Grand Ridge EarthCache

Grand Ridge

Why does the wind blow?

The wind blows because the sun heats up the Earth!
The atmosphere surrounds the Earth. The inner part of the atmosphere is called the troposphere. The troposphere is about 10 km high and consists of air.
There are two main causes for wind.

• The Earth is always revolving around its own axis.
  • If you were to imagine that the troposphere – that is the air – stood still, you would feel the air as wind when the Earth was revolving. Luckily the air in the lowest couple of hundred meters follows the rotation of the Earth, so it is not as windy as it would be if the air stood completely still.
• The other cause for wind is the fact that the sun does not heat the Earth evenly.
  • You can see that the sunrays cover a much greater area at the poles than at the equator. That is why at the equator, one square meter of surface will be heated a lot more than at the poles. The warm air rises from the equator and floats towards the poles. This makes room for cold winds from the north and south to blow towards the equator.

Summing up, the wind we feel is caused by two things:

1. The rotation of the Earth
2. The differences in temperatures on the Earth

Well then, why are the prevailing winds more West-East or East-West than North-South or South-North? That's when the spin of the earth comes in. Just like the center of a record spins slower than the edge because it has a shorter path to travel, the earth's equator spins faster than higher latitudes. This means that air that is travelling towards the equator is deflected westward and air that is travelling towards the pole is deflected eastward. This breaks up the wind patterns of the globe into 3 overall "cells" per hemisphere. That is why the winds in the tropics blow mainly east to west, and at mid latitudes, the winds blow mainly west to east. This also controls precipitation patterns on a large scale because air that is rising often loses its moisture as rain.

How was the land here formed to be rolling hills and ridges?

The Great Lakes Basin (the Great Lakes and the surrounding area) began to form about two billion years ago – almost two-thirds the age of the earth. During this period, major volcanic activity and geologic stresses formed the mountain systems of North America, and after significant erosion, several depressions in the ground were carved. Some two billion years later the surrounding seas continuously flooded the area, further eroding the landscape and leaving a lot of water behind as they went away.

More recently, about two million years ago, it was glaciers that advanced over and back across the land. The glaciers were upwards of 6,500 feet thick and further depressed the Great Lakes Basin. When the glaciers finally retreated and melted approximately 15,000 years ago, massive quantities of water were left behind. It is these glacier waters that form the Great Lake today.
Many glacial features are still visible on the Great Lakes Basin today in the form of "glacial drift," groups of sand, silt, clay and other unorganized debris deposited by a glacier. Moraines, till plains, drumlins, and eskers are some of the most common features that remain. "Drift" is the generic term for all glacially deposited material.

Grand Ridge would be an example of a lateral moraine.

Here's a short glossary of different types of glacial and ice sheet depositions:

• Glacial flour - rock ground to the texture of a fine powder. It usually flows out of a glacier as sediment in a glacial meltwater stream running from the glacier.
• Till - refers to an unconsolidated and unsorted mixture of sediment, clay, gravel, and rocks deposited by a glacier.
• Moraine - a French word that refers to any glacier-formed accumulation - there are a variety of moraines.
• Terminal moraine - an accumulation at the outermost edge of where a glacier or ice sheet existed.
• Recessional moraine - moraine located "behind" the outermost edge of a glacier, formed when the glacier lingers in one spot for a long time.
• Ground moraine - gently rolling hills and plains deposited by ice.
• Lateral moraine - ridges of till on the sides of a glacier.
• Medial moraine - a moraine formed when two glaciers merge (a tributary and trunk glacier) and their lateral moraines come together to form a single moraine.
• Push moraine - a moraine created by till that was a moraine deposited by an earlier glacier that once covered the area.
• Ablation moraine - a moraine formed from material that fell upon the glacier.

Harnessing Wind for Power

At Grand Ridge, a wind farm was built. The wind turbine units with blades that reach 389 feet high were brought to their sites in sections and assembled with the help of cranes on concrete bases. Each windmill is in 387 yards of concrete. Concrete trucks had to run 24/7 to fill the holes! A concrete truck holds 9 yards of concrete, hence the expression “the whole 9 yards”.

