Energy and Human Ambitions on a Finite Planet, 2021a

14 Biological <strong>Energy</strong> 234
food energy consumed [97]. In a sense, we are eating 27 our fossil fuels! [97]: Pfeiffer (2006), Eating Fossil Fuels
It also points to an EROEI of 0.1:1, which is well below break-even. 27: ...oratleast subsidizing the energy
Obviously in times prior to fossil fuels, when we used human <strong>and</strong>
animal labor in our agricultural pursuits, an EROEI less than 1:1
would spell starvation: more energy going in than was recouped
from the l<strong>and</strong>. Today, fossil fuels give us a temporary exception, so
Table 14.2: Summary: EROEI of biofuels.
that we can afford to lose useful energy in the bargain, turning 10
units of fossil fuel energy into one unit that we eat. We might view Source
EROEI
this as a negative aspect of the Green Revolution.
14.3.2 EROEI of Biofuels
Various estimates exist for the EROEI for different biofuels. Unfortunately
for the U.S., the corn ethanol industry is estimated to have an EROEI
of anywhere from 0.8:1 to 1.6:1. The former would mean it’s a net loss
of energy, <strong>and</strong> that we would have more energy available if we did not
spend any of it trying to get ethanol from corn. Biodiesel (a non-ethanol
biofuel produced from vegetable oils or animal fat) is estimated to have
an EROEI of 1.3:1 [98]. Sugar cane may be anywhere from 0.8:1 to 10:1
[99] (see Table 14.2).
To explore an example of how this all plays out, let’s say that corn ethanol
provides an EROEI of 1.2:1—in the middle of the estimated range. This
means that in order to get 1.2 units of energy out, one unit has to go in.
Or for every 6 units out, 5 go in. If we use that same resource as the energy
input—in other words, we use corn ethanol as the energy input to grow,
harvest, distill, <strong>and</strong> distribute corn ethanol—then we get to “keep” one
unit for external use out of every 6 units produced. For the U.S. to replace
its 37 qBtu/yr oil habit with corn ethanol, it would take six times this
much, or 220 qBtu (2.3 × 10 20 J) of corn ethanol production each year. If
the growing season is 5 months, the solar input is 250 W/m 2 on average,
<strong>and</strong> the corn field is 1.5% efficient at turning sunlight into chemical
energy, then each square meter of corn-l<strong>and</strong> produces 4.9 × 10 7 Jof
energy 28 <strong>and</strong> we would therefore need about 5 × 10 12 m 2 of l<strong>and</strong> for
corn. This is an area 2,200 km on a side (Figure 14.4)! The U.S. does not
possess this much arable l<strong>and</strong> (estimated at about 30% of this). About
4 × 10 11 m 2 of l<strong>and</strong> in the U.S. is currently used for corn production,
which is 8% of what would be needed. And of course we must still feed
ourselves. In 2018, 31% of U.S. corn production went into ethanol. We
would somehow need to ramp corn ethanol production up by a factor of
40 to derive our current liquid fuels from corn in a self-sufficient way.
Don’t expect to see this fantasy materialize.
sugar cane ethanol 0.8–10
soy bean biodiesel 5.5
biodiesel 1.3
corn ethanol 0.8–1.6
algae-derived 0.13–0.71
[98]: Pimentel et al. (2005), “Ethanol production
using corn, switchgrass, <strong>and</strong> wood;
biodiesel production using soybean <strong>and</strong>
sunflower”
[99]: Murphy et al. (2011), “Order from
Chaos: A Preliminary Protocol for Determining
the EROI of Fuels”
Figure 14.4: Area of corn growth needed to
displace U.S. petroleum dem<strong>and</strong> if at EROEI
of 1.2:1. This is far larger than agriculturally
productive l<strong>and</strong> in the U.S.
28: 150 days times 86,400 seconds per day
times 250 W/m 2 times 0.015 gives Joules
per square meter produced.
Box 14.5: Why Do Corn Ethanol?
If corn ethanol has such low EROEI, why is it pursued in the U.S.?
© 2021 T. W. Murphy, Jr.; Creative Commons Attribution-NonCommercial 4.0 International Lic.;
Freely available at: https://escholarship.org/uc/energy_ambitions.