Download LESSON 13 Electricity from Photovoltaics: Solar Power

LESSON 13
Electricity from Photovoltaics: Solar Power
Overview
Students share what they know about solar power as an alternative
energy source, including solar as a renewable and green source. Students
explore the application of solar powered electricity to power everyday
items. Students test how increasing the amount of light hitting a solar
panel increases the amount of electricity it generates, and how the angle
of a solar panel to the light affects the amount of electricity it generates.
Student
Learning
Targets
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NGSS
MS-PS3-5.
Background
I can explain how the sun produces enormous amounts of energy
through fusion, and how we use radiant energy that travels through
space to the Earth.
I can give examples of how solar power is a clean, renewable energy
source that can help us reduce our dependence on fossil fuels.
I can use a photovoltaic (PV) cell technology to demonstrate how it
converts radiant energy from the sun into electricity.
I can explain how increasing the amount of light hitting a solar panel
increases the amount of electricity it generates and how the angle of
a solar panel to the light affects the amount of electricity it generates.
Construct, use, and present arguments to support the claim that when
the kinetic energy of an object changes, energy is transferred to or from
the object. [Clarification Statement: Examples of empirical evidence used
in arguments could include an inventory or other representation of the
energy before and after the transfer in the form of temperature changes
or motion of object.] [Assessment Boundary: Assessment does not include
calculations of energy.]
Solar energy is energy from the sun. The sun is a giant ball of hydrogen
and helium gas. The enormous heat and pressure in the interior of the
sun cause the nuclei of two hydrogen atoms to fuse, producing one
helium atom in a process called fusion.
During fusion, nuclear energy is converted into thermal (heat) and
radiant (light) energy. The radiant energy is emitted from the sun in all
directions and some of it reaches the earth. Radiant energy includes
visible light, x-rays, infrared rays, microwaves, gamma rays, and others.
LESSON 13 Electricity From Photovoltaics: Solar Power
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Solar energy warms the earth, powers the water cycle and causes plants
to grow.
In the case of solar produced electricity, radiant energy in the form of
photons from the sun strikes the electrons of atoms in photovoltaic (PV)
cells knocking them free of their atoms. Electrons move through the
electric circuit, creating a current of electricity. The word photovoltaic
comes from the root words “photo”, meaning light, and “voltaic”,
meaning electricity. Photovoltaic cells were first invented in 1954 at Bell
Labs for the space program to power satellites and space technology. On
earth, they are the most cost-effective and reliable source for many
remote applications, like highway signs, navigation buoys, and emergency
call boxes. As the technology advances new applications are being
developed to provide solar electricity for household items, homes and
businesses.
Photovoltaic cells are typically made from very thin slices of silicon, which
is a semiconducting material. A metal like copper, which is found in most
extension cords, is called a conductor because it can conduct electricity
very well. In contrast, a semiconductor is a metal that can only conduct
electricity some of the time. In the case of a photovoltaic cell made with
the semiconductor silicon - it can only conduct electricity when it is
exposed to light!
Now that we're clear about what photovoltaic means, in order to make
things a little simpler, from here on let's use the non-technical word
"solar" in place of photovoltaic.
"Solar" cells are generally small and are used in small things like
calculators and toy solar cars! When we electrically connect a number of
solar cells together they form what we call a solar panel. These are
typically framed panels of 50 to 100 solar cells. When we electrically
connect a number of solar panels, together they form what we call a
solar array. These collections of solar panels, which can be found on
many roofs in Oregon, can generate enough electricity for an entire
family.
Electric current, is the motion of electrons through a conductor. Current
is measured in Amps [A]. Current flows through conductors when
electrons are pushed or pulled by an electric field. Voltage is the
electrical potential difference associated with an electric field that causes
electrons to move, and thus current to flow. Voltage is measured in Volts
[V].
LESSON 13 Electricity From Photovoltaics: Solar Power
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For electrons to flow they must be able to follow a complete and
unbroken path called an electric circuit. A circuit is just an electricity term
for ‘loop’. An electric circuit can be formed by the interconnection of
conductors and electric components.
