by Emil Morhardt
To get electricity from where it is generated to where it is needed requires transmission lines, which inevitably lose some of the power along the way. Using high voltages and transmitting with direct current (DC) rather than alternating current (AC) help. Doing both is best, and with the ultimate goal of being able to move electricity long distances from isolated renewable sources, ultra high voltage direct current (UHVDC) transmission lines are in planning stages or under construction. The first in the US will be a 700-mile long cable from Oklahoma’s wind farms to Tennessee to connect with the Tennessee Valley Authority grid. Similar initiatives are under way in China, Europe, and Brazil. Some lower voltage DC lines have been operating for years; one transmits power along the east side of the Sierra Nevada mountains from the massive hydroelectric dams on the Columbia River between Washington and Oregon to Los Angeles. Others connect oceanic islands; across the English Channel and between New Zealand’s North and South Islands, for example, where AC is impractical because of the losses from interaction of its alternating magnetic fields with ions in salt water.
In China most of the population is over 2000 km from the sources of power. The first of its UHVDC lines operates at 800,000 volts and can transmit 6,400 MW the from the hydroelectric dams in Yunnan to Shanghai. The largest, presently under construction will operate at 1.1 million volts, and carry 12,000 MW (half the average power use of Spain!).
Ultimately this technology, if pushed to its logical limits, will provide solar energy from the daytime side of the world to the nighttime one, and from wherever wind is blowing.
Anonymous, 2017. Rise of the Supergrid. The Economist January 14th, 2017, 71-72.