For centuries, spinning wheels have been used to store energy. That’s how potter’s wheels work, with the energy in the disk helping maintain a consistent velocity. Flywheels are also key components of steam engines, where they convert energy from pistons into consistent rotational motion. Even toy cars with friction motors make use of flywheel technology.
But it is only recently that large cylindrical flywheels have been used to quickly store and release electric power, as a way to keep complex power grids in balance.
One Canadian company, Temporal Power Ltd., is on the leading edge of this technology, making flywheel storage devices that are now being used to add stability to Ontario’s electricity system. In a windowless two-storey building just outside of Harriston, Ont., 150 km northwest of Toronto, 10 of the company’s 4,000 kilogram solid-steel flywheels are sunk into cement vaults in the ground. Linked to the province’s power grid, they rapidly charge and discharge to help maintain the right balance of power as demand fluctuates.
These kinds of installations could become commonplace in the coming years, because every power grid in the world – and especially those with high proportions of renewable power – will likely need more means of fine-tuning the balance between electrical production and demand.
Temporal’s flywheels are, essentially, mechanical batteries that store power in the form of kinetic energy as they spin – unlike normal batteries that hold power as chemical energy.
A Temporal flywheel is “charged” using an electric motor that turns a huge rotating steel cylinder. The motor converts electric power to the mechanical momentum of the rotor, and the rotor speeds up. To release this stored power, the motor switches to become a generator, as the slowing rotor transfers its energy back into electricity.
A flywheel can almost instantaneously switch back and forth between loading up on power and releasing it – a characteristic that makes the technology attractive to electrical system operators that constantly need to balance supply and demand.
“We respond to a grid-wide imbalance of energy,” said Temporal chief executive officer Cam Carver. “Sometimes you have too much and you want it off, sometimes you have too little and you want more. It’s a constant balancing act.” Flywheels are ideal for this delicate task, he said, and they operate will little power loss.