(John Kemp is a Reuters market analyst. The views expressed are his own)
By John Kemp
LONDON, Nov 16 (Reuters) - The concept of a "super-grid" capable of moving huge amounts of electricity over long distances is popular with environmentalists and governments keen to promote the integration of more renewables into the power supply, overcome transmission bottlenecks and bring power to remote communities.
"An electricity super-grid could take green electricity produced in one country to another through thousands of kilometres of sub-sea cables. Wind farms built out at sea could also be connected to a number of countries," Britain's Department of Energy and Climate Change announced last year.
The super-grid would be "a pan-European transmission network facilitating the integration of large-scale renewable energy and the balancing and transportation of electricity, with the aim of improving the European market", according to the Friends of the Super-Grid, a lobbying organisation.
It would connect wind farms in northern Europe with solar power producers in the Mediterranean and North Africa and the massive power-consuming centres in the centre of the continent.
Policymakers should proceed with caution, however, because highly interconnected systems are inherently vulnerable.
"Vulnerability is an unintended side effect of the nature and organisation of highly centralised technologies," Amory and Hunter Lovins explained in a famous report for the U.S. Federal Emergency Management Agency.
"Complex energy devices were built and linked together one by one without considering how vulnerable a system this process was creating," they wrote in 1982 ("Brittle Power: Energy Strategy for National Security").
Super-grids will require significant improvements in control to maintain stability.
Power engineers at ABB recently announced a new generation of super-fast, high-voltage direct current circuit breakers that can stop the flow of power within 5 milliseconds.
"The breaker can cut out the faulty line and keep the rest (of the grid) healthy," according to the company's chief technology officer.
But the much bigger problem is how to keep the system balanced in the event of a failure along one of the ultra-high voltage transmission lines, or if a region exporting power to the rest of the network suffers some sort of failure that abruptly halts exports.
The idea of linking up existing regional and national power networks in a super-grid system is not restricted to Europe.
The United States is backing "Connecting the Americas 2022," a programme that aims to bring power to the 31 million citizens in Central and South America who currently lack access to reliable, clean and affordable electricity within the next decade.
Connecting the Americas backs more electrical links. "Electrical interconnection benefits all countries by allowing those with excess power to export electricity to countries that have a power deficit," according to the U.S. Department of Energy.
"Interconnected power systems allow for greater integration of renewable energy resources as well as power exchanges among countries with varying climate and seasonal needs. Interconnection expands the size of power markets, creating economies of scale, which can attract private investment, lower capital costs and reduce electricity costs for consumers."
Grand plans for connecting up entire continents remain at the conceptual stage, but even without them power networks are becoming increasingly interconnected.
National grids in Finland and Estonia have been linked by a high-voltage, direct current (HVDC) sub-sea cable capable of delivering 350 megawatts (MW) in either direction since 2007 (Estlink 1). Estlink was explicitly intended to link up the Baltic and Nordic power markets. Another cable is planned to come into operation by 2014 (Estlink 2).
In Namibia, the Caprivi Link joins the remote northeast part of the country, which is part of the Zambian grid, with the rest of Namibia.
India's Power Grid Corporation has linked and synchronised four of the country's massive regional power networks (the Northern, Eastern, Western and North Eastern grids) in a super-grid. The final Southern grid will be synchronised by 2014.
No country has done more to build a nationwide super-grid than China.
State Grid Corporation is building an enormous inter-regional transmission system to move power from coal-rich areas in the northwest and hydropower-rich provinces in the southwest to the massive consuming centres including Guangdong, Zhejiang and Shanghai on the east coast.
State Grid has built both alternating current (AC) and direct current (DC) transmission lines operating at ultra-high voltage (UHV) to move power over long distances.
The 1 million volt Jindongnan-Nanyang-Jingmen AC line went live in December 2011, moving electricity from power stations in coal-rich Shanxi east to Hubei province. The 640 kilometre line can transport 5 gigawatts, equivalent to 60,000 tonnes of coal per day.
DC links such as Xiangjiaba-Shanghai and Jinping-Sunan have also gone into operation, connecting the enormous hydro dams in Sichuan to coastal mega-cities such as Shanghai.
Even more ambitious projects are under construction. In May, State Grid commenced work on a vast 2,200 km UHV DC line from Xinjiang in the far west through the provinces of Gansu, Ningxia, Shaanxi and Shanxi all the way to Henan in the east.
State Grid sees a super-grid as essential to meeting the country's energy demand while easing pressure on the railroad system.
In September, however, the Energy Research Institute (ERI) of China's powerful National Development and Reform Commission urged the government to apply the brakes.
"The building of large-scale and long-distance UHV transmission systems should be avoided," ERI warned. "The cost and power loss of long-distance UHV transmission systems are tremendous.
"In addition, this kind of system is relatively fragile. Once an accident happens, widespread power outage and power surplus will co-exist, causing immense damage to the eastern and western regions. If all the country's grids are connected by UHV transmission lines, if the lines broke because of some natural or human incident, it would result in a nationwide power outage. The potential hazard is huge."
Stability is a major concern on massive networks, where a problem in any one part can bring cascading failures across the entire system.
India's widespread blackouts on July 30 and 31, which took out the power supply across the four synchronised regional grids, were a stark reminder of the fragility that can be introduced by creating a widespread network.
At a special conference called to examine the Indian blackouts, China State Grid's power engineers blamed the mass failure on "lack of unified controls and too many rituals causing untimely implementation of orders, which grew into a national blackout".
In contrast to the Energy Research Institute, State Grid officials said they "consider that the interconnection of power grids should be further improved. Otherwise, the partial failure will trigger a chain effect or a considerable drop of power generation, which would bring on a large-scale blackout because of weak mutual support."
The stability of super-grids is controversial. Interconnectedness together with inadequate control systems were responsible for widespread blackouts in the United States in August 2003. However, advocates of super-grids claim they can also be a source of stability.
Much of the controversy focuses upon AC grids, which must be synchronised. In contrast, DC interconnectors between separate AC networks can help ensure that failures in one network are not transmitted to the other.
Siemens, for example, notes that during the August 2003 blackout, power remained on in Quebec because the province was connected to the rest of the North American network only by DC lines, which acted as a firebreak even as failures cascaded across other parts of the Northeast United States and Ontario.
Some super-grid advocates have suggested a mixed system - with regional and national AC grids linked by DC interconnectors, providing firebreaks against failure - or a DC pan-continental grid superimposed over separate AC national grids. But that may not be enough.
If the dream of super-grids is to be realised and not become a nightmare, super-transmission will have to be matched with super-control, which may be doable but has yet to be achieved. (editing by Jane Baird)