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A group of researchers at University of California, San Diego, has transferred two racks of servers onto 400 Volt Direct Current power earlier this week with the goal of measuring and proving the increase in the amount of compute work per one watt of power the system is expected to achieve.
 
This is a unique approach to powering servers, whose power supplies have traditionally accepted Alternating-Current electricity. Proponents of feeding DC power to servers argue that this approach will substantially increase energy efficiency in data centers because it eliminates multiple conversion steps electricity has to go through in a traditional system before it reaches the servers. 
 
The experimental DC-power set-up at UCSD is part of Project GreenLight, which currently consists of a 20 foot data center container by Sun Microsystems that contains eight racks for compute and networking equipment. 
 
"GreenLight is an instrument that has measurement equipment on it to help researchers figure out how to increase work per watt," said Greg Hidley, technical director of the project. The DC-power experiment is only one of the areas the set-up is used to research. 
 
"DC (power experiment) is just another experiment that we’re attempting to use to show the extent to which you could anticipate more efficient power usage in a server facility," Hidley said. 
 
In a traditional set-up, high-voltage AC power is fed into the UPS system, where it is converted to DC to charge the batteries. It is then converted back to AC before being fed to the servers’ power supplies. Every conversion step results in electrical losses, driving down energy efficiency of the system. 
 
The GreenLight DC set-up feeds 10 servers whose power supplies have been modified to accept DC power fed to them from a 20kW DC power rectification system made by Emerson. The rectification system is installed in the rack enclosure and feeds 400 Volts of DC power to the power supplies designed to take 380 Volts. 
 
Participants in the project anticipate to expand the experiment in the future, which will entail installing an entire DC-powered data center module next to a future fuel cell, expected to generate 2.8MW from methane gas. If the project progresses, the GreenLight data center will use energy from the fuel cell, as well as from the university’s existing and future photovoltaic generation capacity and an energy storage facility.