Can you answer these questions?
• How is wind created?
• How do wind turbines create electricity?
• What are the advantages and disadvantages of using wind energy?
Join us on the field trip to find out!
Wind is an important form of energy because it is clean, safe, and perpetually renewable. Using renewable energy is important in establishing global sustainable systems and reducing our country's dependency on foreign non-renewable resources. “About 2% of the sun's energy striking the Earth is converted into wind” (Chiras 2001). The earth has a curved spherical shape; as a result, the area in the middle, closest to the equator receives the most intense solar radiation and is warmer than those areas toward the poles. Air expands as it is warmed and contracts when it is cooled. Warm air is lighter and less dense than cold air so it rises. Wind currents are created as air flows from cooler to warmer. Warm air rises at the equator. As it rises it cools, until it reaches latitudes of about thirty degrees where most of it sinks to the surface. Some other sinking air moves poleward. Winds are also redirected as a result of the rotating motion of the earth; this is called the Coriolis Effect.
There are also small scale, or local, wind systems resulting from sea breezes and topography. No matter its origin, wind can be harnessed to do work such as grinding grain, pumping water, and generating electricity . Wind energy is the fastest growing renewable source of energy in the world. There are windy areas on every continent but meteorologists and wind turbine designers have designated some areas as more suitable for large-scale development than others. This depends on geography, altitude, and specific site anomalies. Wind maps are available for most areas of the globe and are a valuable source when making a site determination.
from: Renewable Resource Data Center
Germany, Spain, and Denmark “accounted for 90 percent of the capacity to generate wind energy in Europe during 2002" (Worldwatch 2003). Germany currently has 38% of the world's wind capacity. Spain recently surpassed the United States to rank second worldwide (Worldwatch 2003). Plains, mountain ridges, and coastlines of oceans and large lakes are the best locations for wind turbines. In the United States, the states with the greatest wind potential are North Dakota, Texas, Kansas, and South Dakota. “According to one estimate, the states of North and South Dakota alone have enough wind energy to meet 80 percent of the electricity needs of the U.S.” (Hydrogen 2000).
The Worldwatch Institute estimates that wind energy could easily provide 20 to 30% of the electricity needed by many countries (Chiras 2001; WorldWatch Institute 2003). A study done by the European Wind Energy Association and Greenpeace contends that “there exist no technical, economic or resource barriers for … wind to provide 12 percent of the world's electricity by 2050” (Worldwatch 2003). Modern technology now enables small-scale electricity generation (like that needed for a home) with as little as 6 mile-per-hour winds. Large-scale electricity generation like that needed to supply a whole community or town requires certain site requirements and an average year round wind speed of about 13 to18 mph.
There are two basic types of wind turbines: horizontal axis turbines (HATs) and vertical axis turbines (VATs). Vertical axis wind turbines “can harness winds from any direction without the need to reposition the rotor when the wind direction changes. … However, the unusually-shaped blades are difficult to manufacture, transport and install” (Boyle 2004).
Presently, the most common wind turbine type is the horizontal axis with two or three blades. Multi-bladed horizontal types were commonly used for water pumping even prior to the Industrial Revolution (Boyle 2004). Today, two or three blades are most common. The photo below includes two examples of horizontal axis turbines: a three-bladed turbine and a multi-bladed turbine.
Modern technology has improved and designed blades based on already successful technology of aircraft propellers and aircraft wings. Many wind turbines grouped together in the same locale for the purpose of electricity generation is called a wind farm.
Our objectives for this field trip are to:
- learn how wind energy creates electricity, and how that electricity enters the grid
- learn the advantages and disadvantages of wind energy
We will be visiting the Garrett Wind Farm in Somerset, Pennsylvania.
As we take the trip be sure to make notes of:
- how the electricity is generated
- the two types of wind turbines
- how electricity is sent to the power grid
- advantages and disadvantages of wind energy.
The Garrett Wind Farm is located on top a hill near the small borough of Garrett in Somerset County, PA. The Decker family owns the land and is the host for the six wind turbines on their farm.
The wind turbines are owned, operated and jointly developed by National Wind Power of the United Kingdom and Distributed Generation Systems, Inc. of Evergreen Colorado. The turbines are manufactured by Nordex GmbH of Denmark. The basic components of a wind turbine are the blades, hub, rotor, shaft, electric generator, and tower. The blade of a wind turbine is shaped in such a way that when the wind is blowing air pressure is lower on one side than on the other. The differences in air pressure create lift, which forces the blade to move. The three blades, which collectively create a 230 foot diameter circle, are connected to a central point called the hub. Collectively the blades and hub are called the rotor. When the wind direction changes, a measuring unit senses the change and a motor located on the top of the hub turns the entire rotor and generator unit toward the new wind direction. This is referred to as yawing. It ensures optimal performance that is, greatest electrical output. The rotor is connected to a shaft through gears to an electric generator . Rotation of the generator creates electricity (Green Mountain Energy 2004).
The six Garrett wind turbines produce 10.4 megawatts of electricity when operating at full speed. This electricity is carried by copper wires down the towers of the wind turbines, underground to a substation. From the substation the electricity enters the grid. The electricity is purchased by the Green Mountain Energy company of South Burlington, Vermont.
“Over its working lifetime, a wind turbine is able to generate some 80 times the energy required to produce it” (Boyle 2004).
