A new report from Powerlink Queensland looks at the challenges of expanding Australia’s grid for renewable energy, and the trade-offs between overhead & underground transmission lines.
At least $21.4T needs to be invested in electricity grids worldwide by 2050 to support a net-zero trajectory. Australia has set a goal of more than 80% of electricity coming from renewable energy by 2030, but here too it will rely on significantly upgrading the way its carried.
One long running debate has been about whether to put transmission cables underground with price often the sticking point. Ausgrid says it costs about $2.5M per km to put wires underground—15 times more expensive than above-ground wiring—and would cost between $72B and $130B over 40 years to bury their entire network.
But their are a lot of arguments in its favour too. Western Power, for instance, says undergrounding power offers improved reliability and safety, and “has a greater power supply capacity than the overhead network, meaning more renewable generation can be connected, and provides improved opportunities for emerging technologies.”
But the Powerlink research found arguments for underground lines like the environment, aesthetics or reduced maintenance didn’t convince people in Queensland based focus groups to discount cost issues. The report also said it’s difficult to ascertain the capital cost of underground compared to overhead transmission for all sorts of reasons, including construction type, route length and specific project factors.
But overseas experience shows undergrounding certain sections of transmission lines was necessary in specific locations, particularly urban and environmentally significant areas.
The Powerlink report says striking a balance is key—“While there is no one size fits all answer, involving both project developers and communities in open discussions can help to build trust in the process and more successfully lead to the identification of a preferred option,” it said.
Aluminium & copper can be used in undergrounding, but most reports suggest copper is preferred given its higher volumetric electrical and thermal conductivities that help to conserve space, minimise power loss, and maintain lower cable temperatures.
