Tailem Bend's 95-megawatt, $200 million solar farm is officially open and already pumping out power.
A ceremony was held at the plant, three kilometres southeast of town, on Thursday afternoon.
State MP Adrian Pederick said the development formed an important part of South Australia's transition to renewable energy.
"This project will insulate the regional energy market from fluctuations in fuel prices, putting prices down for families and businesses," he said.
The industry played to South Australia's strengths, he said, including abundant sunshine and open space.
Solar and wind would provide 75 per cent of the state's energy by 2025.
It would be the state government's job to ensure that energy remained affordable, reliable and secure, through strong leadership and careful planning.
Construction of the plant began in April 2018, and at its peak involved more than 250 workers, half of whom were local and 20 of whom were Aboriginal.
That would have been good for local businesses, Vena Energy managing director Anil Nangia said: hardware stores, eateries, accommodation providers, fuel retailers, supermarkets and the likes of the Riverside Hotel, who he singled out for special thanks.
The plant incorporates about 400,000 solar panels, enough to power 40,000 homes, and began supplying energy to the grid in February.
Snowy Hydro will purchase 100 per cent of its output for the next 22 years, for sale through its retail arm, Lumo Energy.
Coorong Mayor Paul Simmons said the council had not received a single complaint about the project.
He thanked Mr Nangia for choosing Tailem Bend, and said he looked forward to future projects.
Vena Energy has plans to build another of similar size, plus a grid-scale battery, nearby.