section_path: Wind energy resources
section_name: Wind energy resources
paragraph_text: Wind energy resources
  
  Wind is air movement in the Earth's atmosphere. In a unit of time, say 1 second, the volume of air that had passed an area A {\displaystyle A} is A v {\displaystyle Av}. If the air density is ρ {\displaystyle \rho }, the mass of this volume of air is M = ρ A v {\displaystyle M=\rho Av}, and the power transfer, or energy transfer per second is P = 1 2 M v 2 = 1 2 ρ A v 3 {\displaystyle P={\tfrac {1}{2}}Mv^{2}={\tfrac {1}{2}}\rho Av^{3}}. Wind power is thus proportional to the third power of the wind speed; the available power increases eightfold when the wind speed doubles. Change of wind speed by a factor of 2.1544 increases the wind power by one order of magnitude (multiply by 10).
  
  The global wind kinetic energy averaged approximately 1.50 MJ/m over the period from 1979 to 2010, 1.31 MJ/m in the Northern Hemisphere with 1.70 MJ/m in the Southern Hemisphere. The atmosphere acts as a thermal engine, absorbing heat at higher temperatures, releasing heat at lower temperatures. The process is responsible for the production of wind kinetic energy at a rate of 2.46 W/m thus sustaining the circulation of the atmosphere against friction.
  
  Through wind resource assessment, it is possible to estimate wind power potential globally, by country or region, or for a specific site. The Global Wind Atlas provided by the Technical University of Denmark in partnership with the World Bank provides a global assessment of wind power potential. Unlike 'static' wind resource atlases which average estimates of wind speed and power density across multiple years, tools such as Renewables.ninja provide time-varying simulations of wind speed and power output from different wind turbine models at an hourly resolution. More detailed, site-specific assessments of wind resource potential can be obtained from specialist commercial providers, and many of the larger wind developers have in-house modeling capabilities.
  
  The total amount of economically extractable power available from the wind is considerably more than present human power use from all sources. The strength of wind varies, and an average value for a given location does not alone indicate the amount of energy a wind turbine could produce there.
  
  To assess prospective wind power sites, a probability distribution function is often fit to the observed wind speed data. Different locations will have different wind speed distributions. The Weibull model closely mirrors the actual distribution of hourly/ten-minute wind speeds at many locations. The Weibull factor is often close to 2 and therefore a Rayleigh distribution can be used as a less accurate, but simpler model.