RE: (ET) e12 hybrid?

I'm not quite sure why you supplement power by generators; they are typically 40 to 70% efficient, and the 'modified sine-wave' most produce can mess up some loads. With fuel prices what they are that might not ever pay for the generators. If there is a utility near-by, they are a cheaper supplement. But that's your business. Over a long term, you should be able to charge the system with just about anything as long as you can overcome the internal resistance of the batteries; eventually even a 1 amp 42V charger should bring the tractor to a full charge. That would take about 15 days. A 3 hp motor produces about 2300 watts of power. 60 Amps at 36 V is indeed 2160 watts, but there is no generator marketed that will produce 2160 watts on 36V off of 3 hp; the best ones are 70%, and 'automotive' models are 55% efficient. You will need 4.5 to 6 hp to run a commercial 36V, 60A alternator at full load. BTW, typical loads on an E12 as measured by a clip-on hall-effect current meter are about 50 to 70 amps mowing. At 36V, that's only about 1800 to 2500 watts. I'm not trying to dissuade you, but you might as well just use a gas (or diesel, lp, etc.) tractor. If you are using this size system, you could use much lower capacity batteries, as most of the time the load will be carried by the generator, not the batteries.

I just purchased an e12 unseen for 350 dollars, but in good condition with a front mower and snowblade. I produce all my power from solar and wind supplemented by generators, and it is difficult to supply the 10 KW to fully charge the batteries. I plan to charge my batteries from a small 3 horsepower turning a 60 amp alternator and controlled for 36 Volts. When batteries are low, turn on the generator, instead of pulling in to plug in just charge while you mow. I'll post my progress.