The pros and cons of DC power
New Data Center Strategies Newsletter By Andreas M. Antonopoulos, Network World, 08/22/06
Tesla and Edison fought over the question of whether alternating current (AC) or direct current (DC) is best for transmitting power. The fight continues today, as the costs to power and cool data centers climb to become the predominant costs of running a data center. Fifteen percent of participants in Nemertes Research benchmark study on Data Centers are evaluating DC power.
The vast majority of equipment in the data center today uses AC power at 110V or 240V. The AC power is delivered to the data center, distributed to the racks and then converted to DC inside individual servers. Only a small subset of telecommunications equipment is routinely deployed with DC power.
The reason DC power is being considered outside the telecom sphere is that each one of the small AC-to-DC converters in the various pieces of equipment generates heat as energy is lost during the conversion. Consolidating all the power conversion into one central large AC-to-DC converter cuts down on heat loss and increases efficiency.
Increased efficiency would mean less power consumption and less heat output, meaning less cooling is required. Studies in DC power by the Lawrence Berkeley National Laboratory show efficiency gains reducing power consumption by up to 15%.
Implementing DC power in an existing data center is most likely prohibitively expensive because of the need to upgrade or replace equipment. In a green-field deployment, however, it is worth considering. Here are some of the pros and cons:
Pros:
* Centralized conversion of AC to DC cuts heat losses and increases efficiency. Less power lost, less heat generated
* Simpler power supply units (PSU) mean less chance of a PSU failure in a server, cutting maintenance and redundancy costs.
* A single standard (DC) for both live power and battery power, which is DC by design, simplifies failover
* Lower cost for servers and other rackable equipment, once it is mass-produced
Cons:
* DC requires thicker cables to deliver the same amount of energy
* Retrofitting an existing data center is probably too expensive
* DC equipment is produced by fewer vendors, creating potential supply problems and higher prices
* AC power distribution systems are well understood. New skills and expertise would need to be developed to support a DC power distribution infrastructure
* Virtualization, multi-core and power-efficient chips may provide a cheaper way of reducing power needs
DC power is making a comeback as it gets more and more expensive to power and cool data centers. At the moment it is mostly seen in telecom data centers and limited pilots and research projects, but mainstream adoption is increasing as demonstrated by the sales of Rackable Systems servers, which are DC-powered. Perhaps it is time to evaluate DC power for your new data center.