The term Emergy was originally coined by David M. Scienceman in collaboration with the late Howard T. Odum. H.T.Odum used 'emergy' to mean both sequestered energy and emergent property of energy use . However Scienceman also used the term 'emergy' to refer to the concept of energy memory, a concept which motivated Scienceman and B.M. El-Youssef to propose the addition of a new dimension to physics, [P] for "past". Some researchers maintain that it can be expressed as a scientific unit which is called the "emjoule", a contraction of "emergy joule". When solar energy is the reference the emjoule is called the solar emjoule, which is designated with the symbol "sej". Odum identified an associated concept of emergy flow, or "empower", and suggested that the maximization of empower was an organizing principle of systems at any scale. In 2005 Corrado Giannantoni proposed maximum empower as a possible Fourth Thermodynamic Principle.

Historical development

As a word, emergy is a simple contraction of the term "embodied energy". The need for the new word of "emergy" arose apparently because of an important difference in the way the two related disciplines of systems ecology and energy analysis were using the term "embodied energy". As H.T.Odum observed "There is more than one type of embodied energy". Various authors have struggled to clarify their usage, and ambiguity seems to continue in the literature to this day.

Prior to 1986, both systems ecologists and energy analysts used "embodied energy" to refer to the sum over time of all energy of one type required to generate a flow of energy . Energy embodied in water was also defined in this way as the energy required directly and indirectly to generate the flow in processes of the biosphere or a typical desalination plant for example.

However unlike energy analysts, systems ecologists were, and continue to be also interested in the relationship of structure and function of ecological systems, together with the biophysical properties that afford plants the ability to accumulate and transform radiant energy into a structural form usable by other organisms, Scienceman observed this difference noting that the systems ecologist H.T. Odum had introduced an additional factor into the definition of embodied energy:

Odum ... introduces the maximum power principle into his definition: "The concept here retains the meaning that the embodied energy is what is required to do the work (at maximum power). Byproducts of a work transformation have the same embodied energy because they couldn't be generated with less"

The term "embodied energy" was therefore also used by systems ecologists to describe the energy that had been used in, and accumulated into structure-development and which could be fed back into the system to draw in more energy . This structural-cybernetic aspect of ecosystem research was apparently not included in the energy-analytic definition of "embodied energy". However the fact that both systems ecologists and energy analysts used the same term but with different levels of content seems to have led to considerable confusion.

Enter Scienceman

It was within this context of ambiguity that Scienceman proposed the emergy nomenclature as a means of simplifying scientific discussions. (But also apparently to unify science). Scienceman proposed that the term "emergy" be used to refer the ecosystem-derived concept of embodied energy to make it distinct from the energy-analytic conception. Ten years after proposing the emergy nomenclature in 1987, D.M.Scienceman wrote that his suggestion came as a consequence of studying H.T.Odum's book Systems Ecology (later published as Ecological and General Systems 1994) for a period of about 2 years. With a background in, "mathematics, practical and theoretical physics (including Einstein's unified field theory) and research in chemical engineering" , Scienceman had never before heard of the 'embodied energy' concept, and found Odum's use of it opaque:

Owing to great confusion in the scientific literature, and in order to clearly distinguish the theories of H.T.Odum, new concepts - energy memory, emergy, transformity, informity, empower, emtropy, emformation, emtelligence, emprice, emdollars, emtrons and soals - are introduced plus their appropriate units.

With this new terminology, Scienceman sought to clarify two issues:

  1. the combining of energies of different forms;
  2. the process of embodying energies of different forms, or using them up.

