Emergy

Emergy is the available energy (exergy) of one kind that is used up in transformations directly and indirectly to make a product or service. Emergy accounts for, and in effect, measures quality differences between forms of energy. Emergy is an expression of all the energy used in the work processes that generate a product or service in units of one type of energy. The unit of emergy is the emjoule, a unit referring to the available energy of one kind consumed in transformations. Emergy accounts for different forms of energy and resources (e.g. sunlight, water, fossil fuels, minerals, etc.). Each form is generated by transformation processes in nature and each has different ability to support work in natural and human dominated systems. The recognition of these differences in quality is a key concept of the emergy methodology.

History

The theoretical and conceptual basis for the emergy methodology is grounded in thermodynamics, general system theory and systems ecology. Evolution of the theory over the first thirty years was documented by H.T Odum in Environmental Accounting. Beginning in the 1950s Odum recognized principles of energy quality as an outgrowth of his investigations and simulation modeling of ecosystems of humans and nature (e.g. Silver Springs, Florida; Eniwetok atoll in the south Pacific; Galveston Bay, Texas and Puerto Rican rainforests, amongst others) where energies of many different forms at many different scales were observed. His investigations about energy flows in ecosystems and the differences in the work potential of sunlight, fresh water currents, wind and ocean currents and even fossil fuels made it clear that when two or more different energy sources drive a system they cannot be added without first converting them to a common measure that accounts for their differences in quality. This lead to the concept of "energy of one kind" as a common denominator with the name "energy cost". The first formal recognition of energy quality was in Odum's book Environment Power and Society

Beginning in the last century man began to develop an entirely new basis for power with the use of coal, oil, and other stored-energy sources to supplement solar energy. Concentrated inputs of power whose accumulation had been the work of billions of acres of solar energy, became available for manipulation by man.

It appears that the first quantitative evaluation of energy quality was in 1975 in the acceptance speech for the Prize Institute la Vie in Paris, which contained a table of “Energy Quality Factors”, or the kilocalories of sunlight energy required to make a kilocalorie of a higher quality energy. This is the first mention of the energy hierarchy principle which stated that “energy quality is measured by the energy used in the transformations” from one type of energy to the next. These energy quality factors, were placed on a fossil fuel basis and called "Fossil Fuel Work Equivalents (FFWE) and the quality of energies were measured based on a fossil fuel standard with rough equivalents of 1 kilocalorie of fossil fuel equal to 2000 kilocalories of sunlight. "Energy quality ratios" were computed by evaluating the quantity of energy in a transformation process to make a new form and were then used to convert different forms of energy to a common form, in this case fossil fuel equivalents. FFWE's were replaced with Coal equivalents (CE) and by 1977, the system of evaluating quality was placed on a solar basis and termed solar equivalents (SE).

The term "embodied energy" was used for a time in the early 1980s to refer to energy quality differences in terms of their costs of generation, and a ratio called a “quality factor” for the calories (or joules) of one kind of energy required to make those of another. However, since the term embodied energy was used by other groups who were evaluating the fossil fuel energy required to generate products and were not including all energies or using the concept to imply quality, embodied energy was dropped in favor of “embodied solar calories” and the quality factors became known as "transformation ratios". "Embodied energy" was abandoned altogether in 1986 when David Scienceman, a visiting scholar at the University of Florida from Australia, suggested the term “emergy” and "emjoule" or "emcalorie" as the unit of measure to distinguish emergy units from units of available energy. The term transformation ratio was shortened to transformity in about the same time. It is important to note that throughout this twenty years the baseline or the basis for evaluating forms of energy and resources shifted from organic matter, to fossil fuels and finally to solar energy.

Between 1986 and today, the emergy methodology has continued to develop as the community of scientists has expanded and as new applied research into combined systems of humans and nature has presented new conceptual and theoretical questions. The maturing of the emergy methodology has resulted in more rigorous definitions of terms and nomenclature and refinement of the methods of calculating transformities. There is now an International Society for the Advancement of Emergy Research and a biennial International Conference held on the campus of the University of Florida.

The following table is a chronology of the evolution of the emergy methodology and nomenclature providing a brief insight into the development of the concept.

Definitions and examples

Given next are definitions of most important terms used in the emergy methodology.

