I wrote a blog a couple months back talking about how environmentalists should avoid lumping all ethanol together as “bad” renewable energy because the Energy Return on Energy Investment (EROEI) is very low. First of all, new ethanol plants being built today do have a net energy gain on a well-to-wheels basis (the critics are using decade old data), and so long as the energy inputs come from renewable sources, ethanol looks like a decent way to turn other forms of renewable heat energy into something we can put into our tank and drive around with.
E3 Biofuels is doing just that with a 25 million gallon “closed loop” ethanol plant in Mead Nebraska. The distiller’s grain byproduct of the ethanol production is fed to cattle at an adjacent feedlot. This saves energy by avoiding having to dry the grain and transport it to where the cattle are. The manure from the feedlot is passed into an anaerobic digester which not only produces 100% of the energy necessary for the ethanol distillation process in the form of methane, but it also helps solve the nasty environmental problems caused by the massive supply of manure feedlots produce. It was runoff from cattle manure that caused the problems with our spinach supply recently.
Other benefits are that by running the manure through the digester, odor is reduced, and methane from the manure decomposition does not escape into the atmosphere. Methane is a much more potent greenhouse gas than is CO2.
If you believe the promoters that “This plant will make ethanol more than twice as energy-efficient as any other method of producing ethanol or gasoline,” I estimate that the well-to-wheels EROEI is between 2 and 4 (probably closer to 2.) It’s not the great EROEI’s we get from Wind and geothermal, but it’s a liquid fuel we can use in our existing vehicle fleet (either as E85 in Flex-Fuel vehicles, or as E10 or E20 in standard gasoline engines.)
Without liquid fuel, we’re in great danger of economic disruption due to peak oil, but unless we get that liquid fuel in a manner less carbon intensive than conventional corn ethanol, we’ll be up to our ears in melted icecaps.
Obviously, what we really need is much more energy-efficient cellulosic ethanol which does not compete with our food supply for feedstock, and it will be great if that process is powered by renewable heat (methane form digesters, or solar thermal) but given that we’re unlikely to stop eating beef anytime soon, this is an elegant, closed process.