Scienceman (1997) noticed that the efficiency ratios used in engineering thermodynamics to quantify the transformations of energies from one form into another form were the same kind of ratios that H.T.Odum referred to as energy quality ratios. However in 1986 the National Bureau of Standards did not include any symbol for the notion of 'energy quality', a concept which is pivotal for understanding emergy, and later referred to by the term "energy transformation ratio", or "transformity". Scienceman and H.T.Odum subsequently collaborated on a linguistic project of simplifying and unifying the scientific lexicon by introducing and clarifying new terms. As H.T.Odum later noted,

In 1983 our concept of embodied energy (the available energy of one kind previously used up directly and indirectly in transformations to make a product or service) was given the name “EMERGY” and its unit names the “emjoule” or “emcalorie.” What is called an “energy transformation ratio” in this chapter was renamed the “transformity” with the unit “emjoule per joule” (not a dimensionless ratio)

H.T.Odum also used the word 'enmergy' briefly, before using 'emergy' as a standard. Because it can be confused with the word 'energy', some authors use the 'eMergy', and 'EMERGY' notations to emphasize the difference.

Emergy: a systems concept

According to the Emergy Systems school, like the concept of sustainability, "Emergy is a systems concept that is context driven, and cannot be fully understood or utilized outside of systems context." This school has therefore promoted emergy as a concept that is useful for establishing the metric for a rigorous and quantitative sustainability index.

The USEPA recently produced an emergy analysis of West Virginia.

Aims of emergy models: integration of human economic and ecological systems

The aim of an emergy model is to quantify the value (see below) of both energy and material resources to humans and non-human systems (e.g., the photosynthetic activity driven by the solar radiation, the dilution of pollutants by the wind, etc.) within a common framework. Hence services provided by the environment which are free and outside the monied economy are included in an emergy model, but may be omitted from an economic model because they are non-monied flows.

This framework attempts to give additional factors to the measurement of value other than monetary cost and consumer's willingness to pay. Non-emergy approaches to the evaluation of ecological, sociopolitical-economic, and industrial processes most often evaluate only non-renewable resources, depending on what human technologies are able to extract from them (user-side quality). Evaluation methodologies seldom have an accounting procedure for the value of human labor, societal services and information. That is, for those flows which carry negligible energy or money, but are supported by a huge indirect flow of resources and perform high quality control, innovation and maintenance actions (contributions to Wikipedia could be considered a good example of such). Emergy evaluation aims to include all of this, perhaps not perfectly, but in a way to help us understand that there is a huge network of supporting energies necessary to support any particular economic activity in human societies and ecological activity in non-human communities. Laganisa and Debeljakb write that

The emergy synthesis method was introduced from Odum in the 1980s ... with the aim of taking into account the different quality of driving forces supporting a process and allowing their comparison on the same basis. It attempts to solve the problem of multi-quality inputs by transforming them to an equivalent of energy of a single quality, which is usually solar energy

S.E. Jorgensen, S.N.Nielsen and H.Mejer write, "Emergy calculations have the same aim as exergy: to capture the energy hidden in the organization and construction of living organisms." .

Method: draw a system boundary diagram and account for all inputs and outputs

Often considered the first step in construction of a quantitative emergy synthesis simulation model is to define the system of interest. This is usually done using the Energy Systems Language to diagrammatically define a systems boundary. This diagram should illustrate all of the flows of emergy and energy into and out of the system of interest, as well as the storages within the system. In addition if system function is influenced by economics, then money flows and stores are also tracked, and again if information is used in system control, this is also diagrammed. The energy, emergy or mass value of these flows is then determined, and placed into an emergy synthesis spreadsheet. These values are then multiplied by either a coefficient to derive a solar emjoule value per joule of available energy in the system of the component (known as a transformity), the solar emjoule value per gram of flow (a specific emergy), or the emergy per dollar value (emdollar).

The purpose of these machinations being to place all components of the system on a common basis, such as the solar energy required to create it. Once this is accomplished it is hoped that the results can be useful to making decisions about public policy, development, trade and engineering that make the overall system more sustainable than it would have been using a non-renewable energy focused evaluation methodology. However in practice there are very few real practical examples in either law, policy making, management accounting, or ecological engineering.

Definition in words

Emergy can be defined as the total solar equivalent available energy of one form that was used up directly and indirectly in the work of making a product or service .

