Limits to Wind Energy
There are limits to the amount of wind energy that can be extracted from the atmosphere. In a paper by Kravitz and Caldeira in 2013 titled "Geophysical limits to global wind power" [1] they investigated the theoretical maximum wind power could be collected.
Under some simple assumptions and using the Community Atmosphere Model (CASM 3.5 [2]), they determined the maximum amount of power that could be collected using wind turbines. The maximum was found assuming the whole earth was covered with wind turbines and the density was maximized so that any additional wind turbine would decrease the extracted power. Two cases were considered. One case was with wind turbines located on the surface. The other was with wind turbines located throughout the whole atmosphere.
The paper clearly states that the analysis considers "only geophysical limitations, not technical or economic constraints on wind power". Two interesting numbers come out of this analysis. The first is that the absolute maximum amount of energy that could be extracted from the atmosphere is 1800 TW. This would involve filling the land, sea, and skies with wind turbines. The 1800 TW is 100 times the power used today [4]. The other case considered wind turbines on the surface evenly distributed everywhere covering all of the land and seas. In this case, with tall enough wind turbines, it would be possible to extract 400 TW of power. Using only the surface, more than 20 times the amount of power used globally today is available.
This sounds great.... except additional constraints that should be considered.
Assuming only agricultural land could be covered by wind turbines, only about 11% of the globe [5] is available to install surface wind turbines. Ocean based wind is typically withing 30 km of land [6]. So this is limits sea based wind turbines to an estimated additional 1% of the earths surface. A total of 12% of the earth's surface would be feasible for surface wind generation. This reduces that maximum surface wind power to 48TW. Considering the estimated energy demand in 2100 is 123 TW [4], surface wind turbines will not be enough.
Surface wind turbines might meet current global energy needs, but it would be tight. Even with technology advances allowing wind power extraction throughout the atmosphere, its will be very difficult for wind alone to meet global energy at the the century. With ecological constraints, mineral constraints and EROI considered, wind energy extraction will limit wind to a tiny fraction of what is possible.
Collecting solar power in orbit and beaming to earth (SBSP) can scale to meet current and future energy demands comfortably. Delivering 100 or more TW by the end of the century can be done with less minerals, less land use, and less environmental impact than other options while working within the constrains that are approaching.
References:
[1] Marvel, Kate & Kravitz, Ben & Caldeira, Ken. (2013). Geophysical limits to global wind power. Nature Climate Change. 3. 118-121. 10.1038/nclimate1683. - https://www.researchgate.net/publication/258806701_Geophysical_limits_to_global_wind_power
[2] https://www.cesm.ucar.edu/models/cam
[4] https://www.anthropocenemagazine.org/howmuchenergy/
[5] https://www.fao.org/sustainability/news/detail/en/c/1274219/
[6] https://www.sciencefocus.com/planet-earth/how-far-offshore-can-we-build-wind-farms