Emergy

Emergy is the amount of energy consumed in direct and indirect transformations to make a product or service. Emergy is a measure of quality differences between different 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. Emergy is measured in units of ''emjoule''s, a unit referring to the available energy 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 a different ability to support work in natural and in human systems. The recognition of these quality differences is a key concept.

History

The theoretical and conceptual basis for the emergy methodology is grounded in thermodynamics, general system theory and systems ecology.Odum, H. T. 1983. ''Systems Ecology: An Introduction''. John Wiley, NY. 644 p. Evolution of the theory by Howard T. Odum over the first thirty years is reviewed in ''Environmental Accounting'' and in the volume edited by C. A. S. Hall titled ''Maximum Power''.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.

Background

Beginning in the 1950s, Odum analyzed energy flow in ecosystems (''e.g.'' Silver Springs, Florida;Odum, H. T. 1957. Trophic structure and productivity of Silver Springs, Florida. ''Ecol. Monogr''. 27:55-112. Enewetak atoll in the south Pacific;Odum, H. T. and E. P. Odum. 1955. Trophic structure and productivity of a windward coral reef at Eniwetok Atoll, Marshall Islands. ''Ecol. Monogr.'' 25:291-320. Galveston Bay, TexasOdum, H. T. and C. M. Hoskin. 1958. Comparative studies of the metabolism of Texas Bays. ''Pubi. Inst. Mar. Sci.'', Univ. Tex. 5:16-46. and Puerto Rican rainforests,Odum, H. T. and R. F. Pigeon, eds. 1970. ''A Tropical Rain Forest''. Division of Technical Information, U.S. Atomic Energy Commission. 1600 pp. amongst others) where energies in various forms at various scales were observed. His analysis of energy flow in ecosystems, and the differences in the potential energy of sunlight, fresh water currents, wind and ocean currents led him to make the suggestion 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 energy quality. This led him to introduce the concept of "energy of one kind" as a common denominator with the name "energy cost".Odum, H. T. 1967. Energetics of food production. In: The ''World Food Problem, Report of the President's Science Advisory Committee, Panel on World Food Supply, Vol. 3''. The Whitehouse. pp. 55-94. He then expanded the analysis to model food production in the 1960s, and in the 1970s to fossil fuels.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. and E. C. Odum. 1976. ''Energy Basis for Man and Nature''. McGraw-Hill, NY. 297 pp

Odum's first formal statement of what would later be termed emergy was in 1973:

Energy is measured by calories, btu's, kilowatthours, and other intraconvertable units, but energy has a scale of quality which is not indicated by these measures. The ability to do work for man depends on the energy quality and quantity and this is measurable by the amount of energy of a lower quality grade required to develop the higher grade. The scale of energy goes from dilute sunlight up to plant matter, to coal, from coal to oil, to electricity and up to the high quality efforts of computer and human information processing.Odum, H. T. 1973. ''Energy, ecology and economics''. Royal Swedish Academy of Science. AMBIO 2(6):220-227.

In 1975, he introduced a table of "Energy Quality Factors", kilocalories of sunlight energy required to make a kilocalorie of a higher quality energy,Odum, H. T. 1976. 'Energy quality and carrying capacity of the earth. Response at Prize Ceremony, Institute de la Vie, Paris. ''Tropical Ecology'' 16(l):1–8. the first mention of the energy hierarchy principle which states 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).Odum, H. T. 1977. Energy analysis, energy quality and environment. In ''Energy Analysis: A New Public Policy Tool'', M. W. Gilliland, ed. American Association for the Advancement of Science, Selected Symposium No. 9, Wash. DC. Westview Press. pp. 55–87.

Embodied energy

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.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. 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".

Introduction of the term "emergy"

Use of the term "embodied energy" for this concept was modified 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 these 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.

After 1986, the emergy methodology continued to develop as the community of scientists expanded and as new applied research into combined systems of humans and nature presented new conceptual and theoretical questions. The maturing of the emergy methodology resulted in more rigorous definitions of terms and nomenclature and refinement of the methods of calculating transformities. Th
International Society for the Advancement of Emergy Research
and a biennia
International Conference
at the University of Florida support this research.

Chronology

Definitions and examples

''Emergy''— amount of energy of one form that is used 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)'' — the emergy required to generate one unit of output. Types of UEVs:
:''Transformity'' — 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'' — emergy per unit mass output. Specific emergy is usually expressed as solar emergy per gram (seJ/g). 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 is required to concentrate them, both spatially and chemically.

:''Emergy per unit money'' — the emergy supporting the generation of one unit of economic product (expressed in monetary terms)''.'' It is used to convert money into emergy units. Since money is paid for goods and services, but not to the environment, the contribution to a process represented by monetary payments is the emergy that money purchases. 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 emergy supporting one unit of direct labor applied to a process''.'' Workers apply their efforts to a process and in so doing they indirectly invest in it the 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/$) is also used. Indirect labor required to make and supply the inputs to a process is generally measured with the dollar cost of services, so that its emergy intensity is calculated as seJ/$.

