No cost has been given for the replacement but energy experts have estimated it could be in the hundreds of millions and environmentalists have said it should be scrapped and replaced with storage units.

The Queensland Conservation Council said the value of Callide C was written down in value by almost 50 per cent last year because it was unable to compete with new large-scale renewable energy projects and rooftop solar, which are continuing to push wholesale energy prices down.

“It’s as if the gearbox has failed on CS Energy’s 20-year-old car,” QCC director Dave Copeman said.

“Why would they spend money on an inefficient car approaching the end of its life, when they could buy something more reliable, cheaper and fit for the future?”

“Large scale storage could have helped us on the 25 May by responding almost instantaneously to the loss of Callide C. Fast response can stop problems spreading throughout the network. On Tuesday, Powerlink and AEMO didn’t have the technology to stop the spread and three times as much generation was lost across Stanwell, Gladstone, Callide B and solar and wind farms as a result of Callide’s failure and customers were blacked out across the state.

“Rebuilding Callide C4 in an over-supplied, unprofitable market for coal would be sheer perversity on behalf of the Queensland Government. We urge them to work with CS Energy and private partners, Intergen, after the situation at Callide is stabilised, to set out and fund a transition plan to ensure workers and Queenslanders benefit from the energy transformation.”

CS Energy has told the Australian Energy Market Operator that Unit B1 would be returned to service on June 11 and B2 on June 21.

Chief executive Andrew Bills said CS Energy’s first priority was safety as crews work to bring the three generating units back online after the plant incident on Unit C4 last week.

“There are currently 60 to 70 people working on site. Following risk assessments we will look to increase this as the week progresses,” Bills said.

“However, we will not rush this process – we are following our methodical safety procedures at every step.”

CS Energy owns Callide C in a joint venture with InterGen. Callide Power Trading, which trades the output of Callide C on behalf of the JV, has informed AEMO that Unit C3 will return to service on 22 June.

There was no change made to the forecast return date for C4 of 12 months’ time.

Bills, who is returning to Callide tomorrow, said it is CS Energy’s intention to rebuild Unit C4.