By Lewis Jackson

SYDNEY Australia's most populous state will be ready for 100% renewable energy within a decade under a A$16.5 billion ($11.20 billion) infrastructure investment plan announced by a major grid operator on Wednesday.

Transgrid, privatised in 2015, will invest in batteries and other energy storage, as well as 2,500 kilometers (1,553.4 miles) of new transmission lines across an area larger than Texas for "secure operation" of the grid at up to 100% instantaneous renewables.

The company owns and operates over 13,000 km of transmission lines across New South Wales (NSW) state and the Australian Capital Territory.

"There will be no transition without transmission," Chief Executive Brett Redman said in a statement.

"With over 80% of coal-fired capacity in NSW expected to retire and 28 gigawatt of new renewable and storage capacity coming online in the next 10 years, we must urgently accelerate the investment in all areas of the energy transition."

Wednesday's plan highlights the scale of investment required to reach the Labor government's pledge to cut carbon emissions by 43% from 2005 levels by 2030 and how a sizable chunk of the spending falls outside building new wind, solar and hydro projects.

In a decade, 80% of today's coal-fired capacity, concentrated in a score of large plants, will close and billions will be needed to knit together a vast network of new energy to replace it. These will include hundreds of wind and solar projects and tens of millions of rooftop solar panels spread across the world's sixth-largest country.

The bulk of the funds, A$14 billion, will be spent on transmission lines to connect new clean energy projects to customers. Roughly A$2.2 billion will be spent on energy storage to secure the grid as coal plants close, including 10GW of batteries.

A final A$300 million will be spent on new staff and technology to operate the upgraded grid.

Reuters has reached out to Transgrid on how it would finance the investment project.

While work has started on EnergyConnect, a 900km transmission line to connect grids across three states, most of the announced plan has not started.

($1 = 1.4732 Australian dollars)

(Reporting by Lewis Jackson; Editing by Jacqueline Wong)