Hands-on Activity Design a Solar City

Learning Objectives

After this activity, students should be able to:

• Explain what a photovoltaic panel does and how it works.
• Describe the process of designing a house.
• Describe how photovoltaic panels can be used on buildings to create clean energy.

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.

NGSS: Next Generation Science Standards - Science

Common Core State Standards - Math

International Technology and Engineering Educators Association - Technology

State Standards

Materials List

For the teacher demo during the Introduction/Motivation section:

• mini solar PV panel
• piece of foam core board, on which to tape the solar panel
• 2 small alligator clamps
• a single light, such as a small Christmas tree light or any individual bulb from a hobby/craft/electronics store that can be hooked up in the circuit
• (optional) a voltmeter

Each group needs:

• graph paper and pencils
• measuring ruler
• ¼-inch-thick foam core board, pre-cut into sets of wall and roof pieces that form variously-sized structures (different for each team), such as long skinny rectangular buildings, short squat rectangular buildings, tall skinny skyscraper buildings, big spacious warehouse buildings, little house-sized buildings, etc.; alternatively, for more advanced students, have them design and draw first, then cut out their own wall and roof pieces
• cardboard, for plots of land; suggested size: ~24 x 24 in (~61 x 61 cm), however, size will vary depending on the size and shape of the building; cut from discarded cardboard boxes
• acrylic paint and paint brushes, for painting foam core buildings and cardboard plot of land
• mini solar PV panel; available online
• duct tape
• scissors
• 2 small alligator clamps
• light, small motor or buzzer, available at amazon, and at hobby or electronics stores such as Radio Shack; NOTE: be sure to purchase lights/motors/buzzers that are compatible with your solar panel; if your solar panels can output 3V, then the lights/motors/buzzers should be in the 1.5-3V range; if the solar panel outputs too much power, just cover some of the panel to decrease the power output, otherwise you may burn up the lights/motors/buzzers; however, if the solar panel cannot output the current required to power the lights/motors/buzzers then they will not work
• Solar City Persuasive Letter Worksheet, one per student

For the entire class to share:

• newspaper, to protect table and desk tops from gluing and cutting
• Xacto^TM knife (and blades) or utility knife or razor blade, for the teacher to use to cut foam core board
• (optional) Foam Core Tips Handout
• hot glue gun and glue sticks (model construction can take a lot of hot glue!)

Note: In this open-ended activity, as students begin to build, they may think of other materials they need, such as craft sticks, thin plastic sheets (or plastic beverage bottles), pebbles, Astroturf, etc.

Worksheets and Attachments

Pre-Req Knowledge

Students should understand the steps of the engineering design process. They should also have a general understanding of what electricity is and how it is used. Students should be able to use a ruler to make measurements, and be able to connect a circuit in series.

Introduction/Motivation

(Have ready to show the students: a small solar panel, and the solar panel connected in series with a light and voltmeter [optional]. See Figure 1.)

How do we use energy at school? (Possible answers from students: Powering the lights, the overhead projector, and all the computers.) Does anyone know from where we get our electricity? Most of the electricity in the US is created by burning coal! What is the problem with burning coal? (Possible answers: This process produces a lot of greenhouse gas emissions that lead to poor air quality and global climate change. Coal is a nonrenewable resource that must be mined from the earth; mining can be harmful to the environment.) These are all good answers! As engineers, we must find better ways to create the energy we rely upon everyday to power our houses, schools, libraries, supermarkets, sports arenas, stores, businesses, and all of the other buildings in our city! Luckily, we have the sun to help us with that!

(Show students a small solar panel.) This device is called a solar panel. It is sort of like a battery, but instead of storing chemical energy, it converts the energy we get from the sun (known as radiant energy) into electricity (or electrical energy). When a house or building uses a row of two or more solar panels, we call this a solar array. Has anyone seen a building with solar panels on it? Where are the solar panels usually located? (On the roof.) Why do you think that is? (The roofs of buildings are exposed to the greatest amounts of sunlight and are better than the ground for being clear of any trees or other buildings that might cause shade.)

Here is a solar panel connected in series with a light (Show students the circuit.) We will know the solar panel is creating electricity when the light bulb is illuminated. Can you see any light? No! So the solar panel must not be working in the classroom. But there is light in this room, so why not is the panel not working? As it turns out, this light is not intense enough to create electricity. Let's go outside to see how it really works! (Take the class outside for a short demonstration.)

