Energy, Sustainability, andEngineeringMartin AbrahamDepartment of Chemical and Environmental Engineering, The University of Toledo, Toledo, OH 43606;mabraha@utnet.utoledo.edu (for correspondence)

Published online 3 May 2005 in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ep.10085

The principles of Sustainable Engineering devel-oped at the Sandestin conference of 2003 [1] providedirection for engineers who strive to develop sustain-able alternatives to current engineering practice. Withinthe United States, recent concerns over the costs ofenergy and the availability of the supply suggest thatenergy use should be a primary component of sustain-able engineering. Yet, the Sandestin principles makeonly passing mention of energy. Should energy be thefocus of a broader discussion within the context ofsustainability, or are the needs of a sustainable energysupply sufficiently imbedded within the principles?This column will attempt to explore this issue.

The only principle that directly mentions energy isthe fourth item, “Ensure that all material and energyinputs and outputs are as inherently safe and benign aspossible.” When we apply this concept to energy pro-duction, we are faced with a difficult political interpre-tation of the effects of the byproducts of combustion.Coal combustion emits mercury and SO2 and all fossilfuel combustion emits CO2; combustion in air gener-ates NOX. The global impacts of fossil fuel combustionare also widely recognized in terms of the well-docu-mented increase in CO2 levels in the atmosphere overthe last century, and its effect on global climate. Sowithout delving too far into the political realm, it can besaid that fossil fuel combustion is neither inherentlysafe nor benign. Because nearly 85% of the energyconsumed in the United States today comes from fossilfuels [2], all new technologies that decrease energyconsumption (such as the development of more fuelefficient vehicles, or energy integration in a manufac-turing facility) must certainly fall within the realm ofsustainable engineering.

Because fossil fuel resources represent the majorcurrent energy provider, it is important to considerwhether the production of energy by fossil fuel com-

bustion is sustainable. Don Hubert, president of ShellHydrogen, has been quoted as saying “the Stone Agedidn’t end because we ran out of stones; the Oil Agewon’t end because we ran out of oil” (this quotation isalso attributed to geologist Chris Stone and probablyothers). Indeed, the basic premise of supply and de-mand economics is that prices increase as resourcesbecome scarce, and thus the price of petroleum-de-rived energy resources should be expected to continueto rise until such time as an alternative energy technol-ogy can compete effectively in the marketplace. Noneof which is to say that the oil supply is unlimited;indeed, it is clearly limited—with current estimates sug-gesting that a maximum in peak oil supply will occursomewhere between 2021 and 2112 [3], depending onthe assumptions chosen in the model. Thus, it is logicalto conclude that we probably will not run out of oil—itwill just become so expensive that it will no longer bean economically viable energy resource.

To make the transition from fossil fuels, we mustconsider the production of energy from renewable re-sources. In most formulations of sustainability (orgreen engineering) principles, there is a statement sug-gesting that the use of renewable resources is desirable.The Sandestin principles state, “Minimize depletion ofnatural resources.” This interesting choice of languagerecognizes that a renewable resource will remain re-newable only as long as it is consumed at a rate nogreater than that at which it is produced. Thus, onemust transfer energy production to biomass resourceswith extreme caution, so as not to rapidly outstrip thebiomass production rates or jeopardize the food supplyand render biomass a nonrenewable resource. Biomassis a unique energy alternative, given that it can be usedfor the direct production of electricity, converted intoliquid fuels, or serve as a basic building block for arenewable chemical economy, through the biomassrefinery that is widely envisioned as part of the futurechemical industry. According to the National Renew-© 2005 American Institute of Chemical Engineers

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able Energy Laboratory, a biorefinery is a facility thatintegrates biomass conversion processes and equip-ment to produce fuels, power, and chemicals frombiomass [4]. Multiple opportunities exist: conversion ofbiomass to ethanol through fermentation, direct burn-ing of solid waste (corn stover, municipal solid waste,etc.), extraction of natural oils, followed by conversionto biodiesel.

How do we evaluate the best opportunities for theuse of biomass resources? Again, a review of the Sand-estin principles suggests the use of systems thinkingand life-cycle analysis. Systems thinking allows societyto evaluate the alternatives for biomass utilizationwithin the global system. The ultimate decision of con-version and use technology rests on the judgment ofsociety, most likely translated into the economic realm,but only if environmental harms are accounted forproperly. Thus, we see the principles of sustainableengineering as fully embodied in the selection of tech-nology—a life-cycle analysis to fully understand thepotential environmental impacts coupled with the in-teraction of societal desires to properly implement en-gineering solutions.

