The enormous demand for data storage is driving exponential data center growth in markets around the globe. Artificial intelligence (AI), the Internet of Things/Industrial Internet of Things (IoT/IIoT), virtualization, the cloud, e-commerce, mobile communications, and social media all depend on the proper and swift handling of vast amounts of data. It is estimated that 24 billion IoT devices will exist worldwide by 2020. Connecting people and things — from cars to home appliances — significantly impacts the amount of data produced and changes how today’s data centers operate.

When it comes to ensuring that data is always available, mega/hyper-scale data centers and smaller distributed data centers such as colocation providers all have one thing in common. The power protection infrastructure needs to be reliable, scalable, and use the smallest amount of space possible; all with optimum energy efficiency. According to a report from Research And Markets, “The global data center construction market will grow to $89.9 billion in 2027 (from 44.1 billion in 2018). The demand of the data center construction market is largely influenced by the rise in demand of green/energy efficient data centers, which are designed to achieve maximum energy efficiency and decrease the environmental impact.”

Protecting critical systems against costly power outages in a manner that is energy efficient, environmentally-friendly, and provides a low total cost of ownership (TCO) is a priority with most data center and facility managers. Pairing double-conversion UPSs with flywheels is the next step in greening the power infrastructure. Data centers for hospitals, supercomputing centers, colocation facilities, and many other operations are reaping the reliability, cost, and environmental benefits of clean energy flywheel systems.

Enabling improvements in recycling, energy conservation, and heat management are important objectives. But how can you achieve all of this out of your power protection solution?


Honey, I shrunk the UPSS

Today’s advanced three-phase UPS systems incorporate much smarter sensors, processors, and more efficient component layout than their predecessors, giving data center managers a considerably more dependable and compact power solution. That’s the good news. However, when it comes to the batteries supplying the UPS — due to their chemical nature — further size reductions are minimal or cost-prohibitive. Climate control, spill containment, seismic rack requirements, conduit, and cable runs as well as ongoing maintenance, safety,  environmental impact, and other issues add considerably to the life-cycle cost of any battery-based system. So, what can you do?


Spin-up energy-saving power

There’s no denying that power equipment can present challenges to data center facilities — especially those with limited floor space. One very reliable, green, and cost-efficient approach is to incorporate flywheels as the energy storage component of the UPS power infrastructure. Flywheel systems store and deliver a constant source of DC power utilizing the kinetic energy of a high-speed flywheel. Working alongside a three-phase UPS, the flywheel interfaces with the DC bus of the UPS, just like a bank of batteries, receiving charging current from the UPS and providing DC current to the UPS inverter during discharge. Flywheels eliminate costly battery maintenance and replacements as well as lower energy costs by not requiring additional cooling for the flywheel system, unlike temperature-sensitive batteries. Today’s flywheel technology enables the flywheel to charge and discharge at high rates for countless cycles without degradation throughout a very typical 20-year life — unlike traditional VRLA batteries that begin to deteriorate in less than half that time.


How flywheels work

Kinetic energy is the energy of motion as quantified by the amount of work an object can do as a result of its motion, expressed by the formula:

Kinetic energy = ½ (mass)*(velocity)2

While flywheels have proven their usefulness for thousands of years — think of potter’s wheels and Neolithic spindles — modern implementations offer a host of new benefits in the most high-tech and demanding environments.

A flywheel system stores energy mechanically in the form of kinetic energy by spinning a mass at high speed. Electrical inputs spin the flywheel rotor and keep it spinning until called upon to release the stored energy. The amount of energy available and its duration are governed by the mass and speed of the flywheel.

Operating as a mechanical battery, the flywheel can be used as an adjunct or as an alternative to battery-based UPSs. Electrical input spins the flywheel rotor up to speed, storing kinetic energy, and a standby charge keeps it spinning 24/7 until called upon to release the stored energy. When used in conjunction with a battery-based UPS system, the flywheel systems take the first “hit” during a power disturbance, preserving the battery for use in longer-term outages and minimizing discharge cycles to prolong overall battery life (Figure 1). In configurations where the flywheel is working alone, typical configurations can provide from 15 seconds to more than two minutes of backup power (depending upon load levels and number of flywheel modules). Since the average backup generator requires less than 10 seconds to come on-line, the flywheel provides plenty of time for a smooth power transfer to the onsite generators.


