The French baselaod power contract for Thursday delivery added 5 euros, or over 18 percent to 32.75 euros ($39.98) a megawatt-hour (MWh).
The equivalent German spot power price gained 5.75 euros, or 21 percent to 31.75 euros/MWh.
Electricity consumption will rise by over 1 gigawatts day-on-day on Thursday in France to 48.1 GW, according to Thomson Reuters data. Average temperature is forecast to drop by 2.5 degrees Celsius.
French wind power generation will drop by 1.2 GW to 3.5 GW during the same period.
In Germany, wind power output is expected to fall by over 700 megawatts (MW) to 17 GW, according one forecast, while consumption will increase by about 500 MW during the same period. ($1 = 0.8191 euros)