Wind Turbine Efficiency Demonstration
In this experiment, we will investigate the efficiency of a system that converts the
energy from wind to electrical energy, using a wind tunnel and DC motor/generator
to simulate a wind turbine.
In order to calculate the efficiency of the energy conversion, we must determine the
input power of the wind and the power generated across the load resistor.
The input power is determined by considering the kinetic energy of the air that
passes the turbine (propeller).
Input Power = Kinetic energy of wind striking propeller blade per second
= 1/2  mass  velocity2


Velocity (m s-1) is measured by the manometer mounted in the tunnel.
Mass of air passing propeller blade each per second is calculated by
determining the volume of air swept out by the propeller per second,
multiplied by the density of the air (1.2 kg/m3)
o Volume of air passing per second V is related to area swept out by propeller and
speed of wind:
V = Area ´ v =
p d2
´v
4
d
The output power is determined using a voltmeter and ammeter
to measure the power dissipated across the load resistor:
DC Motor
acting as a
generator
Output Power = Voltage across load × Current in load.
1
load
Efficiency is then calculated by: Output Power  100%
Input Power
Analysis
1. Construct a simple spreadsheet to calculate the
percentage efficiency of the wind turbine and generator used in the wind tunnel.
 The columns of your spreadsheet should be designed as velocity inputs, while the
rows will calculate input energy, output energy and efficiency for these velocities.
 Be sure to use Standard International (S.I.) units (metres, seconds, volts, amps,
kilograms, watts)
Power calculations
Trials
wind velocity v (m s-1)
2.5
d (m)
0.20
Area = d2 (m2)
0.126
Volume V = Area  wind
velocity (m3)
mass of air passed blade each
second = 1.2  V (kg s-1)
0.314
input energy (J) in one second
input power from wind (J s-1)
1.17
0.37
2.
3.
Use your spreadsheet to produce a graph of input power (y–axis) versus velocity (x–axis).
a. What implications does the Input Power vs. Velocity relationship have for the location
of wind turbine sites?
Use your spreadsheet to produce a graph of percentage efficiency (y–axis) versus velocity
a. Comment on any trend in the data.
4.
If there is time, repeat the efficiency test for other rotors.
5.
Draw a flowchart indicating the various energy conversions that take place, starting with the air
entering the wind tunnel.
6.
Write a conclusion to summarise your findings.
BACK TO REALITY: It is important to remember that, although the efficiency of this turbine seems low
and actually increases at lower windspeeds, large scale turbines behave differently. Gearing systems and
adjustable pitch blades adjust the speed of the shaft in the generator so that power is delivered to suit
application demands.