Direct current (DC) electricity flows from a negative (-) terminal to a
positive (+) terminal. Batteries and solar cells generate direct current and
always have a negative (-) and a positive (+) terminal. So if we could see
the flow of electricity from a battery that is powering a light bulb, we
would see it flowing from the negative terminal of the battery, through
the illuminating element of the light bulb, then back into the battery
through the positive terminal.
Solar cells turn light energy directly into electricity, but they cannot store
it. In order to use the electricity we need to store it in a battery or use it
to do work. One type of work it can do is to turn the rotors of an electric
motor. An electric motor converts electrical energy into mechanical
motion.
If we could see the flow of electricity from a solar panel that is powering
an electric motor, we would see it flowing from the negative terminal of
the solar panel, into one of the leads of the electric motor, into the
spooled wires of the motor that cause the magnets inside to turn the
shaft, then out through the other terminal and back into the solar panel
through its positive terminal. Because an electric motor does not have a
positive or negative terminal, we can change the direction that the motor
spins simply by switching the terminals to which we connect the solar
panels positive and negative wires.
Depending on how solar cells are connected together, the connections
can increase the voltage, the current, or both. If two solar cells are
connected in series, meaning the positive terminal of one is connected to
the negative terminal of the other, the resulting current will be equal, but
the voltage across both solar cells will be equal to their sum total voltage.
Alternatively, if two solar cells are connected in parallel, meaning the
positive terminals of both are connected together and the negative
terminals of both are connected together, the resulting voltage across
both panels will be equal, but the current that flows in and out of the
junction of the terminals will be equal to the sum total current flowing
through both solar cells. Simply put, by connecting solar panels in
different ways, we can increase the amount of work that they can do.
LESSON 13 Electricity From Photovoltaics: Solar Power
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Vocabulary
nuclear energy, fusion, photovoltaic cells, solar panel, solar array, Amps,
photons, voltage
Resources
Solar Oregon – provides workshops to educate about options for
instillation of solar panels; may have resources for speakers in the
classroom: http://solaroregon.org
How Stuff Works – article and video on how solar panels work:
http://science.howstuffworks.com/environmental/energy/solar-cell.htm
Solatron Technologies – learn about wiring solar panels and batteries:
http://partsonsale.com/learnwiring.htm
Materials
For the class
Solar powered items: calculators, yard lights, and flashlights (add
others solar powered items if you want). Note: be sure to leave in
the sun/light prior to class to power up the solar batteries in the
items.
4 Solar World laminated photovoltaic cells
Overhead 1: Science Investigation Report: Solar Powered Fans
Overhead 2: Fusion
Overhead 3: Solar Cells
Overhead 4: Solar Power
White board or newsprint paper
Markers
For each team of 2 to 4 students
Solar panel
Small fans (blade, motor with wires attached)
Table lamps if natural sunlight isn’t available
Handout: Science Investigation Report: Solar Powered Fans
For each student
Science notebooks
Pencil
Preparation
Collect a number of solar powered devices such as flashlights, radios,
calculators, and others to share with students. Prepare team materials.
Invite a speaker from the solar energy industry or from Solar Oregon. You
may want to ask the speaker to bring an actual solar panel (small
version).
LESSON 13 Electricity From Photovoltaics: Solar Power
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Time
30 minutes for activity and 30 minutes for the speaker
Procedure
1. Divide students into groups of 4, have then discuss these questions:
“What do you know about solar energy and how it is used?“ “What
have you heard about the benefits and problems using solar energy?”
“What questions or what do you what to learn about solar energy?”
Then Think-Pair-Share for 5 minutes sharing with as many students in
the other groups as possible.
2. Explain to students that the sun is our greatest energy source. Tell
students with aide of Overheads 2 and 3: “Every day the sun sends
out an enormous amount of energy. It sends out more energy in one
second than the world has used since time began! This energy comes
from the sun itself. Like most stars, the sun is a big ball of gas made
up mostly of hydrogen and helium atoms. The sun makes energy in its
inner core in a process called nuclear fusion.”
