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AC or DC? Should We Switch Our Electric Current?0

Michael Kanellos | Wed Dec 15 2010 |

Direct current didn’t go away. It just went underground.

In 1893, George Westinghouse won the “war of currents” over Thomas Edison and the decision paved the way for electricity to conquer the globe. However, it also created a conflict that has been growing ever since.

Although AC remains the ruling standard transmission, most devices that consume electricity–cars, planes, light rail systems, computers, consumer electronics, and pretty much anything with a battery actually run on DC.

“The old telephone system always worked,” said Brian Fortenberry, a program manager at the Electric Power Research Institute, citing another DC success story. “The reliability is exceptional.”

Solar panels and fuel cells, meanwhile, natively produce DC power.

To pave over the mismatch, electricity is converted from AC to DC and vice-versa, often several times, before it gets consumed. In data centers, AC power gets converted to DC by an uninterruptable power supply, which reconverts it to AC before sending it to the servers, which reconvert it to DC. Each conversion results in losses. The multiple conversions also boost the number of times power has to be stepped from a high to lower voltages.

In buildings, DC power from solar panels becomes AC in an inverter, and DC again when it gets to LED lights. The heat coming off your notebook brick? The waste product of an AC-DC conversion.

Thanks to advances in power electronics, tremendous amounts of power could be saved by curbing these conversions. Validus DC Systems has created a system that converts AC into DC at the data center door and then uses DC throughout the building, effectively turning the data center into a DC microgrid. General Electric, IBM and Sun have partnered with the company.

A recent Duke University test showed that DC data centers consume 15 percent less power. Others peg the potential savings at closer to 30 percent.

As an added bonus, making a data center a DC island reduces components; that boosts reliability, cuts costs and increases the number of computers that can fit in a room, according to James Coakley, CEO of Power Loft Services, which designs energy efficient data centers.

“The greater number of devices between a power source and a computer, the greater number of opportunities for failure,” he said.

Meanwhile, Nextek Power Systems and conglomerates like Panasonic and Sharp are studying ways to bring DC to commercial buildings or homes so solar panels could directly power appliances or electric cars. A 380 volt DC charger can charge an electric car in 10 minutes, said Liang Downey, director of digital applications. A 220 volt AC charger needs five hours.

Even transcontinental DC is on the way; over 145 high voltage direct current (HVDC) projects are underway in China, Texas and elsewhere to bring DC straight from wind farms to urban DC microgrids.

Critics, though, note that power supplies have continued to become more efficient over time. Hybrid buildings also create potential headaches and confusion for tenants and homeowners. AC works everywhere; it’s a big advantage.

Still, policy makers and corporate customers are seeking out any way possible to reduce power consumption.

Will the best way to solve that problem mean going back in time?