How Wind Creates Energy

Wind is a form of solar energy caused by a combination of three concurrent events:

1. The sun unevenly heating the atmosphere
2. Irregularities of the earth's surface
3. The rotation of the earth. 

Wind flow patterns and speeds vary greatly across the United States and are modified by bodies of water, vegetation, and differences in terrain. Humans use this wind flow, or motion energy, for many purposes: sailing, flying a kite, and even generating electricity.

The terms "wind energy" and "wind power" both describe the process by which the wind is used to generate mechanical power or electricity. Wind turbines convert the kinetic energy from the wind into mechanical power. This mechanical power can be used for specific tasks (such as grinding grain or pumping water) or a generator can convert this mechanical power into electricity.

A wind turbine turns energy in the wind into electricity using the aerodynamic force created by the rotor blades, which work similarly to an airplane wing or helicopter rotor blade. When the wind flows across the blade, the air pressure on one side of the blade decreases. The difference in air pressure across the two sides of the blade creates both lift and drag. The force of the lift is stronger than the drag and this causes the rotor to spin. The rotor is connected to the generator, either directly (if it's a direct drive turbine) or through a shaft and a series of gears (a gearbox) that speed up the rotation and allow for a physically smaller generator. This translation of aerodynamic force to rotation of a generator creates electricity.

Types of Wind Turbines

Modern wind turbines fall into two basic groups:

1. Horizontal-Axis Turbines: Horizontal-axis wind turbines (pictured right) are what many people picture when you think of wind turbines. They most commonly have three blades and are operated "upwind," with the turbine pivoting at the top of the tower so the blades face into the wind.
2. Vertical-Axis Turbines: Vertical-axis wind turbines (pictured left) come in several varieties, including the eggbeater-style Darrieus model, named after its French inventor. These turbines are omnidirectional, meaning they don't need to be adjusted to point into the wind to operate.

Wind turbines can be built on land or offshore in large bodies of water like oceans and lakes. The U.S. Department of Energy is currently funding projects that will make offshore wind technology available in U.S. waters. 

Sizes of Wind Turbines

Utility-scale wind turbines range in size from 100 kilowatts to as large as several megawatts. Larger wind turbines are more cost effective and are grouped together into wind farms, which provide bulk power to the electrical grid.

Offshore wind turbines are larger, can generate more power, and do not have the same transportation challenges of land-based wind installations, as the large components can be transported on ships instead of on roads.

Single small turbines—below 100 kilowatts—are typically used for residential, agricultural, and small commercial and industrial applications. Small turbines can be used in hybrid energy system with other distributed energy resources, such as microgrids powered by diesel generators, batteries, and photovoltaic. These systems are called hybrid wind systems and are typically used in remote, off-grid locations, where a connection to the utility grid is not available, and are becoming more common in grid connected applications for resiliency.

When wind turbines of any size are installed on the "customer" side of the meter, or are installed at or near the place where the energy they produce will be used, they're called "distributed wind." You can learn more about distributed wind from the Distributed Wind Animation or read about what the Wind Energy Technologies Office is doing to support the deployment of small and mid-sized turbines for homes, businesses, farms, and community wind projects.

Source: www.energy.gov