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In physics, energy economics, and ecological energetics, energy returned on energy invested (EROEI or ERoEI); or energy return on investment (EROI), is the ratio of the amount of usable energy delivered from a particular energy resource to the amount of energy used to obtain that energy resource. It is a distinct measure from energy efficiency as it does not measure the primary energy inputs to the system, only usable energy. When the EROEI of a resource is less than or equal to one, that energy source becomes a net "energy sink", and can no longer be used as a source of energy, but depending on the system might be useful for energy storage (for example a battery). A fuel or energy must have an EROEI ratio of at least 3:1 to be considered viable as a prominent fuel or energy source.〔Atlason R, Unnthorsson R. 2014. Ideal EROI (energy return on investment) deepens the understanding of energy systems. Energy. 241–45 & Hall CA, Lambert JG, Balogh SB. 2013. EROI of different fuels and the implications for society. Energy Policy. 141–52〕 : 〔Hall CA, Lambert JG, Balogh SB. 2013. EROI of different fuels and the implications for society. Energy Policy. 141–52 & Atlason R, Unnthorsson R. 2014. Ideal EROI (energy return on investment) deepens the understanding of energy systems. Energy. 241–45〕 == Non-manmade energy inputs == The natural or primary energy sources are not usually included in the calculation of energy invested, only the human-applied sources. For example, in the case of biofuels the solar insolation driving photosynthesis is not included, and the energy used in the stellar synthesis of fissile elements is not included for nuclear fission. The energy returned includes usable energy and not wastes such as heat, although depending on source and application, waste heat is used in district heating and water desalination, these cogeneration plants however are rare, globally, and thus usually excluded in EROEI analysis of energy sources. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Energy returned on energy invested」の詳細全文を読む スポンサード リンク
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