The construction of a major energy transmission project from the southeastern Xizang autonomous region to the Guangdong-Hong Kong-Macao Greater Bay Area started on Tuesday, according to the project's constructors.

The ultra-high voltage direct current line, with a rated transmission capacity of 10 million kilowatts, is a key cross-provincial power transmission project under the 14th Five-Year Plan (2021-25) period, with the strongest transmission capacity, the most advanced technology, and the largest investment scale in the world.

The flexible direct current transmission project is jointly constructed by China Southern Power Grid Co and State Grid Corporation of China, following collaborations of a direct current project from the Three Gorges Dam to Guangdong and an interconnection project between Fujian and Guangdong provinces.

The transmission line of the project, which was approved by the National Development and Reform Commission in June, spans about 2,681 kilometers, crossing Xizang, Yunnan province, the Guangxi Zhuang autonomous region, and Guangdong.

Once fully operational in 2029, the clean energy base in southeastern Xizang will be able to deliver over 43 billion kilowatt-hours of electricity annually, or roughly half of the annual electricity generation of the Three Gorges Dam, to the load center of the Greater Bay Area.

Relying on the integrated rich water, wind, and solar clean energy base in Xizang, the project involves construction of two ±800 kV ultra-high voltage converter stations in the sending end in Chamdo and Nyingchi, and another two in the receiving end in Guangzhou and Shenzhen in Guangdong.

The project, with a total investment of about 53.2 billion yuan ($7.47 billion), can replace the consumption of about 12 million tons of standard coal and reduce carbon dioxide emissions by about 33 million tons annually.

"Relying on the direct project, we will overcome world-class technical challenges related to integrating and safely transmitting electricity from high-altitude areas and 10-million-kilowatt-level new energy bases over long distances," Dong Yanle, deputy general manager of the engineering construction department at China Southern Power Grid Co, said. As the first multi-terminal ultra-high voltage flexible direct current project for transmitting clean electricity from Xizang, the project faces challenges such as the development of new technologies for direct current transmission at an ultra-high altitude of 4,300 meters and tackling core technologies for integrating 20 million kilowatts of new energy into a weak grid and transmitting it via direct current, according to Dong.

Nearly 90 percent of the entire transmission line consists of mountainous terrain as it spans three major geographical steps of the Qinghai-Tibet Plateau, the Yunnan-Guizhou Plateau, and hills in South China.