Net Energy Gain (NEG) is a concept used in energy economics 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 joules, differs from the net financial gain that may result from the energy harvesting process, in that various sources of energy (e.g. natural gas, coal, etc.) can be priced differently for the same amount of energy.
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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 and inefficiencies that may be present during the energy harvesting process.
ISO 13602
ISO 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, marking, and labelling, 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 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".
Examples
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 barrels (0.79 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.