The 280 megawatt (MW) Cultana solar project would power GFG's Whyalla steelworks, as well as other industrial and corporate customers.
GFG did not put a price tag on the solar farm, but said it was part of a promise made by GFG Chairman Sanjeev Gupta to spend $1 billion (£790.5 million) in renewables in Australia, which also includes a hydropower dam and a large battery hub.
"Everything is ready so ... We'll start the construction phase fairly soon," Gupta told reporters.
GFG is regenerating the aged steelworks, which it bought from administrators in August 2017. It is looking to expand its annual output to 10 million tonnes from 1.2 million tonnes currently.
Gupta has said he would consider a partial listing of the company's steel assets in Britain, Europe and Australia in the second-half of 2019.
"We are examining ... various options on various capital markets," he said.
He declined to give details on the possible listing, which could include a public offering in one or both of Australia and the United States.
GFG Group early this year said it had signed up with British racing car engineering firm Gordon Murray Design to build an electric vehicle, either at a Holden plant in South Australia or next door at a location in the southern state of Victoria.
"The exact location is still open - whether it's in Victoria or South Australia. There is a lot of work being done ... on what sort of car we should launch first," he said.
"We have narrowed that down and hopefully very soon, certainly within this year we will be announcing ... our detailed plans on what we will build and where."
GFG said it plans to invest in up to 10 GW of large-scale solar and other renewables projects across Australia.
(Reporting by Melanie Burton; Editing by Richard Pullin and Joseph Radford)