Watts to kJ calculation formula
E(kJ) = P(W) × t(s) / 1000
The energy E in kilojoules (kJ) is equal to the power P in watts (W), multiplied by the time period t in seconds (s), divided by 1000.
kJ = W x s / 1000
kilojoule = watt x second / 1000
Power (P) = 450W
Time period (t) = 15s
Energy (E) = 450W x 15s / 1000 = 6,75kJ