Flywheels are turning up in applications where around-the-clock reliability is critical, including such diverse settings as credit card centers, casinos, and health care centers.

By Henry Vere

One such health care application, in which flywheels performed glitch-free during severe thunderstorms, was at Virtua Health, headquartered in Marlton, NJ.

Virtua is a nonprofit, multihospital health care system whose mission is to deliver a world-class patient experience through its programs of excellence in cancer treatment, cardiology, orthopedics, women’s health, pediatrics, surgery, neuroscience, and geriatrics. A nonprofit organization, Virtua employs 7,450 clinical and administrative personnel; 2,100 physicians serve as medical staff members caring for thousands of patients.

As with hospitals throughout the world, Virtua depends on its UPS and batteries to ensure that generators will start in the event of an outside power problem. Keeping the power on is critical to their care. But using batteries as a backup brings a whole list of issues that made alternatives look inviting.

The use of the flywheel as an energy source likely goes back thousands of years, to the earliest days of the potter’s wheel. In more recent times, flywheels have been used for gyrobuses, introduced in Switzerland for commercial service in the 1950s. Gyrobuses are no longer in commercial service—bulky, heavy flywheels limited their adoption—although continues with the use of flywheels for transportation vehicles.

NASA has also been developing flywheels to be used as efficient energy-storage devices in aerospace power systems. In spacecraft, these advanced aerospace flywheels will be able to store energy more efficiently than rechargeable chemical batteries. Down here on earth, flywheels have turned out to be a good fit for the uninterrupted power supply (UPS) industry.

Flywheels are sometimes referred to as “kinetic batteries.” Today’s super flywheels store kinetic energy in a high-speed rotating drum forming the rotor of a motor generator. When remaining electrical energy is obtainable, it is used to speed up the drum. When the energy is needed, the drum provides it by powering the generator. Recent high-energy flywheels use amalgamated rotors made with carbon-fiber materials. The rotors have an especially high strength-to-density ratio and spin at speeds up to 100,000 rpm within a vacuum chamber minimizing aerodynamic losses. Use of superconducting electromagnetic bearings virtually eliminates energy losses through friction.

Despite the many advantages of flywheels for energy, the scale of the engineering challenge should not be taken too lightly. A 1-foot diameter flywheel weighing 23 pounds spinning at 100,000 rpm will store 3 kWh of energy.

However, at this rotational speed the surface speed at the rim of the flywheel will be 3,570 mph or 4.8 times the speed of sound, and the centrifugal force on particles at the rim is equivalent to 1.7 million G. The tensile strength of material used for the flywheel rim must be over 500,000 psi to stop the rotor from flying apart.

The technology seems to have advanced greatly. A 2006 Federal Technology Alert by the US Department of Energy stated that “Flywheels appear poised to replace or supplement batteries as a backup power supply in UPS systems. ... Although the initial cost of a flywheel is typically greater than batteries it would be replacing or supplementing, its longer life and simpler maintenance will often result in lower life-cycle costs.”

Flywheel Reliability in the Face of
Extreme Weather and Unpredictable Events
In June, 2007 the Northeast experienced a period of unexpected power outages. The power system at Virtua’s facility in Gibbsboro, NJ, uses UPSs that protect its servers from utility power disturbances. Virtua uses the Vycon Direct Connect (VDC) flywheel to provide DC power to Virtua’s N Power UPS. Over a period of two-and-a-half hours, the VDC 140 system discharged eight times, providing ride-through power in lieu of the batteries.

“We were very relieved,” says Chas Thawley, Virtua’s network services manager. “An unexpected power outage can cause a number of issues and problems, but Vycon’s flywheel system kicked in just as expected and maintained the power for our systems. We are satisfied with how the situation played out and have total confidence in our flywheel UPS solution.”

The cause was just a normal thunderstorm, something that actually happens quite frequently in the area, according to Thawley. The flywheel picked up the sag in electrical power and provided backup during the event. It went on, holding the power up until the generator started, as the power from the grid was eventually knocked out.

