(Bloomberg) -- Strong wind generation and low demand during the holiday period sent electricity prices below zero in Germany, while wholesale markets turned negative for some hours in France, Denmark and Britain.

The German day-ahead price for Dec. 24 fell to -€3.37 ($-3.72) a megawatt-hour and €0.41 for Dec. 25, according to data from Epex Spot SE, the Paris-based power exchange. The contract for Wednesday, the first working day after Christmas, was €60.80. 

Negative prices are occurring more frequently as the continent adds more weather-dependent renewable power. In Germany, wind-power generation is expected to stay strong for the rest of the week, peaking above 50 gigawatts on Friday, according to Bloomberg’s wind model. Output reached a record 53 gigawatts on Dec. 21.

Sub-zero prices are a preview of what’s to come for European markets if a flood of planned renewable production isn’t met with a shift in demand. The mismatch may get more pronounced until bigger electric car fleets, smarter grids and better battery technologies catch up.

Hourly prices in the UK fell as low as -£9.31 ($-11.84) a megawatt-hour on Dec. 24, while rates dropped to -€11.93 in France and -€8.54 in Denmark on Dec. 25, exchange data show.

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