The evil and necessity of batteries by Doug Mohney

Views and Opinions on Green IT (Jun 25 2009) Construction

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   Lead acid batteries are nearly ubiquitous in data center usage. The technology is cheap, it's well-understood, and, from a green perspective, just butt-ugly.  Unfortunately, replacing them with something more eco-friendly is neither easy nor cheap.

    The technology for lead-acid batteries goes back 150 years and represents the core around which nearly all UPSes operate from, regardless of size.  While lead smelting and all those acidic compounds aren't good for the environment, there's an effective recycling program in place for old batteries. High-tech alternatives such as nickel metal hydride and lithium-ion batteries are able to pack more energy into the same space, but both technologies are expensive and are likely to remain so over the next five years, with supply and demand being driven by the auto industry building hybrid and all-electric vehicles.

    Google's approach to the battery problem is simple and elegant – but not easily repeatable for the rest of the world.  Since Google custom-designs its own servers, it puts a 12 volt line on the mother board for direct DC power, then drops in a small battery on the server itself.  This design allows Google to bypass the use (and expense) of a large battery-based UPS and conversion inefficiencies from DC to AC power.   If you are a member of the professionally paranoid, this approach also avoids making the UPS a single point of failure.

    Still, lead-acid batteries, wherever they are in the power food-chain, need to be replaced every three to ten years, depending on warranty and technology. Large battery rooms come with such fun features as spill containment and neutralization, hydrogen detection and ventilation, eyewashes and showers, and other reminders that lead acid isn't something that is really "green" in any sense of the word.

    Flywheels have become an alternative to the traditional UPS for some. At the heart of the technology, a spinning wheel in a vacuum contains kinetic energy; when the power goes out, the kinetic energy is converted into electricity.  Flywheels can provide backup power for up to 15 seconds – plenty of time to fire up alternative on-site power if the primary grid goes down.  A flywheel system can operate at 98 percent efficiency, as compared to 92 percent for battery systems and can be designed to last up to 20 years. Drawbacks to the flywheel are more money up front in terms of capital expense, but new-build green data centers will likely opt for flywheels over a battery-based UPS.

   Short of investing in flywheels, the best way to shrink the use and expense of lead-acid batteries is to trim down power consumption and find ways to move to a smaller UPS.

   
   

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