Emergy
Encyclopedia
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.
, general system theory and systems ecology
. Evolution of the theory over the first thirty years was documented by H.T Odum
in Environmental Accounting and in the volume edited by C.A.S. Hall titled Maximum Power. 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 led 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
The first formal statement of what would later be termed emergy was in 1973:
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.
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:
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.
|+Table 3. Example emergy evaluation table
|-
! Note !! Item(name) !! Data(flow/time) !! Units !! UEV (seJ/unit) !! Solar Emergy (seJ/time)
|-
| 1. || First item || xxx.x || J/yr || xxx.x || Em1
|-
| 2. || Second item || xxx.x || g/yr || xxx.x || Em2
|-
| -- || || || || ||
|-
| n. || nth item || xxx.x || J/yr|| xxx.x || Emn
|-
| O. || Output || xxx.x || J/yr or g/yr || xxx.x ||
|}
All tables are followed by the numbered footnotes that show citations for data and calculations.
Several other ratios are sometimes calculated depending on the type and scale of he systems being evaluated.
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.
|+Table 4. Fields of Study and Emergy Evalautions
|-
| Emergy and ecosystems
|-
| Emergy and Information
|-
| Emergy and Agriculture
|-
| Emergy and energy sources and carriers
|-
| Emergy and the Economy
|-
| Emergy and cities
|-
| Emergy and landscapes
|-
| Emergy and ecological engineering
|-
| Emergy, material flows and recycling
|-
| Emergy and thermodynamics
|-
| Emergy and systems modeling
|-
| Emergy and policy
|-
|
|}
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, which public policy might benefit from.
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
.
Further reading on the Web
Exergy
In thermodynamics, the exergy of a system is the maximum useful work possible during a process that brings the system into equilibrium with a heat reservoir. When the surroundings are the reservoir, exergy is the potential of a system to cause a change as it achieves equilibrium with its...
) 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 thermodynamicsThermodynamics
Thermodynamics is a physical science that studies the effects on material bodies, and on radiation in regions of space, of transfer of heat and of work done on or by the bodies or radiation...
, general system theory and systems ecology
Systems ecology
Systems ecology is an interdisciplinary field of ecology, taking a holistic approach to the study of ecological systems, especially ecosystems. Systems ecology can be seen as an application of general systems theory to ecology. Central to the systems ecology approach is the idea that an ecosystem...
. Evolution of the theory over the first thirty years was documented by H.T Odum
Howard T. Odum
Howard Thomas Odum was an American ecologist...
in Environmental Accounting and in the volume edited by C.A.S. Hall titled Maximum Power. 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 led 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.
The 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.
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
Embodied energy
Embodied energy is defined as the sum of energy inputs that was used in the work to make any product, from the point of extraction and refining materials, bringing it to market, and disposal / re-purposing of it...
" 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
David M. Scienceman
Dr David M. Scienceman is an Australian scientist; he changed his name from David Slade by deed poll in 1972.Dr Scienceman has a mathematics and physics degree and gained his PhD from the chemical engineering department at Sydney University on a scholarship from the Australian Atomic Energy...
, 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
Transformity
The concept of transformity was first introduced by David M. Scienceman in collaboration with the late Howard T. Odum. In 1987 Scienceman proposed that the phrases, "energy quality", "energy quality factor", and "energy transformation ratio", all used by H.T.Odum, be replaced by the word...
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.
