Cut out the middleman - just eat the oil

July 29, 2008 5:13 AM

Calorie value of food compared to the value to create it. Does it really take more to create than is gained from consuming? If so, do biofuels make an energy profit?

Several years ago I saw a BBC program about farming in the US (although I assume it's the same for all 1st world countries) where they stated that before 1970 the calorie content of a field of wheat was more than the calorie content of the various petrochem requirements to create it. After 1970 it was the other way around, with fuel and chemicals having a greater calorific value than the harvest worth.

Can anyone help me find a cite for this "fact"? I've had no luck with Google.

Additionally, I assume that this ratio differs from crop to crop, but how major an impact does this make on the first generation biofuels market? Presumably a similarly huge amount of the harvest worth cancelled out by the energy requirements of growing and harvesting the crop? How does one find out what percentages are lost?

posted by twine42 to science & nature (15 comments total)

I'm afraid this doesn't answer your question, but you might find this new BBC radio series (available online - only started yesterday) of interest - there was quite a lot of material on the cost of food production.
posted by hatmandu at 5:44 AM on July 29, 2008

The laws of conservation of energy say that energy cannot be created or destroyed. But it can be converted. Crops work by converting the energy from sunlight and the nutrients in the soil to caloric energy. The calorie value of "various petrochem requirements", whatever that means, is only part of the picture.
posted by yclipse at 5:49 AM on July 29, 2008

yclipse - Yes, I know my basic physics and I didn't mention natural energy inputs into a field because that's exactly the opposite of what I'm interested in.

By petrochem requirements I meant the diesel used running tractors and harvesters up and down the fields, the petroleum based "costs" of the pesticides, fertilisers, etc. IE, the energy coming out of the field as usable energy (be it food or fuel) vs the energy being deliberately put into the field by a 3rd party.
posted by twine42 at 6:08 AM on July 29, 2008

It's not going to be a single 'fact' that you can easily cite. You're talking about a complex web of processes. I think you have more than one question here.

Firstly, you're asking a really muddled question about food calories. What do you mean by 'create' in terms of food? As yclipse says, crops do most of the work of harvesting energy themselves. The petrochemicals required to plant, harvest, distribute and otherwise manipulate food aren't really part of the same equation. The only direct comparison you could sensibly make would be between the amount of food energy produced by an pre-industrial farmer and the food energy consumed by the same unaided farmer and any livestock and working animals he happens to have.

Secondly, you're asking a reasonable question about the difference in the amount of energy required to produce biofuels and the usable energy derived from those fuels. You'll find plenty of (often contradictory) advice around about that question; of course, when you factor in environmental and economic issues the picture once again becomes very complex.
posted by le morte de bea arthur at 6:10 AM on July 29, 2008

In 1994, David Pimentel and Mario Giampietro estimated the output/input ratio of agriculture to be around 1.4 For 0.7 Kilogram-Calories (kcal) of fossil energy consumed, U.S. agriculture produced 1 kcal of food.

Skip to the section about "Fossil Fuel Costs".

Almost all USA biofuels are net energy losers. Which is terrible, because even 4:1 energy gaining processes are pretty crappy to be trying to support an industrial civilization on.
posted by anthill at 6:30 AM on July 29, 2008 [1 favorite has favorites]

If you Google "calories used to produce crops," you get some relevant results, including the one cited by anthill.
posted by PatoPata at 6:36 AM on July 29, 2008

I just did a quick back-of-the-envelope calculation based on some wheat yield data I found and it looks like a modern farm that produces 50 bushels/acre at a weight of 60 lbs/bushel would yield 89100 kilocalories/acre, 3300 kcal/kg. 3300 kcal = 13.8 MJ/kg

I found this:

"The total energy input into the production of a kilogram of average U.S. wheat grain is estimated to range from 3.1 to 4.9 MJ/kg, with a best estimate at 3.9 MJ/kg. The dominant contribution is energy embodied in nitrogen fertilizer at 47% of the total energy input, followed by diesel fuel (25%), and smaller contributions such as energy embodied in seed grain, gasoline, electricity, and phosphorus fertilizer."

So it appears that the energy inputs for wheat does not exceed the outputs, rather the output exceeds it by about 3.5:1.
posted by electroboy at 6:40 AM on July 29, 2008

You may find this Harper's article useful. It deals with precisely this question. "The oil we eat:
Following the food chain back to Iraq"
posted by bricoleur at 8:16 AM on July 29, 2008

Um, it deals with precisely the first part of your question, I meant to say...
posted by bricoleur at 8:17 AM on July 29, 2008

Not all biofuels fit within the context of this question.

For instance, landfill gas and rendered chicken fat from food production waste are both used to generate electricity.

