How it works
Wind Energy Facts
Wind is air in motion. Winds are caused by the uneven heating of the earth’s surface by the sun. The earth’s surface is made of different types of land and water. These different types absorb the sun’s heat at different rates giving rise to the differences in temperature and subsequently to winds.
During the day, the air above the land heats up more quickly than the air over water. The warm air over the land expands and rises, and the heavier, cooler air rushes in to take its place, creating winds. At night, the winds are reversed because the air cools more rapidly over land than over water.
In the same way, the large atmospheric winds that circle the earth are created because the land near the earth's equator is heated more by the sun than the land near the North and South Poles.
One can hence say that wind energy is derived from solar energy.
Wind energy is hardly new; it has been used in some form or another for centuries. However, large-scale, commercial utilization of wind as a form energy source is relatively recent.
Wind Energy - How it works
Wind energy technology is fairly simple. Wind turbines are located in farms (wind farms) that experience significant winds. The turbine is connected to a generator to generate electricity.
A wind turbine is a rotating machine which converts the kinetic energy in wind into mechanical energy. If the mechanical energy is used directly by machinery, such as a pump or grinding stones, the machine is usually called a windmill. If the mechanical energy is then converted to electricity, the machine is called a wind generator.
Wind turbines can be separated into two types based by the axis in which the turbine rotates.
- Vertical Axis
- Horizontal Axis
Turbines that rotate around a horizontal axis are more common. Vertical-axis turbines are less frequently used.
The wind turbines are grouped in a location to farm a wind farm.
Based on their locations, the different types of wind farms are:
Onshore Wind Farms
Onshore wind farms are the conventional wind farms. These are erected on land, usually in large vacant spaces such as farms.
These types of wind farms have some advantages as well as disadvantages over offshore wind farms.
Advantages - These are cheaper to construct and easier to integrate with the electricity grid. These are also easier to operate and maintain.
Disadvantages - Some of the disadvantages present in these wind farms are in terms of turbulence and obstructions (buildings, mountains, etc.), land-use disputes, limited availability of lands, objections based on visual impact, noise, impact on wildlife, etc.
The disadvantages present in onshore farms – and the wider wind-marine resources and availability – may explain the dislocation of a significant part of the investment in wind energy to offshore systems.
Nearshore Wind Farms
Near shore turbine installations are on land within three kilometers of a shoreline or on water within ten kilometers of land. These areas are good sites for turbine installation, because of wind produced by convection due to differential heating of land and sea each day. Wind speeds in these zones share the characteristics of both onshore and offshore wind, depending on the prevailing wind direction.
Offshore Wind Farms
Offshore wind development zones are generally considered to be ten kilometers or more from land.
The following is the method by which these farms are constructed and operated.
Once a suitable place for the wind farm is found, piles are driven into the seabed. Erosion protection mechanisms are placed at the base to prevent damage to the sea floor, and signs erected to make the wind farm visible to ships.
Once the turbine is assembled, sensors on the turbine detect the wind direction and turn the head, known as the nacelle, to face into the wind, so that the blades can collect the maximum energy. The aerodynamically shaped blades rotate around a horizontal hub, which is connected to a shaft. This shaft, via a gearbox, powers a generator to convert the energy into electricity. Subsea cables take the power to an offshore transformer which converts the electricity to a high voltage before running it back to connect to the grid at a substation on land.
Offshore wind turbines are less obtrusive than turbines on land, as their apparent size and noise is mitigated by distance. Because water has less surface roughness than land (especially deeper water), the average wind speed is usually considerably higher over open water. Capacity factors (utilisation rates) are considerably higher than for onshore and nearshore locations.
In stormy areas with extended shallow continental shelves, turbines are practical to install.
Airborne Wind Farms
Airborne wind turbine is a design concept for a wind turbine that is supported in the air without a tower. A tether would be used to transmit energy to the ground, either mechanically or through electrical conductors. These systems would have the advantage of tapping an almost constant wind and doing so without a set of slip rings or yaw mechanism, without the expense of tower construction.
Of the four types of wind farms mentioned above, the onshore wind farms are the most common.
