The Changji-Guquan transmission line is a colossal feat that will be able to transmit 12,000MW of power, or enough to meet the needs of 26.5 million people, across China. It will transmit the same amount of power as Romania uses in a year, or half of Spain’s energy demands, over a distance greater than Barcelona to Moscow as the crow flies.

Such a huge project is unsurprisingly beset with challenges, as ABB, a key supplier for the project, explains.

“The main challenges have been with going from 800kV DC up to 1100kV DC; this is a large technological step, much larger than going from say 500kV DC up to 800kV DC,” says ABB global product manager of HVDC transformers Markus Pettersson. “Enhanced di-electrical or insulation requirement is one of the biggest challenges as this increases exponentially with voltage; this makes the equipment much larger.

“Also, from a transformer perspective, there's the mechanical side, because we are building things that have never been built. The sizes of all the things that we're building are so much larger that we've never built this before.”

ABB has been working with SGCC on HVDC and UHVDC technology for decades, and has a wealth of experience. Even so, the size and the weight of the transformers meant that it needed to invest in and update its factory in Sweden to deal with the sheer scale.

“An example is the bushing when going from 800kV DC to 1,100kV, which is only 300kV so it doesn't sound like much but that's resulted in wall bushings that are 40% longer and three times heavier than at 800kV, so it's not just an electrical problem, it's a mechanical, structural issue as well,” says ABB global communications manager Ryan Ladd.

China has built more UHVDC transmission lines than anyone in the world as it works to electrify the entire nation. This is complicated by the distance the majority of Chinese cities lie from major generation sources. The country still relies heavily on coal, and three-quarters of coal plants are located in the far north and north-west. Almost all of China’s hydroelectric capacity, four-fifths, is in the south-west of the country. However, the vast majority of citizens live in the east where cities like Shanghai and Beijing are located.

“The reason that we need this is that you have most of the generation of energy located in remote areas where we don't need it, so these long-distance transmission links, the UHVDC links, are needed to bring transmission of the power to the load centres with low losses,” says Pettersson. “We have a lot of renewable energy sources around the world that are not utilised today, which we should utilise more.”

The environmental advantages of UHVDC technology are clear and compelling. Implementation of renewables has been hampered in many areas by the inability to get the power to where it’s needed most. In Germany, the huge wind farms in the north are often switched off as they are incapable of getting the power to the south, where the majority of cities and industry are located.

UHVDC networks would allow for clean power to be quickly distributed over huge distances. This would ease difficulties created by lack of natural energy sources, and take full advantage of times when they were booming.

For example, a recent report by researchers from the Earth System Research Laboratory, published in Nature Climate Change, found that a UHVDC transmission line in the US could cut emissions by as much as 80% by harnessing Wyoming’s abundant wind power potential and transporting the electricity to California.

Initially UHVDC lines are unlikely to enable greater renewables usage in China, because of rigidity in the larger system as opposed to any particular limitation of the technology. But of the UHVDC lines currently under construction or in the planning phase, less than half will be used for renewables as thermal generation can still provide a more reliable, and therefore often more attractive, power source.

But while this may dampen the environmental argument for them on one front, UHVDC along with HVDC transmission greatly reduces the amount of power lost in transit. As such, less generation is required to meet the same amount of demand, ensuring that the most is made from thermal power.

Despite the key benefits of a megagrid, the potential of Chinese expansion throughout Asia and beyond has been met by concern in some quarters.

"The great success of UHV technology application in China represents a major innovation of power transmission technology," SGCC said in a statement in MIT Technology Review. "State Grid would like to share this kind of technological innovation with the rest of the world, addressing a possible solution to vital concerns for humankind for example, environmental pollution, climate change, and lack of access to electricity supply."

The concept of UHVDC interlinking China with other nations in Asia and beyond is seen by some as a financial and geopolitical move.

Having such a large role in developing transmission lines could give China the ability to exert a huge amount of pressure on a country, although defenders are quick to highlight that China wouldn’t necessarily manage the grids, but will simply build the transmission systems.

“All of this fits in with Beijing’s goals of expansion and being a global standard setter,” Erica Downs, an expert on China and energy at Columbia University, told CNBC. “It is also linked to China’s intention to become an advanced industrial superpower. There is a big prestige element in this.”

The concept of interlinking grids between countries is far from new, and already HVDC transmission lines run throughout Europe, connecting countries and increasing energy security.

While we are unlikely to see a colossal crisscross of transmission lines emanating from China immediately, the lure of a secure power network allowing greater utilisation of renewables is unlikely to go away.