As you prepare this lesson, you may want to first view this video entitled What is STEM?
In this lesson, students can first explore the concept of "current" in electrical circuits. Current will be defined as the flow of electrons. Photovoltaic (PV) cell properties can then be introduced. Generally constructed of silicon, photovoltaic cells contain a large number of electrons, BUT a source of energy is required to "free" these electrons if we wish to create current. Light from the sun provides this energy, enabling current to flow. Solar cells transduce light energy into electrical energy. (For a more detailed understanding, please see http://science.howstuffworks.com/solar-cell.htm.) Batteries, on the other hand, store energy and release it over time. Most common batteries contain a mixture of two different chemicals separated by a boundary layer. At this layer, electrons flow from one side to the other, then out of the battery into the circuit. All the energy given by a battery is stored in it from the beginning and will eventually run out, as opposed to a solar cell which can supply energy continuously as long as light is present.
This discussion can lead to the principle of "Conservation of Energy." This principle states that the total amount of energy in a closed system remains constant. It is neither created or destroyed, but instead is transformed.
With a basic understanding of the circuits through Ohm's law, students will see how the energy from the sun can be used to power everyday items, including vehicles. Ohm's law describes how current, voltage, and resistance relate. It states that:
I = (V/R)
where I=Electric Current, V=Voltage and R=Resistance. As the sunlight powers the solar panel, it puts out a voltage (V) much like a AA battery will. This voltage creates a current (I) in the circuit. By passing this current through objects that have resistance (R), such as a motor, we can use the sun's energy to do work.
This lesson utilizes the engineering design activity of building a solar car to help students learn these concepts. The students are encouraged to think about each component of a solar car and how these parts fit and work together. They then translate these thoughts into a design for the car that utilizes the materials available to them. Finally, they use their design to engineer an actual solar car.
Current: Movement of electrons
Voltage: Designates "electric pressure" that exists between two points and is capable of producing a flow of current when a closed circuit is connected between the two points. (This can also be considered with the analogy of elevation; just as a hill will have water flow down it, a voltage will have current flow in the direction from high to low.)
Photovoltaic Cell: This is a semiconductor device that converts the energy of sunlight into electric energy.
Transduce: To convert into another form
Conductor: This is a material that allows electricity to move through it easily. That is, it is a material with low electrical resistance, one in which a fairly small voltage will produce a fairly large current.
Chassis: This is the frame that holds the body and motor of an automobile together.
Axle: This is the supporting shaft on which a set of wheels revolves.