In the past, electrical contracting firms have typically provided standard approaches to power protection, such as UPSs, power management software, backup generators, automatic transfer switches and other supporting power devices. Client server rooms and/or adjacent facilities have become filled with more and more bulky and hazardous lead-acid batteries. UPS battery banks impose a large footprint and create cooling and maintenance problems. It is apparent that not only does proper power management play a critical role in power quality, but the power management components selected to protect infrastructures have an even heavier role in the reliability and uptime availability of a continuous power quality solution.
Managers have begun to look to real-world failures for more understanding. They have noticed a startling trend among the components of each power certainty scheme: lead-acid batteries are clearly the weakest link. With frequent and costly battery maintenance and replacement, temperature control issues and space constraints, the standard battery-based backup option is a headache that keeps returning. In addition, fire hazard permitting, toxic and explosive gas emissions, hazardous material handling, disposal costs and problems, high failure rates and poor predictability have motivated electrical contracting firms and their clients to look to new power quality options in the protection of business continuity.
Enter flywheel technology, the saving grace for many UPS users. It’s a technology that’s been around for decades, but only in the last dozen years has reached true commercial viability. A clean energy storage solution, flywheel technology allows electrical contractors to provide sophisticated power protection that has the capability to solve problems challenging companies every day. Used with double-conversion UPS systems, flywheel technology provides reliable mission-critical protection against transients, harmonics, frequency drift, voltage sags and spikes, outages and other damaging power disturbances. The latest generation of UPS flywheel systems is even more advantageous than the first-generation, providing companies with better energy, space and environmental efficiencies, as well as enormous long-term savings, uptime and dependability.
Total Card Inc., one of the nation’s leading third-party credit card servicers located in Sioux Falls, South Dakota, (fig. 1) is a fine example of flywheel technology solving real world problems. “Our prior locations in the city had limited UPS protection with no generator backup,” remembers Troy Clavel, Total Card’s Chief Information Officer. As business grew, Total Card’s UPS systems “were prone to failure due to overloading or short backup periods due to peak energy demands.” During the freezing winters, utility power interruptions became even more frequent, taking a high toll on the reliability and life expectancy of the battery array. By implementing flywheel technology, Total Card was able to p rovide more than enough time for a gradual genset handoff, increasing battery life and overall reducing costs and the threat of unreliability.
Development of Commercially Available Flywheel Technology
Flywheel UPS technology has had quite a commercial development history. The first successful generation, still sold today, is a simple design construction that yields much higher power density and a smaller footprint than equivalent compact VRLA batteries. Using an 800-pound steel “puck,” the Active Power flywheel system, sold primarily by genset manufacturer Caterpillar, replaces UPS battery strings. This eliminates the need for energy storage HVAC, hazmat handling and all the health and safety issues rife with battery installation, operation and servicing. They do so in about half the floor space of VRLA batteries. The system has the ability to deliver 250 kW to protected loads for 13 seconds, and longer at lower outputs, providing the right amount of time to start and switch over to the UPS’s backup generator.
The development of the next-generation flywheel began in the late ‘90s at a company based in Los Angeles. The new flywheel system that resulted is lighter, faster, smaller and 10 times more energy efficient than first-generation flywheels. Utilizing a fast-spinning, light but stronger-than-steel carbon-fiber-composite cylinder, the new generation flywheel systems have been integrated with major UPS brands and are sold by UPS industry leaders such as Liebert/Emerson Network Power, Toshiba, Socomec and, in Korea, EHWA Technologies. These newer models deliver a lighter, more compact and nearly maintenance free energy storage solution.
Working like a dynamic battery, the flywheel system stores energy kinetically by spinning a mass about an axis. Electrical input to the integrated motor/generator spins the flywheel rotor up to speed, and a standby charge keeps it spinning 24/7 until called upon to release the stored energy. When the stored energy is released, the amount of energy available and its duration is directly proportional to its mass and the square of its revolution speed. First-generation flywheels rely primarily on mass to store energy, but that imposes floor loading and other installation issues. In the flywheel world, doubling mass doubles energy capacity, but doubling rotational speed quadruples it.
Pentadyne Power Corporation was first to offer UPS users a high-speed, carbon-fiber-composite flywheel system that takes the most advantage of the mass times speed squared equation. This is a unique approach, because as speed increases, the amount of mass needed for any given energy output decreases. Smaller, stronger and much lighter mass and innovative technology combined to make full magnetic levitation of the spinning mass a real possibility, assuring electrical contracting firms that operations will be extremely efficient, silent and vibration-free. Full magnetic levitation eliminates the need for bearings that require replacement every couple years at a price of thousands of dollars and the better part of a day’s worth of downtime risk.