| Years | Baseline | Unit Emergy Values | Units | Reference |
|---|---|---|---|---|
| 1967–1971 | Organic matter the baseline. All energies of higher quality (wood, peat, coal, oil, living biomass, etc.) expressed in units of organic matter. | Sunlight equivalent to organic matter = 1000 solar kilocalories per kilocalories of organic matter. | g dry wt O.M.; kcal, conversion from OM to kcal = 5kcal/g dry wt. | |
| 1973–1980 | Fossil fuels and then coal the baseline. Energy of lower quality (sunlight, plants, wood, etc.) were expressed in units of fossil fuels and later in units of coal equivalents. | Direct sunlight equivalents of fossil fuels = 2000 solar kilocalories per fossil fuel kilocalorie | Fossil fuel work equivalents (FFWE) and later, coal equivalents (CE) | |
| 1980–1982 | Global solar energy the baseline. All energies of higher quality (wind, rain, wave, organic matter, wood, fossil fuels, etc.) expressed in units of solar energy | 6800 global solar Calories per Calorie of available energy in coal | Global solar calories (GSE). | |
| 1983–1986 | Recognized that solar energy, deep heat, and tidal momentum were basis for global processes. Total annual global sources equal to the sum of these (9.44 E24 solar joules/yr) | Embodied solar joules per joule of fossil fuels = 40,000 seJ/J | Embodied solar equivalents (SEJ) and later called "emergy" with nomenclature (seJ) | |
| 1987–2000 | Further refinements of total energy driving global processes, Embodied solar energy renamed to EMERGY | Solar Emergy per Joule of coal energy ~ 40,000 solar emjoules/ Joule (seJ/J) named Transformity | seJ/J = Transformity; seJ/g = Specific emergy | |
| 2000–present | Emergy driving the biosphere reevaluated as 15.83 E24 seJ/yr raising all previously calculated transformities by the ratio of 15.83/9.44 = 1.68 | Solar emergy per Joule of coal energy ~ 6.7 E 4 seJ/J | seJ/J = Transformity; seJ/g = Specific emergy |
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:
- 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 — 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.| Term | |Abbreviation | Extensive Properties | ||
|---|---|---|---|---|
| Emergy | The amount of available energy of one type (usually solar) that is directly or indirectly required to generate a given output flow or storage of energy or matter. | Em | seJ (solar equivalent Joules) | |
| Emergy Flow | Any flow of emergy associated with inflowing energy or materials to a system/process. | R=renewable flows; N= nonrenewable flows; F= imported flows; S= services |
seJ*time−1 | |
| Gross Emergy Product | Total emergy annually used to drive a national or regional economy | GEP | seJ*yr−1 | |
| Product-related Intensive Properties | ||||
| Transformity | Emergy investment per unit process output of available energy | Τr | seJ*J−1 | |
| Specific Emergy | Emergy investment per unit process output of dry mass | SpEm | seJ*g−1 | |
| Emergy Intensity of currency | Emergy investment per unit of GDP generated in a country, region or process | EIC | seJ*curency−1 | |
| Space-related Intensive Properties | ||||
| Emergy Density | Emergy stored in a volume unit of a given material | EmD | seJ*volume−3 | |
| Time-related Intensive Properties | ||||
| Empower | Emergy flow (released, used) per unit time | EmP | seJ*time−1 | |
| Empower Intensity | Areal Empower (emergy released per unit time and area) | EmPI | seJ*time−1*area−1 | |
| Empower Density | Emergy released by a unit volume unit (e.g. a power plant or engine) | EmPd | seJ*time−1*volume−3 | |
| Selected Performance Indicators | ||||
| Emergy released (used) | Total emergy investment in a process (measure of a process footprint) | U= N+R+F+S (see Fig.1) |
seJ | |
| Emergy Yield Ratio | Total emergy released (used up) per unit of emergy invested | EYR= U/(F+S) (see Fig.1) |
||
| Environmental Loading Ratio | Total nonrenewable and imported emergy released per unit of local renewable resource | ELR= (N+F+S)/R (see Fig.1) |
||
| Emergy Sustainability Index | Emergy yield per unit of environmental loading | ESI= EYR/ELR (see Fig.1) |
||
| Renewability | Percentage of total emergy released (used) that is renewable. | %REN= R/U (see Fig.1) |
||
| Emergy Investment Ratio | Emergy investment needed to exploit one unit of local (renewable and nonrenewable) resource. | EIR= (F+S)/(R+N) (see Fig.1) |
||
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:-
- {| class="wikitable"
|+Table 3. Example emergy evaluation table
|-
! Note !! Item(name) !! Data(flow/time) !! Units !! UEV (seJ/unit) !! Solar Emergy (seJ/time)
|-
| 1. || First item || xxx.x || J/yr || xxx.x || Em1
|-
| 2. || Second item || xxx.x || g/yr || xxx.x || Em2
|-
| -- || || || || ||
|-
| n. || nth item || xxx.x || J/yr|| xxx.x || Emn
|-
| O. || Output || xxx.x || J/yr or g/yr || xxx.x ||
|}
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 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 is 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
Complex systems
Complex systems present problems in mathematical modelling.The equations from which complex system models are developed generally derive from statistical physics, information theory and non-linear dynamics, and represent organized but unpredictable behaviors of systems of nature that are considered...
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.