Emergy expresses the cost of a process or a product in solar energy equivalents. The basic idea is that solar energy is our ultimate energy source and by expressing the value of products in emergy units, it becomes possible to compare apples and pears. (S.E.Jorgensen 2001, p. 61)

H.T.Odum said that the notion of embodied exergy could be used to evaluate structure (1994, p. 266), and Chen (in press) goes further to define embodied exergy as emergy. For Shu-Li Huang and Chia-Wen Chen (2005), "intensive and diversified emergy sources build up the structure and enhance metabolism in urban areas." (p. 49).

Mathematical definition

To understand the concept of emergy it is first necessary to understand Exergy: the real proportion of the energy that can drive mechanical work.

E_x = (mbox{Gibbs free energy}) + (mbox{gravitational potential energy}) + (mbox{kinetic energy})

The Gibbs free energy is the available thermodynamic/chemical energy. Forms of energy such as radiation and thermal energy can not be converted completely to work, and have exergy content less than their energy content, see entropy.

The exergy power is the rate of change of exergy with time

P_x = {d E_x over dt}

an equivalent of the concept of power for exergy.

Emergy is then defined as the integral of the exergy power over time

E_m = int_{t=-infty}^{t_0} P_x, dt

i.e. the total change in exergy until t_0. This is a slight simplification of the formula in (Giannantoni 2002).

Solar emergy
The unit of solar emergy is U. Brown and Ulgiati (2001) define the solar emergy of a flow coming out of a given process as the solar energy that is directly or indirectly required to drive the process itself.

U = sum _i Tr_i E_i,

where E_i is the available energy (or free energy) content of the i th independent input flow to the process, and Tr_i is the solar transformity of the i th input flow. The solar transformity of direct solar radiation (Tr_s) is set equal to 1.

Scienceman wrote: "Energy obeys conservation algebra; emergy obeys memory algebra."

Energy memory, energy in a body

Scienceman's inclusion of the term energy memory in the definition of the word emergy implies that the properties of physical-biological-chemical materials can be included within the domain of the emergy schema. In pronouncing the new nomenclature, Scienceman (1997, p. 210-211) wrote:

I now describe 'emergy' as meaning 'energy memory', meaning a measure of the quantity of original form energy [fJ] which has been totally used up or transformed into a new form of energy. The original form has disappeared and has become only a memory, a memory stored up in emergent properties and transformity.

Scienceman and El-Youssef (1993, p. 219), constructed the system of emergy units where the symbol for energy memory is a prefix, 'em-', which is expressed in terms of SI base units of p, meaning "past". In contrast, Bastianoni et al (2007) define energy memory as: "the embodiment or enfolding in processes or products of energy from different sources", with the same dimensions as energy [ML²T-2] .

As it is used by Scienceman, the term "energy memory" implies a "memory algebra" (1997, p.211), which does not appear to obey the "energy conservation algebra" (Ibid.). This non-conservative view of systems is motivated by similar questions posed by Dirac. The energy conservation algebra simply states that the sum of the mass and energy must be conserved in any energy transformation, so that the sum of mass and energy in the universe remains constant forever (see for example Ohta 1994, p.3). While it is useful to assume that the sum of mass and energy in the universe remain constant forever, distributions of mass and energy in the universe do not remain constant forever. For example, the earth accumulates energy through the energy transformations carried out during photosynthesis. Another example is the hypertrophic growth of a heterotrophic organism. Consider also a simple closed electronic circuit with battery, and resistor. Because this circuit is closed, the quantity of electrons is constant. This is to say that the electrical form energy [e-fJ] is conserved. However the chemical form of energy that provides the force to move electrons in this circuit is not conserved. The heat energy form dissipates across the resistor as the chemical form of energy performs the work of moving electrons. Depending how one understands the concepts of open and closed systems, the circuit can be called closed to electron flow, but open to heat flow. In thermodynamics it is considered a closed system, but one that is isolated to electron flow, and not isolated to heat flow.

The memory algebra was designed to give a quantitative account of non-conservative energy transformations. The memory algebra also seems to have a connection with the physiological application of the cybernetic concept of "error" which is sometimes referred to as "memory". In addition to this H.T.Odum offered the theory that the toxic action of any substance is proportional to the emergy. This theory was partly based on research which found that pollution stress was greater on organisms with higher transformity (H.T.Odum 1994, p. 529). Further to this, G.P.Genoni, E.I.Meyer and A. Ulrich (2003) used the transformity measure to examine the hypothesis of a positive relationship between the “rarity” of a chemical element and its tendency to bioaccumulate, as energy in the body/entity under examination.

