The Return of Direct Current Power Transmission

By Norman Chan

While alternating current is still the dominant standard for our electrical grid, renewed interest in direct current may vindicate Thomas Edison.

Thomas Edison killed an elephant to prove a point. Over a hundred years ago, the notorious inventor was engaged in a embittered rivalry over the best standard for electricity distribution in the United States' budding power grid. The debate, known as the War of Currents, pit Edison's direct current standard against Nikola Tesla and George Westinghouse's alternating current as a way of distributing electricity from power plants to homes. As a way of discrediting alternating current, Edison electrocuted a New York zoo elephant in front of a crowd of 1,500 with 6,600 volts from an AC charge, killing the animal instantly (cyanide-laced carrots ensured it). Unfortunately for Edison, AC eventually won out for its ability to transfer power at high voltages of long distances with the installation of local distribution stations, and it's still the dominant standard we use today.

But a century later, Edison's standard may be vindicated. After all, direct current actually used in most of your electronic devices, like your smartphone, television, and computer. Any piece of technology that uses transistors relies on direct current, which is why we have to use power supplies and adapters to convert AC from the wall to usable stable-voltage DC. According to power consumption studies, DC power used by these devices account for a fifth of our overall power usage, which could grow to 50 percent in the next few decades. The rise of high-voltage rechargeable batteries in electric vehicles could prompt that growth. Using AC to move power over long distances and then locally transforming it to DC will of course still work, but the idea of a DC grid is making a comeback as a way to increase power efficiency.

Photo Credit: Flickr User Thehenryford via Creative Commons

When electricity is converted from AC to DC and vice versa, energy is wasted in the form of heat. This is why your laptop power supply gets hot over time. The amount of wasted energy can accumulate to around 15 percent, plus that extra heat has to be dissipated in commercial buildings like data centers, which requires using more energy in air conditioners.

Many different DC-centric solutions are being proposed, including taking the AC-DC conversion process out of the home and into more centralized regional converters. Direct current is also being used in long-distance transmission lines in the form of High-voltage direct current systems, which more efficiently tap into renewable energy sources like solar and wind farms, which use DC power banks to store energy before feeding to the grid. Building out a DC-based infrastructure is an expensive endeavor, and not everyone is on board with the idea of even using it as a complement to AC power, let alone a future replacement. Facebook, for example, has bought into DC data center technology but Google has not, citing that the investment in refitting its existing data center wouldn't pay out in savings over the long run.

Direct current never went away; it just had to play second fiddle to the practicality of alternating current in the formation of our nation's grid infrastructure. But if DC proponents have their way, the standard may have a chance of becoming more, well, standard.