Estimates of world wind resources
Based on wind resource data and estimates of the efficiency of actual wind turbines, many researchers have made estimates of potential wind power in several regions of the world, as well as for the entire planet. The maximum theoretically obtainable power output from the kinetic energy of the wind is 60% of the available power.
The electrical power output of wind energy can be estimated using regional wind resource estimates. It is important to distinguish the various types of wind energy potential that can be estimated. This estimation method (World Energy Council, 1993) divides the wind energy potential into the following five categories:
(1) Meteorological potential. This is equivalent to the available wind resource.
(2) Site potential. This is also based on meteorological potential, but limited to those sites where power yield is geographically achievable.
(3) Technical potential. Technical potential is calculated based on site potential and available technologies.
(4) Economic potential. Economic potential can be thought of as the technological potential that is economically achievable.
(5) Implementation potential. Implementation potential refers to the wind turbine operating capability determined after considering various restrictions and incentive policies and can be implemented in a certain period of time.
In worldwide wind resource assessments, at least the first three categories have been considered. For example, the earliest estimates of global wind energy resources were conducted by Gustavson (1979). In this study, Gustavson used the solar energy reaching the earth as an input and considered how much of the solar energy was converted into useful wind energy for resource estimation. On a global scale, he estimates the global resource to be around 1000×1012kWh/yr. The global electricity consumption at that time was about 55×1012kWh/yr.
The World Energy Commission (1993) estimated the global wind resource using world average estimates of the meteorological potential of wind energy and taking into account machine efficiency and availability (percentage of time online). They estimate the onshore wind resource to be approximately 20×1012kWh/yr, which is still a considerable resource. Recent work on the technological potential of onshore wind in the world is summarized in Hoogwijk et al. (2004), who concluded that the technical potential of onshore wind energy with current technology is about 6-7 times the world electricity consumption (2001).
Multiple wind resource estimates have been made for the U.S. wind energy potential. Estimates published in the 1990s are more realistic than previous estimates because they take into account the characteristics of the machine as well as the constraints of ground conditions (technically with site conditions), and they also use extended data collection methods and improved analysis techniques. Elliot et al. (1991) used this modified analysis and used U.S. wind resource data (Elliot et al., 1987) to conclude that wind energy could meet at least 20% of U.S. electricity demand, if the average wind speed at a height of 30 meters is not less than 7.3m/s (16mile/h), the wind energy in the area is developed. To provide this portion of U.S. electricity demand (about 600 billion kilowatt-hours per year), 0.6 percent of the land in the lower 48 states (about 18,000 square miles) needs to be developed. Most of this part of the land is in the west, away from the residential center. Therefore, site selection issues such as the layout of transmission lines need to be considered when actually using these lands.
As pointed out in The Facts (EWEA, 2004), Vol. 1 of the journal Wind Energy, estimates of onshore wind potential in Europe are few and the assumptions that exist are too conservative for current wind system technology. For example, EWEA estimates (from a 1993 study) that the technology potential in Europe (EU-15 and Norway) is about 0.65×1012kWh/yr. For the offshore wind field, the summary prediction results are 0.5~3×1012kWh/yr. Further, the paper states that estimates of wind resource potential are not fixed but time-varying as technology evolves and more environmental and social issues are considered that affect wind turbine density and location. An example in support of this view is that (mainly due to the increased size of wind turbines) the actual European resource potential estimated in 1997 was almost double the 1994 estimate.