You cocked up the calculation with a misplaced decimal point. You obviously meant 14.4KWH. The electricity cost is around 15p a unit (give or take). If we use your calculations (corrected) and a more realistic estimate of electricity costs, you'd have been suggesting a figure of £21.60.
Guessing at about half a 20 litre tank of petrol per lap and estimating the costs for an electric equivilent coming out at half of that or even less, I'd estimate the figure may be closer to 6 quid a lap rather than
22 quid.The highest energy density figure I've seen quoted for L-ion rechargables (2011 figures) worked out to a mere 240WH per Kilogram. It seems you'd be looking at 100Kg for a 24KWH's worth of energy storage. A 16KWH battery would weigh in at about 67Kg.
The electric motors used are tiny compared to the ICE it replaces and a box of electronics replaces the gearbox. ISTR efficiency figures for these motors being around the 97% mark (it's simply a specialised transducer of an energy type that's already in a useful form - no converting heat energy into mechanical motion at a conversion efficiency of around 25% or so).
Although battery weights of some 67 to 100 Kg seem a very high price to pay compared to 18Kg of fuel plus a 2 or 3 Kg tank, the weight penalty is largely offset by eliminating a heavy ICE and gearbox.
For a single lap time trial 'race' of the 37.75 mile TT course, the battery weight is a manageable handicap. It's only when we consider longer races that the ICE power trains win out big time (but even the ICE powered bikes have to refuel every two laps).