Emergy - Definitions and Examples

Definitions and Examples

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

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

Unit Emergy Values (UEVs) are computed based on the emergy required to generate one unit of output from a process. There are several types of UEVs, as follows:

Transformity — the emergy input per unit of available energy output. For example, if 10,000 solar emjoules are required to generate a joule of wood, then the solar transformity of that wood is 10,000 solar emjoules per joule (abbreviated seJ/J). The solar transformity of the sunlight absorbed by the earth is 1.0 by definition.

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

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

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

Empower — 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).