Download How do we get our electricity? - Mr. Stewart`s Physical Science

Where does our electricity come
from?
• Electricity is made or generated in different ways.
• Most of our electricity is made using fossil fuels.
gas
oil
coal
Electricity by definition is electric current that is used as a power source!
This electric current is generated in a power plant, and then sent out
over a power grid to your homes, and ultimately to your power outlets.
The movement of charges such
as electrons is called current, and
this electrical current is what
powers household appliances.
Charge Passing
Through A Given Area
Electric Current = ------------------------------Time
An easier way to think of electric current is to picture cars going
through a Turnpike or Parkway Toll.
The cars could represent
electrons or charge, and the
toll booth could represent the
cross sectional area of the
wire at a certain point.
If you counted the number of cars or electrons, that passed through
the toll booth or a certain cross sectional area of the wire, and divided
that number by the time it took for those cars or charges to pass,
you would get the current!
Electric current generation - whether
from fossil fuels, nuclear, renewable
fuels, or other sources is usually
based on the:
In September of 1831, Michael Faraday
made the discovery of Electromagnetic Induction.
Faraday attached two wires to a disc and
rotated the disc between the opposing
poles of a horseshoe magnet creating
an electric current.
If you place a magnet and a conductor (copper wire), in a room together
there will be no electric current generated.
This is because motion, from our equation for electricity, is missing!
An electric current is not generated unless the magnetic field is moving
relative to the copper wire, or the copper wire is moving relative to the
magnetic field.
So simple electric generators found in power plants contain, magnets
and copper wire that when put into motion relative to one another
create the electric current that is sent out to homes.
The major problem in
electricity generation
Is where does the
Motion come from
that keeps the
copper wire and
magnets moving
relative to one
another.
In this case, wind power applies a force to the blades that turns them.
The spinning blades, spin an armature that turns the copper wire
relative to the magnetic field. As long as the blades spin, electricity
will be generated!
- Alternating Current of 60 Hz produced by generator
- Resistance losses are smallest at high voltages and low currents
At home, electric current
that was generated by
generators in the power
plant is used to power
electric appliances.
The electric current,
running through the
copper wire causes
the armature to spin
which is how most
motors generate
motion.
Why do you think these are called
fossil fuels?
Millions of years ago, before the dinosaurs roamed the earth,
lots of plants grew strong from the energy of the sun. Then they
died and became buried in thick layers beneath lots of mud and
soil. The remains of animals became buried as well. Over the
millions of years, the mud and soil changed to rock and the
layers above the rotting plants and animal remains grew heavier
and heavier and thicker and thicker.
All these organic remains (dead plants and animals) got
squashed and a mixture of pressure and heat turned some
organic material into coal, some into oil and some into natural
gas. People found out that if they dug down deep enough and
got these fossil fuels out, they could burn them to get energy.
So how do we get electricity from
fossil fuels?
• Most electricity is produced by burning fossil fuels in
power stations.
• Coal, oil and natural gas are burned in furnaces to heat
up water. The boiling water makes steam which pushes
the gigantic blades of a turbine to produce electricity.
Power stations give off lots of steam
which you can see.
Power stations give off pollution,
which you can’t see.
When we burn fossil fuels we put
lots of carbon dioxide into the air.
This is a cause of Global Warming.
2. Burn biomass,
fossil fuels, or
natural gas to
release the stored
chemical energy is
used to heat water
to produce steam
and transform it into
heat. The steam is
used to turn a
turbine that is
connected to an
electrical generator.
3. Burn natural gas
and use the hot
gases that are
released to turn a
turbine that is
connected to an
electrical
generator.
It takes millions of years to make
fossil fuels
• What will happen when they run out?
• Because fossil fuels won’t last for ever we call
them non – renewable. This means they can’t
be renewed.
• Look at a piece of coal – think how long it took it
to be formed. What is it like?
Fossil Fuels – Oil Refinery
Pasadena - Texas
Standard Large Power Plants Provide 1 Giga-watt of electric power
and releases 2 Giga-watts of thermal power as waste heat. An
efficiency averaging around 30%.
-9000 tons of coal a day
-40,000 barrels a day or one tanker a week of oil
-generates about 5.3 x 10^9 kwh/year
-powers a city of a million people
-total world production in 2009 of
petroleum is 84,000,000 barrels / day
-an average well in the US produces
only 11 barrels / day
-In Saudi Arabia an average well
produces 9600 barrels /day
Oil Drilling Platform
Cook Inlet, Alaska
-Conversion from potential energy of
water to electric energy is at 80 – 90%
efficiency
-Hydroelectric projects in the United
States have rated capacities from
950 – 6480 MW
-The use of Water Power is much
greater in some other countries.
Norway obtains 99% of its electricity
from water power. Nepal, Brazil, and
New Zealand are close seconds.
Water generated - Hydroelectric
Shasta Dam In California
- Hydroelectricity has dropped from producing 30 % to 10% of US electricity
- Large fluctuations in output are mainly due to variable rainfall totals
-About 50% of the United States potential for hydroelectric energy has been
tapped. However, further advances are unlikely.
-The Wild and Scenic River Act and the Endangered Species Act have
inhibited development of some sites
