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Does DC power win the direct current vs. alternating current debate?

In the debate over direct current vs. alternating current, AC power is considered less risky. But should data centers reconsider the potential cost-saving benefits of DC power?

Oftentimes, people revisit old ideas to see if they can be used today. This is certainly the case when considering direct current vs. alternating current power for mainstream electrical applications.

Direct current (DC) power, for example, has emerged smaller products, including cell phones and processing chips. Alternative energy systems, such as photovoltaics, also use DC power. Combine these factors with data centers’ insatiable power needs and the potential to maximize energy efficiency, and you get a confluence of reasons to consider direct current as your data center power distribution method.

Benefits of DC power for data center power distribution
According to a 2006 Lawrence Berkeley National Laboratory (LBNL) study, direct current technologies bring significant power savings. LBNL was able to demonstrate a 28% energy savings using DC over alternating current (AC) power when using traditional data center power distribution, according to Guy AlLee, a research scientist at Intel Labs.

“From an operational cost point of view, [DC] is the most efficient power distribution method we are aware of. We looked at that in terms of medium-sized data centers and 100,000 servers. [In those data centers] you are looking at tens of thousands, if not hundreds of thousands, of dollars of savings [per] year in electrical costs,” AlLee said.

Challenges of using DC vs. AC
Proponents of alternating current data center power distribution, like American Power Conversion's Senior VP Neil Rasmussen, say the challenges of DC power implementation include a lack of DC-compatible products, improvements in AC power distribution efficiency and the risks involved with adopting an experimental data center design approach before it’s standardized.

But Brian Patterson, chairman of EMerge Alliance, a vendor consortium pushing DC power standards, said the biggest hurdle to DC power adoption is educating data center managers about the technology.

"The second hurdle is creating an ecosystem of equipment suppliers offering the alternative DC products. Once people understand DC power, using it is kind of easy,” Patterson said.

While direct current technology is mature, application in data center environments is in its infancy. For the early adopters, AlLee sees two main challenges, the first of which is the initial cost. The first data centers to convert from AC to DC power must deal with first-generation products and their market prices. The second challenge is figuring out how DC power will work in an existing data center without a blueprint to reference.

When looking at equipment changes, “you have to have IT equipment that starts out at DC voltage, and you would need to have a rectifier taking you from an AC to DC voltage,” said Bill Tschudi, senior program manager at LBNL. There are only a few established vendors that are starting to manufacture DC equipment, according to Tschudi. 

Direct current power research and pioneers
LBNL and Intel are currently studying microgrids and on-site power generation in commercial facilities housing data centers and utilizing DC power. Tschudi is working with the University of California, San Diego, where a 24-volt DC microgrid system was built in the school’s new Sustainability Resource Center in 2009. The center also incorporates on-site solar panels and uses 380-volt DC equipment.

At Intel's New Mexico Energy Systems Research Center, the company is building a microgrid that will use both 24- and 380-volt DC standards. The facility will house a data center to be built in early 2011. AlLee is managing this research center and predicts reportable results on DC power usage should be available by mid-2011.

The EMerge Alliance expects that research equipment used on these projects will eventually evolve into commercially viable products.

For the most part, data center professionals are conservative and want to use proven technology with clear incentives for implementation.

“I think it is more of a mindset issue right now [than] a practical training issue. If you are running a mission-critical facility, you are going to be scared to try something that is not widely used,” Tschudi said.

So what is the tipping point for more widespread use of DC power as a data center power distribution method?

“The people that are doing it right now are early adopters," Tschudi said. "If we got enough case studies up and running, [other companies] would come along because they would see that it is OK.”

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