France called on companies to use less power and Britain's grid warned of tight supplies on today as a heat wave sweeping northern Europe hampered nuclear stations and boosted energy demand.
Wholesale power prices, which form the basis for final bills to consumers, hovered around the previous day's highs in France, Germany and the UK.
Soaring temperatures heightened concerns over security of energy supplies as air conditioning use went into overdrive.
France's main electricity provider said it had been forced to import supplies to cover shortages.
The heat forced EDF to buy 2,000 megawatts electricity abroad - roughly equivalent to the capacity of a large nuclear stations. Traders said they believed EDF had bought the power from Germany.
EDF Chairman and Chief Executive Pierre Gadonneix said the heatwave highlighted EDF's investment needs in order to secure its supplies.
EDF plans to invest in France over the 2006-2010 period around €20 billion in the production, transport and distribution sectors.
EDF said it was focusing production on reactors cited on the coast, rather than inland plants, in a move to avoid a repeat of problems encountered during a heatwave in 2003.
"Sea water cools down faster than river water," an EDF spokeswoman said, adding that the Rhone and Garonne rivers were being closely watched.
"During the 2003 heatwave some nuclear plants based by the sea had been stopped and that shouldn't happen again," she said.
German utility RWE said all its nuclear power plants were operating normally Wednesday, despite high temperatures.
Britain was forced to call on expensive oil-fired stations to meet demand as the heatwave coincided with maintenance shutdowns at several large plants. One of the country's biggest coal-fired plants, the Ratcliffe station in central England, is standing idle after a recent accident.
Britain's government in a review of energy policy last week called for the construction of new generation of reactors to secure future power supplies and keep down emissions of greenhouse gases.