Empower and maximum empower

Empower refers to the flow rate of emergy: "The time rate of change of emergy is empower, analogous to the time rate of change of energy, power." (Scienceman 1987, p. 262.) Maximum empower therefore refers to the maximum flow rate of emergy. Considered as a principle, maximum empower has been proposed as a corollary of the maximum power principle, and is assumed to describe the organisational law of evolution. Accordingly H.T.Odum suggested that Lotka's maximum power principle be restated as the "Maximum Empower Principle"

The "Maximum Em-Power Principle" (Lotka-Odum) is generally considered as the "Fourth Thermodynamic Principle" (mainly) because of its practical validity for a very wide class of physical and biological systems (C.Giannantoni 2000, § 13, p. 155)

Citing H.T.Odum, J.L.Hau and B.R.Bakshi say that, "this principle determines which systems, ecological and economic, will survive over time and hence contribute to future systems" (2004, p.15).

Definition of the maximum empower principle in words

In the self-organizational process, systems develop those parts, processes, and relationships that maximize useful empower. (H.T. & E.C. Odum 2000, p. 71).

"The maximum empower principle is a unifying concept that explains why there are material cycles, autocatalytic feedbacks, successional stages, spatial concentrations in centers, and pulsing over time. Designs prevail that maximize empower" . This is to say that "those elements or individuals whose patterns of action do not result in maximum production tend to be replaced eventually" (H.T. & E.C.Odum 2000, p.71). M.T.Brown and S.Ulgiati both maintain that "The total available emergy flow drives the system behaviour according to the Maximum Empower Principle, determining the size of the system itself and its growth rate." (2001, p. 109).

Mathematical definition of the maximum empower principle

As a corollary of maximum power efficiency, a mathematical statement of the maximum empower efficiency principle still needs to be clarified - see Emergy

Emergy accounting and emergy "analysis" vs emergy synthesis

Emergy accounting is a GLOBAL method of accounting concerned with the input of solar energy equity at the global level. The emergy accounting methodology seeks to account for the energy used in developing energy of higher quality, which are capable of controlling ecosystem and economic functions. M.T.Brown and S.Ulgiati say that emergy accounting is a "method of valuation" that, "uses the thermodynamic basis of all forms of energy and materials, but converts them into equivalents of one form of energy, usually sunlight." (1999, p. 4). Emergy "analysis", therefore aims to identify how this energy, and its comparable inputs as fossil fuels etc., are distributed. Emergy accounting assumes three things:
1. That every sector of the world economy is, in the final analysis, dependent on the total global energy budget.
2. None of the sectors of the world economy overlap in their function.
3. Non-human sectors (i.e. non-human ecological systems) are included in the world economy
The sum result of these assumptions is that all sectors considered together produce a "complete" economy. It therefore includes energy, emergy, commodity and money flows. The method rests heavily on H.T.Odum's use of the "maximum power principle". In an evolutionary sense the use of this principle to analyse the world economy implies that the global economy will run close to optimal efficiency if and only if competition is unimpeded by cultural, communication, geographical, legal or other matters. However because emergy involves the combination of heterogeneous energy forms, D.M.Scienceman now only refers to Emergy Synthesis, preferring to see the notion of "emergy analysis" as an oxymoron.


Acceptance of nomenclature and units

Corrado Giannantoni maintains that the maximum empower principle is generally accepted as the fourth thermodynamic principle (see above quote and reference). However the exchange between Scienceman (1997), H.T.Odum (1997), and Brown (1997), highlights the fact that various authors who have used the nomenclature are not agreement about how it is to be used - there appears to be significant differences of opinion regarding the physical, and scientific basis of the concept. To demonstrate this point, some authors such as Bastianoni et al. (2007, p.1159) writing that transformity is a dimensionless function, but others such as Odum (1994 p.251, 1988, p.1135) stating that it is not a dimensionless ratio, with Scienceman (1997, p.212) writing that:

no one, to my knowledge has displayed any new dimensions of emergy or transformity in relation to the SI units, except my own provisional paper (Scienceman, 1993) which inserted a 'p' (meaning 'past') in the dimensions of relevant qualities.

