Science

Generating electricity

Electricity is a very convenient form of energy that can be generated using different energy resources. Some of these resources are renewable and some are non-renewable. Each resource has advantages and disadvantages.

Fossil fuels

Fossil fuels for power stations

Chemical energy stored in coal. This energy is transferred as heat and this energy is stored in water as steam. The energy in steam is transferred to movement in a turbine and to electrical energy in the turbine.

Energy transfer for the generation of electricity from a fossil fuel

The fossil fuels are coal, oil and natural gas. They are fuels because they release heat energy when they are burned. They are fossil fuels because they were formed from the remains of living organisms millions of years ago.

About three-quarters of the electricity generated in the UK comes from power stations fuelled by fossil fuels. To the right is an energy transfer diagram for the generation of electricity from a fossil fuel such as coal.

Disadvantages of using fossil fuels

Fossil fuels are non-renewable energy resources. Their supply is limited and they will eventually run out. Fossil fuels do not renew themselves, while fuels such as wood can be renewed endlessly.

Fossil fuels release carbon dioxide when they burn, which adds to the greenhouse effect and increases global warming. Of the three fossil fuels, for a given amount of energy released, coal produces the most carbon dioxide and natural gas produces the least.

Coal and oil release sulfur dioxide gas when they burn, which causes breathing problems for living creatures and contributes to acid rain.

Check Fuels from crude oil to make sure you understand these points.

Nuclear fuels

You should be able to outline how electricity is generated using nuclear fuels.

Uranium and plutonium

The main nuclear fuels are uranium and plutonium. These are radioactive metals. Nuclear fuels are not burnt to release energy. Instead, the fuels are involved in nuclear reactions in the nuclear reactor, which leads to heat being released.

The rest of the process of generating electricity is then identical to the process using fossil fuelsfossil fuels: Fuels such as coal, oil and natural gas, made from the remains of ancient plants and animals.. The heat energy is used to boil water. The kinetic energy in the expanding steam spins turbines, which then drive generators to produce electricity.

Advantages

Unlike fossil fuels, nuclear fuelsnuclear fuels: Radioactive materials, usually uranium or plutonium, used in nuclear reactors. do not produce carbon dioxide or sulfur dioxide.

Disadvantages

Watch

You may wish to view this BBC News item from 2006 about the arguments for and against nuclear power.

Like fossil fuels, nuclear fuels are non-renewable energy resources. If there is an accident, large amounts of radioactive material could be released into the environment. In addition, nuclear waste remains radioactive and is hazardous to health for thousands of years. It must be stored safely.

Make sure that you understand radiation by visiting Radioactive substances.

Wind energy

You should be able to outline how electricity is generated using wind energy.

Big convection currents

The wind is produced as a result of giant convection [convection: The transfer of heat energy through a moving liquid or gas. ] currents in the Earth's atmosphere, which are driven by heat energy from the sun. This means that the kinetic energy in wind is a renewable energy resource: as long as the sun exists, the wind will too.

Wind turbines

A wind turbine

Wind turbines have huge blades mounted on a tall tower. The blades are connected to a nacellenacelle: The part at the top of the tower of a wind turbine. The blades of the turbine are joined to the nacelle, which contains gears linked to a generator. or housing that contains gears linked to a generatorgenerator: An 123 electromagnetic device that produces electricity when it is turned.. As the wind blows, it transfers some of its kinetic energy to the blades, which turn and drive the generator. Several wind turbines may be grouped together in windy locations to form wind farms.

Advantages

Wind is a renewable energy resource and there are no fuel costs. No harmful polluting gases are produced.

Disadvantages

Watch

You may wish to view this BBC News item from 2006 about the arguments for and against wind power.

Wind farms are noisy and may spoil the view for people living near them. The amount of electricity generated depends on the strength of the wind. If there is no wind, there is no electricity.

Check that you understand convection currents by visiting Heat transfer and efficiency.

Water energy

You should be able to outline how electricity is generated using water.

Wave energy

The water in the sea rises and falls because of waves on the surface. Wave machines use the kinetic energy in this movement to drive electricity generators.

Tidal barrage

Huge amounts of water move in and out of river mouths each day because of the tides. A tidal barrage is a barrier built over a river estuary to make use of the kinetic energy in the moving water. The barrage contains electricity generators, which are driven by the water rushing through tubes in the barrage.

