Datalogging in Science

Wind turbines can generate electricity

Overview
This investigation introduces the idea of wind power as an alternative energy source. The current generated by a wind turbine will be measured and the corresponding wind speed estimated. The results of several trials at different wind speeds will be compared.

A model of a wind turbine is shown in the diagram and an electric fan provides a controllable source of wind.

Background
Wind turbines have been in use for thousands of years. The type of windmill still seen in Holland, were once more widespread. A typical windmill could do the work of 200 people. They have been used for many purposes, including grinding corn, pumping water and operating machinery. The windmills lost favour about a hundred years ago, when other forms of energy became cheaper and more reliable. Rising fuel costs and the fear of global warming are making windmills increasingly popular again.
Windmills that generate electricity are properly called wind turbines. They are made of a set of blades (sails) tilted at a slight angle and attached to a central shaft. The turbine works by wind turning the blades of the wind turbine and the shaft. The shaft turns magnets (or coils) inside a generator and electricity is produced. The amount of electricity generated depends on several factors apart from the wind speed and wind availability. Modern interest in wind turbines has come from the ability of the turbine to harvest the power of the wind to generate electricity.

Apparatus

1. Datalogger
2. Current sensor (±100 mA).
3. Small low voltage DC motor
4. Set of blades as shown.
5. Electric desktop fan (will be suitable for developing a constant breeze)
6. Measuring stick
7. Anemometer

Note: Most small electric motors will have a rotation speed of several thousand RPM, but it is unlikely you will get anywhere close to this with wind energy. Also, the output is likely to be less than 150 mV.

Procedure
1. Connect a current sensor to a data logger.
2. Connect the wires from the wind turbine to the current sensor.
3. Launch the graph software and set it to record current for a minute.
4. Switch on the fan and after a few seconds (when the blades are turning at a constant speed) begin logging. A graph of current against time will be produced in "Real Time".
5. When logging has stopped, switch off the desktop fan and let the wind turbine come to a stop.
6. From the Graph, calculate the average value of current generated during the trial
7. Estimate the average wind speed for this trial by following the guidelines further down this page.
8. Record the results from 6 & 7 in a table as shown below.
9. Change the speed of the wind source a number of times (perhaps by moving it further from the turbine) and record the wind speed and current generated in each subsequent trial.


Results

Use the Analysis features of the software to determine the average value of current generated by the wind turbine over the course of the recording period (of a minute).
Determe the wind speed in each trial, using an anemometer (or the alternative shown below). Plot a graph of current generated against wind speed for the various trials. Analyse the graph and draw conclusions.

Extensions

Construct a wind turbine with a different design....perhaps fewer sails, and perhaps angled differently and investigate the current generated by your own design.

Wind Speed Measurement
If an anemometer is available, use it to measure the wind speed exactly at the position used for the centre of the blades of the windmill
If no anemometer is available try making your own wind speedometer as shown below:

Homemade Wind Speedometer
- clamp and stand
- table tennis ball attached to light nylon thread
- protractor

1. Tie the thread around the centre of the protractor as shown.
2. Clamp the protractor so that the thread hangs vertically (through the 90 degree line, when the air is calm. The ball must be able to swing freely.
3 Place the ball so it’s in the position immediately in front of the centre of the windmill blades. Remove the windmill.
4 Start the electric fan. It should be in the same position as when it was used to generate electricity. Measure the angle of the nylon thread when the ball is blown in the wind and record your result in your table.
5 Take two further measurements of the angle and so calculate the average angle.
(Note: If one value is at odds with the other two, do not include it in your calculation. If all three values are very different, take more readings.)

6 Draw a calibration curve from the data supplied in the Table below and use this graph to determine the approximate wind speed corresponding to the average angle of thread in your investigation.

7 Copy this table into your notebook or file and record your results in it:

Data Harvest users

1. Connect the sensor to the datalogger and the logger to the computer
2. Then click the Set Up icon to the right of this message.
3. When the software opens, click the Play button.