-
- {| class="wikitable" Width="75%"
|+Table 4. Fields of Study and Emergy Evalautions
|-
| Emergy and ecosystems
- Self-organization (Odum, 1986; Odum, 1988)
- Aquatic and marine ecosystems (Odum et al., 1978a; Odum and Arding, 1991; Brandt-Williams, 1999)
- Food webs and hierarchies (Odum et al. 1999; Brown and Bardi, 2001)
- Ecosystem health (Brown and Ulgiati, 2004)
- Forest ecosystems (Doherty et al., 1995; Lu et al. 2006)
- Complexity (Odum, 1987a; Odum, 1994; Brown and Cohen, 2008)
- Biodiversity (Brown et al. 2006)
|-
| Emergy and Information
- Diversity and information (Keitt, 1991; Odum, 1996, Jorgensen et al., 2004)
- Culture, Education, University (Odum and Odum, 1980; Odum et al., 1995; Odum et al., 1978b)
|-
| Emergy and Agriculture
- Food production, agriculture (Odum, 1984; Ulgiati et al. 1993; Martin et al. 2006; Cuadra and Rydberg, 2006; de Barros et al. 2009; Cavalett and Ortega, 2009)
- Livestock production (Rótolo et al.2007)
- Agriculture and society (Rydberg and Haden, 2006; Cuadra and Björklund, 2007; Lu, and Campbell, 2009)
- Soil erosion (Lefroy and Rydberg, 2003; Cohen et al. 2006)
|-
| Emergy and energy sources and carriers
- Fossil fuels (Odum et a.l 1976; Brown et al., 1993; Odum, 1996; Bargigli et al., 2004; Bastianoni et al. 2005; Bastianoni et al. 2009)
- Renewable and nonrenewable electricity (Odum et al. 1983; Brown and Ulgiati, 2001; Ulgiati and Brown, 2001; Peng et al. 2008)
- Hydroelectric dams (Brown and McClanahan, 1992)
- Biofuels (Odum, 1980a; Odum and Odum, 1984; Carraretto et al., 2004; Dong et al. 2008; Felix and Tilley, 2009; Franzese et al., 2009)
- Hydrogen (Barbir, 1992)
|-
| Emergy and the Economy
- National and international analyses (Odum, 1987b; Brown, 2003; Cialani et al. 2003; Ferreyra and Brown. 2007; Lomas et al., 2008; Jiang et al.,2008)
- Trade (Odum, 1984a; Brown, 2003)
- Environmental accounting (Odum, 1996)
- Development policies (Odum, 1980b)
- Sustainability (Odum, 1973; Odum, 1976a; Brown and Ulgiati, 1999; Odum and Odum, 2002; Brown et al. 2009)
- Tourism (Lei and Wang, 2008; Vassallo et al., 2009)
|-
| Emergy and cities
- Spatial organization and urban development (Odum et al., 1995b; Huang, 1998; Huang and Chen, 2005; Ascione, et. al 2009)
- Urban metabolism (Huang et al.,2006; Zhang et al., 2009)
- Transportation modes (Federici, et al. 2003; Federici et al., 2008; Federici et al., 2009; Almeida et al., 2010 )
|-
| Emergy and landscapes
- Spatial empower, Land development indicators (Brown and Vivas, 2004; Reiss and Brown, 2007)
- Emergy in landforms (Kangas, 2002)
- Watersheds (Agostinho et al., 2010)
|-
| Emergy and ecological engineering
- Restoration models (Prado-Jartar and Brown, 1996)
- Reclamation projects (Brown, 2005; Lu et al., 2009 )
- Artificial Ecosystems: wetlands, pond (Odum, 1985)
- Waste treatment (Kent et al. 2000; Grönlund, et al. 2004)
|-
| Emergy, material flows and recycling
- Mining and minerals processing (Odum, 1996; Pulselli et al.2008)
- Industrial production, ecodesign (Zhang et al. 2009; Almeida et al., 2009)
- Recycling pattern in human-dominated ecosystems (Brown and Buranakarn, 2003)
|-
| Emergy and thermodynamics
- Efficiency and Power (Odum and Pinkerton, 1955; Odum, 1995)
- Maximum Empower Principle (Odum, 1975; Odum, 1983; Cai e al., 2004)
- Pulsing paradigm (Odum, 1982; Odum, W.P. et al., 1995)
- Thermodynamic principles (Giannantoni, 2002, 2003)
|-
| Emergy and systems modeling
- Energy systems language and modeling (Odum, 1971; Odum, 1972)
- National sustainability (Brown et al. 2009)
- Sensitivity analysis, uncertainty (Laganis and Debeljak, 2006; Ingwersen, 2010)
|-
| Emergy and policy
- Tools for decision makers (Giannetti et al., 2006; Almeida, et al. 2007; Giannetti et al., 2010)
- Conservation and economic value (Lu et al.2007)
|-
|
References for each of the citations in this table are given in a separate list at the end of this article
|}
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, which public policy might benefit from.
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
Mechanical equivalent of heat
In the history of science, the mechanical equivalent of heat was a concept that had an important part in the development and acceptance of the conservation of energy and the establishment of the science of thermodynamics in the 19th century....
). 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
Uncertainty
Uncertainty is a term used in subtly different ways in a number of fields, including physics, philosophy, statistics, economics, finance, insurance, psychology, sociology, engineering, and information science...
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
Willingness to pay
In economics, the willingness to pay is the maximum amount a person would be willing to pay, sacrifice or exchange in order to receive a good or to avoid something undesired, such as pollution...
.
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.