To make this activity into an engaging engineering project, have each group pick a goal. A group may decide that it wants to make the most powerful turbine, but there are other options. Other examples include making a turbine that
can lift a heavier weight
is more efficient in lower or higher wind speeds
While many teachers would be inclined to assign a single task for the class, letting each group set its own goal has many advantages. Students tend to be more invested in the design and work harder. Groups don’t just copy the work of other groups. Voices that are less often heard may be more likely to express themselves.
Help students to understand that this is the engineering process. Engineering uses a cycle of
determining a problem, identifying what’s needed to solve the problem, trying and testing possible solutions, optimizing, and iterating.
All grades should be able to get something out of building a wind turbine. Younger children will be less able to build components and may need to have more things already sturdily built. They may also struggle to understand the process of optimizing, and so their goals for the project may need to be left fairly wide open.
Middle grade students may struggle with narrowing down their ideas. Encourage them to write down what they have done so that they can figure out what is successful.
Older high school students should be able to follow the derivation of the wind power equation. A wind turbine extracts energy from the air. The rate that it can extract energy is called the wind turbine’s power. Power is energy extracted per unit of time.
Since almost all of the available energy is from the motion of the air, the turbine extracts kinetic energy from the air.
The power is how fast that energy is removed per second.
Looking at the equation, the hardest part is figuring out how much mass of air passes through the turbine’s blades per second.
So, let's imagine a parcel of air that is about to move through the turbine.
The mass of air in it is proportional to the volume of the cylinder of air and the density of the air.
Substituting back into the power equation
The equation can be rearranged.
Length divided by time is speed, so the equation can be rewritten as
This equation is known as the wind power equation, an expression of the maximum power a wind turbine can produce. Real turbines can’t extract all of the available energy. If such 100% efficiency were possible, the air would stop moving altogether and block any additional air from coming in. In reality, only about half the energy that is in the moving air can be extracted.