The world’s wind energy resource is estimated to be about one million GW for total land coverage. Assuming only 1 per cent of the area is utilised and allowance is made for the lower load factors of wind plant, the wind energy potential would correspond to around the world total electricity generation capacity (WEC 2007).
The windiest areas are typically coastal regions of continents at mid-to high latitudes and in mountainous regions. Locations with the highest wind energy potential include the westerly wind belts between latitudes 35? and 50?. This includes the coastal regions of western and southern Australia, New Zealand, southern South America, and South Africa in the southern hemisphere, and northern and western Europe, and the north eastern and western coasts of Canada and the United States. These regions are generally characterised by high, relatively constant wind conditions, with average wind speeds in excess of 6 metres per second (m/s) and, in places, more than 9m/s.
Regions with high wind energy potential are characterised by:
- high average wind speeds;
- winds that are either constant or coinciding with peak energy consumption periods (during the day or evening);
- proximity to a major energy consumption region (i.e. urban/industrial areas); and
- smooth landscape, which increases wind speeds, and reduces the mechanical stress on wind turbine components that results from variable and turbulent wind conditions associated with rough landscape.
Because of wind variability, the energy density at a potential site – commonly described as its capacity factor – is generally in the range of 20-40 per cent. While the majority of areas in locations convenient for electricity transfer to the grid are located onshore, offshore sites have also been identified as having significant potential for wind energy, both to take advantage of increased wind speeds and to increase the number of available sites. Offshore locations also help reduce turbulence and hence stress on machine components. There have been wind turbines deployed in shallow seas off northern Europe for more than a decade. Offshore sites are expected to make an increasingly significant contribution to electricity generation in some countries, notably in Europe, where there are increasing difficulties in gaining access to onshore sites.