-Silt collection in hydroelectric Dam storage volumes over time causes
maintenance issues, as well as environmental concerns
-The loss of free flowing streams and land due to flooding behind the dam
disturbs the life of species: eg – Salmon
- Possibility of dam failure
Some countries use nuclear power
Nuclear
power
plant
Nuclear power plants use a
material called uranium to produce
electricity.
Nuclear power plants make
electricity by splitting tiny atoms of
the uranium to release energy.
Nuclear plants also have waste
materials that are very dangerous
and have to be looked after safely
for thousands of years.
4. Split uranium
atoms to release
nuclear energy
that is used to
heat water to
produce steam to
turn a turbine that
is connected to an
electrical
generator.
-There are 109 power reactors in the United States
-Produce 22% of nation’s electricity
- In France 79% of electricity comes from nuclear reactors
Nuclear Power
-Plant electrical output 1220 MW
-Plant efficiency 34%
Diablo Canyon - California
-In normal operations a nuclear reactor produces some environmental
emissions. E.g.: escape of radioactive fission products through cracks and
diffusion, radioactive H3 in small amounts in discharged water
-Core meltdown is possible, but unlikely due to negative feedback and
shutdown systems
-Even after shutdown there is 7% of normal power generation still in the
reactor fuel rods. This may be sufficient enough to melt core and destroy
the reactor, if cooling water is not supplied
-A study entitled “Severe Accident Risks: An Assessment for Five US
Nuclear Power Plants” conducted by NRC in 1990, shows that for all the
109 reactors now operating in the United States over a 30 year lifetime
there is about a 1% chance of a large release due to internal events.
How else can we produce
electricity?
Photo
Wind
turbines
Voltaic
panels
These are some of the
ways we can get
‘renewable’ energy.
This means that the
source of the energy
will not run out.
Water
wheels
How is the
electricity
being
generated?
5. Use a
photovoltaic cell
to convert the
suns energy into
electricity.
1. Use Mechanical
energy, wind, or
moving water to
turn a turbine
that is connected
to an electrical
generator.
Where does the motion needed to keep the copper wire moving relative
to the magnetic field come from?
-attains between 50 – 70% efficiency
- one windmill’s average energy
output ranges from 11.4 W/m^2 –
57 W/m^2 depending on how windy
-wind farms tend to generate between
50 and 600 Kw
- California currently produces ¾
of all the wind generated electricity
in the world.
Wind generated
Kilronan Wind Farm In Ireland
-North Dakota with 20 times the wind potential of California has not
erected a single wind turbine
-Wind variability must be overcome by system design
- Basic energy Storage
- Differences in pressure gradients around wind turbines affect birds
-Noise from the turbines affects people and animals
-Eyesore, the appearance of mile after mile of wind machines with
transmission lines is of concern to the public
-Solar Power – uses the sun energy to either boil water or directly converts
solar energy to electrical energy
-Ocean Thermal Energy Conversion – uses temperature differences
between different depths of ocean water to drive a heat engine. Working
fluid is ammonia which is gas at room temperature.
-Biomass Energy: Municipal Solid Waste – burning wastes to drive heat
engines
-Geothermal Energy – based on naturally occurring heat in the Earth in the
Earth due to radioactive decay
-Tidal Energy – uses the gravitational pull of the moon on our oceans to
drive turbines
Proportion of World’s energy
consumption - 1997
Proportion of the world’s
Electricity generation - 1997
Renewables
Non-renewables
Electricity
?
• Electricity is all about electrons, which are the
fundamental cause of electricity
• Static Electricity - involves electrons that are
moved from one place to another, usually by
rubbing or brushing
• Current Electricity - involves the flow of electrons
in a conductor
On the Move
• Electrons in the outer rings or shells of atoms are
bound more loosely to the nucleus
• Such electrons tend to break free from the nucleus
and wander around amongst other nearby atoms
• Such electrons are called free electrons
Current =
Conduction
Such movement of these free electrons
creates an electric current
 Materials with large numbers of free
electrons are called electrical conductors. They
conduct electrical current.
 Movement of the electrons physically from
one place to another is slow. Transfer of the
energy from one electron to another happens
fast.

Conductors and
Insulators
• In conductors, electric charges are free to move
through the material. In insulators, they are not.
• In conductors:
– The charge carriers are called free electrons
– Only negative charges are free to move
– When isolated atoms are combined to form a
metal, outer electrons of the atoms do not
remain attached to individual atoms but become
free to move throughout the volume of the
material
Other Types of
Conductors
• Electrolytes
– Both negative and positive charges can move
• Semiconductors
– In-between conductors and insulators in their
ability to conduct electricity
– Conductivity can be greatly enhanced by adding
small amounts of other elements
– Requires quantum physics to truly understand how
they work
Simple
Circuits
• Don’t let the name fool you
• Bottom line: For electric current to
flow, there has to be a complete
pathway for it…a complete circuit.
Closed and Open
Circuits
Closed Circuit - an unbroken path of
conductors through which electric current flows

 Open Circuit - a circuit with a break in the
conductive path, so no current flows
Series
Circuits
 An electrical circuit with only one path
for the electrical current to follow
Parallel
Circuits
 An electrical circuit that provides more than
one path for the electrical current to follow.
Static Electricity
Who hasn’t rubbed a balloon
on their hair and stuck it to
the wall?
 Buildup of charge (static, not moving)
in one place.
 Charge can be either positive or negative