standard-title Wind Energy

Wind Energy

WIND ENERGY

Wind energy is now the second fastest-growing source of electricity in the world, with a global installed capacity of 539,581 megawatts (MW) at the end of 2017. There are also over 89,000 MW of wind capacity operational in the U.S., as of January 2018. (You can see U.S. wind farm locations on the U.S. Geological Survey’s interactive map). Why is wind energy generation such a popular choice? Harnessing energy from the wind and turning it into renewable electricity has many advantages. And although wind energy has a long history dating back as far as 5,000 BC, the technology has never been better or more cost effective than it is right now. Each year, U.S. grid operators continue to use wind power to meet an ever-increasing amount of their electricity needs, peaking at over 50 percent in the Southwest Power Pool (SPP), covering the Great Plains states, and in Texas, which is monitored by the Electricity Reliability Council of Texas (ERCOT). Similarly, the Midwest Independent System Operator (MISO), which monitors electricity supply for the Upper Midwest, recorded a record 14 gigawatts of wind supply in mid-2017.
ENERGY FROM MOVING AIR: HOW UNEVEN HEATING OF WATER AND LAND CAUSES WIND
Wind is simply air in motion. It is caused by the uneven heating of the Earth’s surface by the sun. Because the Earth’s surface is made of very different types of land and water, it absorbs the sun’s heat at different rates. One example of this uneven heating can be found in the daily wind cycle.
WIND TECHNOLOGIES
Wind energy technologies use the energy in wind for practical purposes, such as generating electricity, charging batteries, pumping water, and grinding grain. Mechanical or electrical power is created through the kinetic energy of the wind. Wind power available is proportional to the cube of its speed, which means that the power available to a wind generator increases by a factor of eight if the wind speed doubles. The turbine’s blades are similar to the propeller blades on an airplane. The hub of the turbine is rotated as the rotor blades generate lift from the passing wind. This rotating action then turns a generator, which creates electricity. When the wind blows a pocket of low-pressure air forms on the downwind side of the blade. The low-pressure air pocket then pulls the blade toward it, causing the rotor to turn. This is called lift. The force of the lift is actually much stronger than the wind’s force against the front side of the blade, which is called drag. The combination of lift and drag is what causes the rotor to spin. Since the wind’s speed typically increases with height above ground (due to decreasing friction with the ground), wind turbines are mounted on a tower to capture more energy. At 100 feet (30 meters) or more above ground, they can take advantage of faster and less turbulent wind. Wind turbines are mounted on a tower to capture the most energy. At 100 feet (30 meters) or more above ground, they can take advantage of faster and less turbulent wind. For the best utilization of wind turbines, they should be placed where wind speeds reach 16-20 mph and are at a height of 50m. It is also important that utility-scale power plants are located near existing power lines and in the windiest sites available. Wind energy technologies can be used as stand-alone applications, connected to a utility power grid, or even combined with a photovoltaic system. For utility-scale sources of wind energy, turbines are usually built close together to form a wind farm that provides bulk power. Stand-alone turbines are typically used for water pumping or communications. However, homeowners and farmers in windy areas can also use small wind systems to generate electricity.

WIND TURBINE DESIGN

There are different styles and many different sizes of wind turbines to accommodate different needs. The most common style, large or small, is the “horizontal-axis design” (with the axis of the blades horizontal to the ground). On this turbine, two or three blades spin upwind of the tower.
Less common are the vertical-axis turbines: the Savonius and the Darrieus. The Darrieus turbine was invented in France in the 1920s and is often described as looking like an eggbeater. It has vertical blades that rotate into and out of the wind. The Savonius turbine is S-shaped if viewed from above. This drag-type turbine turns relatively slowly but yields a high torque. It is useful for grinding grain, pumping water, and many other tasks, but its slow rotational speeds are not optimal for generating electricity.
Small wind turbines are used for providing power off the grid, and range from very small, 250-watt turbines designed for charging batteries on a sailboat to 50-kilowatt turbines that power dairy farms and remote villages. Like old farm windmills, they have tail vanes that keep them oriented into the wind.
Large wind turbines, used by utilities or independent generators to provide power to a grid, range from 100 kilowatts up to the enormous multi-megawatt machines that are being tested in Europe. Large turbines sit on towers that are up to 100 meters tall and have blades that range from 30 to 60 meters long. Utility-scale turbines are usually placed in groups or rows to take advantage of prime windy spots. Wind farms like these can consist of a few or hundreds of turbines, providing enough power for whole towns.