Emergy is the available energy of one form that is used up in transformations directly and indirectly to make a product or service. The unit of emergy is the emjoule or emergy joule. Using emergy, sunlight, fuel, electricity, and human service can be put on a common basis by expressing each of them in the emjoules of solar energy that is required to produce them. If solar emergy is the baseline, then the results are solar emjoules (abbreviated seJ). Although other baselines have been used, such as coal emjoules or electrical emjoules, in most cases emergy data are given in solar emjoules.

Unit Emergy Values (UEVs) are computed based on the emergy required to generate one unit of output from a process. There are several types of UEVs, as follows: :Transformity - the emergy input per unit of available energy output. For example, if 10,000 solar emjoules are required to generate a joule of wood, then the solar transformity of that wood is 10,000 solar emjoules per joule (abbreviated seJ/J). The solar transformity of the sunlight absorbed by the earth is 1.0 by definition.

:Specific emergy - the emergy per unit mass output. Specific emergy is usually expressed as solar emergy per gram (seJ/g). Material resources may best be evaluated with data on emergy per unit mass. Because energy is required to concentrate materials, the unit emergy value of any substance increases with concentration. Elements and compounds not abundant in nature therefore have higher emergy/mass ratios when found in concentrated form since more environmental work was required to concentrate them, both spatially and chemically.

:Emergy per unit money - the emergy supporting the generation of one unit of economic product (expressed as currency). It is used to convert money payments into emergy units. Since money is paid to people for their services and not to the environment, the contribution to a process represented by monetary payments is the emergy that people purchase with the money. The amount of resources that money buys depends on the amount of emergy supporting the economy and the amount of money circulating. An average emergy/money ratio in solar emjoules/$ can be calculated by dividing the total emergy use of a state or nation by its gross economic product. It varies by country and has been shown to decrease each year, which is one index of inflation. This emergy/money ratio is useful for evaluating service inputs given in money units where an average wage rate is appropriate.

:Emergy per unit labor- the amount of emergy supporting one unit of labor directly supplied to a process. Laborers apply their work to a process and in so doing they indirectly invest in it the whole emergy that made their labor possible (food, training, transport, etc). This emergy intensity is generally expressed as emergy per time (seJ/yr; seJ/hr), but emergy per money earned (seJ/$) is also used. Indirect labor required to make and supply the inputs to a process is generally measured as dollar cost of services, so that its emergy intensity is calculated as seJ/$.

Empower is a flow of emergy (i.e., emergy per unit time). Emergy flows are usually expressed in units of solar empower (solar emjoules per time, seJ/s, seJ/yr).

Emergy nomenclature

To avoid confusion with other forms of analysis and to rigorously define concepts, an emergy nomenclature has been developed that defines terms, units, and ratios used in emergy evaluations. The following table shows terms, abbreviations, definitions and units related to emergy, summarized from the literature.

The emergy accounting method

Emergy accounting uses the thermodynamic basis of all forms of energy, resources and human services, and converts them into equivalents of one form of energy, usually solar emergy. To evaluate a system, first a system diagram is drawn to organize the evaluation and account for all inputs and outflows. A table of the actual flows of resources, labor and energy is constructed from the diagram and all flows are evaluated. The final step of an emergy evaluation involves interpreting the quantitative results. In some cases, the evaluation is done to determine the fit of a development proposal within its environment. In others, it may be a question of comparing different alternatives, or the evaluation may be seeking the best use of resources to maximize economic vitality (Table 4, below lists some of the many published emergy evaluations of systems and processes).

Emergy evaluations are both synthetic and analytic. Synthesis is the act of combining elements into coherent wholes for understanding of the wholeness of systems, while analysis is the dissection or breaking apart of systems to build understanding from the pieces upward. In the emergy method of evaluation, sometimes called emergy synthesis, first the whole system is considered through diagramming, then the flows of energy, resources and information that drive the system are analyzed. By evaluating complex systems using emergy methods, the major inputs from the human economy and those coming “free” from the environment are integrated to analyze questions of public policy and environmental management.

