ARENA is providing almost $90 million of grant funding towards the 12 projects in NSW, Queensland and Western Australia, which together will triple Australia's big solar capacity.
Eight of the projects are also receiving a total of $320 million debt finance from the Clean Energy Finance Corporation.
ARENA CEO Ivor Frischknecht said the large scale solar competitive round meant utility scale solar was now almost as cheap as wind energy, at least five years earlier than expected.
"This competitive round is the perfect demonstration of how ARENA is accelerating Australia's shift to a low emission, renewable energy future," Frischknecht said.
"From zero to more than 20 plants in five years, Australia's large-scale solar industry has grown at a tremendous pace thanks to concerted efforts by ARENA and the CEFC.
"We know of at least six new plants that are being developed without any ARENA grant funding support.
"In practical terms, this latest milestone means each of the 12 projects is fully financed and has locked in engineering, construction and connection agreements, along with council approvals and environmental approvals.
"Significantly, this round has unlocked a billion dollars in investment from other sources."
He said regional economies would also be big winners, seeing an estimated 2300 direct jobs and thousands more indirect jobs created.
Works have already begun on nine of the 12 plants, with work on the remainder to commence imminently.
Frischknecht said when ARENA developed its competitive funding round in 2015, it expected $100 million funding to support 200MW of new projects.
"We've managed to more than double this: 490MW of big solar with $87 million funding. It's enough renewable energy to power 150,000 Australian homes and generate one-tenth of the new capacity needed to meet 2020 Renewable Energy Target."
Frischknecht said planning, developing and financing large-scale solar projects remained a complex task involving multiple different parties, so it required project developers to share the learning from each stage of development, construction and connection with the renewable energy sector.
"Our support for Whitsunday Solar farm assisted project developer Edify Energy to secure debt finance for two additional plants, Hamilton Solar farm in Queensland and Gannawarra Solar farm in Victoria. ARENA is benefitting from knowledge sharing activities across the three projects," he said.
"This invaluable knowledge from 14 solar farms in total will further accelerate the growth of our large-scale solar industry."
The projects are expected to be completed between late-2017 and mid-2018.
Separately, the Sunshine Coast Council in Queensland has become the first local government to offset 100% of its electricity consumption across all its facilities and operations from renewable energy thanks to the Sunshine Coast solar farm.
The council expects to save around $22 million per annum, after costs, over a 30-year period based on today's cost of electricity.
The farm, the country's fifth largest installed solar plant and was built on 24 hectares in Valdora, by Downer.