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A Layperson's Guide On How Wind Turbines Make Energy And How To Store It Too

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The President of the United States recently suggested that wind energy was not viable because it only "blows sometimes." It is true that the intermittent nature of wind can be a challenge for energy production. However, it is comforting to know that a country that put rovers on Mars and humans on the Moon can figure out how to store renewable energy. My goal is not to debate the merits of the inevitable transition to a renewable energy-based economy but to provide an overview of wind energy that any person can understand.

Getty

A complete discussion of wind power would extend beyond the 800 words that I have for this column. However, an overview of the "basics" does fit and enablesntelligent conversation on the topic. Since I am an atmospheric sciences professor, let's start with a definition of wind. According to the AMS Glossary of Meteorology, wind is "Air in motion relative to the surface of the earth." Wind is caused by a variety of processes that create a pressure gradient: uneven heating of the surface by the sun, land - water contrasts, terrain differences or complex meteorological systems. According to the Argonne National Laboratory website, wind energy or wind power is defined as,

the process by which the wind is used to generate mechanical power or electricity. Wind turbines convert the kinetic energy in 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...

U.S. Department of Energy

The process is actually very simple:

  1. Large wind turbines consist of a rotor or blade, some type of generator system, tower, and supporting electrical-mechanical systems.
  2. The blade is aerodynamically-engineered to produce a slight difference in pressure on one side like an airplane wing.
  3. The wind turns the blades connected to a shaft (graphic above).
  4. The rotation of the shaft is connected to a generator that produces electricity.

Most modern wind turbines are horizontal-axis models, but vertical-axis models exist. A large area of wind turbines is called a wind farm, and they distribute their energy to a utility grid.

The energy produced by wind depends on wind speed raised to the third power. Stronger wind speeds have greater power generation potential. If you double the wind speed, the energy potential increases by a factor of 8.  The wind resource is used to asses wind power generation costs and is based on wind speed. According to the Union of Concerned Scientists website,

Wind speeds are divided into seven classes — with class one being the lowest and class seven being the highest. A wind resource assessment evaluates the average wind speeds above a section of land (e.g. 50 meters high), and assigns that area a wind class. Wind turbines operate over a limited range of wind speeds. If the wind is too slow, they won't be able to turn, and if too fast, they shut down to avoid being damaged. Wind speeds in classes three (6.7 – 7.4 meters per second (m/s)) and above are typically needed to economically generate power.

Many places in the United States and around the world produce suitable wind speeds for wind energy.  In 2017, wind energy accounted for roughly 6.3% of utility-scale electricity generation in the United States, and this number is expected to rise. A list of the top wind energy-generating countries can be found here. China is at the top of that list.

NREL

Isn't it true that the wind doesn't always blow? Absolutely, but really smart scientists and engineers noticed that along time ago too. The website Windpowerengineering.com provides an overview of at least six energy storage mechanism (click this link for more details): Solid-state batteries, Ultra or Super-capacitors, Flywheels, Pumped Hydroelectric Storage Dams, Rail Energy Storage, and Compressed Air Storage. Each of these methods has their advantages and disadvantages, but the important point is that storage technology is present and will improve over time. The U.S. Department of Energy Energy Storage website says,

As America moves closer to a clean energy future, energy from intermittent sources like wind and solar must be stored for use when the wind isn’t blowing and the sun isn’t shining. The Energy Department is working to develop new storage technologies to tackle this challenge -- from supporting research on battery storage at the National Labs, to making investments that take startup concepts to grid-scale solutions.

Thomas Dolby is one of my favorite recording artists. His brilliant song "Windpower" from the early 1980s is playing as I write this. Dolby was ahead of his time with this song, but he also understood something very important. Problems like "intermittent wind" and energy generation are perfect for creativity, imagination, science and technology.

U.S. Department of Energy

 

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