Wind Resources
Where Does Wind Energy Come From? | The Need for Wind Energy in a Sustainable Energy System | The Future for Ocean Thermal Energy | Further Information | ReferencesWhere Does Wind Energy Come From?
Wind energy is an indirect form of solar energy. Between 1 - 2% of the solar radiation that reaches the Earth is converted into energy in the wind. This is about 50 to 100 times the energy that is converted from all the plants on earth through photosynthesis. Winds result from an unequal heating of different parts of the Earth's surface, causing cooler dense air to circulate to replace warmer, lighter air (Figure 1).
(courtesy of the Australian Bureau of Meteorology).
While some of the Sun's energy is absorbed directly into the air, most of the energy in the wind is first absorbed by the surface of the Earth and then transferred to the air by convection. Wind occurs at all scales, from local breezes generated by heating of land surfaces and lasting tens of minutes, to global winds resulting from solar heating of the Earth. The two major influences on the atmospheric circulation are the differential heating between the equator and the poles, and the rotation of the planet, called the Coriolis effect. (Wikipedia, 2007).
Seasonal variations in the speed (see Figure 2) and direction of the wind result from the seasonal changes in the relative inclination of the Earth towards the Sun, which in turn changes the patterns of differential heating. Daily, or diurnal, variations are caused by differential heating of local regions, such as adjacent land and oceans (see Figures 3a and 3b).
This air movement is complicated by a number of global scale factors such as the Earth's rotation, continents, oceans and mountain ranges and on a local scale by hills, vegetation and lakes. Air-flow is rarely smooth, with most sites experiencing fairly rapid changes in wind speed and direction. The wind speed also increases with the height above the ground, due to the frictional drag of the ground, vegetation and buildings. It is clear that any plans to harness the wind must take into account these variables.
The greatest challenge to the development of a truly huge wind industry is the wind resources inherent variability. There are very few areas on the Earth where wind is relatively constant throughout the day and throughout the year, and therefore the challenge to provide reliable power using solely wind is considerable.
The Need for Wind Energy in a Sustainable Energy System
The need for low cost large generating systems are part of developing a sustainable energy system. Currently there is more wind power generated than any other renewable technology except for large hydro. The development of favourable economics for wind generation projects has been apparent by the number of wind farms being established in places with excellent wind resources. It is, and will be a significant sector of the energy mix in a sustainable energy system.
The Future of Wind Energy
The future of large grid-connected wind energy power systems is promising, with several utilities operating wind farms and monitoring stations for even greater capacity installations. Although the generation of electricity from wind turbines has been economically marginal for many years, the future looks quite optimistic following the development of large-scale systems in both Europe and the United States. This has been greatly assisted by an improved understanding of the wind resource itself. Notwithstanding these large-scale developments, small-scale wind technologies continue to supply small requirements to operations that are often off-grid in remote regions. The combination of both large and small-scale technologies allow people to make use of the wind resource for a variety of sustainable applications.
Further Information
Information regarding renewable energy resources, technologies, applications, systems designs and case studies.
National Renewable Energy Laboratory (USA)
