Lesson From Sunlight to Electric Current

Learning Objectives

At lesson end, students should be able to:

• Define current.
• Explain why a solar photovoltaic panel is like a battery.

Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

Common Core State Standards - Math

International Technology and Engineering Educators Association - Technology

State Standards

Worksheets and Attachments

Introduction/Motivation

How might you take the same energy that the sun provides to cook food in our solar ovens and use it to power _______ (insert any one of a number of electric devices)?

Conduct this related demonstration to grab students' attention. The electrons in silicon (Si) generally do not contain enough energy to jump the "band gap" and so they are considered frozen. To demonstrate this, a bucket filled with ice cubes can represent silicon with electrons in the frozen state. Connect the bucket to another bucket by a clear plastic tube attached towards the bottom of each bucket. Represent the sun by a hair dryer. The hair dryer melts the ice representing the release of the electrons by the sun. Additionally, the sun raises the electric potential (voltage difference from one point to another) of each PV cell (creating an electric field at the PN junction—this does not need to be taught to the students). The melted ice (water) now flows in the direction of the other bucket, representing current.

Lesson Background and Concepts for Teachers

How Photovoltaic Cells Work

Energy of sunlight is transferred to electrons, allowing them to jump to the next orbital and cross the band gap. These electrons are now mobile and current will flow.

Use the Photovoltaic Cell Handout for diagrams and an explanation of how photovoltaic cells work, including their design (layers, materials) and functionality. Following the handout, have students complete the hands-on Racing with the Sun - Creating a Solar Car activity.

For a more detailed understanding of photovoltaic cells, please see http://science.howstuffworks.com/solar-cell.htm.

Associated Activities

• Racing with the Sun - Creating a Solar Car - Students construct and test small-sized model solar-powered cars.

Lesson Closure

Distribute solar panels to each group of two students. With a digital multimeter (DMM), go around to each group and run a personal demonstration soliciting student input. For example, hook up the DMM leads to the solar panel when it is placed in the dark (in a desk for example). Expect students to understand that without any light energy, the panel will not create any current or voltage. Similarly, expose the panel to a bright flashlight and prompt students to explain why current and voltage now exist.

Note: For solar panels, use those that come with the Junior Solar Sprint solar car kit that will be used for the associated Racing with the Sun - Creating a Solar Car activity. Thus, this also serves as an excellent transition to the activity.

Vocabulary/Definitions

conductor: A material in which electricity moves easily. That is, it is a material with low electrical resistance, one in which a fairly small voltage produces a fairly large current.

current: Flow of electrons.

photovoltaic cell: A semiconductor device that converts the energy of sunlight into electric energy.

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 (can also be understood 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).

Assessment

Assessment is closely tied to the Lesson Closure use of solar panels. By doing this, you can directly ascertain whether the students "get it" based on their ability to discuss and describe the behavior of the solar panels. Further questioning can easily be worked in regarding the other concepts such as current, conservation of energy, light interaction, etc., as they all relate to the PV cell.

Copyright

Contributors

Supporting Program

Acknowledgements

This content was developed by the MUSIC (Math Understanding through Science Integrated with Curriculum) Program in the Pratt School of Engineering at Duke University under National Science Foundation GK-12 grant no. DGE 0338262. However, these contents do not necessarily represent the policies of the NSF, and you should not assume endorsement by the federal government.