Going the Distance With UHV
Posted by Big Gav in electricity grid, uhv
The Wall Street Journal has a special segment on energy, including this article on long distance electricity transmission (using UHV rather than HVDC) - Going the Distance.
China wants to use melting snow on the Tibetan Plateau to power neon lights more than a thousand miles away in Shanghai. And to make that vision a reality, it is dusting off a 40-year-old technology for moving electricity -- ultra-high-voltage power lines.
UHV lines can not only carry more electricity than regular lines but also move it vast distances with less loss of power. That makes UHV ideal for bringing electricity from remote areas, such as hydropower projects in the foothills of the Himalayas, to China's eastern urban centers.
A number of countries gave the idea a test run decades ago, but improved technology has made it a lot more practical -- and attractive. Now China is betting that UHV can solve its massive energy dilemma. Most of the nation's resources, such as coal and hydropower, are located far from the booming cities that need electricity most. And trucking coal across the country, or building more power plants near cities, would make China's pollution even worse.
The developments are being closely watched around the world. Densely populated India and Brazil also see the technology as a way to secure future energy supplies. In the U.S. and Europe, meanwhile, utilities need to build high-voltage transmission lines to carry electricity from remote regions rich in solar and wind power.
"I would expect that the more countries use renewable energy," the more they look to UHV technology, says Daniel Assandri, senior vice president and head of the power-system division for ABB Ltd. in China and North Asia, which is working on China's UHV project.
China's proposed network will cover 56,000 miles and allow up to 6.4 gigawatts of power to be transmitted on each line -- equivalent to nearly two-thirds of the entire generating capacity of Singapore. State Grid Corp., one of two state-owned power distributors, has said it is seeking regulatory approval to spend as much as $14.6 billion over the next three to four years to roll out UHV power lines.
It's an ambitious plan, but China is in urgent need of an upgrade. According to a 2007 report by the International Energy Agency, China needs to invest $1.51 trillion in its grid through 2030 to accommodate soaring demand for power. And the potential power sources are far from the growing eastern cities where electricity is needed.
Two-thirds of China's coal deposits are concentrated in a handful of inland provinces, more than 620 miles from the manufacturing hubs of the Pearl River Delta. Government planners want power generators to build plants closer to coal supplies and then ship their electricity via the grid.
China also wants to make better use of its renewable-energy resources, particularly hydropower, but two-thirds of its dams are located in distant southwestern provinces such as Yunnan and Sichuan. Hydropower currently accounts for nearly a fifth of China's electricity generation, but much of it is used locally rather than shipped to cities because the grid is inadequate.
The quest to transmit electricity greater distances at higher voltages dates back decades. Governments and utilities began to look seriously at the problem in the aftermath of World War II as a way to meet rising energy demand, particularly in cities.
Conventional transmission lines, which use alternating current, can carry up to 500 kilovolts of energy from power plants to substations for distribution. But they're limited in how far they can transmit power, typically up to about 530 miles. And they lose a significant amount of power -- about 7% of capacity -- in transit, requiring power plants to produce more electricity than is used.
In looking for an alternative, engineers tried a couple of different paths. One was direct-current power lines, which can transmit electricity at greater distances than AC lines, with less power loss. But many utilities felt DC lines were too expensive, since they required converter stations to turn the power to AC so it could be distributed to utilities and consumers.
An electricity worker sits atop a newly constructed high-tension electricity tower located on the outskirts of Kangding in Sichuan province. The State Grid Corp. of China aims to at least triple its ultra-high voltage power transmission lines by 2012.
The other avenue of exploration was higher-voltage AC lines. They first appeared in Canada in 1965, spurring interest in the technology from Tokyo to São Paulo. Several test lines were built during the 1970s in the U.S., but the most progress was made in the Soviet Union. However, interest waned in the 1990s after the Soviet Union collapsed and power demand in Japan stagnated.
Now improved technology has made UHV more feasible. For instance, insulators on UHV systems used to be made of porcelain. Now it's possible to use materials like silicone rubber.
China currently has only one functioning UHV line, a 1,000-kilovolt AC pilot project that represents the highest-voltage system operating commercially anywhere in the world. The line connects two big power grids: one in Shanxi province in northern China, which relies heavily on coal-powered plants, and another in the central province of Hubei, which has abundant hydropower resources, including the Three Gorges dam, the world's biggest. The line enables power to be transferred between the grids whenever there is a shortfall in supply.
More UHV AC lines are planned, but Beijing concedes the technology isn't commercially viable yet. Suppliers haven't achieved economies of scale on core equipment, and the lines aren't yet carrying enough power to show real savings over conventional systems.
As a result, State Grid and China Southern Power Grid Co., another state-owned power distributor, are pushing most aggressively into building UHV DC lines. Despite the need for converter stations, the DC approach is still cheaper for the time being; according to ABB, it's about 25% less expensive than UHV AC over 1,240 miles or more.
State Grid has awarded tenders to ABB, Siemens Ltd. and local companies to build an 800-kilovolt DC line from a hydropower station in southwestern China's Sichuan province to Shanghai. Lu Jian, head of the development and strategic-planning department at State Grid, says the company plans to have around 56,000 miles of UHV lines in operation by 2020, up from about 400 miles now.
Also in the section is an article on ocean energy in Scotland - Surf's Up.
Scotland, which boasts some of the fastest-flowing tides in the world, is placing a big bet on what many believe is the next wave of renewable energy -- marine power.
The government is encouraging companies to invest in projects designed to convert the motion of tides and waves into electricity with the aim of generating as much as one gigawatt of electricity -- enough to power roughly 940,000 homes -- from its coastal waters by 2020.
Although some experts say Scotland eventually could rely on marine power for 40% or more of its electricity needs, the technology is still in its infancy. Among the industry's biggest challenges: developing equipment that can withstand the punishing environment off the Scottish coast and reducing the cost of generation so that marine power can better compete with more established sources of energy. Making things even more difficult is the credit crisis, which has made project financing harder and more expensive to get.
Neil Kermode, managing director of the European Marine Energy Centre, a marine-energy testing site located in Orkney, Scotland, sees a parallel with the early days of the aviation industry, saying that while wave and tidal equipment is well along in terms of development, lengthy testing is required before it can be deployed on a commercial scale.
"I believe we're now where the Wright brothers were when they did the first tentative flights, but they still needed to do short hops and then longer hops before they got to master the sky," he says.
The wave- and tidal-power devices in use today are small -- most are less than one megawatt, or about a third of the size of a typical commercial-scale wind turbine -- and are deployed individually or in very small arrays. To date, only about 10 megawatts of wave and tidal power have been installed world-wide, compared with 120 gigawatts for wind power.
Nevertheless, the potential of marine energy has drawn the attention of Europe's top utilities, including Spain's Iberdrola SA, Germany's RWE AG and E.ON AG and the U.K.'s Scottish & Southern Energy PLC. They are investing in wave and tidal technologies with the aim of eventually installing arrays across the U.K. capable of generating tens of megawatts of electricity each.
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