Hydroelectric power (HEP)

Like tidal barrages, hydroelectric power stations use the kinetic energy in moving water. But the water comes from behind a dam built across a river valley. The water high up behind the dam contains gravitational potential energygravitational potential energy: The energy stored by an object lifted up against the force of gravity.. This is transferred to kinetic energy as the water rushes down through tubes inside the dam. The moving water drives electrical generators, which may be built inside the dam.

Advantages

Water power in its various forms is a renewable energy resource and there are no fuel costs. No harmful polluting gases are produced. Tidal barrages and hydroelectric power stations are very reliable and can be turned on quickly.

Disadvantages

It has been difficult to scale up the designs for wave machines to produce large amounts of electricity. Tidal barrages destroy the habitat of estuary species, including wading birds. Hydroelectricity dams flood farmland and push people from their homes. The rotting vegetation underwater releases methane, which is a greenhouse gas.

Geothermal energy

You should be able to outline how electricity is generated from geothermal energy.

Volcanic areas

Several types of rock contain radioactive substances such as uranium. Radioactive decay of these substances releases heat energy, which warms up the rocks. In volcanic areas, the rocks may heat water so that it rises to the surface naturally as hot water and steam. Here the steam can be used to drive turbinesturbines: Revolving machinery with many blades turned by wind, water or steam. Turbines in a power station turn the generators. and electricity generators. This type of geothermal power station exists in places such as Iceland, California and Italy.

Hot rocks

In some places, the rocks are hot, but no hot water or steam rises to the surface. In this situation, deep wells can be drilled down to the hot rocks and cold water pumped down. The water runs through fractures in the rocks and is heated up. It returns to the surface as hot water and steam, where its energy can be used to drive turbines and electricity generators. The diagram below shows how this works.

cold water is pumped down and steam and water come up

How a generating station creates energy

Advantages

Geothermal energy is a renewable energy resource and there are no fuel costs. No harmful polluting gases are produced.

Disadvantages

Most parts of the world do not have suitable areas where geothermal energy can be exploited.

Solar energy

You should be able to outline how solar energy is used to generate electricity and to produce hot water.

Solar cells

a motorist buying a ticket from a solar-powered ticket machine

Solar-powered ticket machine

Solar cells are devices that convert light energy directly into electrical energy. You may have seen small solar cells in calculators. Larger arrays of solar cells are used to power road signs in remote areas, and even larger arrays are used to power satellites in orbit around Earth.

Solar panels

Solar panels do not generate electricity, but rather they heat up water. They are often located on the roofs of buildings where they can receive heat energy from the sun. The diagram outlines how they work.

Cold water is pumped up to the solar panel, there it heats up and is transferred to a storage tank.

A pump pushes cold water from the storage tank through pipes in the solar panel. The water is heated by heat energy from the sun and returns to the tank. In some systems, a conventional boiler may be used to increase the temperature of the water.

cold water is pumped up to the solar panel, there it heats up and is transferred to a storage tank

Solar panel

Advantages

Solar energy is a renewable energy resource and there are no fuel costs. No harmful polluting gases are produced.

Disadvantages

  • Solar cells are expensive and inefficient, so the cost of their electricity is high.
  • Solar panels may only produce very hot water in very sunny climates, and in cooler areas may need to be supplemented with a conventional boiler.
  • Although warm water can be produced even on cloudy days, neither solar cells nor solar panels work at night.

Resources compared

You should be able to compare and contrast the different energy resources used to produce electricity. You may be given information in the examination for you to discuss.

Power stations

Power stations fuelled by fossil fuels or nuclear fuels are reliable sources of energy. This means they can provide power whenever it is needed. However, their start-up times vary according to the type of fuel used.

This list shows the type of fuel in order of start of time going from short to long.

  1. gas-fired station (shortest start-up time)
  2. oil-fired station
  3. coal-fired station
  4. nuclear power station (longest start-up time)

Nuclear power stations and coal-fired power stations usually provide 'base load' electricity - they are run all the time because they take the longest time to start up. Oil-fired and gas-fired power stations are often used to provide extra electricity at peak times, because they take the least time to start up.

The fuel for nuclear power stations is relatively cheap, but the power stations themselves are expensive to build. It is also very expensive to dismantle old nuclear power stations and to store their radioactive waste, which is a dangerous health hazard.

Renewable resources

Renewable resources of fuel do not cost anything, but the equipment used to generate the power may be expensive to build. Certain resources are reliable, including tidal barrages and hydroelectric power. Others are less reliable, including wind and solar energy.

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