How to convert electric power in watts (W) to energy in kilojoules (kJ).
You can calculate kilojoules from watts and seconds, but you can't convert watts to kilojoules since watt and kilojoule units represent different quantities.
The energy E in kilojoules (kJ) is equal to the power P in watts (W), times the time period t in seconds (s):
E(kJ) = P(W) × t(s) / 1000
So
kilojoules = watts × seconds / 1000
or
kJ = W × s / 1000
What is the energy consumption of an electrical circuit that has power consumption of 300 watts for time duration of 3 seconds?
E(kJ) = 300W × 3s / 1000 = 0.9kJ