Herbivore Tractor

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Did you know that it takes less energy to feed an herbivore tractor (a tractor burning biomass pellets in a modern steam engine) than it takes to feed a human to do the same work?

This is the math that we're using, starting with discussion of gasoline energy and human energy:

1 tank of gas is 5 years of human toil? Not.

Here is a calculation as a first principles check:

1 gallon is 132 megajoules of energy. Our body under rigorous exercise uses 8 megajoules per day. 1 gallon thus gives us 17 days of equivalent human labor. It looks like a 20 gallon tank is about 1 year of rigorous human labor. Since gas engines are 20% efficient, a gas tank is eqiuvalent to about 1/5 of a year of rigorous labor, 24/7. That makes more sense, the 5 years is a little high.

How much do we eat in that time?

1 kg of bread is about 8 megajoules. So we need 82 of these huge loaves to equal one tank of gas.

So one tank of gas is 82 large loaves of bread (1/6 acre of wheat production).

20 gallons is less than 1/20 of an acre of equivalent biomass pellet crop.

Thus, it is easier to feed machines than humans to perform useful work, where the fuel/food comes from plant crops?


This makes a case for using machines (herbivore machines, though) to produce our food instead of using people power to produce our food, as machines use less energy. We can thus save human energy (less food consumed) and save the environment (less food production) the more that we use machines to do work instead of humans? Think of machines as herbivores: the modern steam engine with pelletized biomass uses less plant energy than a human to do work, because humans need to eat high-grade plant matter (such as carbohydrate or starch instead of cellulose).

The above is true because:

1. The human body burns food at 10% efficiency, comparable to the burn efficiency of a steam engine 2. High grade foods are 10% of a plant.

So in principle, using a modern steam engine with pelletized biomass is 10x more efficient than feeding a human to do labor, on energy considerations alone (that of sunlight being trapped in plants).

That's an interesting point.