Wind Farm Capacity
Since wind speed is not constant, a wind farm's annual energy production is never as much as the sum of the generator nameplate ratings multiplied by the total hours in a year. The ratio of actual productivity in a year to this theoretical maximum is called the capacity factor. Typical capacity factors are 20-40%, with values at the upper end of the range in particularly favorable sites. For most calculations, a capacity factor of 30% is taken. For example, a 1 megawatt turbine with a capacity factor of 30% will produce only 2628 MWh (0.30x24x365) and not 8,760 megawatt-hours in a year (1x24x365)
Applications of Wind Energy
Data and Statistics
Wind Energy Status and Trends
Global Installed Capacity of Wind Power (Current)
Source: Global Wind Energy Council Report, 2008
Observations from the above chart:
CAGR of cumulative installed capacity between 1996 and 2008: 28.25%
CAGR of cumulative installed capacity between 1996 and 2002: 31.2 %
CAGR of cumulative installed capacity between 2002 and 2008: 25.37%
One can see that the growth rate has been high and consistent over the past 12 years, and this trend is expected to continue. Assuming a CAGR of 25 % for the next five years 2008-13, the following are likely to be the global installed capacity.
Regional Wind Energy Scenario:
Annual Installed Capacity by Region 2003-2008
Total installed capacity end 2008 (GW)
Africa & Middle East
Latin America & Caribbean
Source: Global Wind Energy Council Report, 2008
Wind Energy Installed Capacity in Top Ten Countries (2008)
Top 10 Total and New Installed Capacities
Top 10 Total Installed Capacity %
Top 10 New Capacity %
Rest of the World
Rest of the World
Total top 10
Total top 10
Source: Global Wind Energy Council, Global Wind Report 2008
Global Wind Energy Council (GWEC) is predicting the global wind market to grow by over 155% from its current size to reach 240 GW of total installed capacity by the year 2012. This would represent an addition of 146 GW in 5 years, equaling an investment of over €180 billion (277 billion US$, both in 2007 value). The electricity produced by wind energy will reach over 500 TWh in 2012 (up from 200 TWh in 2007), accounting for around 3% of global electricity production (up from just over 1% in 2007). The main areas of growth during this period will be North America and Asia, and more specifically the US and People's Republic of China (Source: GWEC – Global Wind 2007 Report)
Wind Energy Projects & Companies
The table below provides the current wind energy projects that have applied for registration under CDM (clean development mechanism, under the Kyoto Protocol) in various countries worldwide. As you can observe, not all projects in all the countries have applied for this, owing to a number of reasons.
Wind CDM* Projects (As of May 2008)
# of Projects
Source: 2007 Global Wind Report
*: Clean Development Mechanism
Highlights from the above table:
- India’s individual project capacities are much smaller than those of most other countries. On average, each wind project in India has about 21 MW, while for China it is 52 MW and for countries such as Egypt and Mexico, it is over 100 MW.
- India and China together constitute over 80% of the total installed capacity under these projects.
Horse Hollow, TX
Babcock & Brown, Catamount
Peetz Table, CO
Capricorn Ridge, TX
Buffalo Gap, TX
Source: AWEA 2008 Annual Rankings Report, www.awea.org/
Note: Horse Hollow, completed in 2006, remains the largest single wind farm in operation in the U.S. for the second year. All of the top five wind farms are located in the Southwest, where large projects continue to be built.
Wind Energy – Barriers
The main difficulty faced while using wind to produce electrical power arises from the extreme variability of the wind, which is poorly adapted to satisfy a power demand which follows quite different trends. For this reason, a fossil fuel based back-up energy system is needed. In spite of this drawback, many people are developing wind power plants. While developing the power plant, other barriers that one should consider are as follows:
- Most of the developing countries face this barrier. There is lack of data (e.g., detailed wind mapping or wind atlas) needed to forecast wind profiles. This leads to high uncertainties regarding wind power outputs, thereby discouraging investors from developing wind power.
- Equipment misspecification or lack of harmonizing in local systems also poses constraints. For example, at the early stage of wind power development in the Indian State of Gujarat, second-hand equipments purchased from California could not operate effectively within the Western Electricity Grid of India, which typically undergoes large fluctuations in frequency and where outages are common-place (Amin, 1999).
- Wind energy cannot be stored, unless expensive batteries are used
- Given the intermittent nature of wind, integrating the electricity into the grid can pose many challenges and limit the output that can be successfully integrated into a power system.
- The extremely rapid growth of global wind energy capacity has led to a situation in which the demand for wind turbines significantly exceeds supply. As a result, the parts for wind turbines are becoming increasingly more difficult to purchase. There can be long waiting lists for the necessary turbine components, significantly adding to project lead times. Manufacturing capacity is now being added around the world to address this issue.
- In developing countries, wind turbines are in general smaller, as they are located in rural areas away from large electricity grids. These plants face logistics problems: Large cranes for the erection and major overhaul of large-sized turbines are not available at reasonable cost, while road, bridge and tunnel infrastructure are incapable of moving rotor blades of 40 m length or more.
- Compared to conventional diesel generators, the capital cost for wind turbines is higher, though the capital cost for wind energy based electricity generation is one of the lowest among those for all renewable energy sources. There is also uncertainty regarding financial returns resulting from lower than anticipated capacity factors.
