It's a not a new battery or super-hot liquid salt . But while they are not the sexiest of innovative power solutions, there is much to love about flywheels. Yes, flywheels. The energy storage technology--rapidly spinning discs that can discharge their energy in a matter of minutes--has languished as the materials needed to use them to efficiently store and transfer energy were not up to snuff. But the benefits abound. No expensive batteries. Supplies are not mined and controlled by the Chinese government. And if they fail, the fallout amounts to scrap metal.
Now, advances in carbon fiber and magnetic bearings have put flywheel applications back on the table. Or, as it turns out, on wheels.
Automakers are beginning to install flywheel technology--in place of batteries--on new test vehicles. The technology has already done thousands of laps in Formula 1 racing cars by Ferrari, Renault, BMW, and McLaren  where it has been used to juice acceleration times, rather than save energy or cut pollution. But the same principles could apply to the family sedan: Volvo will be road-testing a car with the technology this fall.
The flywheels act much like a regenerative braking systems in hybrid-electric cars powered by batteries. Every time the driver brakes, energy is stored by spinning up the flywheel. Energy is returned to the wheels through a variable mechanical transmission or magnets. Newer systems overcome past problems with efficiency and weight by using vacuum-sealed carbon-fiber discs rotating on low-friction bearings or superconducting magnets. If successful, the devices are expected to achieve 60,000 rpm and put out 80 horsepower, while cutting fuel consumption by 20%. Volvo expects the flywheel cars to hit the road by 2013.
Cars aren't the end of the innovation line. Flywheels hold several advantages over electric batteries in general: They last years or even decades, store high amounts of energy, "recharge" (i.e. spin up) in several minutes, and require just a fraction of the space and cost to store the same amount of energy.
In fact, one of the nation's first flywheel power plants came online this June in New York. Beacon Power's 20 MW plant can quickly add or absorb energy from the grid using its 200 flywheels , avoiding construction of new fossil fuel plants and solving some of the problems of storing energy from renewables. Who knows what the application will be when flywheels really get revved up.
[Image: Flickr user loop_oh ]