Wholesale power prices are expected to spike and Australia’s energy grid will be under more pressure in summer after CS Energy announced it was pushing back the long-awaited return of its Callide C coal-fired power station in Central Queensland to mid next year.

More than two years after the mysterious explosion at the C4 unit that temporarily cut off Queensland from the National Electricity Market, the state-owned company said on Tuesday it would not meet its October 31 deadline for the return of C4.