Both the first generation and the new generation of flywheels spin in a vacuum chamber to minimize aerodynamic drag. Most flywheels today utilize a continually running vacuum pump to maintain that vacuum. The lightweight carbon-fiber system deploys a different offering: a factory-sealed vacuum and patented molecular vacuum sleeve integrated within its center shaft. The rapid rotation of the center shaft allows helical grooves in the maintenance-free sleeve to maintain the high vacuum, eliminating the need for a mechanical pump and its inherent point of failure, frequent oil changes and costly, semi-annual pump replacements. (fig. 2)
It’s these advances, combined with Pentadyne’s patented synchronous reluctance motor/generator, that combine to create an amazingly energy efficient device: the entire system uses only 275 watts, the same or less than the float charge of a battery array. This saves thousands of dollars per year per unit deployed compared with the 3,500 watt standby consumption of a steel flywheel.
Flywheel Technology vs. Batteries
For those electrical contractors and end users who have already established a “relationship” with batteries, it can be a difficult transition when moving on to a more reliable, energy-efficient solution. Lead-acid batteries have skyrocketed in cost due to rapidly increasing lead commodity pricing, but they’re still cheaper at first glance than a flywheel solution. As such, many experienced users have resigned themselves to put up with their foibles, taking a cross-your-fingers approach to power quality and continuity. This approach to power protection is dicey at best, yet batteries continue to be installed, along with requirements that include:
- Frequent and costly maintenance
- Dedicated HVAC needs
- Expensive monitoring
- Large footprint
- Massive weight, limiting placement flexibility
- Slow recharge
- Frequent individual cell replacement
- Frequent downtime due to servicing and failures
- Second string redundancy to halve high failure odds
- Fire hazard permits, employee safety and OSHA requirements for toxic chemicals, acid spills and explosive gases
- Environmental and disposal issues
- Separate replacement battery storage requirements
- An gambling approach to power reliability
- Expensive “pro-rated” limited warranties
Replacing batteries with a flywheel system can actually reverse the negative impact of each of the above, resulting in:
- Infrequent, low-cost maintenance (near none with carbon fiber flywheels)
- No temperature control or ventilation requirements
- Built-in precise monitoring, event logging and diagnostics
- Minimal footprint/high power density
- Low weight/virtually unlimited siting flexibility
- Rapid recharge functionality (symmetrical discharge/recharge with carbon fiber flywheels)
- No major maintenance module replacement for at least 20 years
- Redundancy due to poor reliability is not required
- Infrequent downtime due to infrequent serving needs (near none with carbon fiber flywheels)
- No hazmat or dangerous emissions
- No disposal issues
- No separate storage room required
- A reliable strategy for power reliability
- Warranties included (1 year on steel flywheels, 5 years on carbon fiber models)
Power Quality: Goodbye to Batteries?
In light of the negative implications batteries have on the quality and reliability of the power infrastructure, should electrical contractors give batteries the brush off? Battery management systems provide frequent testing and estimates on future performance, but the only real way to know when batteries will be effective is when they are actually needed to respond to real load in a real world situation. Like a string of old Christmas lights with one bad bulb, one dead cell in a string of VRLA batteries renders the entire string inoperable. What’s more, battery manufacturers state that UPS battery life can be maintained as advertised if, and only if, they are temperature controlled to a constant 72° - 75°F and experience no excessive cycling, i.e., they’renot used.
Batteries fail due to a number of reasons: issues with heat or cold, poor maintenance, corrosion, loose connectors and ripple current. The number one source of battery failure, however, actually has to do with usage. According to the electric utility group Electrical Power Research Institute (EPRI), 84 percent of all disturbances and outages last less than 2 seconds, and 99 percent last less than 10 seconds. That’s what UPS batteries must respond to UPS environments with no step loads (such as IT server loads). When protecting more challenging loads, such as those in medical, manufacturing, broadcasting and other industries, the disturbance comes from the load itself.
“One of the first installations of our equipment in a medical application really brought this to light,” said Pentadyne Vice President of Marketing Keith Field. “Two of our flywheels were installed as the sole source of energy storage on a 500-kVA UPS system protecting cardiac catheterization equipment at Scripps Green Hospital here in Southern California. When we dialed into the flywheels a week after commissioning, we found that they had cycled more than 350 times!
“Turns out that the step loads of cath lab equipment, as well as that of scanners and other medical systems, have very high but very brief demands. The UPS rectifier wasn’t able to keep up, so the energy storage had to keep the UPS DC bus voltage level. With flywheels, that’s no problem since cycling has no effect on performance and they can recharge as quickly as they discharge. With lead-acid batteries, it’s a whole other story. That’s why Scripps had to change out their entire VRLA battery string every year, as well as replace several cells in even less time,” Field added.