A clean energy storage alternative

While lead-acid batteries are a standard energy storage component of UPSs, mostly due to price, battery readiness is always in question. Due to their chemical nature, it’s difficult to accurately predict battery reliability. Important considerations when designing a system that incorporates lead-acid batteries include:

  • Hazmat permits
  • Acid leak spill containment
  • Floor loading issues
  • Slow recharge times
  • Lead disposal compliance and transporting
  • Temperature control

These reasons prompt data center consultants and facility managers to evaluate energy storage alternatives. Some UPS manufacturers are starting to use Lithium-Ion (Li-ion) batteries instead of VRLA batteries. However, while these options offer advantages, such as longer life and lower cooling requirements compared to lead-acid batteries, safety remains the number one concern.  The latest 2018 fire code (NFPA 855) standards for Li-ion batteries stipulate that for each cabinet of Li-ion batteries, a 36 in. clearance is required.  This means that a one-megawatt UPS needs five battery cabinets. With each cabinet at 26 in. wide, an additional 36 in. of more space is required than a comparable VRLA battery configuration. Real estate in today’s densely populated data centers is a valuable commodity that can be allocated for more revenue producing activities.

Regardless of battery technology, reliability is always in question. Are the batteries fully charged? Has a cell gone bad in the battery string? When was the last time they were tested? Some facility managers resist testing their batteries as each battery test depletes battery life to some degree. By contrast, “always-on” flywheel systems provide reliable energy storage instantaneously to assure a predictable and seamless transition to the standby generators. Also, through graphic displays, there is no guessing of the current status of the flywheel system.  System status, operating parameters, rotor speed, charge capacity, discharge event history, and event log menus assure the user of current operational condition.


Are flywheels the right choice for our data center?

Countless data center operators are reaping the reliability and cost benefit of using flywheels. Cavern Technologies, a Kansas City colocation provider, needed a power protection alternative for their 3-million-sq-ft facility that is 125-ft deep underground. For Mike McDaniel, vice president of facility engineering for Cavern, selecting a new energy storage solution was predicated on reliability and durability.

“Knowing the available energy level at any point in time is a key differentiator for flywheels versus batteries. Given the ability of our generator plant to be online in under 10 seconds, the flywheels were a perfect fit for our design. Since the flywheels have been installed, we have performed in-house testing as well as experienced a few weather and utility power issues. In each occurrence, the flywheels have performed flawlessly,” said McDaniel.

Today’s flywheel systems are easy to use, maintain, and monitor with self-diagnostics, log files, adjustable voltage settings, RS-232/485 interface, alarm status contacts, soft-start precharge from the DC bus, and push-button shutdown. Available options include DC disconnect, remote monitoring, Modbus and SNMP communications, and real-time monitoring software.


Long, predictable life

Over the 20-year life of the flywheel, the total cost of ownership is less than that of a lead-acid battery-based UPS due to minimal maintenance requirements, no disposal issues, and no cooling costs. Cost savings from a hazmat-free flywheel versus a five-minute VRLA battery bank are in the range of $100,000 to $200,000 per flywheel deployed. In fact, the return on investment calculation for a flywheel works out to a full payback in just four years. In addition, flywheels with a contact-free magnetic levitation system can save users an additional $10,000 as there are no bearings to replace.

Batteries do provide a longer back up time — usually 10 minutes to a typical flywheel configuration that provides 20 seconds. However, if during a power outage the generator doesn’t start-up after a few seconds then it’s unlikely to kick in after 10 minutes.


Benefits of flywheel technology

From 40kVA to over a megawatt, clean energy flywheels are increasingly being used to ensure the highest level of power quality and reliability for mission-critical applications — from hospitals to government facilities. The flexibility of these systems allows a variety of configurations that can be custom-tailored to achieve the exact level of power protection required by the enduser based on budget, space available, and environmental considerations (Figure 2).

In any of these configurations, the user will ultimately benefit from the many unique benefits of flywheel-based systems including:

  • No cooling required
  • High power density - small footprint
  • Parallel capability for future expansion and N+1 redundancy
  • 99% efficiency for reduced operating cost
  • No special facilities required
  • Front access to the flywheel that eliminates space issues and provides site flexibility for future operational expansions and re-arrangements
  • Reduced maintenance
  • 20-year useful life
  • Simple installation and quiet operation
  • Wide temperature tolerance (-4°F to 104°F)
  • Adherence to UL and CE safety standards
  • Enabling organizations to obtain LEED® credits

As the demands of processing IoT/IIoT data increase and become more complex, data center managers, engineers, and consultants are continually assessing power solutions that can improve efficiencies while enhancing energy reliability. While system availability is always the first requirement, being environmentally-friendly and lowering carbon footprint have moved higher on the wish list. By enhancing battery strings or eliminating them with the use of flywheels, managers take one more step in greening their facilities and lowering TCO.

In many cases, incorporating flywheel energy storage technology in a new or retrofit electrical system design can serve as an excellent foundation for achieving the sometimes-conflicting goals of maximizing dependability and reducing operating costs. With the added benefit of providing an environmentally friendly energy source, it’s well worth considering using flywheels in data center operations.

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