Even before the end of the 1970s, serious scientific discussion had commenced regarding the thermodynamics of fuel ethanol production from biological sources. The first in-depth study that compiled energy expenditures for ethanol production from sugarcane, sorghum, and cassava under Brazilian conditions concluded that the net energy balance (NEB), that is, the ratio between the energy produced (as ethanol) and the total energy consumed (in growing the plants, processing the harvest, and all the various stages of the ethanol production process) was positive.60 This issue must not be confused with economic price but is one of thermodynamics: does the production of ethanol require a net input when a summation of the inputs is made, including such obviously energetic factors as the heat employed to distill the ethanol from the aqueous fermentation broth and also more subtle energy costs such as those involved in the manufacture of fertilizers and pesticides?

Thermodynamically, energy can be neither created nor destroyed but merely converted from one form into another. Energy is unavoidably expended in the production of ethanol, and the summation can be made across the entire produc­tion process including human labor (that must be replenished, i. e., energy goes into supplying the food for the work force), machinery, fuel, seeds, irrigation, and all agro­chemicals (many of which are derived from petrochemicals); these can be described as “direct” or “mechanical” as distinct from essential environmental energy inputs such as sunlight.[8] The output (i. e., ethanol) has a measurable energy yield in internal combustion engines; the energy inputs I have termed “energy conversion debits” that can be — although they are not unavoidably — fossil fuel consumptions (as diesel, coal, natural gas, etc.). The ratio between energy in the ethanol produced and the energy consumed in the conversion debits is the net energy yield or energy balance.

Four distinct cases can be distinguished with far-reaching implications for mac­roeconomics and energy policy:

1. Ethanol production has a net yield of energy and has no absolute depen­dency on nonrenewable energy inputs.

2. Ethanol production has a net yield of energy but has a dependency on non­renewable energy inputs.

3. Ethanol production has a net loss of energy (a yield of <1) but has no depen­dency on nonrenewable energy inputs.

4. Ethanol production has a net loss of energy as well as being dependent on nonrenewable energy inputs.

Viewed broadly, the most acceptable conclusion economically as well as to policy makers is case 1. Case 2 would pose problems to the short-term adoption of biofu­els, but eventually, there could be no insuperable requirement to either “fund” bio­ethanol by expending fossil-fuel energy as alternative energy sources become more widely available or to support the required agricultural base with agrochemicals derived exclusively from petrochemicals or other nonrenewable sources (especially if fermentation-derived bioprocesses supplanted purely synthetic routes). Moreover, cases 3 and 4 are not in themselves intrinsically unacceptable — as Sama pointed out nearly 20 years ago, power stations burning oil or coal all show a net energy loss but that is not used as an argument to shut them down.61 Domestic and industrial devices that are electrically driven require power stations as an interface for energy conversion, with the associated economic and thermodynamic costs. Filling gaso­line tanks with sugar, corncobs, or wood chips cannot fuel automobiles; converting these biological substrates to ethanol can — but again at economic and energetic costs. Case 3 and especially case 4 are equivalent to wartime scenarios where fuel is produced “synthetically”; case 3 is one of sustainable, long-term development if nonfossil energy sources such as hydroelectric, geothermal, wind, wave, and solar can be used to meet the net energy costs inherent in bioethanol production.

A review of a broad portfolio of renewable energy technologies in the mid-1970s that included methane production from algae and livestock waste as well as sugar­cane, cassava, timber, and straw concluded that only sugarcane-derived ethanol was capable of yielding a net energy gain.62 Data from early Brazilian and U. S. studies of sugarcane-derived ethanol are summarized in table 1.7. It was evident even in these early studies that the NEB was highly influenced by the utilization of bagasse, that is, the combustion of the waste product to supply steam generation and other energy requirements on-site or (although not considered at that time) as a saleable power commodity to the broader community. The energy balance was, however, much lower than the comparative quoted case of gasoline produced from oil extracted in the Gulf of Mexico oil fields, that is, 6:1.63

Several reports of the technical feasibility of ethanol production from corn had been published by 1978. Researchers from the University of Illinois, Urbana, collected the data and developed a mathematical model that extended the analysis to include mileage estimates and measurements for 10% ethanol blends with gasoline.64 From the data, the overall energy balance could be computed to be small (approximately 1.01); even attaining the energy break-even point required the efficient utilization of wastes for on-site energy generation and the sale and agricultural use of by-products counted as energy outputs (see figures 1.21 and 1.22). Few data were available at that time for mileages achieved with gasohol blends; if positive advantages could be gained, this would have translated into significantly increased net energy gains in what was, in effect, the first testing of a “well-to-wheel” model for fuel ethanol.64

