucial if, in the long term, we’re to become independent of fossil fuels such as coal, oil and gas,” says Søren Peder Madsen.

He is in charge of the development of numerical methods to calculate the composition of the new materials to improve the properties of the magnets.

“We need to develop algorithms that can calculate the best material combinations in the magnets and in the flywheel. The aim is to make sure they can keep the floating cylinder in the air and, at the same time, tolerate rotating at up to 100,000 rpm. The quicker we can get the wheel to rotate inside the airtight box, the more energy we can store,” he says.

Researchers from Aarhus University are working with the companies Haldor Topsøe and Sintex on developing the small magnets.