The Earth’s winds contain vast amounts of energy. People have harnessed this energy for thousands of years to sail ships, grind grain and pump water. Today, advanced wind turbines offer an efficient means of capturing wind energy and using it to produce electricity. Wind turbines are used for individual homes and also grouped together in wind farms to generate electricity for utility grids. Wind turbines have two or three long, light-weight blades that turn quickly. The longer the blade and the greater the wind speed, the more electricity generated. Steady wind speeds of no less than 12 miles per hour year round are required to effectively generate electricity.
CAUTION: Take precautions when working with fans and electricity.
PROJECT #1 WHAT TECHNIQUES CAN BE USED TO MEASURE AND COMPARE WIND DIRECTION AND SPEED?
Materials Beaufort Wind Scale , wind vane, and anemometer. Calibrate vane with a compass and calibrate the anemometer through the window of a car.
Ideas to Study
1. Compare the Beaufort Wind Scale to the wind vane and anemometer for measuring wind direction and speed at a specific site for a determined time period (e.g., morning, noon, and afternoon or evening for a six week period of time). At what time of day do the fastest winds usually occur? Which method is more reliable and why?
2. Compare the design of the wind vane and/or anemometer for efficiency at a specific site over a period of time.
3. Compare different sites for collecting wind energy using the wind vane and/or anemometer for a given period of time.
4. Determine how the topography affects the results in one of the studies above.
5. Determine how the height of the device (wind vane or anemometer) affects the results in one of the studies?
6. Make a map of measured wind versus location, time of year, and time of day.
Materials Fan (2-3 speeds) or hair blower, a 1.5 v dc motor, voltmeter (0-5 v), a 100-ohm resistor, and insulated wire that is typically available from your Physics instructor. Propellers (model airplane from a hobby shop or see Appendix 2 for building three different wind propellers) .You should also design and build your own wind propeller. See sketch for experimental set up. You might want to do your study in a wind tunnel, which you can make from cardboard.
Ideas to Study
- Compare the blade angles and how the propeller spins. Attach Model 1 to the motor shaft. Tilt the blades so that they are perpendicular to the end of the cork (Figure A). Place the wind machine in front of a working fan (or a hair blower). If the propeller doesn’t spin, slightly rotate the blades so that they are at a small slant (Figure B). Place the propeller in front of the fan or hair blower. Keep tilting the blades in small increments until the propeller starts spinning. When this happens, measure the voltage produced. Keep titling the blades of the propeller to see which angle produces the greatest voltage. Deduce if the speed of the blades varies with the angle between wind direction and blade. How might the material from which the blade is made (paper, stock paper, plastic, etc.) affect the propeller spin? How might the number of blades (1,2,3,etc.) affect the spin of the propeller?
2. Compare the size of the wind blades with how fast a propeller can turn. Keep the wind blade on Model 1 at the angle at which they produced the greatest voltage. Measure the voltage. Then, attach Model 2 wind propeller to the motor shaft, with the blades at the same angle. Put it in front of the fan or hair blower at the same distance as you did with the first propeller (Why?). Measure the voltage by this wind turbine. Repeat for the other models. Determine if the amount of energy derived from the wind varies with the area swept by the blades or the size of the blades (diameter of the wheel).
3. Compare the shape of the propeller blades and how fast they can spin. Keep the wind blades on Models 1 and 2 at the same angle as in the previous study. Measure the voltage again. Then attach Model 3 wind propeller to the motor shaft, with the blades at the same angle as the Models 1 and 2 wind propellers? Measure the voltage. Repeat with the wind propeller you designed, and measure the voltage. Deduce if the shape of the blades in a wind propeller determine the efficiency of conversion.
4. Compare how wind speed affects the electricity output of wind machines. Use any of the propellers, and place the wind machine in front of a two-speed fan. Turn fan on low speed. Measure voltage. Then turn fan of high speed and repeat measurement. Determine if there is a mathematical relationship between the energy derived from the wind and the wind speed. Deduce how concentrating the wind speed through a cone affects the electricity output.
5. Alter any of the wind turbines such that it is strong enough to power a flashlight bulb (average voltage 2.5 volts). Were any of the models you used here strong enough?
PROJECT #3 WHAT IS THE MOST EFFICIENT SPACING OF WIND TURBINES FOR “FARMING” WIND IN A GIVEN UNIT OF SPACE?
Procedure Set up each turbine as illustrated in Project #2 and below. A simple wind tunnel could be constructed of cardboard to decrease variations of airflow generated by a fan.
