Two power plants are to be put into a "dormant state of managed preservation" to allow administrators more time to recover costs for creditors.
The operating companies for Severn Power Station, Newport, and Sutton Bridge, Lincolnshire, called them in after holding company, Newport-based energy group Calon Energy, went into administration in June.
Both plants employ 68 staff combined.
A third site, Baglan Bay Power Station, Port Talbot, is unaffected.
It is part of the group but remains under the control of its directors, said administrators at KPMG.
Joint administrator Jim Tucker said: "The recent and ongoing challenges facing the UK power market mean that these power stations are currently not generating sufficient returns to continue trading effectively.
"It has therefore been determined that the power plants will be placed into a safe and dormant state of managed preservation to provide more time to explore all options in order to recover value for the group's creditors."
The company's three sites all operate combined cycle gas turbines.
It had plans to build a new combined cycle gas turbine at the former Willington power station in Derbyshire.
The administration appointments include Severn Power Limited, Calon Energy (Severn) Limited, Sutton Bridge Power Generation, Sutton Bridge Power Systems (London) Limited and Calon Energy (Sutton Bridge) Limited.