Wind Energy - FAQ
Q: What is wind energy?
A: Wind energy is essentially a converted form of solar energy. Radiation from the sun heats different parts of the earth at different rates, most notably during the day and night, but also as various surfaces absorb or reflect at different rates. In turn, this causes portions of the atmosphere to warm differently. Hot air rises, reducing the atmospheric pressure at the earth's surface, and cooler air is drawn in to replace it, resulting in wind. Because air has mass, when it is in motion it contains the energy of that motion --- kinetic energy. Wind turbines convert the kinetic energy present in the wind into more useful forms of energy such as mechanical energy or electricity.
Q: What is a wind turbine and how does it work?
A: A wind energy system transforms the kinetic energy of the wind into mechanical or electrical energy that can be harnessed for practical use. Wind electric turbines generate electricity for homes and businesses and for sale to utilities. There are two basic designs of wind electric turbines: vertical-axis, egg-beater style, and horizontal-axis, propeller-style, machines. Horizontal-axis wind turbines are most common today and make up nearly all of the utility-scale turbines in the global market. Turbine subsystems include:
- A rotor or blades, which convert the wind's energy into rotational shaft energy
- A nacelle (enclosure) containing a drive train, a gearbox* and a generator
- A tower to support the rotor and drive train
- Electronic equipment such as controls, electrical cables, ground support equipment and interconnection equipment
*Some turbines do not require a gearbox
Q: How much electricity can one wind turbine generate?
A: The output of a wind turbine depends on the turbine's size and the wind's speed through the rotor. Wind turbines being manufactured now have power ratings from one megawatt to two megawatts. For example, a 10 kilowatt wind turbine can generate around 10,000 kilowatt hours annually at a site with average wind speeds of 12 miles per hour. This is approximately enough energy to power a typical household for a year. A 1.8 megawatt turbine can produce more than 5.2 million kilowatt hours in a year, which is enough to power more than 500 households. Wind speed is a crucial element in projecting turbine performance, and a site's wind speed is measured through wind resource assessment prior to a wind system's construction. Generally, an annual average wind speed greater than four meters per second (9 mph) is required for small wind electric turbines. Utility-scale wind power plants require minimum average wind speeds of six meters per second (13 mph). It is important to understand that a small difference in wind speed can mean a large difference in available energy and in electricity produced and a large difference in the cost of the electricity generated. Also, there is little energy to be harvested at very low wind speeds. That is why it is imperative to properly assess possible wind farm sites to ensure the optimal amount of energy is being produced.
Q: What are wind turbines made of?
A: The rotor blades are made of fiberglass-reinforced polyester or wood-epoxy and the towers, which are generally tubular, are made of steel.
Q: How big is a wind turbine?
A: Utility-scale wind turbines for land-based wind farms come in various sizes, with rotor diameters ranging from 50 meters to 90 meters with tower heights between 50 meters to 90 meters. A 90 meter turbine would require a 90 meter tower and would have a total height from the tower base to the tip of the rotor of approximately 135 meters (442 feet). Offshore turbine designs now under development will have larger rotors. Currently, the largest rotor is 110 meters in diameter. It is easier to design larger turbines for offshore because it is easier to transport rotor blades by ship than by land. There are also smaller wind turbines that are intended for residential use or small businesses. These would have a rotor diameter of eight meters or less and would be on towers 40 meters in height or less.
Q: How many turbines does it take to make one megawatt (MW)?
A: The amount of turbines required would depend on the scale of the machines. Most utility-scale turbine manufacturers offer machines in the one megawatt to two megawatt range. It takes a single one megawatt machine to produce one megawatt. Subsequently, 10 one megawatt turbines would make a 10 megawatt wind plant, while 10 two megawatt machines would make a 20 megawatt facility. In the future, machines of larger size will be available, although they will probably be installed offshore, where it is easier to transport and larger construction equipment can be used. Currently, units larger than 4 MW in capacity are now under development.
Q: What is a wind power plant?
A: A wind power plant, or wind farm, is a large grouping of wind energy turbines. Wind plants can range in size from a few megawatts to hundreds of megawatts in capacity. Wind power plants are modular in that they consist of small individual modules (turbines) that easily be made larger or smaller as needed. Maintenance is also less obtrusive on a wind farm. At some conventional power plants, the entire plant may have to be shut down for repairs whereas at a wind farm, maintenance takes place one turbine at a time. Wind power plants can be built quickly, a 50 megawatt wind farm can be completed in as little as 18 months. The majority of that time is needed to measure the wind and obtain the appropriate construction permits--- the actual construction of wind farm can occur in less than six months.
Q: Will using more wind energy help to prevent global warming?
A: Yes, carbon dioxide is main greenhouse gas responsible for negatively effecting the changes in the world's climate. Major contributors of carbon dioxide emissions are fossil fuel energy plants. According to experts, in order to avoid a dangerous level of climate change we must cut our carbon dioxide emissions by 80 to 90 percent by 2050. While we will constantly require sources of energy, it is pressing we look to cleaner sources that don't produce carbon dioxide. Wind power is a clean, renewable form of energy that produces zero emissions of any kind. Wind power is the best placed renewable technology to deliver carbon cuts quickly on a large scale. It is the least expensive, most developed renewable energy technology and the fastest to build.