cloudjunkie,
darnit, you beat me to it on the perpetual motion post.. I was sooo looking forward to typing that in.
A few nits about your calculations, though. 1 HP is 746 watts, so 10 HP is 7.46 KW not 7.6.
AFAIK 100 watt bulbs are off road, not DOT, not that I mind
Now lets look at losses in the alternator, which I think are significant.
200 W at (assume)12 V = 16.67 amps. Assume the diodes in the alt. have a .7 volt forward voltage drop. We waste 16.67 * .7 = 11.7 watts just in the diodes. Then there are other losses that I cannot really estimate: losses in the windings, both the rotor and the stator. Voltage regulator losses. There are belt flexing losses driving the alt. plus the possibility of a tiny bit of belt slip or creep. Bearing losses. Possible increase of friction in the crank pully engine bearing due to the greater tension of the tight side of the belt, although you could also argue it makes no difference. Then there is reduced lifetime of the alternator, which has some cost as well.