Electrons on the Go: A lesson on solar energy
Essential Questions
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What are the properties of electricity?
What are the parts of an electrical circuit?
How can you use the sun to create electricity?
How does renewable energy compare to non-renewable energy?
Background
All matter is made up of atoms, and atoms are made up of smaller particles. The three main particles
making up an atom are the proton, the neutron and the electron. Electrons spin around the center, or
nucleus, of atoms, in the same way the moon spins around the earth. The nucleus is made up of
neutrons and protons.
Electrons contain a negative charge, protons a positive charge.
Neutrons are neutral – they have neither a positive nor a negative
charge. No matter how many particles an atom has, the number
of electrons usually needs to be the same as the number of
protons. If the numbers are the same, the atom is called
balanced, and it is very stable.
So, if an atom had six protons, it should also have six electrons.
An atom that loses electrons has more protons than electrons
and is positively charged. An atom that gains electrons has more
negative particles and is negatively charge. A "charged" atom is
called an "ion."
Electrons can be made to move from one atom to another. When those electrons move between the
atoms, a current of electricity is created. The electrons move from one atom to another in a "flow."
One electron is attached and another electron is lost. The
charge is passed from atom to atom when electricity is
"passed."
Scientists and engineers have learned many ways to move
electrons off of atoms. That means that when you add up the
electrons and protons, you would wind up with one more
proton instead of being balanced. Since all atoms want to be
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balanced, the atom that has been "unbalanced" will look for a free electron to fill the place of the
missing one. We say that this unbalanced atom has a "positive charge" (+) because it has too many
protons. Since it got kicked off, the free electron moves around waiting for an unbalanced atom to give
it a home. The free electron charge is negative, and has no proton to balance it out, so we say that it
has a "negative charge" (-).
When electrons move among the atoms of matter, a current of electricity is created. This is what
happens in a piece of wire. The electrons are passed from atom to atom, creating an electrical current
from one end to other. Electrons with a negative charge can't "jump" through the air to a positively
charged atom. They have to wait until there is a link or bridge between the negative area and the
positive area. We usually call this bridge a "circuit." When a bridge is created, the electrons begin
moving quickly. Depending on the resistance of the material making up the bridge, they try to get
across as fast as they can.
Solar Power
Using solar cells, we can use the sunlight to create electricity. Solar cells are
also called photovoltaic cells – or PV cells for
short. They were first developed in the 1950s for
use on U.S. space satellites. They are made of
silicon, a special type of melted sand. When
sunlight strikes the solar cell, electrons (red
circles) are knocked loose. They move toward
the treated front surface (dark blue color). An
electron imbalance is created between the front and back. When the two
surfaces are joined by a connector, like a wire, a current of electricity occurs
between the negative and positive sides.
These individual solar cells are arranged together in a PV module and the
modules are grouped together in an array.
The sunlight falling on the United States in one day contains more than twice the energy we consume
in an entire year. Assuming intermediate efficiency, solar photovoltaic (PV) modules covering 0.4% of
U.S. land area could supply all of the nation’s electricity – 1.2-6.2 acres per GWh per year. 1 While solar
PV modules produce no emissions during operation, they are not without environmental impact. Toxic
substances, e.g., cadmium and arsenic, are used in manufacturing PV technologies.
Fossil Fuels
U.S. sources of energy consumption are: petroleum (35%), natural gas (26%), coal (20%), and nuclear
electric power (8%). Renewable energy accounts for 9% of U.S. energy sources.2 Whenever we burn
fossil fuels such as coal, oil (petroleum), and natural gas—whether it's to drive our cars, use electricity,
or make products—we are producing carbon dioxide.
1
U.S. DOE, National Renewable Energy Lab (NREL) (2004) “PV FAQs- How much land will PV need to supply our electricity?”
2
U.S. Energy Information Administration, Annual Energy Review 2011, Tables 1.3, 2.1b-2.1f , 10.3, and 10.4.