Once the generator starts, it provides power to keep operations going. The generators are actually designed to keep going in providing power, even 45 minutes after power is restored from the grid, just in case the power goes out again.

“This particular event happened after hours. Within our complex there had been times before when virtually everyone was without power—except for us, because we do have the generator with the UPS and the flywheel connection,” says Thawley.

Previously, Virtua had batteries as backup, and while the system still has batteries, they are secondary to the flywheel. What occurred in this case is that the flywheel prevented the batteries from having to take the sag in electricity, which in turn saves lifespan on the battery, resulting in one less cycle the battery has lost.

There are four levels of UPS to bridge the gap between the time grid power is lost and when it is regained: the VDC flywheel, two battery systems, and the generator.

An automatic transfer switch detects when there is loss of electricity from the electric company and it tells the generator to start. This transfer switch is located near the generator. In the data center, a UPS monitors the amount of electricity coming from either the generator or the electric company. If the UPS detects a sag (drop in electricity) then it will call for extra power from a ride-through power source, such as the flywheel or a battery string. If there is a spike (too much electricity) then the UPS conditions the power to the proper level, so that it does not affect the equipment in the data center.

The Vycon flywheel was installed as a first source of ride-through power in front of the two existing battery strings (primary and secondary). With the flywheel being first it handles the ride through power until it is discharges, then the battery strings can pick up if needed. With the Virtua Data Center (VDC), the flywheel can power the entire data center until the generator is up to full speed/power (less than 10 seconds).

During the thunderstorm, there were about six sags that the UPS detected and the flywheel was called for. Then the power fully went out, and the VDC covered until the generator started (less than 10 sec). After the power had been restored by the electric company, the transfer switch waited 30 minutes to ensure clean power, then switched the data center back to electric company power.

The first set of batteries would have backed up the flywheel if it hadn't worked. The flywheel would have to fail, along with the first and second sets of batteries, in order for power to have finally been lost. “What the flywheel does, however, is to supply us with a good, clean, renewable, reliable energy source in place of battery technology. This is the main reason we bought into this flywheel system,” says Thawley.

The VDC is a robust and dependable, high-speed flywheel system designed to provide backup power that is fast, predictable, and seamless. It provides the highest level of reliability to mission-critical applications. The VDC is also more cost-effective and environmentally responsible than lead batteries, according to Tony Aoun, president and chief executive officer for Vycon.

“These types of events allow our system to show customers the advantages of the flywheel technology over battery systems,” says Aoun. “The VDC is capable of supporting multiple outages on a daily basis without any concerns about reducing system life. We are very happy that our system was there to protect Virtua when they needed it most.”

The Question of Batteries
As the battery strings need replacing, Virtua will be looking to do so with flywheels that can be used in a daisy-chain fashion to provide ride-through power and protect their systems.

Vycon’s VDC is designed to provide backup power that is fast, predictable, and seamless.

Thawley says there is always a certain amount of risk involved with batteries because there is a chance that they may not work. Plus, the batteries’ lives are shortened each time they are tested (a monthly requirement). “Hospitals are now required to do a monthly generator test with load by the Joint Commission on Accreditation of Health Organizations. While this is a sound practice that Virtua endorses, it requires us to employ a generator and a battery. Every cycle on a battery lessons its lifespan; therefore, what’s stamped on a battery, 10 years for instance, is most likely going to last only four to five years for us.”

Batteries have a reputation for requiring a lot of maintenance and testing. This issue may be compounded when as many as 40 batteries—each at least the size of the one in your car—are placed together. Their maintenance and replacement is a real issue to deal with.

UPS systems typically use batteries to provide the ride-through when utilities have disturbances. The two types of battery technology generally used in the UPS industry include the sealed or maintenance-free lead acid battery and flooded lead acid batteries.

The flooded lead acid batteries are contained in polycarbonate jars in order to see the lead plates and sulfuric acid within the battery. They may also leak and require a great deal of maintenance. Whether sealed or flooded, when there are 40 batteries in a series and one fails to open, that in essence breaks the link. But the reason for batteries in the first place is providing uninterrupted power. One major problem with batteries is that it is very difficult to determine when a battery cell is open.