1. Energy Systems Diagram

Systems diagrams are used to show the inputs that are evaluated and summed to obtain the emergy of a resulting flow or storage. The purpose of the system diagram is to conduct a critical inventory of processes, storages and flows that are important “drivers” of the system (all flows that inflow across the system boundary) and are therefore necessary to evaluate. A simple diagram of a city and its regional support area is shown in Figure 1 (many example diagrams can be found at the EmergySystems.org web site).

2. Preparation of an Emergy Evaluation Table

A table (see example below) of the actual flows of resources, labor and energy is constructed from the diagram. Raw data on inflows that cross the boundary are converted into emergy units, and then summed to obtain total emergy supporting the system. Energy flows per unit time (usually per year) are presented in the table as separate line items. Tables are usually constructed in the same format, as given by the column headings and format below:

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Column #1 is the line item number, which is also the number of the footnote found below the table whereraw data sources are cited and calculations are shown.

Column # 2 is the name of the item, which is also shown on the aggregated diagram.

Column # 3 is the raw data in joules, grams, dollars or other units.

Column # 4 shows the units for each raw data item.

Column # 5 is the unit emergy value, expressed in solar emergy joules per unit. Sometimes, inputs areexpressed in grams, hours, or dollars, therefore an appropriate UEV is used (sej/hr; sej/g; sej/$).

Column # 6 is the solar emergy of a given flow, calculated as the raw input times the UEV (Column 3 timesColumn 5).

All tables are followed by the numbered footnotes that show citations for data and calculations.

3. Calculating Unit Emergy Values

After the table is prepared that evaluates all the inputs, a unit emergy value of the product or process ise calculated. The output (row “O” in the example table above) is evaluated first in units of energy or mass. Then the input emergy is summed and the unit emergy value is calculated by dividing the emergy by the units of the output. The unit values that result for each evaluation are useful for other emergy evaluations. Thus, emergy evaluations generate new emergy unit values.

4. Performance Indicators

The systems diagram in Figure 2 shows non-renewable environmental contributions (N) as an emergy storage of materials, renewable environmental inputs (R), and inputs from the economy as purchased (F) goods and services. Purchased inputs are needed for the process to take place and include human service and purchased non-renewable energy and material brought in from elsewhere (fuels, minerals, electricity, machinery, fertilizer, etc.). Several ratios, or indices are given in Figure 2 that are used to evaluate the global performance of a process as follows: :Emergy Yield Ratio (EYR). Total emergy released (used up) per unit of emergy invested. The ratio is a measure of how much an investment enables a process to exploit local resources in order to further contribute to the economy. :Environmental Loading Ratio (ELR). The ratio of nonrenewable and imported emergy use to renewable emergy use. It is an indicator of the pressure of a transformation process on the environment and can be considered a measure of ecosystem stress due to a production (transformation activity. :Emergy Sustainability Index (ESI). The ratio of the Emergy Yield Ratio to the Environmental Loading Ratio. It measures the contribution of a resource or process to the economy per unit of environmental loading. :Aerial Empower Intensity. The ratio of total emergy use in the economy of a region or nation to the total area of the region or nation. Renewable and nonrenewable emergy density are also calculated separately by dividing the total renewable emergy by area and the total nonrenewable emergy by area, respectively.

Several other ratios are sometimes calculated depending on the type and scale of he systems being evaluated. :Percent Renewable Emergy (%Ren). The ratio of renewable emergy to total emergy use. In the long run, only processes with high %Ren are sustainable. :Emprice. The emprice of a commodity is the emergy one receives for the money spent. Its units are sej/$. :Emergy Exchange Ratio (EER). The ratio of emergy exchanged in a trade or purchase (what is received to what is given). The ratio is always expressed relative to one or the other trading partners and is a measure of the relative trade advantage of one partner over the other. :Emergy per capita. The ratio of total emergy use in the economy of a region or nation to the total population. Emergy per capita can be used as a measure of potential, average standard of living of the population.

Uses of emergy methodology

The recognition of the relevance of energy to the growth and dynamics of all complex systems has resulted in increased emphasis on methods of environmental evaluation that can account for and interpret the effects of matter and energy flows, at all scales in systems of humanity and nature. The following table lists some general areas in which the emergy methodology has been employed.

