# P3 Sustainable energy

## Energy sources

Primary energy source: Used in the form that it is found. They include:

• Fossil fuel: e.g. coal, oil and gas
• Nuclear fuel: e.g. uranium and plutanium
• Biofuels: From plants and animals
• Wind, waves and sunlight

Primary energy sources can transfer this energy to secondary energy sources e.g. electricity.

Many primary energy sources are used to make electrcity. Most is made from burning fossil fuels. Fossil fuels are a non renewable energy source.

The burning of fossil fuels is increasing the amount of carbon dioxide in the atmosphere.

The greenhouse effect is causing global warming, an increase in the temperature of the Earth.

Global warming is likely to result in climate change, leading to floods and storms.

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## Power

Power: The amount of energy transferred in one second (the rate of energy transfer).

A power of one watt (W) transfers one joule of energy in one second:

Energy transferred (J) = Power (W) X Time (S)

A joule is a small amount of energy. So domestic electricity measures energy transfer in Kilowatt-hours.

Kilo-watt = 1000 watts

A kilo-watt hour is the energy tranferred by a power of 1KW in an hour:

Energy transferred (KWh) = Power (KW) X Time (h)

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## Current

Current: The flow of electricity in a circuit, measured in Amperes.

Electric current in an appliance transfers energy to it from the power supply.The rate at which this is done is found using this equation:

Electric Power (W) = Current (A) X Voltage (V)

The power of an electrical device is the rate at which it transfers energy from the power supply. This is usually given as a rating.

For an electric device of a given power rating and an electric supply of a given voltage, the current the device needs to work is found using the equation:

Appliance current (A) = Appliance power (W) / Supply voltage (V)

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Current in a circuit results in both useful and unwanted energy transfers.

• Current in a component transfers electrical energy into other useful forms.
• Current in connecting wires wastefully transfers electrical energy into heat.

An electricity meter records the amount of electrical energy transferred into a house.

Electricity is metered in KWh or Units to keep the numbers small and manageable.

Electricity supplied to a component (Units) = Power (Kw) X Time (h)

Cost of electricity = Number of Units supplied X Cost per unit

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## Energy diagrams

Imformation about energy use can be displayed as:

• A pie chart to compare different uses of electricity
• A bar chart to show the amount of electricity used by different components.
• A line graph to show how the number of units consumed changes over time.

Sankey diagrams show the energy transfers in a component. The sum of the energy transfers out of a component equals the input energy. This shows that energy is conserved.

In a sankey diagram for a component:

• Energy flows in from the left. The amount of energy input is shown at the left of the arrow tail and is proportional to the thickness of the arrow tail.
• The sum of the widths of the new arrows at a split is equal to the width of the arrow before the split.
• Each energy output should be shown on the right with an arrow head. Usual energy transfers flow to the right. Wasteful energy transfers flow down.

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## Efficiency

The efficiency of a component tells you the proportion of electricity that it transfers into a useful form. It is found using the equation:

Efficiency x Energy usually transferred / Total energy supplied

Values for efficiency can range from 1.00 (100%) to 0.00 (0%).

Components with a high efficiency e.g. 95%, don't waste much electricity.

Components with a low efficiency e.g. 20%, waste a lot of electricity.

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## Using less electricity

Individually we can use less electricity by:

• Using high efficiancy, A-rated appliances
• Turning of components when they aren't needed
• Not boiling more water than is necessary and cooking food in a microwave oven

As a nation we could use less by:

• Using more efficient cars
• Living in houses with better insulation
• Building more efficient power stations and improving the output of old power stations

Global demand for energy and other resources will rise in the future as the population increases and the quality of life for many people improves.

All human activity has an impact on the environment, this can be reduced by:

• Recycling resources
• Generating electricity from renewable sources of energy
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## Generators

Moving a magnet near a circuit causes an electric current to flow in the circuit.

The current flows only when the magnetic field is changing- that is when the magnet is moving.

Power stations use this idea to produce mains electricity with generators.

A generator contains an electromagnet near a coil of wire. There is a voltage across the coil when the electromagnet spins.

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## Generators

Power stations use primary fuels, such as fossil, nuclear and biofuels to boil water into steam.

The steam passes through a turbine, makings its shaft spin round. The turbine shaft spins the magnet inside the generator.

Increasing the current drawn from the coil requires an increase in the rate of transfer of energy from the primary fuel i.e. an increase in the amount of primary fuel used each second.

Primary energy sources used to turn turbines directly include wind and water.

New developments in electricity generation must conform to government regulations.

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## How power stations work

The turbine spins the shaft of the generator to make electricity.

It is set spinning by steam, hot exhaust gas, wind and water.

Thermal power stations use coal, oil, gas and nuclear power to spin the turbine from high pressure steam.

• Coal-fired power stations do this by burning coal to transfer energy into water.
• Gas-fired power stations burn natural gas to make hot gas for a turbine: another turbine is spun by steam from water heated by hot gas.

