Gray's design also makes it easier to control the possible failure of its most critical parts: the wheel itself and the bearings. Because the flywheel is a bundle of thousands of fibers, if one fiber breaks, it will just wiggle out of the bundle rather than directly stressing the rest of the wheel and causing it to break. The flywheel would simply "shed" lightweight material.
For the bearings, the Velkess uses "angular contact ceramic hybrid" (silicon nitride) ball bearings running in a stainless steel track, where both the bearings and the thrust load are floating on magnets. If the bearings began to fail, the heat they generate would be detected early on by a simple temperature sensor.
Either type of failure could be easily detected long before a catastrophic event, allowing the device to throw a warning and trigger a shutdown. In an off-grid shutdown the device would discharge hot air until it spun to a stop—roughly equivalent to a 1,500-watt hair dryer running for 10 hours. In an on-grid application, it could simply dump the power to the grid.
The whole device is contained in a vacuum-sealed steel box with about the same footprint as a household refrigerator, only a bit shorter. The flywheel itself is about 66 by 66 centimeters in height and diameter, and weighs about 340 kilograms.
It will be optimized to provide up to three kilovolt-amps of continuous power output at 27 amps, but can handle higher "burst" power loads that occur when heavy-draw appliances like water pumps and circular saws start up. The unit could discharge at any rate up to three kilowatts until the flywheel spins down to its "fully discharged" speed of 9,000 revolutions per minute.
Gray intends to target the 48-volt off-grid residential market initially, where the Velkess would be a drop-in replacement for typical 48-volt battery systems. After that would come the 240-volt residential and small commercial markets, where the Velkess could provide the backup for grid-connected solar PV systems when the grid goes down. Eventually he hopes to get into the 600-volt utility-scale solar market.
Velkess could succeed where Beacon failed on several counts. The latter device, like most of its competitors, could only discharge large amounts of power for very short durations, whereas Gray's would do the opposite: It could discharge as slowly as needed for hours. And where Beacon's system was so expensive that it only really made sense for industrial applications, Gray's would be cheap enough to make good economic sense in the residential and small commercial markets.
Further, the Velkess satisfies the final crucial factor for electrical storage—scaling. Multiple units can be linked together in parallel.
According to an analyst at Boston-based Lux Research, energy storage services could be a $31.5-billion market globally by 2017. If the Velkess prototype can be built at the price and performance advertised, it could take a big chunk of that market, and solve the intermittency problem of renewables once and for all.