Run electric fans all the time?

A quick Google shows that a typical car alternator is 55% efficient, not "10-20%". Also, 40 amps is what the well-regarded Contour fans draw when both are on full speed. No one would ever have two 40 amp fans.
So your 9.65 hp drain is WAY overestimated. That'd also be pretty hard to transmit through a single small V-belt going around a 2.5" pulley...