Draft Power Electric

You could do it. Whether it would be worth the effort is another question.

The low-hanging fruit of energy capture from draft animals is direct use of their pulling power, or failing that, to transfer pulling power into rotary power (as in having oxen turn a millstone, or walk on a treadmill to accomplish work with the rotary motion of the treadmill shaft). Any proposition of transferring the energy to electricity and storing it, and then using the stored electricity later in a motor will involve such losses along the way as to make it very technology and time-intensive relative to the benefit.

for instance if you have two oxen walking on a treadmill, they will apply about 1600 watts to the treadmill shaft (about 2 hp). But the shaft speed is low and you will need to use a gearbox to increase RPM, which will reduce efficiency. With a 75% efficient gearbox you could apply about 1200 watts of power to your alternator. If your alternator has 80% efficiency you have 960 watts available to store. If your storage system is 90% efficient then you have 864 watts available to use, or 0.86 kilowatt hours, for each hour the team of oxen work. This is worth about 20 cents at the rates I pay. Then to use this stored electricity in a vehicle you need to buy and maintain a storage system and voltage regulator as well as maintain your EV itself. All these components age and need to be replaced at intervals.

You could do it, theoretically, but all the tech to accomplish this is pricy, and the management of the team on the treadmill takes up your time. The gain is small. And in the end, you have your electric vehicle charged up. It can zip around a little faster than a team of oxen with a cart, but that zipping comes with a heavy price tag. Easiest way to use drafts for transportation is to come up with a cart and hit the road. Our problem with that is that as a culture we feel we must have speed. But though slow, it is many times more efficient than any electric application of draft animal power.

As for manure digesters, many of the same issues apply. It is unlikely that you could capture enough energy in a small-scale digester to measure up to the amount of energy you could capture just by using the drafts to accomplish mechanical tasks directly. Large-scale digesters aren’t any better, really, at best they recapture a fraction of the (fossil fuel) energy being wasted in large-scale livestock operations.

Green mountain college built a cool little trailer that the oxen pull for exercise, the wheels are attached to a pulley that drives a car alternator and charged some batteries. you could build something like that for nearly free if you look around for scraps to build it with. Its not the most effecient thing but if you want to exercise your team and charge some 12v batteries it was pretty slick. Maybe even just retrofit it to some existing wheeled equipment and charge batteries while you work.

Jared