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Controversies

The concept of emergy has been controversial within several academic communities including ecology, thermodynamics and economy. Emergy theory has been criticized under the assumption that it fosters an energy theory of value to replace other theories of value. This criticism may miss the fact that the goal of emergy evaluations is to provide an "ecocentric" value of systems, processes, and products as opposed to the anthropocentric values of economics. Thus it does not purport to replace economic values but to provide additional information, from a very different point of view, with which public policy might benefit.

While energy quality has been recognized, somewhat, in the energy literature where different forms of fossil energy are expressed in coal or oil equivalents, and some researchers have even expressed electricity in oil equivalents by using 1st law efficiencies, many researchers have been reluctant to accept quality corrections of other forms of energy and resources. The idea that a calorie of sunlight is not equivalent to a calorie of fossil fuel or electricity strikes many as absurd, based on the 1st Law definition of energy units as measures of heat (i.e. Joule's mechanical equivalent of heat). Others have rejected the concept as being impractical since from their perspective it is impossible to quantify the amount of sunlight that is required to produce a quantity of oil. This latter issue results from a concern about the uncertainty involved in such quantification. In combining systems of humanity and nature and evaluating environmental input to economies, mainstream economists criticize the emergy methodology for disregarding market driven values as determined by willingness to pay.

Notes

See also

Energetics

Maximum power principle

References for Table 2

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Time's speed regulator: the optimum efficiency for maximum power output in physical and biological systems. American Scientist, 43: 331-343. :Odum H.T., 1983. Maximum power and efficiency: a rebuttal. Ecological Modelling, 20: 71-82. :Odum H.T., 1988. Self organization, transformity and information. Science, 242: 1132-1139. :Odum H.T., 1996. Environmental Accounting. Emergy and Environmental Decision Making. John Wiley & Sons, N.Y. :Odum, E.C., and Odum, H.T., 1980. Energy systems and environmental education. Pp. 213-231 in: Environmental :Education- Principles, Methods and Applications, Ed. by T.S. Bakshi and Z. Naveh. Plenum Press, New York. :Odum, E.C., and Odum, H.T., 1984. System of ethanol production from sugarcane in Brazil. Ciencia e Cultura, 37(11): 1849-1855. :Odum, E.C., Odum, H.T., and Peterson, N.S., 1995a. Using simulation to introduce systems approach in education. Chapter 31, pp. 346-352, in Maximum Power, ed. by C.A.S. Hall, University Press of Colorado, Niwot. :Odum, H. T., Brown, M. T., Whitefield, L. S., Woithe, R., and Doherty, S., 1995b. Zonal Organization of Cities and Environment: A Study of Energy System Basis for Urban Society. A Report to the Chiang Ching-Kuo Foundation for International Scholarly Exchange, Center for Environmental Policy, University of Florida, Gainesville, FL. :Odum, H.T, M.T. Brown, and S. Ulgiati. 1999. Ecosystems as Energetic Systems. pp.281-302 in S.E. Jorgensen and F. Muller (eds) Handbook of Ecosystem Theories. CRC Press, New York :Odum, H.T. 1971a. Environment, Power and Society. John Wiley, NY. 336 pp. :Odum, H.T. 1971b. An energy circuit language for ecological and social systems: its physical basis. Pp. 139-211, in Systems Analysis and Simulation in Ecology, Vol. 2, Ed. by B. Patten. Academic Press, New York. :Odum, H.T. 1972b. Chemical cycles with energy circuit models. Pp. 223-257, in Changing Chemistry of the Ocean, ed. by D. Dryssen and D. Jagner. Nobel Symposium 20. Wiley, New York. :Odum, H.T. 1973. Energy, ecology and economics. Royal Swedish Academy of Science. AMBIO 2(6):220-227. :Odum, H.T. 1976a. 