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Carbon dioxide is a heat-trapping greenhouse gas and because people are adding these gases to the
atmosphere, the Earth is getting warmer. Warmer temperatures are causing other changes around the
world, such as melting glaciers and stronger storms. These changes are happening because the Earth's
air, water, and land are all linked to the climate. The Earth's climate has changed before, but this time
is different. People are causing these changes, which are bigger and happening faster than any climate
changes that modern society has ever seen before.3
Resources
Energy Quest’s The Energy Story http://energyquest.ca.gov/story/index.html
U.S. Energy Information Administration / Annual Energy Review 2011
http://www.eia.gov/totalenergy/data/annual/pdf/aer.pdf
Black Rock Solar’s Student and Teacher Resources http://www.blackrocksolar.org/education/educationresources/
Vocabulary
Atom - The atom is a basic unit of matter that consists of a dense central nucleus surrounded by a
cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons
and electrically neutral neutrons (except in the case of hydrogen-1, which is the only stable nuclide
with no neutrons). The electrons of an atom are bound to the nucleus by the electromagnetic force.
Battery - A battery is a device that can store electricity. Some are rechargeable, and some are not.
They store direct current (DC) electricity. The chemical reactions that occur in a battery are exothermic
(Heat is produced) reactions. For example, if you leave your laptop on for a long time, and then touch
the battery, it will be warm or hot.
Carbon Dioxide: A colorless, odorless, non-poisonous gas (CO2) that is a normal part of Earth’s
atmosphere. Carbon dioxide is a product of fossil-fuel combustion as well as other processes. It is
considered a greenhouse gas as it traps heat (infrared energy) radiated by the Earth into the
atmosphere and thereby contributes to the potential for global warming. The global warming potential
(GWP) of other greenhouse gases is measured in relation to that of carbon dioxide, which by
international scientific convention is assigned a value of one (1).
Climate Change: A term used to refer to all forms of climatic inconsistency, but especially to significant
change from one prevailing climatic condition to another. In some cases, “climate change” has been
used synonymously with the term “global warming”; scientists, however, tend to use the term in a
wider sense to include natural changes in climate as well as climatic cooling.
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A Students Guide to Global Climate Change, U.S. Environmental Protection Agency,
http://www.epa.gov/climatestudents/index.html
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Coal: A readily combustible black or brownish-black rock whose composition, including inherent
moisture, consists of more than 50 percent by weight and more than 70 percent by volume of
carbonaceous material. It is formed from plant remains that have been compacted, hardened,
chemically altered, and metamorphosed by heat and pressure over geologic time.
Electrical Circuit – An electrical circuit is a path which electrons from a voltage or current source flow.
Emissions: Anthropogenic releases of gases to the atmosphere. In the context of global climate
change, they consist of radiatively important greenhouse gases (e.g., the release of carbon dioxide
during fuel combustion).
Energy Source: Any substance or natural phenomenon that can be consumed or transformed to supply
heat or power. Examples include petroleum, coal, natural gas, nuclear, wood, waste, electricity, wind,
geothermal, sunlight (solar energy), water movement, and hydrogen in fuel cells.
Lead - In electronics, a lead is an electrical connection consisting of a length of wire or metal pad (SMD)
that comes from a device. Leads are used for physical support, to transfer power, to transmit
information, and sometimes as a heatsink.
Photon- Photons in many atomic models in physics are particles which transmit light. In other words,
light is carried over space by photons. Photon is an elementary particle.
Photo-voltaic - A solar cell or photovoltaic (PV) cell is a device that changes light energy into electricity.
Photovoltaics are best known as a method for making electricity by using solar cells to change energy
from the sun into a flow of electrons. The photovoltaic effect was first noticed by Alexandre-Edmond
Becquerel in 1839.
EXTEND
Following teacher instructions, work with solar kits to measure voltage from 1, 2, then 3 connected
solar modules. Use the electricity from the solar modules to power a water pump. Record
observations.
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