High-speed flywheel system is key to manufacturer’s power backup needs
When a 2005 power outage hit MasterBrand Cabinets (Jasper, IN), one of the nation’s leading cabinet manufacturers discovered firsthand that UPS batteries are trouble.
Fig. 1. A flywheel system is essentially a dynamic battery that stores energy mechanically in the form of kinetic energy by spinning a mass about an axis. Electrical input to the system’s integrated motor/generator spins the flywheel rotor and keeps it spinning 24/7 until called upon to release the stored energy through the motor/generator.
One cell in their UPS battery cabinet faulted, and that rendered the string’s dozens of others useless right when MasterBrand needed them the most. That’s one of the many shortcomings of UPS batteries. Just like a bad bulb in old strings of Christmas lights, a single battery failure in a string of UPS batteries renders the entire string inoperable.
“The cost to MasterBrand of that outage was substantial,” says Rick Shipley, IT contracts manager.
“We decided that we needed a redundant power backup system,” says Shipley, so work began with their UPS supplier. Instead of having one UPS and a single cabinet of batteries, MasterBrand spec’d out paralleling two of each. Should one UPS or a battery cell fail, the redundant machine or battery string would be there.
Battery strings are clearly acknowledged as the weakest link in any UPS configuration. Hanging the company’s productivity and balance sheet on two weak-link chains is better than one, but it’s still a risk.
During the process, MasterBrand began to learn about energy storage alternatives. They were particularly impressed with the newer generation technology made by Pentadyne. The Pentadyne flywheel system employs a lightweight, carbon-fiber-composite flywheel to store energy kinetically.
A flywheel system is essentially a dynamic battery that stores energy mechanically in the form of kinetic energy by spinning a mass about an axis. Electrical input to the system’s integrated motor/generator spins the flywheel rotor and keeps it spinning 24/7 until called upon to release the stored energy through the motor/generator. The amount of energy available and its duration is governed by the flywheel mass and speed.
The kinetic energy generated by a flywheel is proportional to its mass and the square of its revolution speed:
KE ~ M(rpm)2
Where KE = kinetic energy
M = mass of the rotating object
rpm = revolutions per minute of the rotating object
Until recently, commercially available flywheels relied on mass as a source of energy; doubling the mass doubles the energy capacity. Using a large mass, however, limits maximum rpm. Limiting rpm hampers energy density.
Los Angeles-based Pentadyne Power Corporation broke the mold several years ago by perfecting a high-speed flywheel. Instead of utilizing the mass as a primary source of energy, it takes advantage of rotational speed. The higher the speed, the smaller the mass needed for any given energy output. And while doubling mass doubles stored energy, doubling speed quadruples stored energy.
The flywheel itself is relatively small, housed inside a canister about 23 in. high and 18 in. in diameter (Fig. 1). This relatively small size is accomplished by spinning the magnetically levitated flywheel in a vacuum at 52,000 rpm (heavy steel flywheel systems operate at about 7,000 rpm). The flywheel encounters near zero aerodynamic drag inside the vacuum-sealed primary housing. Upon starting, the 52-lb flywheel/rotor shaft is immediately levitated by the lower radial electromagnets. The other four electromagnets (two at the top and two at the bottom) maintain precise shaft centering and perpendicularity.
Fig. 2. Rick Shipley, IT contracts manager for MasterBrand, shows off the Pentadyne Flywheel System.
In the event of a blackout, Pentadyne’s current model can provide up to 190 kW of continuous power for 10 seconds. This allows for a smooth hand-off of power responsibility to an on-site emergency generator, which can be online and ready to take the load within 6 to 8 seconds.
For lighter loads, the flywheel delivers longer runtimes. At MasterBrand, one flywheel can carry the load of the company’s IT and fire-suppression equipment for more than 30 seconds. Heavier loads can be carried by multiple modules of flywheels, which can be arrayed together exactly like battery cabinets on the UPS’s DC bus — no communications gear needed. Previous to this writing, the largest such array was 20 Pentadyne units operating on a common UPS bus to support a Department of Defense supercomputer. That has since been eclipsed. A data center in Omaha has commissioned an array of 24 units.
The cost to routinely maintain and replace a comparable-capacity 5-minute VRLA battery string over the 20-year design life of a Pentadyne flywheel system is many times the cost of the flywheel. That’s why many sites opt to use a flywheel as their sole source of DC energy storage, saving upwards of $150,000 per unit deployed compared to VRLA batteries.
But once burned, the management of MasterBrand was understandably twice shy. So their power continuity system now features a Pentadyne flywheel in parallel with batteries. Fig 2.
One of the great advantages of running a flywheel in parallel with batteries is that the flywheel acts as the first line of defense. This ensures an uninterrupted ride-through of all power anomalies up to its capacity or, in the case of longer duration outages, transitioning to the generator or battery strings.
That’s assuming the batteries are ever used.
Since the flywheel has a higher programmable discharge setpoint than batteries, it always carries the load for more than enough time to perform a gradual transition to the backup generator. Batteries would only be called upon if the generator ever failed to start. This would be an unlikely occurrence according to an exhaustive study compilation by the IEEE that found backup generators (including those that are rarely, if ever, maintained) have a better than 99.5% rate of start on the first attempt.
Every time a string of lead-acid batteries is used, the batteries become less able to respond to the next need. By essentially eliminating all battery cycling, “10-year” VRLA batteries may even approach their life claims, instead of needing to be replaced, on average, every two or three years in a manufacturing setting. Costly battery servicing needs, assuming proper temperature maintenance, should also be greatly reduced.
First-generation steel flywheels require much less maintenance than UPS batteries. The Pentadyne carbon fiber model needs nearly none, so compared to other flywheels on the market, maintenance cost is vastly lower and uptime availability is the highest of any UPS energy storage device. What’s more, the energy efficiency of a Pentadyne flywheel saves thousands of dollars per year in utility costs over other flywheels for each unit deployed.
The dual-UPS system at MasterBrand Cabinets ensures continuous power to the facility’s IT center, telecommunications equipment, a fire-suppression system, and other aspects of the building, including some emergency lighting.
“MasterBrand’s Pentadyne system has been running here since March 2006 without any issues or problems whatsoever,” Shipley says. Since then, MasterBrand has been hit with a number of utility power glitches, but never one that the flywheel couldn’t handle.
Want more information? Click below.
Pentadyne
© Nelson Publishing, Inc. All Rights Reserved