In perhaps the worst case, a customer may only find out that there is a problem with the battery when there is a disturbance with the utility and suddenly there’s no backup or ride-through.

Virtua was determined to find a technology that was more reliable, less hazardous, less toxic to the environment and had fewer disposal issues. So in December 2005, the company purchased the Vycon VDC 140 Bearing-less Flywheel Energy Storage System to be better able to protect its services during utility power disturbances.

“This technology will save Virtua money by providing clean, reliable power for 15 to 20 years compared to the typical battery-driven technology life cycle of five to seven years,” says Thawley.

Virtua installed two sets of battery strings, as they had some battery issues which resulted in battery replacement. This was before the installation of the flywheels. Therefore, the company is able to compare its flywheel system and the associated batteries to the batteries that don’t have a flywheel associated to them.

“We are getting side-by-side, real-time comparisons in all sorts of power situations,” says Thawley. “At the end of this study we’re going to have excellent data to publish in order to reveal some findings on the benefits of the flywheel technology.”

The comparison study will take two to three years. The flywheel system has been in place for approximately a year-and-a-half now. There is a great deal of data to interpolate and amass. Similar studies showed that after three years or a comparable period of time the system where the flywheel was present and connected had batteries that looked more like relatively brand-new batteries than the other set.

Vycon’s flywheel monitoring equipment is designed to record disturbances of any time frame. The interesting part about the event, according to Louis Romo, Vycon vice president of sales and marketing, was that in this case there were eight disturbances lasting between one and three seconds. The VDC-140 picked them up without a problem. Some of the disturbances occurred back to back, which is difficult for other technologies, such as batteries, to handle.

“Back-to-back coverage is actually something fairly easy for the flywheel to do,” says Romo. “We also developed the Regen System, a flywheel application for use on shipyard cranes and other high-cycling applications. With a crane, there is a charging and discharging cycle every minute on the Regen for 16 hours per day, six days a week. When you compare those amounts to an uninterruptible power source, eight discharges in two hours would be a lazy day at the shipyard. This is quite impressive in a UPS situation because those kinds of interruptions are so rare.”

Bringing in the New
Virtua will be building a new facility in Voorhees Township, NJ, and plans to use the flywheel technology in that facility, too. The coming center will feature the latest healthcare technology. In addition to clinical services, the new facility will also include a new data center. Thawley describes the facility as a state-of-the-art “digital hospital.”

Virtua will be doing everything from generating its own power to supplying chilled water and steam. All of these systems will be designed to use the new flywheel technology, according to Thawley. “This is our first experience with flywheel technology, and it has proved to be very beneficial to us.” The building is still in design development, and is expected to open in three to four years.

As with hospitals everywhere, keeping the power on is critical to health care.

Simple Care
Another plus for the flywheel is that it is virtually maintenance-free.

A flywheel has a spinning or rotating component within. As the discharge takes place, the speed of the wheel slows down; as recharging occurs, the wheel spins at a faster rate.

The use of noncontact magnetic bearings eliminates maintenance requirements. In order to have the best efficiency with a rotating machine, air is pulled out from the cavity in which it spins. This counteracts the heating of the molecules of air if gas is not drawn from the space.

“What we do is install a vacuum pump, which pulls the air from the cavity simply to minimize heat,” says Romo. “The pump works constantly to remove air and small particles from the cavity. This prevents dust and other particles from entering the pump and eventually fouling its oil. The pump’s manufacturer recommends that the oil be changed once each year. It’s a simple task to loosen the screw, drain the oil and replace it in the pump—a 15-minute job.

“Here in California, emissions reduction is a key motivator, even over reducing fuel consumption. We’re marketing the product in California primarily as an emission reduction machine, which also provides a return on investment as a result of fuel savings.”

Writer Henry Vere is a frequent contributor to Forester publications.

DE - November/December 2007