Energy "return on investment" (EROI) study for biofuels

When you consider whether to use an energy alternative to the existing fuels (a.k.a. fossil fuels) part of the analysis has to be whether it is sustainable. Whether the world can continue using that energy alternative for a decade or more.

In producing any energy product, you have an "energy input" which is the energy consumed to produce the energy product. Once the product is available you have "energy output" which is the energy available from that product.

Sustainability comes when energy input is less than energy output. If the input is greater than the output, then you have an energy deficit that has to be replenished from somewhere.

This is important because, as the oil peak scenario becomes reality, we won't have that oil lying around to make up the deficit. Either the alternative energy source does the whole job, or it doesn't, and we'll all starve.

Academic Study Discredits Ethanol, Biodiesel (July 15, 2005, RenewableEnergyAccess.com)

The article discusses a study from Cornell University and UC Berkeley that shows the EROI for Ethanol and Biodiesel is negative. That is, the energy input for both is greater than the energy output. In running the study they took into account as many factors as they could, such as e.g. the fuel running the tractors on the farm, or the oil used in producing fertilizers used to grow the crops, etc.

What's most interesting is to read the comments to the article.

For example the US Department of Energy has been studying the same issue, and found that biodiesel has a positive EROI rather than the negative EROI claimed by these researchers. Now, maybe the DoE has been compromised by big money interests, as claimed in the other comments. Or maybe the DoE (or even these researchers) are missing something.

Another point is that the study only looked at Ethanol from Corn, and Biodiesel from soybeans. There are probably more efficient ways to produce either one of those. For example rapeseed produces much more oil than does soybeans.

I'd earlier showcased a method to produce biodiesl from algae where the majority of the energy input is solar energy, to produce the light and heat required to grow the algae.

This shows a different way to interpret EROI. Not all energy has to come from oil. If you calculated the EROI for the biodiesel-from-algae process, you would include as energy input the solar energy. If you do, you might end up with a negative EROI (input greater than output). But in this case the energy input is free because it doesn't come from fossil fuel, but rather from the Sun.