How Much Wind Energy is there?
Wind Site Evaluation Ltd.
21st Sept. 2010
The starting point is an estimate of the total quantity of kinetic energy in the atmosphere. Lorenz gives 1.5 x 106Joules/m2 as the quantity of kinetic energy contained in the atmosphere(1). Smil gives a figure described as the annual “solar radiation reaching the earth” as equal to 5.8 x 1024Joules, or 1.84 X 1017W, and 360W/m2(2). The annual Solar radiation absorbed by earths surface(land and sea) is 2.9 x 1024Joules, or 9.19 X 1016W, and 180W/m2. Note the solar constant is 1,366W/m2. Smil refers to a source from Lorenz(1976) that “atmospheric motion” was about 2% of 3.5PW of insolation, ie the energy arriving from the sun ( Applying 2% to Smil’s 9.19 X 1016W giving 1.84 X 1015W with his figure for winds below 1km 1.22 x 1015W is the right order of magnitude). Smil gives a figure, 3.8 x 1022 Joules, for the annual flux for the winds in the atmosphere below a height of 1km(2). He puts the maximum convertible at 3.8 x 1021 Joules or 1.1 x 106 TWh.
World Wind Resources
One of the early studies estimated the world’s wind resources to be 50,000 TWh/year(3). The total potential is calculated by taking the land with an average wind speed above 5.1 m/s at 10 m height. Then it has been reduced by 90 % to take into account other uses, population density etc. The assessment does not include Greenland, the Antarctic or offshore areas. Another early assessment by Wijk and Coelingh, giving 20,000 TWh/year, is more conservative (4)
Region (3) TWh/annum
North America 14000
Latin America 5400
Eastern Europe + CIS 10600
Rest of Asia 4900
Approx. land based World Total 50 000
None of these studies include the offshore potential which is estimated to be in excess of 3000 TWh/annum in European waters alone within a distance of 30km from shore and in depths less than 40m(6). Comparing the Smil figure, 1,100,000TWh, and that from Wind Energy-The Facts report, 50,000TWh, it is to be noted that the Smil figure is for the whole globe both land and sea, whereas the Wind Energy-The Facts report one is the amount that could be extracted by wind turbines in the first 120m of the 1km considered by Smil. It also takes into account loss and reduction factors. (2)(3).
Another source gives a higher total figure of 106,458TWh/year for the OECD countries only(5). This includes New Zealand and Japan. A Stanford University study found that the total wind power potential over land can be estimated roughly as 72 TW, corresponding to 6.27 x 1014 kWh or 627,000TWh (8). An updating of a previous study of the US alone done by AWS and NREL have come up with a figure of 37,000TWh (11), which is between the higher and lower figures in the table above.
A study published in 2003 by the German Advisory Council on Global Change (WBGU), “World in Transition – Towards Sustainable Energy Systems” calculated that the global technical potential for energy production from both onshore and offshore wind installations was 278,000 TWh per year. The report then assumed that only 10–15% of this potential would be realizable in a sustainable fashion, and arrived at a figure of approximately 39,000 TWh supply per year as the contribution from wind energy in the long term. The WBGU calculations of the technical potential were based on average values of wind speeds from meteorological data collected over a 14 year period (1979–1992). They also assumed that advanced multi-megawatt wind energy converters would be used. Limitations to the potential came through excluding all urban areas and natural features such as forests, wetlands, nature reserves, glaciers and sand dunes. Agriculture, on the other hand, was not regarded as competition for wind energy in terms of land use.(9)
Another recent study published in the Proceedings of the National Academy of Science by a team at Harvard University assessed the global capacity for wind power. The team used a simulation of global wind fields from NASA's Goddard Earth Observing System Data Assimilation System. The analysis, based on using 2.5-megawatt (MW) turbines onshore restricted to non-forested, ice-free, non-urban areas operating at a capacity factor of 20%, could supply greater than 40 times current worldwide consumption of electricity, and greater than 5 times total global use of energy in all forms. Estimates are also given for quantities of electricity that could be obtained by using a network of 3.6-MW turbines deployed in ocean waters with depths less than 200 m within 50 nautical miles (92.6 km) of closest coastlines.(10)
A 2009 report from the European Environment Agency confirms wind energy could power Europe many times over.(12)
In conclusion the order of magnitude of the wind resources worldwide from the more recent studies can be defined as follows. The lower limit is given by the German Advisory Council on Global Change (WBGU), World in Transition – Towards Sustainable Energy Systems study giving 39,000 TWh (9). The upper limit is given by the team at Harvard University giving 720,000TWh (10). The world’s electricity consumption was about 18,000 TWh/year for 2005(7). The total available global wind resource on land is therefore more than adequate to supply a very significant proportion of the overall world’s electricity demand.
A recent investigation of the effect of large wind farms on energy in the atmosphere in Energies by Magdalena R.V. Sta. Maria and Mark Z. Jacobson claimed that should wind supply the world's energy needs it estimates energy loss in the lowest 1 km of the atmosphere to be ~0.007%, which would be an order of magnitude smaller than atmospheric energy loss from aerosol pollution and urbanization, and orders of magnitude less than the energy added to the atmosphere from doubling CO2. It added that the net heat added to the environment due to wind dissipation is much less than that added by thermal plants that the turbines displace.(13)
Note on offshore wind resources.
Offshore wind is only now receiving attention with significant projects being realized. All of this is in shallow seas where it is technically possible to put down foundations on the sea bed. Further wind resources, an order of magnitude greater, is being explored using a new technology, floating offshore wind turbines. The first pilot schemes are in the water now several years. The first wind farms are at a proposal stage using this technology. To understand the potential an initial view can be formed, and the available technical resource may be calculated. The following link to a paper looks at the resource available in the Exclusive Economic Zone in the seas around Ireland:
1. Lorenz, Edward N., The nature and theory of the general circulation of the atmosphere., p110 WMO No. 218 TP.115. World Meteorological Organization
2. Smil, Vaclav. Inherent limits of renewable energies. 2004
3. Wind Energy – The Facts. Volume 1. European Commission
Directorate-General for Energy. 1999.
4. van Wijk, A.J.M. and Coelingh, J.P., Wind Power Potential in the OECD Countries, December 1993. Report commissioned by the Energy Research Center, The Netherlands (ECN)
5. personal communication from Hughes, P, and Hurley, B. Airtricity, circa 2003.
6. Garrad Hassan and Partners, Germanischer Lloyd, Windtest KWK. 1995.
7. BP Statistical Review of World Energy June 2006
8. Archer, Cristina L. and Jacobson, Mark Z. Evaluation of global wind power. 2005
9. Global Wind Energy Outlook. 2008. GWEC
10. Global potential for wind-generated electricity Xi Lua, Michael B. McElroy and Juha Kiviluomac, School of Engineering and Applied Science, Cruft Lab 211, and Department of Earth and Planetary Sciences, Harvard University, 100E Peirce Hall, 29 Oxford Street, Cambridge, MA 02138; and VTT Technical Research Centre of Finland, P. O. Box 1000, 02044 VTT, Finland
11. Update by AWS and NREL of US onshore wind resources at 80m. 6th Mar. 2010.
12. Europe's onshore and offshore wind energy potential - An assessment of environmental and economic constraints. EEA Technical report No 6/2009
13. Investigating the Effect of Large Wind Farms on Energy in the Atmosphere', in Energies 2009, 2, 816-838 by Magdalena R.V. Sta. Maria and Mark Z. Jacobson of the Atmosphere/Energy Program, Civil and Environmental Engineering Department, Stanford University. http://www.mdpi.com/1996-1073/2/4/816/pdf