'A bullet train for power': China's ultra-high-voltage electricity grid

This article was originally published by the BBC, 2024. The article has been republished here with minor modifications, with the permission of the original authors.

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In a sleepy village on the fringes of Shanghai, China's megacity of 25 million people, a hulking green building surrounded by a labyrinth of electric wires and poles stands in contrast with the landscape around it. Surrounding this beast, not far from the coastline of Hangzhou Bay, the vast funnel-shaped inlet of the East China Sea, are an array of vegetable plots, winding country paths and a tranquil canal.

This oddly out-of-place building is the Fengxian Converter Station, a hub for receiving electricity that has travelled some 1,900km (1,200 miles) before it is routed to power Shanghai's homes, offices and factories. At the other end of the transmission line lies the Xiangjiaba Hydropower Station in south-west China, which harnesses the energy of the mighty Jinsha River, the upper stretches of the Yangtze River.

The Xiangjiaba-Shanghai transmission link, which went into service in 2010, is one of China's first ultra-high-voltage (UHV) projects – a technology designed to deliver electricity over long distances. It spearheaded an era that would see the country build a vast network of UHV infrastructure, dubbed the "bullet trains for power", to send electricity generated from hydro and coal in remote regions to populous cities.

China now considers these huge power cables key to its rapid buildout of wind and solar power bases, which are concentrated in several far-flung regions. Countries such as the UK, India and Brazil have adopted similar strategies.

Although using UHV isn't the only way to transmit renewable energy, its application in China – home to the world's largest national power system – can provide valuable lessons in a global quest for solutions to fast-track the energy transition.

The 'bullet train for power'

In a nutshell, UHV transmission lines work to the principle that the higher the voltage is, the lower the electric currents are for the same amount of power transmitted. Lower currents lead to less heat loss as power moves through cables, enabling it to travel long distances with greater efficiency.

The Chinese call them the "Shinkansen for power", using the Japanese name for bullet trains, a symbol of speed and efficiency.

For Guo Liang, an engineer at the Chinese Academy of Sciences, the fastest way to supply electricity is to wire it to its users rather than transporting raw materials to power plants that are closer to them.

Electricity travels nearly as fast as light and is expensive to store. "As soon as it is generated, it needs to be sent out. That's why we need such a network, the Shinkansen for power, to ensure its transmission" to those who use it, Guo said during a talk show on China Central Television.

Different countries have different thresholds for what is considered a UHV line. China defines those sending direct currents (DC) at voltage levels of 800 kilovolts (kV) or above and alternating currents (AC) at 1,000 kV or above as UHV links. DC systems can carry more power with less loss than AC, and are used to cover greater distances, but they are more expensive to build. In comparison, AC lines can be connected to the local grids enroute, so they are more flexible. But their lengths typically do not exceed 1,500km (930 miles), so as to be cost-effective. China has a mix of them.

Although China now regards the technology as a key part of its wind and solar plan, it didn't set out to build them for renewables. China's State Grid, one of the country's two grid operators, proposed the technology to the government in 2004 to connect the country's hydro and coal power stations with the economic hubs that gobbled electricity hundreds of miles away.

"Most of China's natural resources are situated in the north, north-west and south-west, while the highest electricity demand and population are concentrated on the southern and eastern coast," says Deng Simeng, a Shanghai-based renewables analyst at Norwegian consultancy Rystad Energy.

In the early 2000s, China was experiencing regular power shortages. Even though three-quarters of the country's freight traffic was devoted to transporting raw materials, especially coal, resources weren't arriving fast enough. At that point, the central government was also seeking ways to develop its vast western regions by tapping into its resources.

Liu Zhenya, the then head of China's State Grid and dubbed by the Chinese media as the "father of UHV power lines", envisioned a future where a mega grid would end the country's blackouts – by transmitting electricity nationwide – and make China a global leader in transmission technologies. But his idea was met with staunch opposition. In the years to come, his opponents, which included officials and prominent scholars, repeatedly highlighted to the government their concerns, such as the reliability of the technology and its impacts on the environment.

"[Liu's] proposal was really bold and a novel concept at the time, and gained traction amongst Chinese policy makers," says Fiona Quimbre, a Cambridge-based analyst focusing on China at RAND, a global research organisation. The State Grid, a major state-owned company, managed to align itself "really well with other government priorities", including a plan to foster domestic supply chains, she says.

In 2006, developing UHV made into Beijing's five-year plan, a sign that it had become a national strategy. China began constructing its first project in the same year, a 640km (400-mile) AC link connecting its coal heartland of Shanxi in the north to the central province of Hubei, via a stop in the middle. It went into operation in early 2009.

More ambitious projects quickly followed. The Xiangjiaba-Shanghai line, completed in 2010, was the longest and most powerful transmission system worldwide at the time. With 3,939 pylons carrying cables over gorges, rivers and rolling fields across eight provincial-level regions, the DC link sends Jinsha River's hydropower directly to Shanghai at a maximum capacity of 6.4 gigawatts, meeting up to 40% of the city's power demand.

As of April 2024, China had put into operation 38 UHV lines, which deliver not only hydro and coal power, but also wind and solar power, according to China Power Equipment Management Net, an industry website. Among them, 18 were AC lines and the rest DC lines.

Delivering renewables

UHV technology was not invented by China, but Beijing has made these projects "business as usual", says Ismael Arciniegas Rueda, a Washington DC-based economist at RAND who specialises in energy and transmission infrastructure.  

"China has taken [UHV] to the next level and pushed the envelope" in a way it has with many technologies associated with energy transition, Arciniegas says.

He describes China as "the only game in town" when it comes to the number of miles built of this technology. Other countries, such as India and Brazil, also have some of the longest UHV lines in the world, but they do not use them at quite the same scale or operate at the same level of voltages.

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