Italian company wins $1 billion cable contract for Battery of the Nation sub-sea link

Italian company Prysmian has been awarded the $1 billion contract to supply the high-voltage direct current (HVDC) cables that are the core of Marinus Link, the sub-sea cable that is key to the so-called “Battery of the Nation” project.

The contract covers the design, manufacturer, supply and installation of the 750 megawatt (MW) single cable line from Tasmania to Victoria. 

Prysmian expects to start work on the 320 kV single-core cables with XLPE insulation and single-wire armouring in 2025 – all will be made in Europe – and be finished by 2030. 

It has promised its most advanced ship, the Leonardo Da Vinci, will handle the €600 million job.

The 177 metre long vessel is designed to lay cables in oceans at a depth of up to 3,000m — the deepest part of Bass Strait is 155m – and carries more than 13,000 tonnes of cables. The ship comes with a helipad, and accommodation and recreation areas for a crew of 120, and two 750 kW batteries support the six diesel generators.

It can also come with its own digging apparatus so it can bury cables as it lays them.

The Marinus Link cable itself will be buried, or where it can’t be buried covered with a concrete ‘mattress’, for the whole distance between the two state-of-the-art converter sheds that will swap the current from AC to DC and back. 

The cables will cross a distance of 345 km: 255 km will be undersea across the Bass Strait and 90 km will be underground in Gippsland.

Faults will be detected via a permanent PRY-CAM monitoring system that uses electromagnetic sensors to detect problems with the underground cable. 

The power cables contain fibre optic strands which are used to monitor the cables performance and also enable a fault to be pinpointed, should an event like anchor strike cause damage to the cable.  Accuracy is about 2m.

The Italian company was chosen for its proven and global expertise in delivering projects like the Tasmania-Victoria cable, says Marinus Link CEO Caroline Wykamp.

The company was tee’d up in September last year to be the cable supplier, with its involvement made possible by a $152 million underwriting agreement with the federal government.

Marinus Link is neither the longest nor the deepest transmission project Prysmian has done. 

The 1,250km Viking interconnector was finished in January to link England and Denmark, while the 936km North Sea Link between the UK and Norway was operational in 2022. 

It also laid the 722km SAPEI cable connecting Sardinia and Italy, which is the world’s deepest at 1,600m below the Tyrrhenian Sea.

The Australian Energy Regulator (AER) gave the Marinus Link project the green light in December 2023, but only after the controversial project had been cut in half. 

In September, Tasmania struck a new deal with the federal and Victorian governments after baulking at the rising cost of the project. 

The new deal saw the so-called “Battery of the Nation” cut to just one 750MW sub-sea link instead of two, and the federal government will take a bigger stake in the project to reduce the financial burden on Tasmania.

The cost of the project had almost doubled which led to analysts questioning whether it would be financially viable. The halved project will still cost $3-3.3 billion – the same as what the original 1500 MW dual cable was supposed to be.