Answer

What's limiting on-site DC data center power supply?

Is grid dependence the real limiter against on-site DC power for data centers? I know someone who has high, over fuel cell, energy-efficiency generation tech. He just doesn't know where to go to connect with data center power infrastructure decision makers.

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Direct current (DC) power in the data center and as a means of power transmission is very misunderstood.

Direct current (DC) power in the data center and as a means of power transmission is very misunderstood.

There are very practical reasons to use alternating current (AC) power transmission. However, there are high-voltage DC power transmission lines in operation today in the U.S., Canada, Asia, South America, and even undersea, with more proposed. The operative phrase here is "high-voltage," namely, 500,000 to 800,000 volts. High-voltage power doesn't run around cities or into homes and buildings because wire losses would be too great at buildings' voltages (480/208/120 in the USA, and 415/240 in Europe).

DC to the computing equipment is different. The data center industry standardizes on 380 volts for direct current power to the servers. This is the same voltage that computer power supplies develop internally from the 120/208/240-V line that comes in from residential and business power sources. 380 volts DC can also be obtained from fuel cells, rotary converters or flywheel uninterruptible power supplies.

The electric utility does not deliver 380-V DC power to a building, but that in no way limits your ability to distribute DC power to the data center equipment. Limitations come from a lack of familiarity with DC distribution and a resulting reluctance to use it, as well as limited availability of computing equipment designed to run off of DC power.

There are still debates as to the actual efficiency gains DC power delivers. Consult available literature on DC vs. AC before making the decision as to which power system to use. Talk with the major DC data center power system vendors, current DC data center operators and the Lawrence Berkeley Labs investigators who did the 2007 demonstration project on DC powering.

About the author:

Robert McFarlane is a principal in charge of data center design at Shen Milsom and Wilke LLC, with more than 35 years of experience. An expert in data center power and cooling, he helped pioneer building cable design and is a corresponding member of ASHRAE TC9.9. McFarlane also teaches at Marist College's Institute for Data Center Professionals.

This was first published in April 2014

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