Hydroelectric power stations use a jet of high pressure water at the base of a dam to spin a turbine..

Wind driven power stations use convection currents in the atmosphere caused by the heating effect of the sun on the land.

Coal burnt in furnace - Water heated to produce steam - Jet of steam spins a turbine - turbine spins the generator - Electricity produced by generator

Nuclear power stations make high pressure steam by:

• Putting fuel rods close together in the reactor so they heat up.
• Taking away the heat from high pressure water circulating around the rods.
• Using the high pressure water to boil low pressure water in a boiler.
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## Waste from power stations

Waste from nuclear power stations is radioactive and a serious health risk.

Nuclear waste must be carefully stored until it becomes safe.

Nuclear waste emits ionising radiation, which affects body cells.

An object is only irradiated when it is placed in the path of the radiation.

An object is contaminated when it gets mixed up with radioactive material.

Contamination can be a more serious hazard than irradiation because; it can result in a longer exposure to radiation; it is difficult to remove the radioactive material; it is difficult to stop the radioactive material spreading through the environment.

We often overestimate the risk from ionising radiation because: it cannot be seen or felt; its effects take a long time to develop; people worry about unfamiliar technology.

Statistics about death rates can be used to: compare risks from different technologies; decide which technologies need to be controlled; decide which risks are too small to worry about.

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## Renewable energy sources

A renewable energy source can be used over and over again.

Renewable energy sources that can spin turbines to make electrcity are :

1. Hydroelectric schemes
2. Wind turbines
3. Wave technology
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## Hydroelectric

• Provides large amounts of electricity
• They can be turned on and off quickly
• They can pump water back behind the dam to store energy.

• They flood large areas of land
• Rotting plants in the water produce methane gas
• They cost alot to build

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## Wind turbines

• They are inexpencive to make
• They need very little maintenance

• They need to be put in windy places
• They can only generate electricity when there is enough wind.

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## Renewable energy

Wave technology is still being developed.

The environmental impact of renewable energy sources can be reduced by careful planning, e.g. sitting wind turbines offshore, using hydroelectric dams to control rivers.

The financial impact of building these sources can be offset by the benefits of their use.

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## The national grid

Electricity is convenient because it can transfer energy over long distances for many uses.

National grid: A network of cables which carries electricity throughout the UK.

Power cables warm up because they wastefully transfer electrical energy to thermal energy.

Increasing the voltage of a power cable decreases the current. The national grid carries electricity at a very high voltage to reduce wasteful energy transfers in the cable.

Substations connected to the National grid  reduce the voltage to 230 V for our homes.

There are wasteful transfers of electricity as it is generated and transmitted to the consumer.

Wasteful energy transfers in transmission are much smaller than those in the power station.

The efficiency of electricity generation is the proportion of energy in the original fuel that is finally delivered to the customers as electricity.

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## Choosing energy sources

The energy sources that produce large amounts of electricity are: fossil fuels; nuclear power; hydroelectricity; biofuels.

The energy sources that rely on the right type of weather are: Wind, waves and solar.

Energy sources that do not produce greenhouse gases are nuclear power, wind, waves, solar ang geothermal.

Some energy sources have environmental impacts:

• Fossil fuels produce green house gases. Extracting them is dangerous and a pollution risk.
• Nuclear power produces radioactive waste.
• Wind farms can cause noise and visual pollution.
• Hydroelectric and tidal dams flood large areas.

Some energy sources will eventually run out: fossil fuels and nuclear power.

Some energy sources are free: hydroelectric, tidal, solar and geothermal.

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## Choosing energy sources

When choosing an energy source you should consider:

• The impact on the environment.
• The cost of building and running the power station.
• How much carbon dioxide and other waste it produces.
• The reliability of the energy source.
• The cost of the energy source.
• The efficiency of the transfer of energy to electricity.

The power output of a power station is measured in millions of watts or megawatts (MW).

A power station  which uses nuclear or fossil fuel has a steady output of about 1000 MW and a lifetime of about 40 years.

Wind farms have a steady output of 300 MW, varying with the weather, and a lifetime of about 20 years.

Hydroelectric power stations can have power outputs of about 10,000 MW with life times of about 80 years.

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## Future energy demand

In response to global warming many countries have agreed to limit their production of carbon dioxide. They do this by using less energy for transport, heating and electricity.

Vehicles, factories and power stations emit less carbon dioxide if they become more efficient.

Switching off appliances at home when they aren't needed reduces energy use.

Global energy use in the future is likely to rise because:

• There will be more poeple, especially in developing countries.
• Many of them want the high-energy lifetyles of industrialised countries.

To reduce global energy demand, people in industrialised countries have to use less.

Industrialised countries allready use cleaner, more efficient technology in their workplaces.

Many goods imported by industrialised countries are made in the developing world with polluting and inefficient technology.

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## Future energy demand

A secure energy supply in the future requires us to:

• generate enough energy to avoid power cuts.