Net energy gain
Net Energy Gain is a concept used in energy economics
Energy economics
Energy economics is a broad scientific subject area which includes topics related to supply and use of energy in societies. Due to diversity of issues and methods applied and shared with a number of academic disciplines, energy economics does not present itself as a self contained academic...

 that refers to the difference between the energy expended to harvest an energy source and the amount of energy gained from that harvest. The net energy gain, which can be expressed in joule
The joule ; symbol J) is a derived unit of energy or work in the International System of Units. It is equal to the energy expended in applying a force of one newton through a distance of one metre , or in passing an electric current of one ampere through a resistance of one ohm for one second...

s, differs from the net financial gain that may result from the energy harvesting process, in that various sources of energy (e.g. natural gas
Natural gas
Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...

, coal
Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...

, etc.) can be priced differently for the same amount of energy.

Calculating NEG

A net energy gain is achieved by expending less energy acquiring a source of energy than is contained in the source to be consumed. That is,

Factors to consider when calculating NEG is the type of energy, the way energy is used and acquired, and the methods used to store or transport the energy. It is also possible to overcomplicate the equation by an infinite number of externalities
In economics, an externality is a cost or benefit, not transmitted through prices, incurred by a party who did not agree to the action causing the cost or benefit...

 and inefficiencies that may be present during the energy harvesting process.

Sources of energy

The definition of an energy source is not rigorous. Anything that can provide energy to anything else can qualify. Wood in a stove is full of potential thermal energy
Thermal energy
Thermal energy is the part of the total internal energy of a thermodynamic system or sample of matter that results in the system's temperature....

; in a car, mechanical energy
Mechanical energy
In physics, mechanical energy is the sum of potential energy and kinetic energy present in the components of a mechanical system. It is the energy associated with the motion and position of an object. The law of conservation of energy states that in an isolated system that is only subject to...

 is acquired from the combustion
Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame...

 of gasoline, and the combustion of coal is converted from thermal to mechanical, and then to electrical energy.
Examples of energy sources include:
  • Fossil fuels
  • Nuclear fuels (e.g., uranium and plutonium)
  • Radiation from the sun
    Solar power
    Solar energy, radiant light and heat from the sun, has been harnessed by humans since ancient times using a range of ever-evolving technologies. Solar radiation, along with secondary solar-powered resources such as wind and wave power, hydroelectricity and biomass, account for most of the available...

  • Mechanical energy from wind, rivers, tides, etc.
  • Bio-fuels derived from biomass
    Biomass, as a renewable energy source, is biological material from living, or recently living organisms. As an energy source, biomass can either be used directly, or converted into other energy products such as biofuel....

    , in turn having consumed soil nutrients during growth.
  • Heat from within the earth (geothermal radiation)

The term net energy gain can be used in slightly different ways:


The usual definition of net energy gain compares the energy required to extract energy (that is, to find it, remove it from the ground, refine it, and ship it to the energy user) with the amount of energy produced and transmitted to a user from some (typically underground) energy resource. To better understand this, assume an economy has a certain amount of finite oil reserves
Oil reserves
The total estimated amount of oil in an oil reservoir, including both producible and non-producible oil, is called oil in place. However, because of reservoir characteristics and limitations in petroleum extraction technologies, only a fraction of this oil can be brought to the surface, and it is...

 that are still underground, unextracted. To get to that energy, some of the extracted oil needs to be consumed in the extraction process to run the engines driving the pumps, therefore after extraction the net energy produced will be less than the amount of energy in the ground before extraction, because some had to be used up.

The extraction energy can be viewed in one of two ways: profitable extractable (NEG>0) or nonprofitable extractable (NEG<0). For instance, in the Athabasca Oil Sands
Athabasca Oil Sands
The Athabasca oil sands are large deposits of bitumen, or extremely heavy crude oil, located in northeastern Alberta, Canada - roughly centred on the boomtown of Fort McMurray...

, the highly diffuse nature of the tar sands and low price of crude oil rendered them uneconomical to mine until the late 1950s (NEG<0). Since then, the price of oil has risen and a new steam extraction technique has been developed, allowing the sands to become the largest oil provider in Alberta (NEG>0).


The situation is different with sustainable energy
Sustainable energy
Sustainable energy is the provision of energy that meets the needs of the present without compromising the ability of future generations to meet their needs. Sustainable energy sources include all renewable energy sources, such as hydroelectricity, solar energy, wind energy, wave power, geothermal...

 sources, such as hydroelectric
Hydroelectricity is the term referring to electricity generated by hydropower; the production of electrical power through the use of the gravitational force of falling or flowing water. It is the most widely used form of renewable energy...

, wind
Wind power
Wind power is the conversion of wind energy into a useful form of energy, such as using wind turbines to make electricity, windmills for mechanical power, windpumps for water pumping or drainage, or sails to propel ships....