“During nuclear fusion, the high pressure and temperature in the
sun’s core cause hydrogen (H) atoms to come apart. Four hydrogen
nuclei (the centers of atoms made up of neutrons and protons)
combine or fuse, to form one helium atom. During the fusion process,
radiant or light energy is produced.” Use Overhead 2 as a visual to
help with explanation and direct students to copy into journal.
“Every day enough energy from the sun hits the United States to
supply the nation’s energy needs for one and a half years. About 15
percent of the radiant energy that reaches the earth is reflected back
into space. Another 30 percent is used to evaporate water, driving
the earth’s water cycle. Radiant energy is also absorbed by plants to
produce food through photosynthesis, and some is used to heat the
land and oceans.”
“Because radiant energy from the sun is scattered over such a large
area it is difficult to capture a concentrated amount of it to generate
electricity. However, engineers are figuring out new technology every
day to help us do this. One kind of technology used to capture radiant
energy from the sun and convert it to electricity is the Photovoltaic
Cell or Solar Cell. We often call them solar panels.” Use Overhead 3 as
a visual.
LESSON 13 Electricity From Photovoltaics: Solar Power
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“The small dark square that powered the fan is called a ‘Photovoltaic
Module’ or PV Module for short. Photo is a Greek word for light, and
voltaic is from the word volt which is a measurement of electricity
and was named after Alexander Volta, a pioneer in the study of
electricity. A photovoltaic cell converts sunlight particles called
‘Photons’ into electricity. If you put a lot of photovoltaic cells
together, you get a solar module or solar panel. How many of you
have seen a solar panel before?”
“Photovoltaic cells convert sunlight to electricity without any moving
parts, noise, pollution, radiation, or maintenance! This makes them a
clean and renewable energy source.”
3. Using Overhead 1 (Science Investigation Report: Solar Powered Fans)
ask the students to form hypothesis (make a prediction) to Questions
A, B, and C in the form of a statement. Explain that a hypothesis is
their prediction as to what they think is the answer to the question.
4. Show the students the materials you will give to each team to
conduct the science experiment, and write them on the board.
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Solar panel
Small fan (blade, motor with wires attached)
Sunlight or table lamp
Handout: “Science Investigation Report: Solar Powered Fans”
Note: if it is a cloudy day or no sun is available from windows,
explain to students that they can use a table lamp as the sun.
5. Pass out a laminated PV cell to each student team.
6. Have students study the laminated PV cell. Explain that each PV cell is
made from a mineral called silicon. Share with them that silicon is the
most abundant mineral on the earth and is a large component of sand
(show photos of silicon sand & rock). Tell students that “silicon is
purified and made into very thin wafers to form the solar/PV cells.”
If a guest speaker is available you may want him/her to explain how
solar cells & panels are manufactured. If not, use graphics and photos
from Solar World website or those provided in the solar world
booklet that comes with the kit.
LESSON 13 Electricity From Photovoltaics: Solar Power
Nagele, et al. 2016
page 144
7. Explain that “when photons, which are tiny particles of light hit the
silicon it excites the atoms. In all the excitement, the electrons of the
silicon atoms become free and begin moving.” Use Overhead 4 of 4.
8. Explain that “if we make a closed circuit with wires connecting the
silicon wafers to a “load” and then back again to the silicon wafer,
electrons will follow the path (circuit). So long as the sun is hitting the
solar panel, its photons continue to excite the atoms freeing the
electrons and making them flow along the circuit. Remind them that
flowing electrons are energy in the form of electricity”. Add wires,
load, and moving electrons to diagram on board. Direct students to
copy into science journal.
LESSON 13 Electricity From Photovoltaics: Solar Power
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9. Tell students they will use energy from the sun to power the fan
motor and make the fan turn. Ask a student volunteer to
demonstrate how this works with the materials.
10. Pass out or have a team member collect the supplies: small fan with
motor, solar cell, wire connectors and sun (or table lamp if no strong
sunlight available).
