The Energy Return of Food

[Projectile Vomit]

I recently posted an essay on my website entitled The Energy Return of Food, it takes a bit of a different tack than my earlier one entitled The Energy Cost of Food. I talk a little about the benefits of fermenting food (effectively allowing bacteria to predigest it so that we don't have to cook it) from an energy perspective. Among other things.

[cherimoya_kid]

That was good. As far as the dairy farm, did you count the grass that the cows eat into the equation, or not?

[eveheart]

Nice article - I enjoy both your content and your style.

[jessica]

That's an excellent essay.  I really have such a hard time with agriculture these days.  I cant believe we are so arrogant to not have noticed or cared to destroy our best land, forests, rivers, streams.  We pollute the very things that feed and norish us.  And the complete inherited ignorance of our time, not to know our true roots and place was among nature.  I would love to see a huge forest revolution, where people realize that if we leave areas undisturbed, make our lives small and our foot prints smaller, stop wanting for anything we can create and just be in what we have now, remediate and reforest natural and progress towards making systems more simple.  I mean it will never happen, people haven't even been engulfed in the luxury or nature, its true what they say that we have 'nature deficit disorder'.  Forests are food, clean lush vibrant land, clear air and streams are food

[Projectile Vomit]

That was good. As far as the dairy farm, did you count the grass that the cows eat into the equation, or not?

Nope, the energy value of the grass wasn't counted. Just the energy, mostly from fossil fuels, that people invested in the process. Sunlight, by convention, is considered a freebee when doing these calculations, so the energy value of plants is considered a freebee too as it comes from stored sugars and starches that originated from sunlight.

And Jessica, as is often the case you hit the nail squarely on the head. I actually struggle working in the agricultural sector, and food system sector more generally, for this very reason. So it goes...

[cherimoya_kid]

Nope, the energy value of the grass wasn't counted. Just the energy, mostly from fossil fuels, that people invested in the process. Sunlight, by convention, is considered a freebee when doing these calculations, so the energy value of plants is considered a freebee too as it comes from stored sugars and starches that originated from sunlight.

How about the initial cost of the land where the grass grows?  I'm just curious.

[Projectile Vomit]

The calculations I do all revolve around energy values, not dollar values. So the cost of the land, in dollar terms, isn't involved in the ratios I estimate.

[cherimoya_kid]

The calculations I do all revolve around energy values, not dollar values. So the cost of the land, in dollar terms, isn't involved in the ratios I estimate.

But the cost of the land is never computed, is it, no matter what type of farm is looked at, right?  So it all roughly equals out.

What about any machinery involved?  Are the costs of the machinery or the fossil fuels needed to produce the machinery included?

[Projectile Vomit]

The dollar costs of the machinery are not included, but the energy needed to manufacture, deliver and maintain the machinery are. So a highly mechanized system will end up being far more energy intensive than a system powered by human (or animal) labor, because muscle power is far more energy efficient per unit work than a system powered by machines.

The dairy I audited fared so well because it was pasture-based, which means the only machines involved were used to make hay, and to power the largely manual milking system. Vegetable production systems depend heavily on machines, and deliver calorie diffuse products on top of that, so they are not as energy efficient in terms of their output-input ratios.

[cherimoya_kid]

Interesting.

[Dr. D]

Quite interesting. My assumption would have been that machines are more efficient because it relieves the calorie deficit of the human. Digging a 20'x20'x20' hole is no problem with a backhoe.

I guess you still can't beat out nature in terms of efficiency.

[Projectile Vomit]

Digging a 20x20x20 hole is certainly far easier for a human when using a machine, because the human isn't doing the real work. The person is enlisting the help of a machine that was very energy intensive to manufacture, deliver and maintain, and further enlisting the help of many gallons of diesel fuel that also required energy to manufacture and deliver.

In other words, the embodied energy in the backhoe and the diesel that runs it is effectively an energy subsidy that makes it appear as if it's more efficient to dig the hole with a backhoe than with a shovel. If humans did the work, there would be far less total energy invested in digging the hole than if you had the machine do it.

Same is true in industrial farming. If you have the machines do the work, then the people involved burn less calories because their labor is being replaced by that of the machines. If the people do the work though, it takes far less energy overall.

[Iguana]

Yes, that’s it.

An automotive sized diesel engine has a thermal efficiency at it’s best operating point (that is near full load, around middle rpm) of about 43%. A car’s spark ignition engine can at best attain 35% efficiency, but operates under low load most of the time, therefore below 30 % efficiency. This is without taking into account the energy needed to make the engine.

Explanation of a physicist friend of mine:
“Muscle of animals, an invention of life on this planet, can convert chemical energy, eg fat, directly into mechanical work by gentle catalyzed oxidation and energy transfer to the movement of a very specific bio-molecule. This happen without significant heat generation, as dissipation can in theory be as small as 5% which corresponds to operating temperatures of 6000 K for an hypothetical engine that efficient — of course, something definitely impossible to realize. In practice, the muscle efficiency is about 70%, which is still quite remarkable.

Combustion of 3-5 kg of wood is necessary to provide as much heat as that produced by the combustion of one kg of oil refined into gasoline, diesel fuel or kerosene. This energy also corresponds roughly to the mechanical work that can provide twenty strong laborers during a day, for example 20 rowers on a Roman galley!"