Now we see the light bulb turns on! This direct sunlight is perfect for creating electricity! Notice how the tilt of the solar panel and the direction the panel faces affects the brightness of the light bulb. Which direction is best? (Answers: In the direction of direct sunlight, which is east in the morning, west in the afternoon, south at midday, and towards the south in general.) So if you were an architectural or building engineer, where would you place the solar panels? (Answer: On a south-facing sloped roof or overhang of a building.) Great!

Do you think all schools, houses, libraries and supermarkets in every part of the world have electricity? As it turns out, many countries suffer from what is sometimes called "energy poverty." When no electricity is available or when an electricity shortage exists in a city or town, we say this area suffers from energy poverty. This happens because a country cannot afford or does not have enough resources to create all of the electricity it needs. Sometimes these areas are without power for hours or days! Some places exist without any electricity at all! Can you imagine what it would be like to wake up in the morning and not have any electricity? What would school be like without electricity? Do you think these areas could benefit from using photovoltaic panels?

Now that you know how a solar panel works, how they can be applied to buildings? Let's start designing Solar City!

Procedure

Background

A photovoltaic cell converts radiant energy from the sun directly into electricity. Photovoltaic (PV) cells use materials called semi-conductors. When solar radiation falls on these materials, one side of a plate becomes positively charged while the other becomes negatively charged, creating a potential difference. These oppositely-charged plates create a flow of electrons, or electricity.

Three types of solar panels are available: monocrystalline silicon, polycrystalline silicon (or multicrystalline silicon) and amorphous silicon (or thin film). Monocrystalline panels are the most efficient (15-18%), followed by polycrystalline panels (12-14%), then thin film (5-6%). Monocrystalline panels use individual cells to make up a module, while a polycrystalline panel is solid with flake-like pieces of silicon pressed together. Thin film comes in flat, thin, flexible sheets.

Although solar arrays are a way to free a building from fossil fuel energy, some building and home owners do not like the appearance of roof-mounted systems (see Figure 2). Building integrated photovoltaics (BIPVs) use thin film technology to incorporate the PV paneling into building materials such as roofs, façades, awnings or covered walkways (see Figure 2), so they are hardly noticed.

Since the amount of electricity produced by PV cells is related to how much sunlight it receives, it is important to mount the panels on a surface that receives direct sunlight and is not shaded by trees or other buildings. An array has the greatest output when mounted on a roof that gets a lot of sun (in the northern hemisphere, this means a south-facing roof; see Figure 3). An array on a roof can be angled to take advantage of how the earth tilts during its orbit around the sun.

Tracking systems move some solar panels so they follow the sun across the sky during all times of the year, which produces the greatest amount of energy possible. However, these moving systems are typically not found on buildings.

Many benefits are associated with the use of PVs for building applications. Because of the increasing concern over greenhouse gas emissions and other environmental issues resulting from burning fossil fuels, electricity made from the sun provides a way to make electricity with no direct emissions. Using solar PVs are also beneficial in remote locations where power lines are difficult to access — because the solar energy is produced and used on site. Having a PV system also provides protection against blackouts in regions where energy production is unreliable or limited.

Some disadvantages to using solar PVs are worth considering. For example, solar panels are still expensive. For people in remote villages and those who suffer from "energy poverty," acquiring a PV system is almost economically impossible. In addition, since the amount of energy produced is dependent on the amount of sunshine available, the system output can fluctuate. The supply of energy must simultaneously meet the demand, and vice-versa, which is often not a reality. Connecting the building to the power grid can compensate by supplying extra electricity when needed or by allowing surplus energy to be fed into the grid. During nighttime hours, energy cannot be generated, so alternative energy sources must be available. Although batteries are available to store unused electricity, these devices are currently very expensive. In addition, some fossil fuel energy and carbon dioxide production is associated with the initial production and installation of PV systems. Some environmental concerns exist about the manufacture and disposal of heavy metals used in some of the current solar cell technologies. Engineers are working to improve upon these issues.

Engineering Design Process: As students conduct this activity, they are performing some of the classic steps of the engineering design process. As makes sense, relate their activity to the real-world. The basic steps include: 1) ask to identify the need and constraints, 2) research the problem, 3) imagine possible solutions, 4) plan by selecting a promising solution, 5) create a prototype, 6) test and evaluate the prototype, 7) improve and redesign as needed; and repeat the cycle, as necessary, to conclude with an acceptable engineering solution. Learn more about the design process at https://www.teachengineering.org/design/designprocess.

