Editing Fuel cell (section)

===Theoretical maximum efficiency===
The energy efficiency of a system or device that converts energy is measured by the ratio of the amount of useful energy put out by the system ("output energy") to the total amount of energy that is put in ("input energy") or by useful output energy as a percentage of the total input energy. In the case of fuel cells, useful output energy is measured in [[electrical energy]] produced by the system. Input energy is the energy stored in the fuel. According to the U.S. Department of Energy, fuel cells are generally between 40 and 60% energy efficient.<ref>[http://www1.eere.energy.gov/hydrogenandfuelcells/fuelcells/pdfs/fc_comparison_chart.pdf "Comparison of Fuel Cell Technologies"] {{webarchive|url=https://web.archive.org/web/20130301120203/http://www1.eere.energy.gov/hydrogenandfuelcells/fuelcells/pdfs/fc_comparison_chart.pdf |date=1 March 2013 }}. U.S. Department of Energy, Energy Efficiency and Fuel Cell Technologies Program, February 2011, accessed 4 August 2011</ref> This is higher than some other systems for energy generation. For example, the internal combustion engine of a car can be about 43% energy efficient.<ref>{{cite web|url=https://www.epa.gov/sites/default/files/2020-08/documents/sae-2019-01-0249.pdf |title= Benchmarking a 2018 Toyota Camry 2.5-Liter Atkinson Cycle Engine with Cooled-EGR|publisher= SAE|accessdate= 2 April 2019}}</ref><ref>{{cite book|chapter-url=https://www.sae.org/publications/technical-papers/content/2021-01-1241/ |chapter= Development of 43% Brake Thermal Efficiency Gasoline Engine for BYD DM-i Plug-in Hybrid|publisher= SAE|doi= 10.4271/2021-01-1241|accessdate= 21 September 2021|title= SAE Technical Paper Series|date= 2021|last1= Yang|first1= Dongsheng|last2= Lu|first2= Guoxiang|last3= Gong|first3= Zewen|last4= Qiu|first4= An|last5= Bouaita|first5= Abdelhamid|volume= 1}}</ref> [[Steam power plant]]s usually achieve efficiencies of 30-40%<ref>{{Cite web|url=https://www.power-eng.com/news/new-benchmarks-for-steam-turbine-efficiency/|title=New Benchmarks for Steam Turbine Efficiency|date=August 2002|access-date=12 March 2022|archive-date=25 July 2021|archive-url=https://web.archive.org/web/20210725190441/https://www.power-eng.com/news/new-benchmarks-for-steam-turbine-efficiency/|url-status=dead}}</ref> while [[combined cycle]] gas turbine and steam plants can achieve efficiencies above 60%.<ref>{{Cite news |title=All Units of Nishi-Nagoya Thermal Power Station Now in Operation |url=https://www.toshiba-energy.com/en/info/info2018_0330.htm |date=2018-03-30 |agency=Toshiba Energy Systems & Solutions Corporation}}</ref><ref>{{Cite news |title=Chubu Electric Power's Nishi-Nagoya Thermal Power Station Unit 7-1 Recognized by Guinness World Records as World's Most Efficient Combined Cycle Power Plant: Achieved 63.08% Power Generation Efficiency |url=https://www.chuden.co.jp/english/corporate/releases/pressreleases/3267653_18939.html |work=Press Release 2018 |publisher=Chubu Electric |date=2018-03-27}}</ref> In [[combined heat and power]] (CHP) systems, the [[waste heat]] produced by the primary power cycle - whether fuel cell, nuclear fission or combustion - is captured and put to use, increasing the efficiency of the system to up to 85–90%.<ref name=Types1/>

The theoretical maximum efficiency of any type of power generation system is never reached in practice, and it does not consider other steps in power generation, such as production, transportation and storage of fuel and conversion of the electricity into mechanical power. However, this calculation allows the comparison of different types of power generation. The theoretical maximum efficiency of a fuel cell approaches 100%,<ref>{{Cite journal|date=3 May 2018|title=Maximum conversion efficiency of hydrogen fuel cells| url=https://www.sciencedirect.com/science/article/abs/pii/S0360319918308371| journal=International Journal of Hydrogen Energy|volume=43|issue=18|pages=9015–9021| doi=10.1016/j.ijhydene.2018.03.076| issn=0360-3199|last1=Haseli|first1=Y.|bibcode=2018IJHE...43.9015H |url-access=subscription}}</ref> while the theoretical maximum efficiency of internal combustion engines is approximately 58%.<ref>[http://www.worldenergy.org/focus/fuel_cells/377.asp "Fuel Cell Efficiency"] {{webarchive|url=https://web.archive.org/web/20140209080834/http://www.worldenergy.org/focus/fuel_cells/377.asp| date=9 February 2014}}. World Energy Council, 17 July 2007, accessed 4 August 2011</ref>