11. Don’t tell them what to do, but ask them to test their hypothesis for
Questions A, B, and C on the “Science Investigation Report” by seeing
if they can use the materials provided to use the energy from the sun
to turn the fan. Students will need to go outside to do this. Direct the
students to record their observations in the table for each hypothesis
they test.
a. If time is available, have students go back outside and try tilting
the solar panel at different angles to the sun. Have one team
member hold the fan and note how fast it spins while the other
team member manipulates the panel. They can record their
results for Question D. Another option is for the students to come
up with their own question to test.
2009-2010 Science of Energy
LESSON 13 Electricity From Photovoltaics: Solar Power
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11. Have students write down a sentence or two explaining why they
observed/saw what they did when testing each hypothesis, under
“Conclusion (Analysis of Results)” on their handout (Overhead 1-2).
Ask a few student teams to share what they observed and why.
12. Ask students what they learned from this experiment? Have the
students complete the last question of the conclusion, explaining how
they think the sun powered their fans.
13. Ask students how many of them had a hypothesis that was correct?
Explain that in science, it doesn’t matter if your hypothesis is correct
or not. If it is not correct, if often generates more questions for
scientists to conduct experiments. We learn from experiments
regardless if our hypothesis is correct or not. Science is all about
learning and sharing that what you learn.
Optional Demonstration: Solar Powered Water Pump
Ask for volunteer students to demonstrate the solar powered water
pump.
a. Select 3 students to help with the demonstration.
b. Tell students that the engineering challenge/problem is to find a
solution using solar energy to move the water from the beaker to
the cylinder.
c. Show all students the components available to build a solarpowered water pump (cylinder, colored water in beaker, pump
motor, solar panel, wires, tube, and sun or lamp). Before class add
food coloring to the water to make it easier to see. If
demonstration is done in-doors use shallow container to catch
over-flow of water in cylinder.
d. Ask the class to raise their hands to give instructions, step-by-step
to the volunteers to design/assemble the water pump. Have
volunteers take turns caring out instructions.
e. Facilitate students’ reasoning for design steps.
f. Once, the class has designed and assemble a system they think
will work to transport (pump) the water from the beaker to the
cylinder, have the volunteers test the design.
LESSON 13 Electricity From Photovoltaics: Solar Power
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g. Repeat the above steps, until you have a design that works. See
design in photo.
h. Have students observe or measure the height of the water in the
cylinder using one solar panel, and record it.
i.
Ask students to re-design their solar-powered pump to increase
the amount of water in the cylinder. Let students know they may
use additional components.
j.
Take suggestions from the students. Facilitate class discussion
asking students to reflect on what they learned previous about
series and parallel circuits. Also have students reflect on how
homes and business install solar panels to get sufficient solar
power (in an array of solar panels).
k. Ask for new volunteers (those students with the most probably
design, or have the other students’ vote whose design they think
most likely to succeed, and select that student(s) to reassemble
the pump components and test their design.
(Solution: connect 3-solar panels in an array with series circuit. By
connecting multiple power sources (i.e. solar panels) in a series
circuit we can increase the amount of power/voltage (total
LESSON 13 Electricity From Photovoltaics: Solar Power
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voltage = sum of the voltage from all solar panels) flowing
through the load (i.e. water pump). See photo below.
Assessment
Collect and score Science Investigation Report.
Extra
Resources
Energy 101: Solar PV 2:01min
Enough energy from the sun hits the earth every hour to power the
planet for a year—and solar photovoltaic (PV) systems are a clean, costeffective way to harness that power for homes and businesses. PV
systems generate power without pollution as they convert the sun's
energy into electricity, and recent advancements have greatly improved
their efficiency and electrical output. This video shows the basics of how
a PV panel converts light radiated from the sun into usable power,
whether on the electric grid or off—and without emissions or the use of
fossil fuels.
http://www1.eere.energy.gov/multimedia/video_energy101_pv.html
Solar webpage with photos and
information https://www.eeremultimedia.energy.
LESSON 13 Electricity From Photovoltaics: Solar Power
Nagele, et al. 2016
page 149