Global population approximately: 8.44E+09, Energy to heat 1 liter of water in electric kettle: 80 watt hours, 1 Watt hour ~ 2.78E-15 exajoules. Global energy consumption approximately: 600 exajoules.

8.44E+980 watt hours(2.78E-15 exajoules/watthours)= 1.88E-03 exajoules 1.88E-03/600 = 3.12E-6 or .000312% of the global energy use.

In simple words. Banning kettles would do nothing to cut global energy use.