Page 592 - Environment: The Science Behind the Stories

Hydropower corn ethanol. Ethanol from sugarcane In 2011, Hall and Doug Hansen of
Coal in Brazil is somewhat more efficient, Hansen Financial Management in San
Oil and gas (1970) showing a value of 5:1 in Murphy and Diego teamed up to edit a collection of
Wind power Hall’s review. studies on the EROI of various energy
EROI values for fossil fuels were sources. Published in a special issue of
Oil and gas (2005) historically very high but have been the journal Sustainability, 33 scientists
Nuclear power dropping through the years (see addressed cutting-edge issues in 20
PV solar Figure 19.5, p. 542) because we articles.
Ethanol (sugarcane) have extracted the easy deposits In one paper from this collection,
Shale oil already and now need to expend more Hall, Bruce Dale, and David Pimentel
Oil sands and more energy to reach the less- sought to clarify why different stud-
Solar collectors accessible deposits that remain. New ies had come up with different EROI
Biodiesel fossil fuel resources such as oil sands estimates for corn ethanol. By carefully
Ethanol (corn) and shale oil have low EROI values. comparing the methods of each study,
0 20 40 60 80 100+ This means that if we switch to these they determined that the differences
sources as conventional oil begins to were due to how the researchers
EROI run out, we will deplete them rapidly, measured energy investment in the
FIGURE 1 EROI values vary from over because some of their energy will many steps involved in producing
100:1 for hydropower down through
1.3:1 for biodiesel and corn ethanol. need to be devoted to extracting and ethanol. They recommended that future
Adapted from Murphy, D., and C. Hall, 2010. processing them. researchers be more transparent and
Year in review—EROI or energy return on (energy) Solar power technologies also explicit about their methods as they try
invested. Annals of the New York Academy of tend to have low EROI values, but as to work out the EROI values of newer
Sciences 1185: 102–118. these young technologies are further biofuels, such as those from switch-
developed and become more efficient, grass and cellulosic ethanol.
of corn or soybeans and then transport we can expect EROI values of solar As studies of EROI become more
the yields to refineries. power to rise. numerous and of higher quality, they
Indeed, ethanol has received more Nuclear power places in the middle will help scientists, engineers, and
research attention than any other fuel in of the pack in Murphy and Hall’s study, policymakers compare the rela-
regard to EROI, and results have varied, with an EROI of 10:1. Nuclear power tive advantages of different energy
but researchers invariably find the EROI produces a large amount of electricity, sources. This will help us to prioritize
of corn ethanol to be remarkably low. but it also requires substantial invest- and make better decisions as we chart
Low EROI values are a large part of the ment in uranium mining and in the our energy future and try to shift from
reason many environmental scientists facilities, equipment, and maintenance fossil fuels to alternative and renewable
oppose U.S. government subsidies for of power plants. energy sources.

burning biomass releases carbon dioxide that plants had how well nations were controlling their emissions under the
recently pulled from the atmosphere during photosynthe- treaty. Negotiators trying to design a follow-up treaty to
sis. However, burning biomass for energy is not carbon- Kyoto have been trying to address this (pp. 528–529). In the CHAPTER 20 • CONVENTI ON AL ENERGY ALTERN ATIVES
neutral if forests are destroyed in order to plant bioenergy meantime, researchers are trying to develop means of using
crops. Forests sequester more carbon (in vegetation and in bioenergy that are truly renewable and carbon-neutral. With
soil) than do croplands (pp. 248-249), so cutting forests to continued research and careful decision making, our many
plant crops will increase carbon flux to the atmosphere.
Bioenergy also fails to be carbon-neutral if we need to use
fossil fuel energy to produce the biomass (for instance, by WEIGHING THE ISSUES
driving tractors, using fertilizers, and applying pesticides BIOFUELS Do you think producing and using ethanol from
to grow biofuel crops). corn is a good idea? Do the benefits outweigh the draw-
International climate change policy so far has failed to backs? Do you think we should invest billions of dollars into
encourage sustainable bioenergy approaches. The Kyoto Pro- developing next-generation biofuels such as algae and cel-
tocol (p. 528) required nations to submit data on emissions lulosic ethanol? Can you suggest ways of using biofuels that
from energy use and from changes in land use, but only the would minimize environmental impacts?
emissions from energy use were “counted” toward judging 591

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