Can't transmission lines go underground?
It can be feasible to place lower voltage distribution lines and direct current (DC) transmission lines underground. However, the larger, renewable energy transmission lines that we need to build will be of high voltage and usually alternating current (AC). Placing AC transmission lines underground is estimated to cost in the order of up to ten times more than placing lines overhead, with these costs being paid for by all of us through our electricity bills.
Sometimes, energy generators or distributors are willing to pay the cost of building a lower-voltage or DC line to improve their social licence and expedite their project’s completion. For example, offshore wind project Star of the South plan to build a connection through Gippsland, which they are planning to build underground for a portion of the route.
More information on the costs of under-grounding transmission lines can be found in the AEMO Transmission Cost Report 2021 (page 23).
Costs aside, underground transmission lines aren’t necessarily safer or more convenient. While they may ease some concerns around the look and feel of a place, they are not necessarily better for the environment or landholders. There are significant land disturbance issues associated with the initial trenching works, and accessing underground lines for maintenance is more invasive as soil including any crops on top of the line must be dug up if there are faults. In contrast, overhead lines accommodate the majority of agricultural land uses.