Although biomass conversion is the only alternativeenergy technology that can produce liquid fuels, thereare other alternatives for the production of electricity.For example, solar power can be used to convert sun-light to electricity. The efficiency of the best solar cellavailable today runs between 10 and 15%, but becausesunlight is free, and the operating costs for the conver-sion are negligible, electricity generation through pho-tovoltaic systems can be relatively inexpensive. On theother hand, solar cells are constructed from nonrenew-able resources such as electronic-grade silicon, andrequire substantial energy resources in the manufactur-ing process. Other alternatives, such as wind, geother-mal, and tidal energy have similar trade-offs. An eval-uation of the potential benefits of any of thesetechnologies requires a thorough life-cycle analysis. Arelatively recent discussion of life cycle for both solarand wind power demonstrated that substantial trade-offs exist and, moreover, depend on the technologiesthat are applied for the manufacture of the energydevice and the cost and form at which the energyresource is available [5]. To best apply the principles ofsustainable engineering, one must exercise systemsthinking to determine the best energy production sys-tem for a specific application, and then apply life-cycleanalysis to evaluate the environmental implications ofthe proposed technology.

Finally, one can consider the hydrogen economyand determine where it will fit into a sustainable future.One of the near-term applications for fuel cells may bethrough the installation of solid oxide fuel cells asauxiliary power units, operating on reformed petro-chemical fuels. For installation in over-road trucks, theenvironmental advantage does not come from the op-eration of the fuel cell, per se, but rather from thebenefits to be derived from producing electricity

through conversion of hydrogen, as opposed to run-ning a large diesel engine to generate small amounts ofelectricity. Longer term, the proton exchange mem-brane fuel cell should be expected to be used as theprimary power source for private and commercial ve-hicles, where one finds a substantial potential environ-mental impact resulting from the extraction of platinummetal [6]. Regardless of the fuel cell system, the overallbenefits relative to conventional gasoline or diesel ve-hicles must be evaluated from an understanding of thecomplete system, including the source of hydrogen.Numerous analyses have shown that the well-to-wheelefficiency of a fuel cell operating on hydrogen withcurrent technologies is less than that of a hybrid dieselengine [7]; thus the use of a hydrogen fuel cell makesenvironmental sense only when considered in thebroader context of its application.

One can find many examples in which energy usehas a substantial impact on the sustainability of a par-ticular manufacturing process. As an interesting irony,the source of energy to manufacture an energy conver-sion or production device is also one of the underlyingfactors in determining the environmental impacts of theenergy conversion system. Although a more sustain-able energy supply will lead to a more sustainablefuture, the path toward sustainable energy remainsunclear, with numerous alternatives. Each of these al-ternatives will likely have its place in the future ofsustainable energy, and the sustainability engineermust be diligent in identifying the opportunities forimplementation of new energy technologies that areintegrated with the needs and aspirations of the localcommunity.

LITERATURE CITED1. Abraham, M.A., & Nguyen, N. (2003). Results from

the Sandestin Conference: Green engineering: De-fining the principles, Environmental Progress, 22,233–236.

2. Department of Energy/Energy Information Admin-istration (DOE/EIA). (2003). Annual Energy Review2003, Report No. DOE/EIA-0384(2003), Washing-ton, DC: DOE/EIA.

3. Wood J.H., Long, G.R., & Morehouse, D.F. (2004).Available on the web at http://www.eia.doe.gov/pub/oil_gas/petroleum/feature_articles/2004/worldoil-supply/oilsupply04.html

4. http://www.nrel.gov/biomass/biorefinery.html5. Jungbluth, N., Bauer, C., Dones, R., & Frischknecht,

R. (2004). Life cycle assessment for emerging tech-nologies: Case studies for photovoltaic and windpower, International Journal of Life Cycle Assess-ment (OnlineFirst), 1–11.

6. Pehnt, M. (2001). Life-cycle assessment of fuel cellstacks, International Journal of Hydrogen Energy,26, 91–101.

7. Kreith, F., & West, R.E. (2003). Gauging efficiency:Well to wheel, Mechanical Engineering Power, June.

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