'Energy quality and carrying capacity of the earth. Response at Prize Ceremony, Institute de la Vie, Paris. Tropical Ecology 16(l):1-8. :Odum, H.T. 1987a. Living with complexity. Pp. 19-85 in The Crafoord Prize in the Biosciences, 1987, Lectures. Royal Swedish Academy of Sciences, Stockholm, Sweden. 87 pp :Odum, H.T. 1987b. Models for national, international, and global systems policy. Chapter 13, pp. 203-251, in Economic-Ecological Modeling, ed. by L.C. Braat and W.F.J. Van Lierop. Elsevier Science Publishing, New York, 329 pp. :Odum, H.T. et al. 1976. Net energy Analysis of Alternatives for the United States. In U.S. Energy Policy: Trends and Goals. Part V - Middle and Long-term Energy Policies and Alternatives. 94th Congress 2nd Session Committee Print. Prepared for the Subcommittee on Energy and Power of the Committee on Interstate and Foreign Commerce of the U.S. House of Representatives, 66-723, U.S. Govt. Printing Office, Wash, DC. pp. 254-304. :Odum, H.T., 1975. Combining energy laws and corollaries of the maximum power principle with visual system mathematics. Pp. 239-263, in Ecosystems: Analysis and Prediction, ed. by Simon Levin. Proceedings of the conference on ecosystems at Alta, Utah. SIAM Institute for Mathematics and Society, Philadelphia. :Odum, H.T., 1980a. Biomass and Florida’s future. Pp. 58-67 in: A Hearing before the Subcommittee on Energy Development and Applications of the Committee on Science and Technology of the U.S. House of Representatives, 96th Congress. Government Printing Office, Washington, D.C. :Odum, H.T., 1980b. Principle of environmental energy matching for estimating potential economic value: a rebuttal. Coastal Zone Management Journal, 5(3): 239-243. :Odum, H.T., 1982. Pulsing, power and hierarchy. Pp. 33-59, in Energetics and Systems, ed. by W.J. Mitsch, R.K. Ragade, R. W. Bosserman, and J.A. Dillon Jr., Ann Arbor Science, Ann Arbor, Michigan. :Odum, H.T., 1984a. Energy analysis of the environmental role in agriculture. Pp. 24-51, in Energy and Agriculture, ed. by G. Stanhill. Springer Verlag, Berlin. 192 pp. :Odum, H.T., 1985. Water conservation and wetland values. Pp. 98-111, in Ecological Considerations in Wetlands Treatment of Municipal Wastewaters, ed. by P.J. Godfrey, E.R. Kaynor, S. Pelezrski, and J. Benforado. Van Nostrand Reinhold, New York. 473 pp. :Odum, H.T., 1986. Enmergy in ecosystems. In Environmental Monographs and Symposia, N. Polunin, ed. John Wiley, NY. pp. 337-369. :Odum, H.T., 1994. Ecological and General Systems: An Introduction to Systems Ecology. University Press of Colorado, Niwot. 644 pp. Revised edition of Systems Ecology, 1983, Wiley. :Odum, H.T., 1995. Self organization and maximum power. Chapter 28, pp. 311-364 in Maximum Power, Ed. by C.A.S. Hall, University Press of Colorado, Niwot. :Odum, H.T., 2000. Handbook of Emergy Evaluation: A Compendium of Data for Emergy Computation Issued in a Series of Folios. Folio #2 – Emergy of Global processes. Center for Environmental Policy, Environmental (http://www.emergysystems.org/downloads/Folios/Folio_2.pdf) :Odum, H.T., and Arding, J.E., 1991. Emergy analysis of shrimp mariculture in Ecuador. Report to Coastal Studies Institute, University of Rhode Island, Narragansett. Center for Wetlands, University of Florida, Gainesville, pp. 87. :Odum, H.T., Gayle, T., Brown, M.T., and Waldman, J., 1978b. Energy analysis of the University of Florida. Center for Wetlands, University of Florida, Gainesville. Unpublished manuscript. :Odum, H.T., Kemp, W., Sell, M., Boynton W., and Lehman, M., 1978a. Energy Analysis and the coupling of man and estuaries. Environmental Management, 1: 297-315. :Odum, H.T., Lavine, M.J., Wang, F.C., Miller, M.A., Alexander, J.F., and Butler, T., 1983. Manual for using energy analysis for plant siting. Report to the Nuclear Regulatory Commission, Washington, DC. Report No. NUREG/CR-2443. National Technical Information Service, Springfield, Va. Pp. 242. :Odum, H.T., M.T. Brown and S.B. Williams. 