Before the Activity

• Gather materials and make copies of the Solar City Persuasive Letter Worksheet.
• Since this is an open-ended activity in which students do most of the designing, as they begin to build, students may think of other materials they need, such as Popsicle sticks, thin plastic sheets, pebbles, Astroturf.
• Pre-cut the foam core board to use as the walls and roofs of the buildings. Vary the sizes so that each group's building has different dimensions.
• Collect enough large pieces of cardboard (cut up large cardboard boxes) so each group has a plot of land on which to build. These can also be different shapes.
• Collect enough lights, buzzers and motors; make sure they are all working properly.

With the Students: Day 1

• Start the activity with the Introduction/Motivation, which includes a teacher demonstration on how the solar panels work: Attach a solar panel to a piece of foam core board and connect a light in series (and optionally, connect a voltmeter across the solar panel; this creates a parallel circuit). Notice that the light bulb in the circuit does not work indoors. The radiant energy from the lights in the room is not powerful enough to generate the required voltage. Take the class outside and show students that the light from the sun is more powerful; the solar panel can create enough electricity to power the light. Tilt the panel to show students how that changes the amount of electricity being generated by the panel. Also show them that the direction the panel faces has a large impact on the amount of electricity created. This can be seen by the intensity difference of the light bulb. Including a voltmeter in the circuit provides measurements of the voltage across the solar panel that further demonstrate these effects.
• After this demonstration, lead a class discussion about where the best place to attach the solar panel would be. (Answer: Attaching solar panels on a south-facing roof produces the most electricity. The optimal angle for a solar panel depends on latitude and climate, but usually falls between 20^o and 40^o from horizontal for most U.S. states. There are many online calculators that will give you an optimal angle for your specific location.)

With the Students: Day 2

1. Divide the class into teams of three or four students each.

2. Begin by having the students brainstorm Solar City building ideas with their groups. What type of building do they want to design and build, as a model? Suggest students make lists and/or draw pictures of their ideas (see finished examples in Figures 4 and 5).

3. Once a group has decided on the type of building they want to build, give them the pre-cut wall and roof pieces for a generic model building. From this, have them measure and draw to make a two-dimensional scaled drawing of the buildings. (Alternatively, for more advanced students, give them graph paper to make a two-dimensional scaled drawing of a building they design from scratch, and then have them cut their own wall and roof pieces from the foam core board.) Tell students what basic construction materials are available. Have them customize for the type of building they are designing. Remind students to address the following in their drawings:

• Placement of doors, windows, roof and solar panel.
• List of construction materials, including any additional ones for the teacher to get.
• What devices they plan to install (light, buzzer, motor), for example, use the motors to make fans, revolving doors or revolving signs. Make fan blades from note cards or thin plastic cut from plastic drink bottles.

With the Students: Day 3

1. Distribute the large pieces of cardboard (for the plots of land) to accommodate students' pre-cut model buildings.

2. Have students draw on the form core board pieces where they want doors and/or windows cut.

3. Have teachers and adults help students cut the board using Xacto^TM knives.

4. Once the doors and windows are cut, have adults help students use hot glue to adhere the building walls onto the cardboard bases, as well as other building design components. This takes a lot of hot glue so have plenty on hand! Tip: Assemble roof geometries, but wait to glue them to the walls until after the wiring is done.

5. Have students paint the exterior building walls and design their plot of land (for example, painting a parking lot, landscaping or lake; attaching pebbles or Astroturf).

6. Math component: Incorporate some math by having students who chose to use Astroturf measure their dimensions and calculate the area needed to cover. Or, have all teams measure and calculate the footprint area of their buildings, then use their drawing scales to convert from model to real-life dimensions.

With the Students: Day 4

1. Attach the solar panels to the roofs of the houses using looped pieces of duct tape. Attach the light, buzzer or motor, in a circuit using wires and alligator clamps (see Figure 5 and the diagram in Figure 1). Then, use hot glue to secure the roofs to the building walls.

2. Once the structures are complete, move them all outdoors into a completed Solar City (see Figure 6). Have each group make a presentation on their building, how they integrated their solar panel, what it is used for and at least one thing they learned during the activity.

With the Students: Day 5

• Lead a class discussion about the use of electricity. Ask the students how they use it at home, at school, or in other buildings in their city. What are the advantages and disadvantages of using photovoltaic panels on building?
• Have students write a persuasive letter to parents or the principal inviting them to tour the class's Solar City, as described in the post-activity assessment in the Assessment section. Have them incorporate their opinions about solar energy use.

