Ultra High Voltage DC Transmission
Can we use the afternoon sun in Perth to power the evening in Sydney? Imagine harnessing sunlight from thousands of kilometers away to power our cities at peak times. In today's article, we explore the groundbreaking energy technology that can do just that. Ultra High Voltage Direct Current, or UHVDC is reshaping how power is transmitted over vast distances.
Perth enjoys about 9 hours of sunshine per day, making it the sunniest capital city in Australia and a prime source of solar power.
As countries globally seek efficient renewable energy solutions, China leads the charge in this technology, successfully employing UHVDC to link its hydro, solar and wind-rich western regions with densely populated eastern cities. This success prompts a critical question: Why haven’t countries like the USA or Australia, with seemingly similar geographies, adopted UHVDC?
Consider the potential — what if UHVDC could link Western Australia's abundant solar resources to the main Australian grid? This could allow Sydney at 5 PM to use solar power generated at 3 PM in Perth. Or in the USA it could be California’s 2 PM sunshine powering New York’s 5 PM or transporting wind from the lightly populated mid-west to the cities. The implications of such a capability are profound and could revolutionize energy use across time zones. So why isn’t UHVDC more widespread?
Understanding HVDC and UHVDC Technologies
High Voltage Direct Current (HVDC) uses direct current (DC) for electric power transmission, in contrast to the more common alternating current (AC) systems. HVDC networks typically operate at voltages ranging from 100 kV to 800 kV. A notable advantage of HVDC is observed in subsea interconnectors, where increasing the voltage to 500 kV and swapping from AC to DC reduces losses and enables longer distances to be covered.
Increasing the voltage to UHVDC reduces power losses to as low as 1.5-3% per 1,000 km.
By stepping up again to 800 or 1,100 kV we get Ultra High Voltage Direct Current (UHVDC) and we see a turbocharged improvement in the efficiency of power transfer, meaning even longer distances can be covered. In fact, losses in HVDC systems are about half those of AC lines at the same voltage level. By further increasing the voltage to UHVDC, power can be transmitted at a lower current, which not only reduces losses further—potentially to as low as 1.5-3% per 1,000 km depending on the voltage—but also allows the use of cables with smaller diameters. Another benefit of having a lower current is that it allows for the use of cables with smaller diameters, which are not only more efficient but also less costly and easier to handle and install.
What is China doing?
There are currently about 40,000 km of UHVDC in the world, and 80% of that it is in China. China has so much renewable energy potential in the west, but its population is mostly located thousands of kilometres away in the east. With such long distances involved, and without a lot of existing transmission already in place it made sense to go as high voltage as possible, so China has invested heavily in this technology. Their first breakthrough came with the Yunnan-Guangdong project, transmitting 5 GW from the hydro-rich Yunnan province to the industrial hub of Guangdong. It commenced operation in 2010.
Since then, they have completed 20 UHVDC lines totalling over 35,000 kilometres. The standout example is the Changji-Guquan link which came online in 2019. It currently holds the record for the world’s longest power transmission line of its kind, spanning over 3,300 km. It is also the highest voltage at 1,100 kV, compared to the 800 kV of China’s other UHVDC, and it transmits up to a massive 12 GW of electricity, which for comparison is about the size of Hungary’s entire electricity grid, in one single transmission line.
The 1,100kV Changji-Guquan transmission line is the world's longest and most powerful ultra-high voltage power line. Image source
There are another eight thousand kilometres of UHVDC under construction in China and plans for further expansion in the latest Five-Year Plan, which continues to work on integrating renewable energy sources like hydro, wind and solar from the north and west into the national grid.
Projects elsewhere
Outside of China, there are only two countries with UHVDC as for now.
India has the North-East Agra Link that connects hydro power in its northeastern regions to Agra. It stretches approximately 1,700 km. There’s also the Raigarh-Pugalur link of approximately 1,800 km, connecting Raigarh in Chhattisgarh to Pugalur in Tamil Nadu. These UHVDC lines not only help mitigate the frequent power shortages but also support the integration of renewable resources into the country’s grid.
