UPS energy storage: Are there alternatives to lead-acid batteries and flywheels?

For a few years now, data centers have been labeled energy hogs. Now, a new study by DatacenterDynamics estimates that the world’s data centers will consume 19% more energy in the next 12 months than they have in the past year. With the increase in energy consumption, it’s is not surprising then that the study found that 44 percent of those surveyed believe increased energy costs will impact significantly on their data center operations in the next 12 months.

But still, most end users meet the idea of experimentation with components of their electrical backup systems to make ther facilities “greener” with little enthusiasm, as Yevgeniy Sverdlik writes in an article for DatacenterDynamics (UPS energy storage – pushing the envelope):

“One of the most crucial components, energy storage for Uninterruptible Power Supplies (UPS), has progressed very little in the data center market, and the exotic alternatives to lead-acid batteries and flywheels have so far remained exotic.”

Sverdlik takes a look at three such alternatives, each with its own advantages and drawbacks.

1. Ultracapacitors, also known as electric double-layer capacitors

They 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. But from a UPS perspective, there’s not a practical solution yet. Ultracapacitors are not cost effective today.

2. Superconducting magnetic energy storage

SMES systems store energy in the magnetic field created by the flow of direct current in a superconducting coil which has been cryogenically cooled to a temperature below its superconducting critical temperature. A typical SMES system includes three parts: superconducting coil, power conditioning system and cryogenically cooled refrigerator. Once the superconducting coil is charged, the current will not decay and the magnetic energy can be stored indefinitely. The stored energy can be released back to the network by discharging the coil.  The drawbacks of SMES are similar to those of ultracapacitors: high upfront cost and shortback-up time.

3. Sodium nickel chloride batteries, also known als Molten salt batteries.

They are a class of primary cell and secondary cell high-temperature electric battery that use molten salts as an electrolyte. They offer both a higher energy density through the proper selection of reactant pairs as well as a higher power density. 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. Within the next two years, some vendors are already planning to bring energy storage solutions based on molten salt batteries to the UPS market.

Conclusion: Although exotic technologies are progressing very slowly into the UPS market, the widely used solutions by the data center industry (acid batteries and fly wheels) have enough drawbacks for all major vendors to consider the alternatives very seriously.

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