For some scientists, there are two fundamental requirements for something to be considered a thermodynamic or energetic principle. Firstly is an experimental technique, or instrument, used to quantitatively measure the phenomenon of interest. In the case of maximum empower this would mean the specification of an instrument that measures 'empower'. A second requirement is a set of mathematical equations that demonstrate, in the current case, an experimentally testable relationship of the phenomenon of "empower" to other thermodynamic variables.

A consequence of the first criteria is that serious scientific scholarship using the emergy nomenclature will need something like an "empower meter". Giannantoni has attempted to give the mathematics, however does not appear to have specified an empower meter by which to quantitatively measure empower. Although the concept of maximum empower has been used in peer-reviewed journals to model and quantify the ecological-economic sustainability of a region and nation, the question remains as to whether it qualifies as the 4th thermodynamic law, and apparently will not be resolved until an empower meter or equivalent is constructed. Given it is proposed as the 4th thermodynamic law acceptance of results would also probably only come more widely with general consensus in well respected physics journals like the The International Journal of Thermodynamics, or perhaps Physical Review. As long as physicists do not recognise it as the 4th thermodynamic law, it is unlikely scientists more generally will accept it and use the concept to unify disciplines like physics, biology and chemistry (not to mention society, economics and religion).

Value theory

A controversial application of the concept is with respect to Value theory. For H.T.Odum, “embodied energy is a measure of value, in one of the meanings of the word 'value'” (H.T.Odum 1994, p.251 - In this quote the term "embodied energy" is synonymous with "emergy", see Embodied energy). H.T.Odum (1996) understood emergy to encompass not only the above considerations, but also the human notion of utility as a "donor-type value." As Scienceman (1987, p.260) noted:

Odum ... clarified his theory of value: "Embodied energy was defined as a way to measure cumulative action of energies in chains and webs. Embodied energy provides an alternative theory of value, is useful for tracing sources, especially net energy, determining relative importance of components, and covering free items that are not covered by money." Of critical importance, Odum ... wrote: "An energy theory of value is based on embodied energy... The energy transformation ratio, by giving the embodied energy per unit of actual energy, provides an intensive factor for value in the way that temperature is an intensive factor for heat".

This conception has not yet received wide support or critical analysis by value theorists. In fact it is this application which seems to act as a block to the wider appeal of Emergy Synthesis in the sciences and arts. This could be due to the attitude which regards the arts, qualitative aesthetics, and spiritual systems of value as incommensurable with rational scientific systems of quantitative value measurement and prediction.

Environmental ethics

Further controversial implications of this conception of value are in the fields of jurisprudence and policy where H.T.Odum suggests a consequentialist ethic. The kind of consequentialism employed is utilitarianism which seeks the quantitative maximization of value. Policies and laws that aim at long term sustainability are, according to this ethic, those that maximize value. From the perspective of emergy synthesis, "value" is defined as "empower". Therefore, from the perspective of emergy evaluation, policies and laws that aim at long term sustainability by maximizing value, consequently aim to maximize empower. Semantically speaking then, emergy theorists imbue the concept of empower with both scientific, and normative content. In this context the division between social and physical sciences melts into air.

Emergy and policy

In terms of energy, and environmental resource policy, H.T.Odum (1995b) maintained that, whether by trial and error or by intent, the maximum empower principle explains what is successful in self-organization. Odum and Odum (2001, p.71) claimed that the maximum empower principle accounts for many features of system performance and design:

It is a guideline for selecting policy. For policy the principle is: Choose alternatives that maximize empower intake and use.


As if matters were not sufficiently controversial, Scienceman (1995, p.1) added further fuel to the embers of confusion with the statement that :

The concept of GOD is merely a 'personification' of emergy


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