NYT:
Thomas Edison and his direct current, or DC, technology lost the so-called War of the Currents to alternating current, or AC, in the 1890s after it became clear that AC was far more efficient at transmitting electricity over long distances.
Today, AC is still the standard for the electricity that comes out of our wall sockets. But DC is staging a roaring comeback in pockets of the electrical grid.
Alstom, ABB, Siemens and other conglomerates are erecting high-voltage DC grids to carry gigawatts of electricity from wind farms in remote places like western China and the North Sea to faraway cities. Companies like SAP and Facebook that operate huge data centers are using more DC to reduce waste heat. Panasonic is even talking about building eco-friendly homes that use direct current.
It's interesting that DC transmission is making a comeback. The reason, efficiency:
The revival of DC for long-distance power transmission began in 1954 when the Swedish company ASEA, a predecessor of ABB, the Swiss maker of power and automation equipment, linked the island of Gotland to mainland Sweden with high-voltage DC lines.
Now, more than 145 projects using high-voltage DC, known as HVDC, are under way worldwide.
While HVDC equipment remains expensive, it becomes economical for high-voltage, high-capacity runs over long distances, said Anders Sjoelin, president of power systems for North America at ABB.
Over a distance of a thousand miles, an HVDC line carrying thousands of megawatts might lose 6 to 8 percent of its power, ABB said. A similar AC line might lose 12 to 25 percent.
Direct-current transmission is also better suited to handle the electricity produced by solar and wind farms, which starts out as direct current.
Efficiency is going to be the main driver of innovation in power transmission in the next couple of decades. People aren't going to use any less power, so we'll have to eliminate some of the waste.
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