The prolonged dry weather however led to a fall in hydro power supply, down 1.4 percent at 3.05 TWh during the month, RTE said in its monthly report.
Relatively low wind availability led to a drop in power generation from French wind turbines, down 3.5 percent at 1.59 TWh compared with September 2017.
Nuclear power supply, which accounts for over 75 percent of French electricity consumption, rose 2.6 percent to 30.1 TWh during the period, while thermal coal and gas-fired power generation tumbled 27.4 percent to 2.16 TWh.
French electricity demand during the month of September fell by nearly 3 percent to 32.67 TWh, RTE said.