Flywheel Energy Storage at Supersonic Speed

Beacon Power Corp. says it has a better idea: massive rotating flywheels that store power like giant alkaline batteries spinning at twice the speed of sound. _BostonGlobe

Flywheel storage stores energy in kinetic form--rapidly spinning wheels, ready for almost instant tapping in case of power failure. But the problem with them is their lack of energy density: they simply cannot hold enough backup energy for more than a short period of time. Rotating energy is defined by its mass and rotational speed. Beacon's flywheels weigh 2500 pounds, but it is Beacon's higher speeds that pack the power:

Beacon Power flywheels are 2,500-pound cylinders made of carbon fiber and fiberglass, and bonded with epoxy. Each is mounted on bearings that generate a magnetic field to support the flywheel, so it floats inside its steel casing. Friction is almost nonexistent. When the flywheel is spun to its full speed of 16,000 revolutions per minute, it can store the energy for hours with little loss.

"The surface speed on this thing would be Mach 2," or twice the speed of sound, Capp said. But these flywheels don't generate a sonic boom, because they operate in a vacuum to reduce friction even more.

At the base of each flywheel is a motor-generator system like those found in hybrid cars. When electricity is added to the system, it acts as a motor, speeding up the rotation. To release power, the system acts as a generator, translating the rotation to electric power and feeding it into the grid....Each flywheel can store enough power to run a typical US home for a full day. But they cost $200,000 apiece, and while Capp hopes to cut the cost to $100,000, they're still far out of the average consumer's price range.

Instead, Beacon Power hopes to address a constant nuisance for electric utilities: precise regulation of power.

...Beacon Power plans to build storage arrays, with dozens of flywheels buried underground inside vaults made from concrete sewer pipes.

A standard shipping container stuffed with computers and power cables controls the array and links it to the electrical grid.

When there's extra power available, Beacon Power would buy it and use it to spin the flywheels. When the grid needs an extra burst of juice, the flywheels can convert the stored energy back into electricity, which is resold to the power network.

"You can almost think of it as recycling electricity," said Gene Hunt, company spokesman. Beacon Power would make its profit by charging a fee for its power regulation service.

Utility load leveling is an incredibly important task. Without utility-scale storage devices, power distribution can be extremely tricky and prone to errors.

In safety terms, it is a good idea for them to bury these massive speedy spinners underground in strong concrete vaults. I wouldn't want to be around when one of these giant tops explodes.

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Can you find the error in this NextEnergyNews article?

The company currently building a massive commercial scale system that is capable of storing 5 million watts of power.

Absolutely right! One can supply 5 mega watts of power, but one cannot store 5 mega watts of power. One stores mega watt hours, not mega watts.