RIP, DC power?

In the high-voltage battle between AC and DC power, DC will be the ultimate loser, predicts Robert Mitchell over at Computerworld.

In the high-voltage battle between AC and DC power, DC will be the ultimate loser, predicts Robert Mitchell over at Computerworld.

The observation is particularly timely in that The Green Grid consortium has just released to the public a new whitepaper titled "Qualitative Analysis of Power Distribution Configurations for Data Centers," which discusses the qualitative differences between seven possible configurations that can either be found in the United States or Canada today, or could be used in the future.

AC power is, of course, the reigning electricity standard these days, but it's garnered criticism from penny- and eco-conscious souls for its inherent wastefulness compared to DC: "IT equipment power supplies convert incoming AC power to the various DC voltages the subcomponents require. While some equipment also accepts DC input power, most data centers distribute 208-volt AC out to the racks. At least 10 percent of the AC power coming into data centers is lost to AC/DC and DC/AC conversion inefficiencies before it reaches the IT equipment," Mitchell writes.

But DC has two factors working against it. First, any company seeing to take the DC route in its datacenter would have to make some hefty infrastracture investment. "Adopting DC would mean maintaining two power distribution infrastructures, since there will always be equipment in the data center that needs AC. And without a major financial payback, organizations are unlikely to invest the time and money to move into new and uncharted territory," Mitchell writes.

Moreover, by some accounts, DC's advantages over AC are negligible. According to a study from APC (American Power Conversion) [PDF], "a detailed analysis and model show that many of the common benefits claimed for DC distribution are unfounded or overstated." Among APC's findings, "the DC approach with the best performance is the high voltage DC distribution architecture, which offers as much as a 4 percent improvement when compared with other approaches. However, this approach requires a new generation of IT equipment that does not yet exist."

The Green Grid's report has similar observations that DC, though possibly more energy-efficient, faces an uphill battle. Of the DC configurations, the consortium is most bullish about 380V DC, which "appears to promise the highest efficiency but will require the introduction of new products, including UPSs, and changes to IT equipment power supplies."

Among the AC configurations, the paper suggests that 400V AC holds the greatest promise. (480V and 600V are currently the standards for datacenters.) "400V AC can be implemented today, is compatible with a wide variety of power distribution and IT equipment, and has the potential to increase system efficiency," the whitepaper says.

The Green Grid, by the way, intends to examine compare AC and DC in quantitatively and in more detail down the road.

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