Giant furnaces at Alinta Energy's Port Augusta power station will fire for the last time today.

Once one of South Australia’s key power supplies, the closure of the coal-fired plant is being used as a symbol of a transition to cleaner era.

Alinta announced the Playford A power station closure after it shut down the coal mine that supplies it – Leigh Creek – last year.

About 140 employees were able to keep working at the power station while it burned through its last stockpiles, but only a handful will be able to stay on for decommissioning.

The shutdown is expected to take up to two years to complete.

Alinta Energy praised both the Port Augusta and Leigh Creek workforce as its greatest assets over the past five years, and has paid $3.5 million for workers’ transition into new work, and $75 million in entitlements and benefits.

Having one less power station will mean less back-up energy during peak demand, according to Australian Electricity Council chief executive Matthew Warren.

“The reality for South Australians is that we're in uncharted waters,” he said.

“There's an increased level of risk that we really haven't seen before anywhere in the world, so it doesn't mean we'll have more blackouts, hopefully if we're smart we can sort out solutions so power supply can be the same as usual, but it's an increased risk.”