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I hear from alarmists that 1 food calorie costs 10 oil calories. Thereby, to produce 10 calories of biodisel, you need to spend 1 calorie of oil. Is it all right? It seems contradictory to me. It tells that you spend 1 calorie of biodisel to produce 10 calories of biodisel and spend those to produce 1 calory of food. But, why producing food is 10 times less efficient than producing food calories? How many extra agricultural biofuel lands do we need to produce the crops sustainably?

  • I think it depends on the food and how it is being produced. Is the food meat or vegetable? If it's meat you've got to deliver the feed which costs fuel and food. Is the crop grown organically in a sustainable way or is it more likely heavily dosed with pesticides and fertilizers which are all fossil fuel dependant and need to be trucked to wherever. Is it irrigated? How is the water pumped? How is the crop harvested? How far does the crop have to be delivered? When it gets there is it put into an animal which is then trucked to slaughter and the meat driven somewhere else? – hortstu Jan 28 '14 at 21:38
  • Hi Val, just to clarify, because there seem to be a few combined questions here. Are you asking for verification of the 10 oil calories for 1 food calorie? Or the 1 oil calorie for 10 food calories? Or the relative energy inputs for food vs biomass? – EnergyNumbers Feb 8 '14 at 19:40
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    It seems that in order to post an acceptable answer to your question above, which mostly involves math, I need to research the figures given in your question, confirm their validity and prepare a list of cites for the same. I honestly don't have the time nor the inclination to do this, so I am withdrawing my answer. – TeresaMcgH Feb 8 '14 at 21:40
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Summary

There are a great many ways to produce biofuels, and a vast and fast-growing amount of literature on the subject. Ratios of energy returned on energy invested (EROEI) are typically in the range 1.6-6, with some particular authors putting corn ethanol at below 1.0, and others putting ethanol from wheat straw at around 35. All the figures here are presented on a well-to-pump basis: that is, everything involved in their production up to the point of delivery, but not including the end-use efficiency of whatever purpose they're put to (because that can vary a lot, depending on the purpose).


Introduction

For the purposes of this answer, I'll just use "biofuels" in the sense of liquid fuels. "Biomass" or "bioenergy" are the terms usually used to refer to wider uses of biological energy sources, although some authors (e.g. ref 1) use "biofuel" to include biological sources of electricity and heat. I've excluded their results that are not for liqud-fuels.


Net energy balance and EROEI

The amount of energy you get out, compared to the amount of energy you put in, is usually referred to as the ratio EROEI (or EROI), Energy Returned on (Energy) Invested. Given the particular value of liquid fuels with high energy density, an EROEI (aka a net negative energy balance) isn't a deal breaker for biomass: it could still be a valuable means of energy storage, and a valuable economic good, though it would no longer be a net energy source.


On the original article

Your linked article says that for one hectare, 82 litres of fuel produces 1029-1356 litres of biofuel. That would be an EROEI of 13-16. Except that not all litres of fuel have the same energy content - it will vary, depending on the specific composition of the fuel.


Values from the scientific literature

The challenge is the overwhelming volume of literature on the subject. This literature search found over 1000 results, and was for biofuel energy balance reviews since 2014, and I did it when 2014 was only six weeks old. Renewable and Sustainable Energy Reviews is pretty well respected, has a high impact factor, and is bang on target, so I searched there in particular, where I found (2), a review of methods. And from GCB Bioenergy, I found (3), a systematic review. I did find (1) from 2004, one of the earlier reviews of different biofuels. Note that I've taken the extremes - the highest and lowest values - from each study. In the biofuels literature, values seem to be commonly given as the ratio of energy in to energy out: that's the reciprocal of EROEI. I've converted to EROEI here.

EROEI  Ref  Biofuel
 35     1   Ethanol from lignocellulosics (wheat straw)
  2.0   1   Ethanol from sugar beet
 24     2   oilseed rape with biomass co-firing
  1.1   2   (1999, Automotive fuels for the future—the search for alternatives, IEA)
 25     3   Bioethanol, energy-grasses, credits for surplus electricity & acetic acid
  1.4   3   Bioethanol from wheat, no co-production credits

There are outliers such as Pimental and Patzak's estimates for corn ethanol, which give an EROEI of below 1.0.

There are also values that are negative: that is, there is no energy in, because the other waste biomass products give more energy than is needed to create the biofuel. These negative values, if valid, would have an effective EROEI higher than any of the positive values above. I've left those out, for now.

Here's a chart from (2) of all of their studies. Note that the x-axis is the reciprocal of the EROEI, so an x-value of 0.5 is an EROEI of 2, and an x-value of 0.2 is an EROEI of 5. The lines joins together an individual study's findings.

enter image description here


Other thoughts

You don't need any oil to make biofuel. You can use oil, but you can use other sources of energy too.

NB Food calories are not the same as biofuel calories. There are biomass sources that are inedible for humans, fast-growing, and don't compete with food crops.


Sources

  1. Elsayed, M. A., Matthews, R., & Mortimer, N. D. (2003). Carbon and Energy Balances for a Range of Biofuels Options. Sheffield. (pdf)

  2. Malça, J., & Freire, F. (2011). Life-cycle studies of biodiesel in Europe: A review addressing the variability of results and modeling issues. Renewable and Sustainable Energy Reviews, 15(1), 338–351.

  3. Whitaker, J., Ludley, K. E., Rowe, R., Taylor, G., & Howard, D. C. (2010). Sources of variability in greenhouse gas and energy balances for biofuel production: a systematic review. GCB Bioenergy.

  4. Patzek, T. W. (2004). Thermodynamics of the Corn-Ethanol Biofuel Cycle. Critical Reviews in Plant Sciences (Vol. 23, pp. 519–567).

  • It is interesting that all researches report two results, one of them is 20 times better than the second. – Val Feb 9 '14 at 14:28
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    @Val, I've taken the extremes of each study: for each study, I've shown the highest and lowest value (and excluded negative values). These studies between them list many many results. – EnergyNumbers Feb 9 '14 at 18:25
  • Is cumbustion engine efficiency (of 20% whereas 80% are lost as en.wikipedia.org/wiki/… says), included into the figures? – Val Feb 11 '14 at 8:27
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    @Val - no, because biofuels can be used for purposes with various efficiencies: so these are what's called well-to-pump figures (even though no well is involved, and no pump need be either) – EnergyNumbers Feb 11 '14 at 8:39

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