Editing Wind power (section)

== Turbine design ==
{{main|Wind turbine|Wind turbine design}}
{{see also|Wind-turbine aerodynamics}}
{{stack|float=right|
[[File:Wind turbine int.svg|thumb| Typical wind turbine components: {{ordered list
 |1=[[Wind turbine design#Foundations|Foundation]]
 |2=[[Wind turbine design#Connection to the electric grid|Connection to the electric grid]]
 |3=[[Wind turbine design#Tower|Tower]]
 |4=Access ladder
 |5=[[Wind turbine design#Yawing|Wind orientation control (yaw control)]]
 |6=[[Nacelle (wind turbine)|Nacelle]]
 |7=[[Wind turbine design#Generator|Generator]]
 |8=[[Anemometer]]
 |9=[[Wind turbine design#Electrical braking|Electric]] or [[Wind turbine design#Mechanical braking|mechanical brake]]
 |10=[[Gearbox]]
 |11=[[Wind turbine design#Blades|Rotor blade]]
 |12=[[Wind turbine design#Pitch control|Blade pitch control]]
 |13=[[Wind turbine design#The hub|Rotor hub]]
}}]]
|[[File: Scout moor gearbox, rotor shaft and brake assembly.jpg|thumb|right|Typical components of a wind turbine (gearbox, rotor shaft and brake assembly) being lifted into position]]}}

[[Wind turbine]]s are devices that convert the wind's [[kinetic energy]] into electrical power. The result of over a millennium of windmill development and modern engineering, today's wind turbines are manufactured in a wide range of horizontal axis and vertical axis types. The smallest turbines are used for applications such as [[Battery charger|battery charging]] for auxiliary power. Slightly larger turbines can be used for making small contributions to a domestic power supply while selling unused power back to the utility supplier via the electrical grid. Arrays of large turbines, known as wind farms, have become an increasingly important source of renewable energy and are used in many countries as part of a strategy to reduce their reliance on [[fossil fuels]].

Wind turbine design is the process of defining the form and specifications of a wind turbine to extract energy from the wind.<ref>{{cite web | publisher =UK Department for Business, Enterprise & Regulatory Reform | title =Efficiency and performance |url=http://www.berr.gov.uk/files/file17821.pdf | access-date =29 December 2007 | url-status=dead | archive-url =https://web.archive.org/web/20090205054846/http://www.berr.gov.uk/files/file17821.pdf | archive-date =5 February 2009}}</ref>
A wind turbine installation consists of the necessary systems needed to capture the wind's energy, point the turbine into the wind, convert [[mechanical energy|mechanical rotation]] into [[electrical power]], and other systems to start, stop, and control the turbine.

In 1919, the German physicist [[Albert Betz]] showed that for a hypothetical ideal wind-energy extraction machine, the fundamental laws of conservation of mass and energy allowed no more than 16/27 (59%) of the kinetic energy of the wind to be captured. This [[Betz' law|Betz limit]] can be approached in modern turbine designs, which may reach 70 to 80% of the theoretical Betz limit.<ref>[[Albert Betz|Betz, A.]]; Randall, D. G. (trans.). ''Introduction to the Theory of Flow Machines'', Oxford: [[Pergamon Press]], 1966.</ref><ref>Burton, Tony, et al., (ed). [https://books.google.com/books?id=qVjtDxyN-joC ''Wind Energy Handbook''] {{Webarchive|url=https://web.archive.org/web/20160105145500/https://books.google.com/books?id=qVjtDxyN-joC |date=5 January 2016 }}, [[John Wiley and Sons]], 2001, {{ISBN|0-471-48997-2}}, p. 65.</ref>

The [[Wind turbine aerodynamics|aerodynamics of a wind turbine]] are not straightforward. The airflow at the blades is not the same as the airflow far away from the turbine. The very nature of how energy is extracted from the air also causes air to be deflected by the turbine. This affects the objects or other turbines downstream, which is known as "[[Wake (physics)|wake]] effect". Also, the aerodynamics of a wind turbine at the rotor surface exhibit phenomena that are rarely seen in other aerodynamic fields. The shape and dimensions of the blades of the wind turbine are determined by the aerodynamic performance required to efficiently extract energy from the wind, and by the strength required to resist the forces on the blade.<ref>{{cite web | url=http://www.alternative-energy-news.info/what-factors-affect-the-output-of-wind-turbines/ | title=What factors affect the output of wind turbines? | publisher=Alternative-energy-news.info | date=24 July 2009 | access-date=6 November 2013 | archive-date=29 September 2018 | archive-url=https://web.archive.org/web/20180929021418/http://www.alternative-energy-news.info/what-factors-affect-the-output-of-wind-turbines/ | url-status=live }}</ref>

In addition to the aerodynamic design of the blades, the design of a complete wind power system must also address the design of the installation's rotor hub, [[Nacelle (wind turbine)|nacelle]], tower structure, generator, controls, and foundation.<ref>{{cite web |author1=Zehnder, Alan T. |author2=Warhaft, Zellman |name-list-style=amp |title=University Collaboration on Wind Energy |date=27 July 2011 |url=http://www.sustainablefuture.cornell.edu/attachments/2011-UnivWindCollaboration.pdf |publisher=Cornell University [[Atkinson Center for a Sustainable Future]] |access-date=22 August 2011 |url-status=dead |archive-url=https://web.archive.org/web/20110901005908/http://www.sustainablefuture.cornell.edu/attachments/2011-UnivWindCollaboration.pdf |archive-date=1 September 2011 }}</ref>