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{{Refimprove|date=August 2008}}
[[File:Efficiency diagram by Zureks.svg|thumb|Output energy is always lower than input energy]]
[[File:Ene Flow Pow Plt uni.jpg|thumb|Efficiency of Power Plant, World total 2008]]

'''Energy conversion efficiency (η)''' is the [[ratio]] between the useful output of an [[energy conversion machine]] and the input, in [[energy]] terms. The useful output may be [[electric power]], [[mechanical work]], or [[heat]].

==Overview==
Energy conversion efficiency is not defined uniquely, but instead depends on the usefulness of the output. All or part of the heat produced from burning a fuel may become rejected [[waste heat]] if, for example, work is the desired output from a [[thermodynamic cycle]]. Energy converter is an example of an energy transformation. For example a light bulb falls into the categories energy converter.  
<math>
\eta = \frac{P_\mathrm{out}}{P_\mathrm{in}}
</math>
Even though the definition includes the notion of usefulness, [[wikt:efficiency|efficiency]] is considered a [[technology|technical]] or [[physics|physical]] term. Goal or mission oriented terms include [[effectiveness]] and [[efficacy]].

Generally, energy conversion efficiency is a [[dimensionless]] number between 0 and 1.0, or 0 to 100%.  Efficiencies may not exceed 100%, e.g., for a [[perpetual motion]] machine.  However, other [[thermal efficiency|effectiveness measures]] that can exceed 1.0 are used for [[heat pumps]] and other devices that move heat rather than convert it.

When talking about the efficiency of heat engines and power stations the convention should be stated, i.e., HHV (aka Gross Heating Value etc.) or LCV (aka Net Heating value), and  whether gross output (at the generator terminals) or net output (at the power station fence) are being considered.  The two are separate but both must be stated. Failure to do so causes endless confusion.

Related, more specific terms include
*[[Electrical efficiency]], useful power output per electrical power consumed;
*[[Mechanical efficiency]], where one form of mechanical energy (e.g. potential energy of water) is converted to mechanical energy ([[Mechanical work|work]]);
*[[Thermal efficiency]] or [[Fuel efficiency]], useful [[heat]] and/or [[Work (thermodynamics)|work]] [[Work output|output]] per input energy such as the [[fuel]] consumed;
*'Total efficiency', e.g., for [[cogeneration]], useful [[electric power]] and heat output per fuel energy consumed.  Same as the [[thermal efficiency]].
*[[Luminous efficiency]], that portion of the emitted electromagnetic radiation is usable for human vision.

==Fuel heating values and efficiency==

In Europe the usable energy content of fuel is typically calculated using the '''[[lower heating value]]''' (LHV) of that fuel, which definition assumes that the [[water vapor]] produced during fuel [[combustion]] (oxidation), remains gaseous, and is not [[condensation|condensed]] to liquid water so the latent heat of vaporization of that water is not  usable. Using the LHV, a [[condensing boiler]] can achieve a "heating efficiency" in excess of 100% ( this does not violate the [[first law of thermodynamics]] as long as the LHV convention is understood, but does cause confusion). This is because the apparatus recovers part of the [[heat of vaporization]], which is not included in the definition of the lower heating value of fuel.  In the U.S. and elsewhere, the '''[[higher heating value]]''' (HHV) is used, which includes the latent heat for condensing the water vapor, and thus the thermodynamic maximum of 100% efficiency cannot be exceeded with HHV's use.

==Example of energy conversion efficiency==

{{Missing information|clear definition of the energy conversion efficiency for light sources. The lighting efficiency is given by the [[luminous efficacy]] which does not allow to give a simple percentage without specifying what "100%" would be. If there is an ISO standard or another reliable source defining the energy conversion efficiency in lighting, please cite it. |date=May 2012}}