Vocabulary/Definitions

architectural engineer: A type of engineer that designs the layout of a building.

blueprint: A detailed plan or technical drawing used to represent the dimensions of a building.

brainstorm: A team creativity activity with the purpose to generate a large number of potential solutions to a design challenge.

dimension: A measurement that describes the size and shape of an object (such as width, height, length).

electrical engineer : A type of engineer that designs the electrical systems of a building.

model: (noun) A representation of something for imitation, comparison or analysis, sometimes on a different scale.

solar array : A group of two or more photovoltaic panels.

solar panel: A device that converts radiant energy from the sun into electricity.

solar power: Electric power created from converting radiant energy from the sun into electricity (or electrical energy) that can be used to do work.

Assessment

Pre-Activity Assessment

Idea Pooling: As a class, make a list of the types of buildings found in a city. Then discuss how these buildings use electricity.

Concept Reflection/Writing: Have students list five devices that they use at home or school that require electricity, followed by a sentence describing hardships that would be faced without these devices.

Activity Embedded Assessment

Measuring & Drawing: Have students use rulers to create scaled drawings of their buildings. To incorporate some math, have students measure and calculate the area to be covered by Astroturf, or the footprint of their building. Then use their drawing scales to convert the areas from model to real-life dimensions. Additionally, have students measure the angle of their roof using a protractor. How does the angle relate to the optimal solar panel angle for their house?

Presentation: Have each group make a presentation to the rest of the class that describes their building, how they integrated the solar panel, what it is used for and at least one thing they learned during the class's creation of Solar City.

Post-Activity Assessment

Class Discussion: As a class, make lists on the board of the advantages and disadvantages of using photovoltaic panels on buildings.

Persuasive Writing: Have students write letters to their principal or parents inviting them to take a tour of Solar City, using the Solar City Persuasive Letter Worksheet. Have them include their opinion on the use of photovoltaic panels (why they think their own school should/should not use them) including some of the statements from the list of advantages/disadvantages. Suggest that they also incorporate ideas from their discussions about energy poverty and the use of electricity.

Investigating Questions

Where is the best place to attach a solar panel so that it creates the greatest amount of electricity possible? (Answer: The best place to put solar panels is on the roof of a house, away from trees or other tall buildings that may block the sunlight. To get the most sunlight possible, angle the solar panel using your understanding of how the earth orbits the sun and the location/latitude of your house.)

What happens when the solar panel is tilted at different angles? (Answer: The amount of electricity produced changes depending on the panel's relative position to the sun. When the entire solar panel is directly facing the sun, it gets the most energy possible and creates the most electricity. As you tilt the panel away from the sun, the amount of solar energy it receives decreases and the amount of electricity generated decreases as well.)

How can solar panels help people that do not have access to the electrical power grid? (Answer: With solar panels, people can generate electricity without needing to be connected to the electrical power grid. This can help people who live in remote areas and who live in countries where power outages are common.)

Safety Issues

Depending on the age and ability of the students, limit their use of hot glue and cutting blades. Use adult assistance and supervision as makes sense. Refer to the attached Foam Core Tips handout.

Troubleshooting Tips

If sunlight is unavailable, a 100-watt incandescent lamp provides enough radiation for each mini solar panel.

To remove the reusable electronic devices, carefully disassemble the roofs using sharp razor blades. Then, if students want to take the buildings home, you may need to re-glue the roofs to the building walls.

Activity Extensions

Roof Redesign for Rainwater Collection: After the electronics have been removed from the houses, have students design a new type of roof that can catch rainwater and store it in a cistern. The roofs must be designed in a way in which they still protect the building interior and its walls from getting wet. Construct roofs from foam core board or cardboard covered with aluminum foil, plastic wrap, wax paper or other waterproof materials that students find. Attach the foil, plastic wrap or wax paper materials with glue.

Mix in Some Math: To increase the amount of math used in the project, ask students to calculate: the area of their roof, the area on the roof covered with photovoltaic panels, and the proportion of the roof covered with photovoltaic panels. For an in-class activity, ask students to write these calculations on the board in a table and compare them to their classmates' answers.

Activity Scaling

• For lower grades, permit drawings to be less detailed and not to scale.
• For upper grades, have students create three-dimensional drawings of their buildings using a computer-aided drawing program.
• For upper grades, ask teams to calculate the area footprint of their buildings and use their drawing scales to calculate the real-life dimensions.
• For more advanced students, do not pre-cut the foam core board into pieces for generic building models. Instead, have students cut out the walls and roofs as specified by their own scaled drawings.

References

Copyright

Contributors

Supporting Program

Acknowledgements

The contents of this digital library curriculum were developed under grants from the Fund for the Improvement of Postsecondary Education (FIPSE), U.S. Department of Education, and National Science Foundation (GK-12 grant no 0338326). However, these contents do not necessarily represent the policies of the Department of Education or National Science Foundation, and you should not assume endorsement by the federal government.