University of Alberta mechanical engineering professors Pierre Mertiny and Marc Secanell are looking to make an old technology new again and save some money for transit train operators, such as the Edmonton light rail transit system while they do it.

“The flywheel is an old technology, but that’s partly what makes it so sensible,” says Mertiny. “Fundamentally, it’s a really simple technology. We already have everything we need.”

The two recently calculated that the use of flywheel technology to assist light rail transit in Edmonton, Alberta, would produce energy savings of 31% and cost savings of 11%. 

A flywheel is a disk, also known as the rotor, that rotates and increases its rotational speed as it is fed electricity. This rotational energy can then be turned back into electrical energy whenever it is needed. It is, in a sense, a mechanical battery. The system loses very little energy to heat or friction because it operates in a vacuum and may even use magnetic bearings to levitate the rotor.

In North America, high-capacity flywheels are also used in areas of high population density, such as New York, Massachusetts and Pennsylvania, to buffer electricity to prevent power outages.

Secanell and Mertiny examined the possibility of using flywheel technology to store energy generated when the city’s LRT trains decelerate and stop. Trains such as the LRT are designed with so-called dynamic braking, using traction motors on the train’s wheels, for smooth stops. But the deceleration generates energy, which needs to go somewhere.

“Electric and fuel-cell vehicles already implement regenerative braking to store the energy produced during braking for start-up, so why would trains not be able to do so?” says Secanell, whose research also focuses on fuel cell vehicle technologies.

Currently that electricity is considered “dirty” electricity because it is intermittent, and therefore, difficult to use. Conventional systems simply send the braking electric power to resistors on the train, which convert the electrical energy to heat that is then released into the air. A flywheel system would take the electrical energy and store it as mechanical energy. This mechanical energy could then be converted back to electrical energy when the train is ready to leave the station again.