The oil-fired Isle of Grain power station in Kent is being put back into service amid fears of an electricity supply crisis this winter.
E.ON, the company which runs Powergen, said predictions of harsh weather and rising gas prices had sparked the move.
Chief executive Dr Paul Golby said: "We don't believe the lights are going to go out... but we do believe this is the responsible thing for us to do."
He said the station is capable of supplying more than a million homes.
"Grain isn't the sort of station that runs all the time - it will only come on line at times of extreme demand, such as during extremely bad weather or if another large power station fails," Dr Golby explained.
The station was also in service last winter.