Subsequently, both the energetics of corn — and sucrose-derived bioethanol pro­cesses have been the subjects of scrutiny and increasingly elaborate data acquisition and modeling exercises. Economic analyses agree that the production of ethanol from sugarcane is energetically favorable with net energy gains that rival or equal those for the production of gasoline from crude oil in subterranean deposits.65,66 For corn-derived fuel alcohol, however, the energy position is highly ambiguous. By 2002, that is, before the steep rise in world oil prices (see figures 1.3 and 1.11) — a factor that might easily have exercised undue weight on the issue — conflicting estimates had appeared, but the published accounts during two decades displayed very different methodological approaches and quantitative assumptions. Even as crucial a parameter as the energy content of ethanol used in the computations varied in the range 74,680 to 84,100 Btu/gallon — the choice of lower or higher heat values (measured by reference to water or steam, respectively) is also required for the energy inputs, and if the choice is used consistently in the calculations, there will be no effect on the net energy gained or lost. Ten of the studies were discussed in a 2002 review.67-76 Table 1.8 collects the data, adding to the comparison an extra publication from 2001.77 The obvious spread of energy balance values has generated a sustained argument over the choice of relevant input parameters, but a more per­tinent conclusion is that none of the balances greatly exceeded 1.00 (the arithmeti­cal average is 1.08); it could have been concluded before 2002, therefore, that only a highly efficient production process (including the maximal utilization of what­ever by-products were generated) could deliver a net energy gain, although changes in agricultural practices, higher crop yields, increased fermentation productivity, and others might all be anticipated to contribute to a gradual trend of piecemeal improvement.

Since 2002, the polemics have continued, if anything, with an increased impres­sion of advocacy and counteradvocacy. Among the peer-reviewed journal articles, the following considered NEB values (on a similar mathematical basis to that used in tables 1.7 and 1.8), but with various assumptions and calculations for energy input data:

• Patzek78 — 0.92 (with no by-product energy credits allowed).

• Pimentel and Patzek79 — 0.85 (after adjustment for the energy in by-products).

• Dias de Oliveira et al.80 — 1.10 (compared with 3.7 for sugar-derived ethanol in Brazil).

• Farrell et al.81 — 1.20.

• Hill et al.58 — 1.25, although this depended mostly on counting the energy represented by the DDGS by-product (Figure 1.21) into the calculations for NEB and NEB ratio.

The continued failure to demonstrate overall NEBs much more than 1.00 is again striking. This has provided an impetus to define better metrics, including decreased fossil fuel usage and greenhouse gas emissions in the assessments.81 Put into the perspective of the historical measures of energy balance from the oil industry corn — derived ethanol remains relatively inefficient.82-84 Assuming an NEB of 1.2, the notional expenditure of 5 units of bioethanol would be required to generate each net unit. This argument against ethanol as a biofuel is, of course, far less persuasive if all the energy needs for bioethanol production are met by renewable sources — this was highly speculative in the 1970s, and energy inputs to biofuels have (implicitly or explicitly) assumed a fossil fuel basis. With an energy input defined as “nonrenewable,” Hammerschlag normalized data from six studies to compute a range of “energy return on investment,” that is, total product energy divided by the nonrenewable energy to its manufacture, of 0.84-1.65.86 For an economy like Brazil’s, where hydroelectricity is the single largest source of power generation (64% in 2002), renewable energy is a practical option, but for the world at large (where hydroelectricity and all other renewable energy sources account for less than 10% of total power generation), the dependency on coal, oil, and natural gas is likely to remain for some decades.87

In comparison with corn ethanol, biomass-derived ethanol has received less attention. Estimates of the NEB range from the “pessimistic” (0.69 from switchgrass [Panicum virgatum], 0.64 from wood) to the “optimistic” (2.0).79,81 Hammerschlag suggested a range for cellulosic ethanol of 4.40-6.61 but ignored one much lower value.86 The Greenhouse gases, Regulated Emissions and Energy use in Transportation (GREET) model developed by the Argonne National Laboratory (Argonne, Illinois) also predicts large savings in petroleum and fossil fuels for ethanol produced from switchgrass as the favored candidate lignocellulosic feedstock.88 Technologies for bioethanol manufactured from nonfood crops appear, therefore, to warrant further attention as energy-yielding processes capable of narrowing the considerable gap in energy gain and expenditure that exists between corn-derived ethanol production and the oil industry.

Why the large discrepancy between corn-derived and lignocellulosic etha­nol? Intuitively, lignocellulosic substrates are more intractable (and, therefore, more costly to process) than are starches. As all practitioners of mathemati­cal modeling appreciate, the answer lies in the assumptions used to generate the modeling. Specifically, modeling methodologies for cellulosic ethanol processes assume that electricity is generated on-site from the combustion of components of biomass feedstocks not used for fermentation (or that are unused after the fer­mentation step) in combined heat and power plants; this was built into the earli­est detailed models of biomass ethanol production in studies undertaken by the Argonne National Laboratory and by the National Renewable Energy, Oak Ridge National, and the Pacific Northwest Laboratories, and the results are pivotal not only for energy balances but also for reductions in pollutant emissions.81,88,89 This methodology approximates energy use in biomass (cellulose) ethanol plants to that in sugar ethanol plants in Brazil (see table 1.7).

