Where does it come from?
The Sun provides 175 million million watts of energy to the Earth’s atmosphere each hour. Of this, approximately 1-2% is converted to wind energy.
As the energy heats the earth’s surface, air rises. This rising air creates low pressure and draws in cooler air, creating circulation patterns – air naturally flows from high pressure to low pressure and this movement is what we call “the wind”.
The highest temperatures are experienced at the equator where much more energy from the sun is received than in the polar regions. Earth then acts as a huge heat transfer mechanism as the hotter air moves from the equator to the polar areas and the cooler area towards the equator.
The movement of air from the equator to the polar regions is not directly north – south. Other forces, predominantly the Coriolis effect have their part to play. The Coriolis effect is caused by the rotation of the earth and results in any moving body above or on the earth’s surface to move to the right in the northern hemisphere and to the left in the southern hemisphere. This effect is caused by the faster rotation eastward near the equator (compared with the poles).
These movements or air or circulation patterns fall into three key areas, the Polar, Ferrel and Hadley Cells as shown in the diagram below.
At the local level we also experience different levels of wind energy. Areas of higher land are windier due to the movement of wind being faster over higher topography. Similarly coastal areas are windier, due to the temperature differences between the landmass and the sea causing a greater movement of air.
Humans and wind- history
Human-kind has been utilising wind energy since early recorded history. Egyptian sailing vessels, transporting construction materials such as huge stones were powered by the wind from around 2500 BC.
In the UK, mills used wind power for grinding wheat to make flour from around the year 1200. Windmills started to appear throughout the UK with the most in the East and South East of England. The first use of a large wind turbine to generate electricity was in Cleveland Ohio 1888. The further development of wind turbines in Europe and the US progressed from the 1940’s motivated by rising fossil fuel costs. Design inspiration for new technology blades was taken from airplane propellers and monoplane wings.
Today, significant industries based in Denmark, Germany and the US supply over 80% of the world’s turbines.