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 suchas electrons is called current, and this electrical current is what powers household appliances.

Electric Current =

Charge PassingThrough A Given Area------------------------------- 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.

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.

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!

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 RefineryPasadena - 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

Oil Drilling PlatformCook Inlet, Alaska

-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

Water generated - HydroelectricShasta Dam In California

-Conversion from potential energy of water to electric energy is at 80 – 90% efficiency

-Hydroelectric projects in the United States have rated capacities from950 – 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.

- 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.

Nuclear PowerDiablo Canyon - California

-Plant electrical output 1220 MW-Plant efficiency 34%

-There are 109 power reactors in the United States

-Produce 22% of nation’s electricity

- In France 79% of electricity comes from nuclear reactors

-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?

Wind turbines

Photo

Voltaic

panels

Water wheelsThese are some of the

ways we can get ‘renewable’ energy. This means that the source of the energy will not run out.

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?

Wind generated

Kilronan Wind Farm In Ireland

-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.

-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