In Europe, where bioethanol production is much less developed than in North America and Brazil, attention has focused on wheat starch and beet sugar. Studies of energy balances with wheat have consistently shown negative energy balances (averaging 0.74), whereas values for sugarbeet range from 0.71 to 1.36 but average 1.02, although projections made by the International Energy Agency suggest that both feedstocks will show positive energy balances as combined fertilizer and pesti­cide usage drops and biotechnological conversion efficiencies improve.90

The question of deriving metrics adequate to accurately compare fuel alcohol and gasoline production processes also continues to exercise the imagination and inventiveness, particularly of European analysts. Portuguese analysts defined energy renewability efficiency (ErenEf) as:

ErenEf = (FEC — Ein, ^ц, prim) x 100 / FEC

where FEC is the fuel energy content and Ein, fossil, prim represents the unavoidable fossil energy input required for the production of the biofuel. Under French conditions, sugarbeet-derived ethanol was renewable even without taking into account any coproduct credits but was maximal with an allocation of the energy inputs based on the mass of the ethanol and coproducts (ErenEf = 37%), whereas wheat grain-derived ethanol was entirely dependent on this allocation calculated for the DDGS (ErenEf = 48%).91 These values were equivalent to positive NEBs of 1.59 (sugarbeet) and 1.92 (wheat). Conversion of the ethanol from either source to ethyl tertiary butyl ether by reaction with petroleum-derived isobutylene results in a product superior as an oxygenate to MTBE, but the energy gains calculated for the fuel ethanol were almost entirely lost if this extra synthetic step was included.

Accepting that the fossil fuel requirement of corn-derived ethanol approximates the net energy value of the product, Nielsen and Wenzel then advanced the argu­ment that gasoline requires an equal amount of energy as fossil fuels in its pro­duction — the net fossil fuel saving when counting in the gasoline saved when corn ethanol is combusted in an automobile therefore generates a fossil energy saving 90% of that of the fuel alcohol.92 No supporting data were quoted for this assertion, that is that gasoline required such a high outlay of fossil fuel, and other analysts markedly disagree.82-84 A commentator from the Netherlands argued that the opportunity costs for crop production must be taken into account, that is, that the energy costs for corn- and biomass-derived ethanol cannot include those implicit in the generation of the fermentation substrate unless the land for their production is otherwise left idle.93 This is again contentious, as no arable land must be gainfully farmed; as a citizen of a European Union state, the Dutch author would have been aware that land deliberately left idle even has a monetary value: the so-called “set-aside” provisions of the Common Agricultural Policy aim to financially encourage farmers not to overproduce agricultural surpluses, which otherwise would require a large financial outlay for their storage and disposal (see chapter 5, section 5.2.3). Even with this economic adjustment, the production of bioethanol was not a net energy process with either switchgrass or wood as the biomass input.

When analysts tacitly assume that all (or most) of the energy required for biofuel production is inevitably derived from fossil fuels, this is equivalent to the

International Energy Agency’s Reference Scenario for future energy demands, that is, that up until 2030, coal, gas, and oil will be required for 75% of the world’s power generation, with nuclear, hydro, biomass, and other renewables accounting for the remaining 25%.94 The agency’s alternative scenario for 2030 postulates fossil fuel usage for power generation decreasing to 65% of the total. In the future, there­fore, the fossil fuel inputs and requirements for corn — and biomass-derived ethanol may significantly decrease, thus affecting the quantitative assessment of (at least) the fossil fuel energy balance. As an interim measure, however, defining the crucial net energy parameter as the ratio between the energy retrieved from ethanol and the fossil fuel energy inputs involved in its production, the “fossil energy ratio” or “bioenergy ratio”66 gives:

(Enet + Ecoproduct)/(EA + EB + EC +ED)

where Ea is the fossil fuel energy required for the production of the plant inputs, EB is the fossil fuel energy required during crop growth and harvesting, Ec is the fossil fuel required during transport of the harvested crop, and Ed is that expended during the conversion process.

On this basis, different industrial processes could result in widely divergent bioenergy ratios (figure 1.26). The most obvious inconsistency is that between two molasses-derived ethanol processes, one (in India) was derived from the case of a distillery fully integrated into a sugar mill, where excess low-pressure steam was used for ethanol distillation, whereas a South African example was for a distillery distant from sugar mills and reliant on coal and grid electricity for its energy needs.66 In terms of energy, corn and corn stover and wheat and wheat straw were all inferior to Brazilian sugarcane, whereas Indian bagasse was a biomass source that gave a high result.

FIGURE 1.26 Ratio of ethanol energy content to fossil fuel energy input for ethanol production systems. (Data from von Blottnitz and Curran.66)