Snowy Hydro has made its first commitment for decades to a new large-scale renewables project, involving a $200 million solar farm in South Australia that will be later supplemented by batteries.

The 22-year power purchase deal, to be formally announced on Wednesday, sees Snowy join with one of Asia's biggest private renewables investors, Singapore-based Equis, for the project at Tailem Bend on the Murray River.

The 100-megawatt solar project, to be completed next year, will be built "battery ready", with the intention of adding up to 100 MW of large-scale electricity storage to make production more reliable. The first chunk of storage, potentially involving Panasonic batteries, could be added within four years, said Snowy chief executive Paul Broad.

A new large-scale solar project is on the cards in South Australia thanks to the Snowy Hydro deal. AP

Mr Broad said Snowy's commitment to buying all the power from the project showed its commitment to expanding its South Australian customer base of 50,000, held under its Lumo Energy business, to about 100,000, potentially within five to 10 years.

He said the deal made sense given the increase in forward prices for power in South Australia from the mid-$40s a megawatt-hour to close to $70 with the closure of baseload power plants in the state.