No need for an alternator, these have DC motors and are used for DIY windmills all the time, just needs a little rewiring. You might also raise the control end as well for better body/slope ratio
Just understand, that even the BEST Athlete, can only generate about 100 Watts for more than an hour at a time..... so that is 100 WattHours of power which ain't much...
The house is surrounded by 18 treadmills: assuming each zombie does an hour at the chelloveck zombie gym before they drop from exhaustion, and given that there will be an unlimited number of zombies in the post apocalyptic zombie world, each day a possible wattage hour output of .25 of an 100 watt hour equivalent athlete, would tote up to some 10,800 watts a day....enough to adequately power a moderate amount of laptop wifi internet connectivity, with enough juice left over to power my mung bean grow light setup for a few hours per day.
But Chell... Have you ever seen a Zombie, that moved, fast enough, to even MOVE a Treadmill???? Look at them, in the movies, they can barely WALK, let alone produce Power on a Treadmill..... Just not Realistic.. to try and harness a Zombie for Power.... Now a Trained Roo... Maybe....
Only fast zombies get keycards to the chelloveck zombie post apocalyptic treadmill gymnasium....I'll throw them the occasional chicken brain as an incentive to keep shambling.