Energy and Human Ambitions on a Finite Planet, 2021a

14 Biological <strong>Energy</strong> 235
Why do we have m<strong>and</strong>ates to introduce ethanol into fuel blends?
Don’t assume that the world is always scientifically rational <strong>and</strong>
run by “adults” whose interests extend beyond personal gain. Many
political factors enter: votes from midwestern swing-states, 29 job
dependencies, influences from a powerful industry, the appearance
of “green” (carbon-neutral) energy 30 all play a role.
29: . . . where corn is grown
30: . . . compromised by low EROEI if using
fossil-fuel inputs to run production
A fundamental reason why the EROEI for biofuels tends to be low is that
processing the material into ethanol requires a fair amount of energy
input in the form of heat. Burning biomass, by contrast, does not have
this requirement. Also, burned biomass is often gathered from untended
(natural) environments that required little deliberate energy input on the
parts of humans. Therefore, low EROEI is more a problem for biofuels
than biomass.
14.4 Upshot for Biomass <strong>and</strong> Biofuels
Wood has always provided a source of heat for people, <strong>and</strong> will continue
to do so. Its use occupied a much higher fraction of energy resources
hundreds of years ago before being supplanted by fossil fuels. Still,
several percent of U.S. energy comes from wood (<strong>and</strong> over 5% globally).
Wood represents a renewable resource that can often be locally obtained,
<strong>and</strong> will likely continue steady use, 31 potentially assuming a greater
fraction again if overall energy expenditure declines.
Biofuels are special due to their liquid nature, as a potential replacement
for oil to drive transportation. Because photosynthesis is not terribly
efficient, <strong>and</strong> the EROEI of biofuels tends to be on the low side, the
amount of l<strong>and</strong> needed to replace petroleum is anywhere from daunting
to prohibitive. This is even before addressing the crunch an extensive
expansion would place on water resources or food supply, or the degradation
of arable l<strong>and</strong> that may result from depleting nutrients in the soil.
Algae may represent another approach, but so far the process appears
to be well below break-even in terms of EROEI (from 0.13–0.71:1 [100]). It
is difficult to see a meaningful path forward for wholesale replacement
of liquid fuels using biological resources.
A final perspective is that the total biological scale on the planet is
estimated to be 100 TW (Table 10.2; p. 168), which is not outrageously
more 32 than the current 18 TW scale of the human endeavor. Can we
really imagine comm<strong>and</strong>eering 20% of all life on Earth to serve our
energy needs? It would actually need to be substantially more than
this, given EROEI limits. It may be that Earth does not possess enough
biology to offer a substitute for our current fossil fuel appetite—even if
we tried to use it all.
31: . . . subject to availability in the face of
deforestation
[100]: Saad et al. (2019), “Algal Biofuels: Current
Status <strong>and</strong> Key Challenges”
32: . . . compared to solar or wind budgets,
for instance, which are 5,000 times <strong>and</strong> 50
times our dem<strong>and</strong>–not just 5 times as is the
case for all biology
© 2021 T. W. Murphy, Jr.; Creative Commons Attribution-NonCommercial 4.0 International Lic.;
Freely available at: https://escholarship.org/uc/energy_ambitions.