FOCUS POWER UPDATE
Issue 17, August/September
FOCUS UPDATE: POWER
some of the newer exotic technologies, most end users meet the idea of experimentation with components of their electrical back-up systems – a cornerstone of their livelihood – with little enthusiasm.
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One of the most crucial components, energy storage for Uninterruptible Power Supplies, has progressed very little in the data center market, and the exotic alternatives to lead-acid batteries and flywheels have so far remained exotic.
Major vendors have invested in research and
development of technologies like
ultracapacitors, flow batteries, superconducting magnetic energy storage, lithium-ion batteries and so on, but none have yet managed to gain traction in the market. Here, we take a look at three such alternatives, each with its own advantages and drawbacks.
ULTRACAPACITORS
Ultracapacitors — or electric double-layer capacitors — are a promising technology that may at some point give orthodox energy storage a run for its money in the market. Storing energy at the surfaces of two carbon plates with opposite charges separated by a sheet of paper and dipped in a liquid electrolyte, ultracaps have a number of attractive properties for data centers operators.
They use less space than lead-acid batteries, require less maintenance, can operate in higher temperatures and use more environmentally friendly materials, according to a recent report by Frost & Sullivan.
Bill Campbell, senior power-systems product manager for Emerson, says that while ultracaps are used in alternative-energy applications, they are not cost effective in the UPS context today. “From a UPS perspective, there’s not a practical solution yet,” he says.
A major obstacle is short ride-through time. Ed Spears, product manager at Eaton’s critical power solutions division, says the technology
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today is used only in applications where required ride-through time is less than 10 seconds. “In a data center, I’m looking usually at… about eight minutes of (average) backup time,” he says.
Spears says many vendors are working on getting ultracap backup time to a more practical range, which will eventually get the cost down to a more palatable level. “We’re wondering if in five years somebody comes up with an ultracapacitor with the same back-up time as the flywheel,” he says. “All of a sudden, the ultracap looks very attractive, but they’re not there yet.”
SUPERCONDUCTING MAGNETIC ENERGY STORAGE
A promising technology that is currently at the level of basic research is superconducting magnetic energy storage (SMES).
In an SMES system, a coil made of a superconducting material is cryogenically cooled below its critical temperature, which gives it the property of ‘zero resistance’. A direct current is supplied to the coil, creating a magnetic field.
The coil’s lack of resistance prevents the energy from dissipating as heat and allows for energy to be stored in magnetic form until required.
Attractive qualities of SMES include the absence of harmful materials and its mechanical simplicity, which makes it more reliable. Some of its drawbacks are similar to those of ultracaps: high upfront cost and short back-up time, usually at about 10 seconds for a UPS system, according to Eaton’s Spears.
Supplying cryogenic cooling capacity to keep the coils below critical temperature and
hile some data center operators
attempt (often
successfully) to make their facilities ‘greener’ by using
PUSHING THE ENVELOPE FOR UPS STORAGE Alternative UPS energy storage solutions have had an uphill battle against lead acid batteries and fl ywheels. Yevgeniy Sverdlik explores the reasons why
maintenance make total cost of ownership for SMES prohibitive.
SODIUM NICKEL CHLORIDE BATTERIES
Within the next two years, GE is planning to bring to the data center UPS market an energy storage solution with cooling requirements completely opposite to those required by SMES: none.
In addition to ‘zero’ cooling needs, the company is promising its sodium nickel chloride batteries to have a 20-year lifecycle and long discharge rates. Trent Waterhouse, VP of marketing at GE’s Lineage division says a single bank of such batteries will serve both AC and DC loads.
Branded “Durathon”, the battery charges when chlorine is extracted from sodium chloride and combined with nickel to form nickel chloride. Sodium ions are then transported through a solid electrolyte to an anode reservoir, leaving electrons (which cannot get across the solid electrolyte) behind.
The process is reversed during discharge. These batteries expel hot air (the electrolyte needs to be melted for discharge) but do not require air conditioning, according to Emerson’s Campbell.
COMPETING WITH LEGACY
Competing with lead acid batteries and flywheels for data center operator’s cash has been tough for alternative solutions. An ideal solution, in Campbell’s opinion, will offer low initial and lifecycle cost, a long lifecycle, high storage density per square foot, wide operating energy range and be environmentally benign.
For the time being, lead acid batteries remain the most widely used solution by the data center industry, followed by flywheels, which have gained a lot of traction in recent years. Both technologies, however, have enough drawbacks for all major vendors to consider the alternatives very seriously.
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