:''Empower'' — a flow of emergy (i.e., emergy per unit time)''.''

Accounting method

Emergy accounting converts the thermodynamic basis of all forms of energy, resources and human services into equivalents of a single form of energy, usually solar. To evaluate a system, a system diagram organizes the evaluation and account for energy inputs and outflows. A table of the flows of resources, labor and energy is constructed from the diagram and all flows are evaluated. The final step involves interpreting the results.

Purpose

In some cases, an evaluation is done to determine the fit of a development proposal within its environment. It also allows comparison of alternatives. Another purpose is to seek the best use of resources to maximize economic vitality.

Systems diagram

System diagrams show the inputs that are evaluated and summed to obtain the emergy of a flow. A diagram of a city and its regional support area is shown in Figure 1.

Evaluation table

A table (see example below) of resource flows, 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.

::
;Legend
* Column #1 is the line item number, which is also the number of the footnote found below the table where raw 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 are expressed 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 times Column 5).

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

Calculating unit values

The table allows a unit emergy value to be calculated. The final, output row (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.

Performance indicators

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 assess the global performance of a process.
* Emergy Yield Ratio (EYR) — Emergy released (used up) per unit invested. The ratio is a measure of how much an investment enables a process to exploit local resources.
* Environmental Loading Ratio (ELR) — The ratio of nonrenewable and imported emergy use to renewable emergy use. It is an indicator of the pressure a transformation process exerts 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 EYR to ELR. It measures the contribution of a resource or process to the economy per unit of environmental loading.
* Areal Empower Intensity — The ratio of emergy use in the economy of a region to its area. Renewable and nonrenewable emergy density are calculated separately by dividing the total renewable emergy by area and the total nonrenewable emergy by area, respectively.

Other ratios are useful depending on the type and scale of the system under evaluation.
* 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 in 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 a trading partner and is a measure of the relative trade advantage of one partner over the other.
* Emergy per capita — The ratio of emergy use of a region or nation to the population. Emergy per capita can be used as a measure of potential, average standard of living of the population.
* Emergy-based energy return on investment was introduced as a way to bridge and improve the concept of Energy returned on energy invested to also include environmental impacts.

Uses

The recognition of the relevance of energy to the growth and dynamics of complex systems has resulted in increased emphasis on environmental evaluation methods 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 academe including ecology, thermodynamics and economy. Emergy theory has been criticized for allegedly offering an energy theory of value to replace other theories of value. The stated goal of emergy evaluations is to provide an "ecocentric" valuation of systems, processes. Thus it does not purport to replace economic values but to provide additional information, from a different point of view.

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).Sciubba, E., 2010. On the Second-Law inconsistency of Emergy Analysis. Energy 35, 3696-3706. Others have rejected the concept as impractical since from their perspective it is impossible to objectively quantify the amount of sunlight that is required to produce a quantity of oil. In combining systems of humanity and nature and evaluating environmental input to economies, mainstream economists criticize the emergy methodology for disregarding market values.

See also

Notes

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:Lu, H., D. E. Campbell. 2009. Ecological and economic dynamics of the Shunde agricultural system under China's small city development strategy. ''Journal of Environmental Management'', Volume 90, Issue 8, June 2009, Pages 2589-2600
:Martin, J.F., S.A.W. Diemont, E. Powell, M. Stanton, S. Levy-Tacher. 2006. Emergy evaluation of the performance and sustainability of three agricultural systems with different scales and management. ''Agriculture, Ecosystems & Environment'', Volume 115, Issues 1-4, July 2006, Pages 128-140
:Odum H.T. and E.C. Odum , 2001. A Prosperous Way Down: Principles and Policies. University Press of Colorado.
:Odum H.T. and Pinkerton R.C., 1955. 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
:S. Giberna, P. Barbieri, E. Reisenhofer, P. Plossi. 2004. Emergy analysis of the phase of operation of the incineration of municipal waste in Trieste
: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
{{refend

External links

Emergy Systems
- University of Florida where publications, systems symbols and diagrams, templates, powerpoint lectures, etc. can be downloaded
Paper by H.T. Odum describing emergy (1998)Environment, Power, and Society for the Twenty-First Century: The Hierarchy of EnergyHall Maximum Power
- The Ideas and Applications of H.T. Odum. University Press of Colorado, Niwot, 454 pp, C. A. S., ed., 1995
Odum H.T. and E.C. Odum, 2001
- A Prosperous Way Down: Principles and Policies. University Press of Colorado]
Marvuglia, Benetto, Rios, Rugani, 2013
- SCALE: Software for CALculating Emergy Based on Life Cycle Inventories

Emergy,
Energy
Systems theory