- Wind resources might not be available near cities and this could give rise to high costs of transmission
- The economic feasibility of wind power remains paramount to the eventual success of a wind industry. Even in rich countries, when it comes to off-grid electrification, companies may be hesitant to make investments because the long-term costs of small, wind-driven grids are difficult to predict and rural communities may lack financial resources to make payments; thus, the off-grid electricity market is somewhat risky (Reiche, Covarrubias and Martinot, 2000). This may be more the case in developing countries where there is also a greater need for off-grid electrification. Thus, wind power developers face difficulties in raising local equity due to the high level of technical and financial uncertainties (e.g., unfamiliar and potentially risky investment with uncertain returns). For the same reasons, wind power developers also face difficulties in securing loans. Loan requests are often declined or face high interest rates due to high risk premiums. Because of these financial barriers, wind power may not be an attractive portfolio for private investors, particularly in developing countries.
In some countries, wind power must meet stringent licensing requirements to make sure that environment is not disturbed.
- Wind turbines along migratory bird paths often need to address specific environmental concerns before they can be erected.
- From an environmental point of view, there is noise produced by the rotor blades, aesthetic (visual) impacts, there is interference on television signals. Hence, developers need to get approval from people around the farm before undertaking the construction of a wind farm
- Wind turbines standing in a big field or coastline do damage the view presented by nature, especially in rural landscapes that attract tourism.
- Unless implemented under the CDM or JI, wind power does not receive ‘green’ benefits, while fossil fuels are not taxed for their environmental externalities. This results in an uneven playing field for wind power as it has to compete with large fossil fuel technologies that are also cheaper and have the opportunity to benefit from economies of scale. This can be a substantial market barrier to wind power.
- Furthermore, wind farms are generally smaller in terms of installed generating capacity, while wind power developers have fewer resources than companies with large thermal power plants. This impedes the ability to borrow capital on similarly favorable terms. In addition, small wind projects face higher transaction costs at every stage of project development cycle.
- Lack of proper institutions and local capacity are additional key barriers to wind power development, specifically in developing countries. In many countries, production and distribution of electricity are still controlled by a monopolist, often the state. There is a general lack of economic institutions for facilitating contracts (power purchase agreements) between the wind power developers and system operators (Beck and Martinot, 2004).
- Further, many wind power projects are implemented as turn-key projects with bilateral or multilateral funding from rich countries. Once the projects are handed over to a local company or system operator, they encounter constraints related to a lack of operating skills and equipment parts. This eventually results in inefficiencies, outages and even shutdown of wind farm facilities. Since it is mainly small-scale, remotely located wind power facilities that suffer from these types of barriers, this could eventually lead to a loss of future interest in small-scale wind power development in remote villages (UNEP, 2001).
Horns Rev Offshore Wind Farm (Denmark)
The Horns Rev oﬀshore wind farm is one of the world’s largest. It was installed in 2002 in the North Sea, 14 km west of the coast of Denmark. The location provides some of the best conditions for wind energy.
The wind farm has eighty 2 MW wind turbines, which are 70m tall and have an estimated lifetime of 20 years. These turbines are made primarily of steel, with high-strength steel foundations. The 28,000 T of steel in the turbines account for 79% of all materials used in the wind farm.
An estimated 13,000 GWh of electricity will be generated during the lifetime of the farm, equivalent to 650 GWh a year. This is comparable to the annual energy consumption of all the residents of Iceland (population: 319,000). If this energy replaces global average electricity, the lifetime CO2 saving provided by the wind farm is nearly 6.5 million tonnes. The wind farm’s lifetime CO2 emissions are only 7.6 g of CO2/kWh. Using LCA, it is estimated that 6,000 MWh of energy is required to construct, operate and dismantle one Horns Rev turbine. This means that the energy pay-back time for each turbine is only nine months.
10 Billion Dollars Wind Turbine Farm - The Largest Ever (USA)
May 20, 2008
An Investor from Texas, T. Boone Pickens has committed to the biggest of all time order for wind turbine generators. This investor placed an order for 667 wind turbines from General Electric, each costing $3 million dollars and the total order is $2 billion. The plan is to develop the world’s largest wind farm in the Panhandle State of Texas.
This is just one quarter of the total amount that T. Boone Pickens programs to purchase. Once assembled, the wind energy facility would feature the electrical capacity to supply power to over 1,200,000 houses in North Texas. The capacity of each turbine will develop 1.5 megawatts of electricity. The initial phase of the project will produce 1,000 Mwh phase. This is sufficiency energy to power 300,000 homes.