2000. Handbook of Emergy Evaluation: A Compendium of Data for Emergy Computation Issued in a Series of Folios. Folio #1 - Introduction and Global Budget. Center for Environmental Policy, Environmental . (http://www.emergysystems.org/downloads/Folios/Folio_1.pdf) :Odum, W.P., Odum, E.P., and Odum, H.T., 1995c. Nature’s Pulsing Paradigm. Estuaries 18(4): 547-555. :Peng, T., H.F. Lu, W.L. Wu, D.E. Campbell, G.S. Zhao, J.H. Zou, J. Chen. 2008. Should a small combined heat and power plant (CHP) open to its regional power and heat networks? Integrated economic, energy, and emergy evaluation of optimization plans for Jiufa CHP. Energy, Volume 33, Issue 3, March 2008, Pages 437-445 :Pizzigallo, A.C.I., C. Granai, S. Borsa. 2008. The joint use of LCA and emergy evaluation for the analysis of two Italian wine farms. Journal of Environmental Management, Volume 86, Issue 2, January 2008, Pages 396-406 :Prado-Jatar, M.A., and Brown, M.T., 1997. Interface ecosystems with an oil spill in a Venezuelan tropical savannah. Ecological Engineering, 8: 49-78. :Pulselli, R.M., E. Simoncini, R. Ridolfi, S. Bastianoni. 2008. Specific emergy of cement and concrete: An energy-based appraisal of building materials and their transport. Ecological Indicators, Volume 8, Issue 5, September 2008, Pages 647-656 :Reiss, C.R. and M.T. Brown. 2007. Evaluation of Florida Palustrine Wetlands: Application of USEPA Levels 1, 2, and 3 Assessment Methods. Ecohealth 4:206-218. :Rótolo, G.C. , T. Rydberg, G. Lieblein, C. Francis. 2007. Emergy evaluation of grazing cattle in Argentina's Pampas. Agriculture, Ecosystems & Environment, Volume 119, Issues 3-4, March 2007, Pages 383-395 :Rydberg, T., A.C. Haden. 2006. Emergy evaluations of Denmark and Danish agriculture: Assessing the influence of changing resource availability on the organization of agriculture and society. Agriculture, Ecosystems & Environment, Volume 117, Issues 2-3, November 2006, Pages 145-158 :Ulgiati, S., Odum, H.T., and Bastianoni, S., 1993. Emergy Analysis of Italian Agricultural System. The Role of Energy Quality and Environmental Inputs.In: Trends in Ecological Physical Chemistry. L. Bonati, U. Cosentino, M. Lasagni, G. Moro, D. Pitea and A. Schiraldi, Editors. Elsevier Science Publishers, Amsterdam, 187-215. :Ulgiati,S. and M.T. Brown. 2001. Emergy Evaluations and Environmental Loading of Alternative Electricity Production Systems. Journal of Cleaner Production 10:335-348 :Vassallo, P.,C. Paoli, D.R. Tilley, M. Fabiano. 2009. Energy and resource basis of an Italian coastal resort region integrated using emergy synthesis Journal of Environmental Management, Volume 91, Issue 1, October 2009, Pages 277-289 :Zhang, X., W.Jiang, S. Deng, K. Peng. 2009. Emergy evaluation of the sustainability of Chinese steel production during 1998–2004. Journal of Cleaner Production, Volume 17, Issue 11, July 2009, Pages 1030-1038 :Zhang, Y., Z. Yang, X.Yu. 2009. Evaluation of urban metabolism based on emergy synthesis: A case study for Beijing (China). Ecological Modelling, Volume 220, Issues 13-14, 17 July 2009, Pages 1690-1696

Further reading on the Web

:1. Web site on emergy at the University of Florida where publications, systems symbols and diagrams, templates, powerpoint lectures, etc can be downloaded: http://www.emergysystems.org :2. Paper by H.T. Odum describing emergy (1998) http://www.emergysystems.org/emergy.php :3. Environment, Power, and Society for the Twenty-First Century: The Hierarchy of Energy :4. Hall, C. A. S., ed., 1995. Maximum Power. The Ideas and Applications of H.T. Odum. University Press of Colorado, Niwot, 454 pp. :5. Odum H.T. and E.C. Odum , 2001. A Prosperous Way Down: Principles and Policies. University Press of Colorado.

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