, solar
Solar power
Solar energy, radiant light and heat from the sun, has been harnessed by humans since ancient times using a range of ever-evolving technologies. Solar radiation, along with secondary solar-powered resources such as wind and wave power, hydroelectricity and biomass, account for most of the available...

, and geothermal energy sources, because there is no bulk reserve to account for (other than the Sun's lifetime), but the energy continuously trickles, so only the energy required for extraction is considered.

In all energy extraction cases, the life cycle of the energy-extraction device is crucial for the NEG-ratio. If an extraction device is defunct after 10 years, its NEG will be significantly lower than if it operates for 30 years. Therefore, the energy payback time (sometimes referred to as energy amortization) can be used instead, which is the time, usually given in years, a plant must operate until the running NEG becomes positive (i.e. until the amount of energy needed for the plant infrastructure has been harvested from the plant).

For photovoltaic cells, the NEG of their production depends on the operating lifetime, and the amount of sunlight available in the operating location. Today the break-even energy payback time (the amount of time required to produce an amount of energy equal to that originally used to manufacture the array) is around two to four years, compared to an effective production life of over 20 to 30 years (e.g. many manufacturers now provide a 25-year warranty on their products).


Net energy gain of biofuels has been a particular source of controversy for ethanol
Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...

 derived from corn
Maize known in many English-speaking countries as corn or mielie/mealie, is a grain domesticated by indigenous peoples in Mesoamerica in prehistoric times. The leafy stalk produces ears which contain seeds called kernels. Though technically a grain, maize kernels are used in cooking as a vegetable...

 (bioethanol). The actual net energy of biofuel production is highly dependent on both the bio source that is converted into energy, how it is grown and harvested (and in particular the use of petroleum-derived fertilizer), and how efficient the process of conversion to usable energy is. Details on this can be found in the Ethanol fuel energy balance
Ethanol fuel energy balance
All biomass needs to go through some of these steps: it needs to be grown, collected, dried, fermented, and burned. All of these steps require resources and an infrastructure...

 article. Similar considerations also apply to biodiesel and other fuels.

ISO 13602

International Organization for Standardization
The International Organization for Standardization , widely known as ISO, is an international standard-setting body composed of representatives from various national standards organizations. Founded on February 23, 1947, the organization promulgates worldwide proprietary, industrial and commercial...

 13602-1 provides methods to analyse, characterize and compare technical energy systems (TES) with all their inputs, outputs and risk factors. It contains rules and guidelines for the methodology for such analyses.

ISO 13602-1 describes a means of to establish relations between inputs and outputs (net energy) and thus to facilitate certification
Certification refers to the confirmation of certain characteristics of an object, person, or organization. This confirmation is often, but not always, provided by some form of external review, education, assessment, or audit...

, marking
Marking may refer to:* An annotation* A perforation* Road surface marking, such as lines or words, or the stripes of a zebra crossing on a road surface* Card marking* Direct part marking * Exam markingPhotographic film markings* Postal marking...

, and labelling
A label is a piece of paper, polymer, cloth, metal, or other material affixed to a container or article, on which is printed a legend, information concerning the product, addresses, etc. A label may also be printed directly on the container or article....

, comparable characterizations, coefficient of performance, energy resource planning, environmental impact assessments, meaningful energy statistics and forecasting of the direct natural energy resource or energyware inputs, technical energy system investments and the performed and expected future energy service outputs.

In ISO 13602-1:2002, renewable resource
Renewable resource
A renewable resource is a natural resource with the ability of being replaced through biological or other natural processes and replenished with the passage of time...

 is defined as "natural resource for which the ratio of the creation of the natural resource to the output of that resource from nature to the technosphere is equal to or greater than one".


During the 1920s, 50 barrels (7.9 m³) of crude oil were extracted for every barrel of crude used in the extraction and refining process. Today only 5 barrel (0.794936475 m³) are harvested for every barrel used. When the net energy gain of an energy source reaches zero, then the source is no longer contributing energy to an economy.

See also

  • ISO 13600
  • Energy balance
    Energy balance
    Energy balance may refer to:* First law of thermodynamics, according to which energy cannot be created or destroyed, only modified in form* Energy balance , a measurement of the biological homeostasis of energy in living systems...

  • Energyware and energy carrier
    Energy carrier
    According to ISO 13600, an energy carrier is either a substance or a phenomenon that can be used to produce mechanical work or heat or to operate chemical or physical processes....

    In physics, energy economics and ecological energetics, energy returned on energy invested ; or energy return on investment , is the ratio of the amount of usable energy acquired from a particular energy resource to the amount of energy expended to obtain that energy resource...

  • Solar cells and energy payback
  • Energy cannibalism
    Energy Cannibalism
    Energy cannibalism refers to an effect where rapid growth of an entire energy producing industry creates a need for energy that uses the energy of existing power plants. Thus during rapid growth the industry as a whole produces no energy because new energy is used to fuel the embodied energy of...

External links

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