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Battery Powered Data Centers?

Dec 12, 2013

Is advanced battery storage to keep a data center operating for extended periods?

Batteries have been around a long time. Benjamin Franklin reportedly “used the term “battery” to describe a set of linked capacitors he used for his experiments with electricity.” (Link to Source) Alessandro Volta is credited with making the first true battery in 1800, an invention that became known as the voltaic pile. It wasn’t until 1836 that the first practical battery was demonstrated by British chemist John Fredrick Daniell. Daniell’s design is the template for today’s lead-acid battery technology.

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Left to Right: Voltaic Pile (Link to Source), Alessandro Volta (Link to Source) Daniell cell (Link to Source)

Data center professionals are very familiar with battery technology as they are generally chosen for UPS applications.  The quick response of battery technology and ability to store, release and recharge electrical power are well known and highly valued. Because of the amount of power required by data centers, UPSs are only expected to provide temporary power until back up diesel generators or other sources come on line to take over until utility electrical service is restored. But is it possible that batteries could take over the complete job of powering a data center for extended periods of time?

Advanced battery technology is being researched and developed at a frantic pace. Applications such as electric vehicles, especially passenger cars and mobile computing devices, provide markets that require more and more power storage so they may operate for days or weeks, not hours. And this power needs to fit into a small, relatively light weight package to make it practical. Lugging around an overweight battery that requires more power than the vehicle and passengers in transportation applications is not going to provide the driving range consumer’s desire in their personal vehicles to make them practical.

Tesla’s Model S is rated for 300 miles using their large battery option based on 55 mph highway speeds and a 70° F outdoor temperature. Night driving on cold Minnesota winter evenings will obviously degrade this performance, but that’s real world. Nissan’s Leaf is advertised to travel a range of 75 miles on a full charge. Since most consumers travel less than 29 miles per day according to Nissan, this is enough for most days. Again using the heater, lights and radio reduce range, so real world performance will be interesting.

Tesla’s Model S with the 300 mile rated range has an 85 kWh capacity. Using a 5 kW per rack power baseline this translates to 17 hours of operation assuming 100% battery utilization which is not reasonable in actual use. A 10 kW rack will operate 8.5 hours with the same parameters. In other words, a 10 kW rack would need three high capacity Tesla batteries to operate one twenty-four hour day. If we could plan on an 8 hour charging cycle we could get by with two batteries per rack. In a data center with 500 racks each consuming 10 kW would need 1000 Tesla batteries, 500 in the charging cycle, 500 to operate the IT racks.  However, assuming server racks only used 50% of the power in a data center, we’re now up to 2000 Tesla batteries, 1000 in recharge, 1000 in use.  That’s a lot of Teslas. 

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Tesla Model S Battery Pack (Link to Source)

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Tesla Powered Data Center?

Okay, batteries need recharging so there’s always a need for power generation from some other source, and despite the potential to offer employees used Teslas as a signing bonus, this idea may be a bit impractical. But what if enough batteries could store enough renewable energy to power a data center for an extended period of time, during low wind or cloudy days at renewable powered data centers for example? There are experiments taking place for battery storage in power grid applications. Portland General Electric’s demonstration project is one such project.  (Link to Article)

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Screen shot from PGE website video showing battery array size. (Link to Source)

Located at the Salem Smart Power Center in South Salem, Ore., the project employs a 5-MW lithium-ion battery array. The array is connected to a smart microgrid serving approximately 500 southeast Salem customers during blackouts and related power disruptions. When to engage the battery array is determined by an algorithm that will allow project participants to make local decisions on how their piece of the smart grid project can support local and regional grid needs.

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EnerDel’s ESS includes 1,440 rack-mounted lithium-ion battery modules monitored by an advanced battery management system to support a 5MW inverter array consisting of twenty (20) 250kW/62.5kWhr channels rated at 600VDC.

The project is part of the $178 million Battelle-led Pacific Northwest Smart Grid Demonstration Project.  Half of the $23 million PGE portion of the project’s costs was provided by the U.S. DOE. Total cost for the battery array and inverters is not readily apparent since they are included in the total project costs. Hopefully the project will provide results that data centers can analyze to determine if battery arrays are capable of becoming more than temporary UPSs and replace generators and the issues related to diesel storage, testing, etc. A super UPS may be in the future, especially as new and improved battery technology developments increase storage capacity while reducing recharging times, size and cost. Until then, we’ll all have to keep an eye on the Tesla to see where the technology leads.

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