Every time a UPS battery bank is used in a deep, brief discharge activity it experiences a chemical “whiplash” or “coup de fouet” effect. This renders the batteries significantly less capable of operating properly in the future. This damaging effect and the resultant decrease in reliability, leads to compromised output and dropped loads.
There is a reprieve for those who can’t bear to part with batteries. Flywheel technology actually allows contractors to offer clients the option of utilizing flywheel technology in parallel with battery strings. This combined system can actually eliminate the whiplash effect by making the flywheel(s) the first line of defense in short-duration disturbances whether on the utility or the load side. Unlike lead-acid batteries, repeated cycling of flywheels has no impact on future performance. So programming a flywheel to discharge if the UPS DC bus drops to, say, 520V versus the 480V discharge of chemical batteries ensures that the flywheel exclusively maintains the DC bus until the backup generator takes over. In the event of a generator failure, the flywheels gradually roll down output voltage to the batteries. So instead of slamming the batteries with the full load, they get a gentle handoff over a couple of seconds, allowing the chemical reaction to take place more gradually and thus preventing the whiplash effect.
For freestanding data centers or corporate IT facilities where continuous power reliability and redundancy is a necessity, flywheel bridging to the genset, with batteries as a secondary energy storage medium, is the ideal solution. (fig. 3) In industrial applications where temperature control is often problematic, or in hospitals where floor space is at a premium, flywheel bridging to the genset is an ideal solution that can entirely eliminate batteries from the equation.
Although there is often concern about genset starting reliability, the IEEE Gold Book (appendix L, table XII) acknowledges that an event such as this is exceptionally uncommon. Compiling six separate studies encompassing 25,000 critical (such as hospital generators) and non-critical (rarely tested) emergency gensets, IEEE reports that 99.5% of gensets start on the first attempt. Interestingly, the leading cause of the 0.5% failure, are the genset batteries. But replacing a couple of cheap genset batteries every 6-12 months is far less costly than dozens or hundreds of much higher priced UPS batteries
Differences in Life Cycle Costs
Comparing the cost difference between a flywheel system and a similarly sized monitored 5-minute VRLA battery bank (the cheapest available), the flywheel system costs about 1.5 to 2 times as much. However, this cost recovers itself rapidly before the first string replacement (1 to 4 years depending on application). Thereafter, the flywheels become an ongoing source of both reliable power security and cost-containment. Over a 20-year design lifespan, the cost savings from eliminated battery maintenance and replacement amount from $100,000 to more than $200.000 per flywheel deployed – enough to repay the cost of the flywheel many times over. For the lowest-maintenance flywheel model on the market, recommended hardware service is just a low-cost, one-hour capacitor replacement once every six years. That is the only downtime maintenance required for the entire 20-year design life of the flywheel system before a recommended factory service. For the same period, battery strings would need to be replaced at least four times based upon an a very optimistic life expectancy of four years. In addition, there would be a number of individual cell replacements, monitoring system costs, temperature control and ventilation expenses, and costs related to battery delivery, installation, disposal, space utilization, fire-hazard permitting, hazardous-materials handling, stored replacement cells, acid spill containment, inspections, OSHA compliance. In the end, none of these costs would compare to the continuous lack of reliability and resulting frequent maintenance/replacement downtime.
Energy efficiency is a hot button in today’s increasingly green-conscious society, and an area where most flywheels fall short. Standby electric usage by steel flywheels is 3,500 watts. The generational leap made by maglev carbon fiber high-speed models, however, use only one-tenth that – less than a mere 300 watts – the same or less than the float charge of a similar sized battery array. Eliminating the temperature control and ventilation needs of batteries, the energy efficiency of flywheel energy storage is vastly better than that of battery arrays.
Nationwide and around the world, data centers, broadcasters, hospitals, laboratories, airports, manufacturers, military facilities and more - are opting to harden battery strings, or eliminate them entirely, by applying flywheel energy storage to UPS systems. Alan Beyea, manager and overseer of Scripps Green Hospital’s engineering services, said it best when he reflected on his experience with batteries before utilizing the flywheel system in Scripps’ catheterization labs. “Dealing with batteries is especially problematic and expensive. Even in the first year, several cells in our battery bank went bad so we’d replace the batteries at very short intervals – way before their stated end of life. In our circumstances, we just can’t take any risks.”
Owners, managers and estimators are now paving the way for business continuity and profitability by employing a solution that embodies true power quality and reliability. With costs slashed, power reliability assured and efficiency at an all time high, contracting professionals can now heave a sigh of relief, knowing that their clients will be confident in leaving power protection to the silently spinning cylinder floating in its cabinet.