In Brazil, there is Belo Monte-Rio de Janeiro line, which extends over 2,500 km, which makes it the second longest in the world, and the longest 800 kV line. It was developed to transport electricity from the Belo Monte hydroelectric plant in the north to the highly populated southeastern states. It was completed in 2019, built with Chinese contractors and suppliers as part of China’s Belt and Road Initiative and it’s owned and operated by Xingu Rio Transmissora de Energia (XRTE), a subsidiary of Chinese state-owned State Grid Corporation of China. That followed on from the 2,100 km Monte Bipole I that connects Xingu in Para to Estreito in Minas Gerais. It was commissioned in December 2017 and is also majority owned by Chinese companies.
Belo Monte UHVDC Bipole II line connects Belo Monte Dam in the north to city areas in the south. Image by Bruno Batista
Why aren’t there many projects outside of China?
Currently, there are no known plans for UHVDC projects in either Brazil or India, nor are there any announced initiatives for such projects outside of China. Why could that be?
While UHVDC offers immense benefits for long-distance power transmission, its deployment outside of China and those few Indian and Brazillian lines is limited by a variety of complex challenges. UHVDC systems demand sophisticated and robust infrastructure, including specialized converter stations and enhanced insulation. This complexity not only increases the initial capital expenditure but also requires advanced engineering expertise and rigorous maintenance to manage risks like insulation failures and corona discharge effects. China, having already installed tens of thousands of kilometres of UHVDC, has largely derisked the technology by now as they have lots of technical expertise and skilled workers to complete projects without surprises.
Furthermore, the scale of investment makes economic sense only for very long transmission lines. This may be justifiable where large, populous cities are far from power generation sites, like China’s hydropower and wind resources in the west.
In contrast, countries that do not face similar geographic challenges, or have already invested in alternative transmission infrastructures, such as traditional HVDC or upgraded HVAC systems will find UHVDC is less compelling, as it involves decommissioning existing systems which are adequate for current needs.
Additionally, implementation of UHVDC can encounter significant regulatory and environmental hurdles. The large-scale nature of UHVDC projects can lead to substantial environmental impacts and public opposition, further complicated when extensive negotiations are required with landowners along proposed routes.
Why is China leading with UHVDC?
China's central planning and national policy strongly support UHVDC as part of a broader strategy to enhance energy security and to lead in high-tech infrastructure sectors. It is simply much easier for a country like China to include UHVDC in their plans because their government is used to centrally planning and implementing large infrastructure projects. They do not have to worry about convincing hundreds of individual landowners along thousands of kilometres of transmission route.
China has built more UHVDC transmission lines than any other country to electrify the nation.
Can we have UHVDC link in Australia?
Should we install UHVDC to connect western Australia to the main Australian grid so that 5 pm Sydney’s peak demand could use solar power from 3 pm Perth?
UHVDC costs about approximately $2 million per kilometer for a 2 GW capacity, and it’s a little over 2,000 kilometers between Perth and Adelaide where the main grid starts. That would be a bit over $4 billion for the transmission lines, plus a few million more for substations either end.
If we have got $4 billion burning a hole in our pocket, why not spend it on grid scale batteries to get that 2-hour time shift instead? Assume $200 per kWh for grid-scale lithium-ion batteries, a $4 billion investment would afford 20 GWh.
We could get 2 hours of 10 GW, which is five times what our transmission line will carry. Or we could get a 5 GW battery that lasts 4 hours which would take us all the way through the evening peak, not just the first part of it. The 2-hour time difference is not quite enough to be super useful.
Investing $4 billion in grid-scale batteries could better address peak demand than a UHVDC link between Perth and Sydney.
Other pros of the battery alternative include not needing to install and then maintain thousands of kilometres of transmission through uninhabited areas, but a con is that you aren’t diversifying your solar resource at all. If it’s been a cloudy couple of days on the east coast, a battery won’t let you take advantage of sunny skies in western Australia.
These economics show that UHVDC doesn’t really make sense when you’ve got local renewable energy resources that could be used instead. Australia has great solar potential on both east and west coast, so it’s better to use them locally in this case.
Conclusion
To summarize, UHVDC needs a pretty specific set of conditions to work. Therefore, it’s unlikely that we’re going to see UHVDC transmission criss-crossing the planet any time soon. Perhaps in time HVDC will creep up in voltage to improve efficiency, but for the moment, UHVDC appears to be a solution particularly suited to China due to their local needs and expertise and the country's advanced expertise in this technology.
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