As renewable energy sources continue to grow in prevalence around the world, questions pertaining to functionality have arisen. Wind energy, which is projected to increase at an exponential rate over the next few decades, is a constant source of inquiry. One of the most common questions, “How do wind turbines work?,” is a topic that will be covered below.
In general, wind is a form of solar energy. Wind is caused by the sun heating the atmosphere, the rotation of the earth, and the irregularities of the earth’s surface. As a result, wind flow patterns vary depending upon the terrain. Historically, people have used wind as a means of transport (sailing), entertainment (kites), and more recently, the generation of electricity. A wind turbine, which comes in numerous shapes and sizes, harnesses the kinetic (moving) energy in the wind into mechanical power. The power generated from the wind turbine can then be used for an assortment of means including pumping water, grinding grain, and being converted into electricity via generators.
The following picture from the U.S. Department of Energy provides insight into the inner workings of a wind turbine. As you can see, there are a lot of components involved in converting wind into electricity. Given the complexity of the system, each term is described in detail.
Anemometer: Measures the wind speed and transmits wind speed data to the controller.
Blades: Most turbines have either two or three blades. Wind blowing over the blades causes the blades to “lift” and rotate.
Brake: A disc brake, which can be applied mechanically, electrically, or hydraulically to stop the rotor in emergencies.
Controller: The controller starts up the machine at wind speeds of about 8 to 16 miles per hour (mph) and shuts off the machine at about 55 mph. Turbines do not operate at wind speeds above about 55 mph because they might be damaged by the high winds.
Gear box: Gears connect the low-speed shaft to the high-speed shaft and increase the rotational speeds from about 30 to 60 rotations per minute (rpm) to about 1000 to 1800 rpm, the rotational speed required by most generators to produce electricity. The gear box is a costly (and heavy) part of the wind turbine and engineers are exploring “direct-drive” generators that operate at lower rotational speeds and don’t need gear boxes.
Generator: Usually an off-the-shelf induction generator that produces 60-cycle AC electricity.
High-speed shaft: Drives the generator. Low-speed shaft: The rotor turns the low-speed shaft at about 30 to 60 rotations per minute.
Nacelle: The nacelle sits atop the tower and contains the gear box, low- and high-speed shafts, generator, controller, and brake. Some nacelles are large enough for a helicopter to land on.
Pitch: Blades are turned, or pitched, out of the wind to control the rotor speed and keep the rotor from turning in winds that are too high or too low to produce electricity.
Rotor: The blades and the hub together are called the rotor.
Tower: Towers are made from tubular steel, concrete, or steel lattice. Due to wind speed increasing with height, taller towers enable turbines to capture more energy and generate more electricity.
Wind direction: This is an “upwind” turbine, so-called because it operates facing into the wind. Other turbines are designed to run “downwind,” facing away from the wind.
Wind vane: Measures wind direction and communicates with the yaw drive to orient the turbine properly with respect to the wind.
Yaw drive: Upwind turbines face into the wind; the yaw drive is used to keep the rotor facing into the wind as the wind direction changes. Downwind turbines don’t require a yaw drive, the wind blows the rotor downwind.
Yaw motor: Powers the yaw drive.