The energy efficiency of using non-renewable energy sources (fossil fuels and nuclear) to grow corn and convert it to ethanol is poor at best—1.39 joules of output for every joule of input. (The gain comes from renewable solar inputs as the corn grows.) In other words, 72% of the energy in this so-called "renewable" fuel actually comes from non-renewable sources. When one considers the best whole State, Iowa, the energy gain drops to 1.32 to 1, and 76% of the energy inputs are non-renewable. In most regions of the US, the net return is negative, meaning the non-renewable energy inputs exceed the energy content of the ethanol output. The geographic region of negative net return expands considerably when the calculations do not give a credit for the 19% of output that is in the "distiller's grains" co-product.
This post and map by "EROI Guy" on The Oil Drum shows that "energy return on investment" depends greatly on where the corn is grown. He points out that as the nation increases its commitment to turning corn into transportation fuels, increasing amounts of corn will have to be grown in marginal regions that require more energy inputs, which will reduce the marginal and average conversion efficiency and drive up corn prices.
To the extent our goal is to reduce CO2 emissions, corn to ethanol is a terrible idea because the proportion of "renewable" content in the ethanol is very small or negative. If we don't care about global climate change or increasing the cost of transportation fuels but do care about minimizing energy imports, corn to ethanol is a way to convert domestic coal to a transportation fuel—not a good way, but a way. Notice that the EROI map closely resembles the political map on this issue.
Excerpt from EROI Guy:
How much of the 36 billion gallons mandated by the RFS [Renewable Fuels Standard] is an net energy profit? The answer depends, in part, on where the ethanol is produced. If the mandate was fulfilled only by ethanol produced in Iowa, which has a refinery-gate EROI of 1.32:1 (Table 1), the net energy profit provided by the ethanol is actually 9 billion gallons. On the other hand if the ethanol were produced in Texas, then the net energy profit is only 4.7 billion gallons.
Clearly, the net gains from this process are less appealing than the gross. The net gains are even lower if co-product credits are removed. Co-products are dry or wet distiller's grains, which are a very contentious subject in the literature on corn-ethanol. This matter is significant because the energy credits allotted to the use of co-products as a by-product of the corn-based ethanol process account for 19% of the total energy gains of the corn-based ethanol process (co-products are allotted 4.13 MJ/L while ethanol is 21.46 MJ/L). More importantly, when this 19% is removed from the EROI calculation, the EROI of corn-based ethanol for marginal lands (e.g. Texas) is less than 1. Which is to say that the net energy profits from the production of 36 billion gallons of ethanol in Texas, for example, would be -1.08 billion gallons [36 billion gallons * (1- (1/0.97))]. In other words, without the energy contained in the co-products, the production of corn-based ethanol on marginal lands creates net energy losses rather than profits.
Whether or not co-products should be included in the calculation of the EROI is a topic for a different discussion, but the impact of excluding them is profound. The primary message to be gleaned from this post is that "scaling-up" corn-based ethanol or other similar biofuel projects usually have complications, such as lower corn yields on marginal lands, and these complications tend to increase the costs, not the gains, associated with converting feedstocks with low energy densities to final products with higher energy densities.
Skeptic