Ideas to Study
1. Determine total electricity produced for a model land area and then calculate the total electricity produced for a larger area by extrapolation.
2. Compare the total electricity produced using variables such as wind direction, topography, andnumber and design of the wind turbines.
PROJECT #4 IS A VERTICAL WIND TURBINE MORE EFFICIENT THAN A HORIZONTAL WIND TURBINE?
Definition A vertical wind turbine is one that looks like a giant eggbeater; a horizontal wind turbine is one with blades like airplane propellers. Projects 1-3 involved horizontal wind turbines. Procedure Construct a vertical wind turbine (see Appendix 3) and then turn your model into a wind generator, by using a ring stand and clamps to support the wind turbine (see below). Attach the bottom end of the shaft (coat hanger) to the shaft on the small motor. Connect wires from motor to voltmeter.
Ideas to Study
1. Determine efficiency of the vertical wind turbine and compare it to the horizontal wind turbines from Project #2. How does the efficiency compare in moderate winds (low fan speeds) and high winds (high fan speeds)? Position the fan in front and then to the side of the turbine. Deduce if there is a loss, gain or no change in efficiency.
BEAUFORT WIND SCALE
This is the Beaufort Wind Scale. It is to measure wind speeds. It relies on human observations, no mechanical devices, to calculate the speed of the wind.
|0||calm (0-1 mph)||smoke rises vertically|
|1||light air (2-3 mph)||smoke drifts slowly|
|2||slight breeze (4-7 mph)||leaves rustle; windvane moves|
|3||gentle breeze (8-12 mph)||twigs move; flags extended|
|4||moderate breeze (13-18 mph)||branches move; dust and paper rise|
|5||fresh breeze (19-24 mph)||small trees sway|
|6||strong breeze (25-31 mph)||large branches sway; wires whistle|
|7||moderate gale (32-38 mph)||trees in motion; walking difficult|
|8||fresh gale (39-46 mph)||twigs break off trees|
|9||strong gale ((47-54 mph)||branches break; roofs damaged|
|10||whole gale (55-63 mph)||trees snap; damage evident|
|11||storm (64-72 mph)||widespread damage|
|12||hurricane (73-82 mph)||extreme damage|
WIND MACHINE INSTRUCTIONS
This sheet tells you how to build your own wind machine for generating electricity.
First, get a small motor and a ruler or piece of wood from your teacher. Attach the motor to the end of the ruler by wrapping it with a rubber band.
Second, cut two 3O-cm pieces of electrical connecting wire. With a pair of scissors, take off 2 cm of rubber insulation from both ends of the two wires. Do this by pinching softly with the scissors on the rubber casing, cutting it slightly; then pull the scissors towards the wire’s end, pulling off the casing.
Next, attach one end of each wire to one of the motor’s outlets. Tape the wires to the molding, at the end without the motor. Attach the other two ends of the wire to a : voltmeter.
Now you’re ready to build the actual wind propellers. There are three models you’ll need to build.
WIND MACHINE INSTRUCTIONS (cont.)
MODEL 1: Take six paper clips. Snip off part of each clip with pliers or wire cutters. Straighten out the bottom part of each clip.
Then cut out six pieces of cardboard 1 cm x 3 cm. Glue / or tape central part of each paper clip to the bottom of a cardboard piece. Leave time for glue to dry (20 min.).
Take a cork and poke the six wind blades into it. Insert the blades at about 5 mm from the end, spaced equally\ around the circumference of the cork. To loosen up a hole, you may want to stick a pin in beforehand.
MODEL 2: Follow the same directions as in Model 1, but this time cut cardboard rectangles that are 1-1!2 cm x 4 cm.
MODEL 3: Follow same directions as Model1, but this time cut cardboard in the following shape: (Note: This: shape has the same surface area as Mode12)
To use a wind propeller, place the cork end furthest away from the wind blades on the motor’s shaft. Make sure the shaft goes in the exact center of the cork and do not wiggle it (this will loosen its hold on the motor).
CONSTRUCTION OF A VERTICAL WIND TURBINE
• 2 cotton reels
• 1 piece 12.5 mm balsa (5 cm x 10 cm) or stiff cardboard and cut out triangle shape with folded edges
• Stanley (utility) knife/scissors
• 1-1/2 to 6v DC motor
• electrical tape
• 2 electrical wires w/ alligator clips
• 1 pair pliers
• retort stand w/ 2 boss-heads and 2 clamps
NOTE: Carefully examine the following diagrams before beginning construction of you model.