What is wind energy?

Wind energy is a converted form of solar energy. The sun’s radiation heats different parts of the earth at different rates – most notably during the day and night, but also when different surfaces (for example, water and land) absorb or reflect at different rates. This is turn 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. The result is wind.

Air has mass, and when it is in motion, it contains the energy of that motion — “kinetic energy.” Some portion of that energy can be converted into other forms — mechanical force or electricity — that we can use to perform work.

What is a wind turbine?

A wind turbine is a device that is built to capture the kinetic energy of the wind. When wind blows past the turbine’s blades, the wind makes the blades turn. This turning motion can then be put to work. There are many types of wind turbines in operation throughout the world today. All convert the energy in the wind to another form of energy, either mechanical (for pumping, grinding, or some other task) or electrical (by turning the rotor in an electrical generator).

Wind turbines have many parts, including:

• a rotor, or blades, which convert the wind’s energy into rotational shaft energy;
• a nacelle (enclosure) containing a drive train, usually including a gearbox and a generator;
• a tower, to support the rotor and drive train; and
• electronic equipment such as controls, electrical cables, ground support equipment, and interconnection equipment.

 

Image from the U.S. DOE's Energy Efficiency and Renewable Energy page "How Wind Turbines Work."

What is a windpark?

A windpark is a group of wind turbines that are sited near one another and are electrically connected.

How much energy can a wind turbine produce?

That depends on many things, including the generating capacity of the turbine, and the amount and speed of wind that flows past it.  A 1.5 megawatt turbine can generate about 4.3 million kilowatt-hours a year — enough clean energy for about 500 homes.

How much energy can a windpark produce?

A 100 megawatt windpark can generate enough electricity for about 33,000 homes.   At the end of 2005, utility-scale windparks installations in 30 states across the U.S. totaled 9,149 MW, which can provide enough electrical energy for 2.3 million average homes. These wind turbines will displace the emission of 15 million tons of carbon dioxide each year. (AWEA)  Industry experts predict that the U.S. could get as much as 20% of its electricity from wind power by 2030. 

How big are wind turbines?

Wind turbines come in many sizes.  GE's 1.5 megawatt turbines are 265 feet tall at the rotor hub, with three blades that are approximately 120 feet long, for a blade diameter of 254 feet.  For more information on GE turbines, visit http://www.gepower.com/prod_serv/products/
wind_turbines/en/downloads/ge_15_brochure.pdf.

What is capacity factor?

Capacity factor is a way of measuring the productivity of a source of electrical generation.  It compares the generation source's maximum potential production with the actual production, and is expressed as a percentage. 

Power plants that run on fossil fuel or nuclear power typically have capacity factors of 80-90%.  Some of these facilities will run at maximum output almost all of the time, and will be shut down only due to equipment problems or for maintenance.  Windparks are built in places with strong, steady winds to ensure that they produce as much power as possible, as much of the time as possible.  However, even in the best locations, the strength of the wind can vary depending on the time of day or the season.  Thus, while windparks are always producing some electricity, they may not always be producing at their maximum rated capacity.  Thus, windparks typically have annual capacity factors in the 30-45% range, although the capacity factor on a given day may often be close to 100%.

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What is “availability” or “availability factor”?

Availability factor (or just “availability”) is a measurement of the reliability of a wind turbine or other power plant.  It refers to the percentage of time that a plant is ready to generate (that is, not out of service for maintenance or repairs).  Modern wind turbines have an availability of more than 98% —   higher than most other types of power plant. After two decades of constant engineering refinement, today’s wind machines are highly reliable.