These are examples of use it or lose it energy: the fuel production costs are largely irrelevant.
posted by Pants! at 8:29 AM on July 29, 2008

There are agricultural approaches that still promise relatively high yields per acre with notably lower energy requirements, but they involve genetically engineered crops + herbicides (ie roundup).

Even without worrying about initial energy inputs, biofuels start at such a disadvantage. Photosynthesis isn't very efficient. A big chunk of the energy that is captured by photosynthsis is used for basic metabolism and doesn't end up as biomass. The biomass has to be hauled and then transformed into a more concentrated liquid form of energy. This fuel then has to be transported again, and finally, is burned in internal combustion engines which are themselves horribly inefficient. Compared to photovoltaic --> electric grid ---> battery ---> electric motor, their is over an order of magnitude difference in overall efficiency (the downside of the electric approach is that energy density of batteries is much lower than even ethanol, so vehicle range is limited). The result, biofuels require a hell of a lot of land when compared to alternatives and the absolute number is huge. Fresh water and topsoil depletion, which are already a concern for our existing agricultural system, loom as limiting factors.

Liquid fuels are essential for some applications (air travel, long haul transportation), and biofuels will likely be an important source.
posted by Good Brain at 9:12 AM on July 29, 2008

With biofuels, it depends on the crop. Corn is subsidised in the USA, so it doesn't matter that biofuel corn loses energy (or gains only a sliver, depending on who you talk to), the subsidies make it the most profitable for farmers.
Note that losing energy isn't necessarily a bad thing - if it converts a form of energy that you have a plentiful source of but can't use easily into an energy (like gasoline) which you have a shortage of and really need, then it can be worthwhile to lose energy in the process, but that's not really what's happening with corn - it's subsidies that are driving the choice in crop.
Brazil is the place to check out for biofuels. They use crops with a much higher energy return, and a large slice of their fuel comes from it.

With food crops, it makes sense to pour more energy into it than what you get out, if it means that the same area of land can feed six times as many people, and you have six times more people than land. There are a LOT of people on planet earth right now - only 60 years ago, I believe the math suggested mass starvations would be inevitable by now. This has been avoided through efforts to develop more intensive farming and so there is still enough food to feed the world. Unfortunately, it's not distributed very evenly around the world, so famine still exists, but it's still a better outlook than was predicted.
posted by -harlequin- at 9:34 AM on July 29, 2008

Almost all USA biofuels are net energy losers.

That's not exactly what that link says. It says at its least efficient they're losers, but so is coal liquefaction and oil shale. At its most efficient there's a modest net gain.
posted by electroboy at 12:17 PM on July 29, 2008

Almost all USA biofuels are net energy losers.

It depends on who you ask (and what you ask about, because biofuel production is a diverse business, as is agriculture). People always cite Pimentel, for example (as seen above) as if he delivered the final word on net energy of ethanol. What is basically never mentioned is that Pimentel's actual discipline is Population Ecology, and that the central thesis of his research is that the human race has far exceeded the Earth's population carrying capacity and that a sustainable human ecology will only be reached with a massive human die-off. This doesn't mean he's wrong but it does mean he has a vested interest in the outcome of his inquiries into alternative energy issues.

Here are a bunch of links on give and take on energy issues. Note that the group hosting that information has its own vested interests. Note also I worked for that group (ILSR) as a researcher many years ago. I don't any more and have no connection to them and my opinions do not represent them in any way.

A big part of the problem with this stuff is that pretty much everybody has vested interests, whether they admit to it (or indeed realize it) or not. Sometimes they are economic, sometimes ideological. I'm no different. People like consistency in their beliefs so they tend to end up "siding" with a particular outlook. Studying these issues is tremendously complicated and you can't get away from estimates and assumptions. I talk in this comment about some of the sorts of complexities that arrive from biofuel net energy research.

To research the subject of biofuels on your own, look into the terms "net energy" or "energetics." Calories, caloric value, calorific value are seldom used in this context.

Finally, these days particularly it has to be said that even if you assume a net-energy gain it doesn't necessarily mean biofuels are a good idea. I used to be much more of a supporter of ethanol, for example, because I really hoped practical cellulosic ethanol would come through within the past decade and because honestly I never thought it would be allowed to come to the point where ethanol production was substantially affecting food prices, which I do believe is now the case, and seems clearly unethical to me.
posted by nanojath at 2:35 PM on July 29, 2008

Adding on to what others said about biofuels being net energy losers- be careful of which statistics you use, because some statistics misleadingly count the energy input of the sun against the net energy balance. As in "20000 btu of sun + 10000 btu of production = 25000 btu of ethanol. OMG, you put in more than you got out! Buy more oil!"
posted by gjc at 3:27 PM on July 29, 2008