{| class="wikitable"
|-
! Conversion process
! Energy efficiency
|-
| colspan="2" style="background:#dfffdf;"|'''Electricity generation'''
|-
| [[Gas turbine]]
| up to 40%
|-
| [[Gas turbine]] plus [[steam turbine]] ([[combined cycle]])
| up to 60%
|-
| [[Water turbine]]
| up to 90% (practically achieved)
|-
| [[Wind turbine]]
| up to 59% (theoretical limit)
|-
| [[Solar cell]]
| 6–40% (technology dependent, 15% most often, 85–90% theoretical limit)
|-
| [[Fuel cell]]
| up to 85%
|-
| World [[Electricity generation]] 2008
| Gross output 39%, Net output 33%.<ref>IEC/OECD [http://www.iea.org/stats/balancetable.asp?COUNTRY_CODE=29 2008 Energy Balance for World], accessdate 2011-06-08</ref>
|-
| colspan="2" style="background:#dfffdf;"|'''Engine/Motor'''
|-
| [[Internal combustion engine|Combustion engine]]
| 10–50%<ref>{{cite web | url = http://www.epa.gov/midwestcleandiesel/publications/presentations/il-finance-09-06/eberhardt.pdf |format=PDF| title = Motivations for Promoting Clean Diesels | year = 2006 | publisher = US Department Of Energy}}{{dead link|date=October 2011}}</ref>
|-
| [[Electric motor]]s
| 70–99.99% (above 200W); 50–90% (between 10–200W); 30–60% (small ones < 10W)
|-
| colspan="2" style="background:#dfffdf;"|'''Natural process'''
|-
| [[Photosynthesis]]
| up to 6% <ref name="urlChapter 1 - Biological energy production">{{cite web | url = http://www.fao.org/docrep/w7241e/w7241e05.htm#1.2.1%20photosynthetic%20efficiency | title = Chapter 1 - Biological energy production | author = Miyamoto K| authorlink = | coauthors = | date = | work = Renewable biological systems for alternative sustainable energy production (FAO Agricultural Services Bulletin - 128) | publisher = Food and Agriculture Organization of the United Nations | pages = | language = | archiveurl = | archivedate = | quote = | accessdate = 2009-01-04}}</ref>
|-
| [[Muscle]]
| 14–27%
|-
| colspan="2" style="background:#dfffdf;"|'''Appliance'''
|-
| Household [[refrigerator]]s
| low-end systems ~ 20%; high end systems ~ 40–50%
|-
| [[Incandescent light bulb]]
| 0.7–5.1%,<ref name="Lighting efficiency">[[Luminous efficacy#Lighting efficiency]]</ref> 5–10%{{Citation needed|date=July 2011}}
|-
| [[Light-emitting diode]] (LED)
| 4.2–14.9%,<ref name="Lighting efficiency" /> up to 35% <ref>{{cite web | url = http://compoundsemiconductor.net/cws/article/news/18263 | title = Cree's blue LED has quantum efficiency of 35% | year = 2003 | publisher = compoundsemiconductor.net}}</ref>{{Dead link|2011-7-6|date=July 2011}}
|-
| [[Fluorescent lamp]]s
| 8.0–15.6%,<ref name="Lighting efficiency" /> 28% <ref name="books.google.com">{{cite book | url = http://books.google.com/books?id=61B_RV3EdIcC&pg=PA463&lpg=PA463&dq=meyer+nienhuis+efficiency&source=web&ots=urgXwn6sPi&sig=zaIKOAxRMmzKjVjaaFd8GsvXNLY&hl=en&sa=X&oi=book_result&resnum=1&ct=result#PPA463,M1 | title = Light Pollution Handbook | year = 2004 | publisher = Springer}}</ref>
|-
| [[Sodium-vapor lamp|Low-pressure sodium lamps]]
| 15.0–29.0%,<ref name="Lighting efficiency" /> 40.5% <ref name="books.google.com"/>
|-
| [[Metal halide lamp]]s
| 9.5–17.0%,<ref name="Lighting efficiency" /> 24% <ref name="books.google.com"/>
|-
| [[Switched-mode power supply]]
| currently up to 95% practically
|-
| Electric shower
| 90–95% (overall it would be more efficient to use a [[heat pump]], requiring less electric energy{{Citation needed|reason=please give a reliable source for this assertion. COP for DHW is contentious. As in, it would be more efficient to use a gas boiler perhaps?|date=January 2009}})
|-
| [[Electric heating|Electric heaters]]
| ~100% (essentially all energy is converted into heat)
|-
| colspan="2" style="background:#dfffdf;"|'''Others'''
|-
| [[Firearm]]
| ~30% (.300 Hawk ammunition)
|-
| [[Electrolysis of water]]
| 50–70% (80–94% theoretical maximum)
|}

==See also==
*[[Energy efficiency (disambiguation)]]
*[[Energy Returned on Energy Invested|EROEI]]
*[[Exergy efficiency]]
*[[Figure of merit]]
*[[Fuel efficiency]]
*[[International Electrotechnical Commission]]
*[[Sensitivity (electronics)]]
*[[Thermal efficiency]]
*[[Relative cost of electricity generated by different sources]]
*[[Electrical efficiency]]
*[[Mechanical efficiency]]
*[[Heat of combustion]]
*[[Lower heating value]]
*[[Higher heating value]]
*[[Perpetual motion]]
* [[Power generating equipment efficiency and carbon footprint]]

== References ==

;Cited
{{Reflist|3}}

;General

==External links==
*[http://ec.europa.eu/energy/intelligent/index_en.html The Intelligent Energy - Europe programme: the EU's tool for funding action towards a more energy intelligent Europe]
*[http://ledcalculator.everlumen.com/ Does it make sense to switch to LED ?]

{{DEFAULTSORT:Energy Conversion Efficiency}}
[[Category:Energy conversion]]
[[Category:Energy conservation]]
[[Category:Dimensionless numbers of thermodynamics]]
[[Category:Building engineering]]