A team of mechanical engineers from the University of Alberta have proposed a concept that takes an old technology and applies it to a modern problem. The flywheel is a mechanical method for storing energy via a rotating disk. The engineers have shown that using flywheel technology could result in significant energy and cost savings if applied to systems such as the light rail transit (LRT) in Edmonton, Alberta.

The light rail transit (LRT) system in Edmonton, Alberta could incorporate flywheel technology to save energy and money.

Mechanical Batteries

A flywheel is a spinning disk, called a rotor, that stores kinetic energy as it rotates around a central axis. This rotational energy can then be converted into electrical energy, and by operating in a vacuum or using magnetic bearings to levitate the rotor, the rotor loses little energy to heat or friction. This makes flywheels effective as mechanical batteries.

The engineers examined applying flywheel technology to the LRT as a way to store energy generated during the train’s frequent passenger stops. Trains like the LRT are equipped with dynamic braking, which uses traction motors on the train’s wheels to allow for smooth stops. And even though decelerating the train generates energy, this energy is currently wasted as heat.

"Electric and fuel cell vehicles already implement regenerative braking in order to store the energy produced during braking for start-up, so why would trains not be able to do so?" asked researcher Marc Secanell.

The flywheel proposal would see the braking energy stored as mechanical energy in flywheels, which could be installed at each train station. When the train is ready to leave, the mechanical energy in the flywheels could be converted back to electrical energy to help power the train.

Illustration of power flow in the LRT flywheel concept. (Image courtesy of Energy.)

"It's difficult to use a conventional battery for this purpose," said researcher Pierre Mertiny. "You need to recharge and discharge a lot of energy very quickly. Batteries don't last long under those conditions."

But flywheels don’t suffer from this drawback. Furthermore, they offer appealing potential savings to a city’s public transit budget. For Edmonton’s LRT system, Secanell and Mertiny calculated energy savings of 31 percent and cost savings of 11 percent.

This concept is also being explored in Europe. "The city of Hannover in Germany is already testing flywheel technology for just this purpose," said Mertiny. "They have banks of flywheels at each station to capture and re-use the electricity generated when their trains come into the station."

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