The best topography for wind farms is an area with subtle hills and slopes (a lateral moraine), free of any obstructions such as tall buildings. As you can see looking around here, this is an ideal spot for harnessing wind power.

How a Wind Turbine Generates Electricity

The wind turns the rotor of the wind turbine.
The rotor turns a generator (a dynamo) which makes electricity.
The parts of the wind turbine are:

Rotor
The rotor is bolted onto the big main shaft. The large rotor has three blades, which catch the wind. The wind will turn the rotor if there is enough power in the wind.
Gearbox
The rotor turns with app. 22 revolutions per minute (RPM). But the generator has to turn 1500 revolutions per minute. The gearbox converts the 22 revolutions to 1500 revolutions.
Generator
The generator (basically copper wire and magnets) makes electricity when it turns. The current is sent down through the tower in large electricity cables.
Yaw motor
The yaw motor turns the nacelle so that the rotor faces the wind. The motor has a cam wheel which fits into the large yaw bearing cam wheel. The controller tells the yaw motor when to turn the nacelle.
Yaw bearing
The large cam wheel is mounted onto the tower. The cam wheel of the yaw motor engages the large cam wheel and turns the nacelle with the rotor into the wind.
Anemometer
The anemometer measures the wind speed. It sends information about the wind speed to the controller all the time.
Mechanical Brake
The mechanical brake is used when the wind turbine has to be repaired or it has to be serviced. It ensures that the rotor will not start turning.
Main Shaft
The rotor turns the large shaft. The shaft is connected to the gearbox. The rotor uses a large force to turn the shaft. Therefore the shaft has to be very thick.
Radiator
When the generator is running it gets very hot. But if it becomes too hot it will break down. This is why it has to be cooled down. In some wind turbines the generator is cooled by water. The radiator cools the water.
Controller
The wind turbine controller is a computer that controls the many parts of wind turbine. The controller yaws the nacelle against the wind and allows the wind turbine rotor to start when the anemometer tells it that there is enough wind.
Wind Vane
The wind makes the wind vane turn. The wind vane tells the controller where the wind comes from. The controller then tells the yaw motor to yaw – that means turn – the rotor up against the wind.
Small shaft
The small shaft leads the power from the gearbox to the generator. The small shaft runs very quickly, approx. 1500 revolutions per minute.

Basic Principles of Wind Turbine Power Production

The output of a wind turbine varies with the wind's speed through the rotor. This relationship is usually shown graphically in a power curve. 
The "rated wind speed" is the wind speed at which the "rated power" is achieved and generally corresponds to the point at which the conversion efficiency is near its maximum.

Note that at lower wind speeds, the power output drops off sharply. This can be explained by the cubic power law, which states that the power available in the wind increases eight times for every doubling of wind speed (and decreases eight times for every halving of the wind speed).

Using the power curve, it is possible to determine roughly how much power will be produced at the average wind speed prevalent at a site. For example, the turbine would produce about 20% of its rated power at an average wind speed of 15 miles per hour. The wind turbines can produce 1650 kW in winds of about 29 mph with the blades turning at 14.4 rpm.
 
Take a look up at a Grand Ridge windmill here!

Please email me the answers to the following questions. You should be able to answer them from your reading with a few calculations.

1. How many wind mills can you see from where you are standing?
2. How many truck loads of concrete were needed for each wind mill?
3. What is roughly the % of rated power being produced at the time of your visit? Use the power curve and the wind conditions at the time of your visit.
   Check the wind conditions at the time of your visit at: http://www.wunderground.com/US/IL/Grand_Ridge.html
4. What is the rpm of the rotor at the time of your visit? (Count the rotations for a minute.)
5. You now know about tills and moraines, tell me what eskers are - I think you'll find it fascinating!
6. And lastly, in what direction does Grand Ridge run at this site?

Sources:
American Wind Energy Association
windpower.org
curious.astro.cornell.edu
Matt Rosenberg