P1.4 Methods we use to generate electricity

Various energy sources can be used to generate the electricity we need. We must carefully consider the advantages and disadvantages of using each energy source before deciding which energy source(s) it would be best to use in any particular situation. Electricity is distributed via the National Grid. Candidates should use their skills, knowledge and understanding to: ■ evaluate different methods of generating electricity ■ evaluate ways of matching supply with demand, either by increasing supply or decreasing demand ■ compare the advantages and disadvantages of overhead power lines and underground cables. Additional guidance: Candidates should be able to evaluate different methods of generating electricity given data including start-up times, costs of electricity generation and the total cost of generating electricity, when factors such as building and decommissioning are taken into account. The reliability of different methods should also be understood. Knowledge of the actual values of start-up times and why they are different is not needed, but the implications of such differences are important. Candidates should be aware of the fact that, of the fossil fuel power stations, gas-fired have the shortest start-up time. They should also be aware of the advantages of pumped storage systems in order to meet peak demand, and as a means of storing energy for later use.

Various energy sources can be used to generate the electricity we need. Fossil fuels Geothermal Nuclear Solar Wind Hydroelectric Tidal We must consider the advantages and disadvantages of using each energy source before choosing which it would be best to use.

A typical Power Station In some power stations an energy source is used to heat water. The steam produced drives a turbine which is coupled to an electrical generator. Boiler Turbine Generator National Grid Chemical Heat Heat Kinetic Kinetic Electrical

Common energy sources include fossil fuels (coal, oil and gas), which are burnt to heat water or air and uranium/plutonium, in which nuclear fission produces heat. They are called non-renewable energy resources. Biofuels are a renewable source that can also be burnt to produce heat. Energy from renewable energy sources, such as water or wind, can be used to drive turbines directly.

Alternative energy There are a number of alternative sources of energy: The Wind The Waves The Tides Hydro-electric dams The Earth (Geothermal energy) The Sun The Earth (Biomass)

The Wind Wind farms are places where the wind is used to make electricity. Most wind turbines have a propeller to turn a large single turbine to generate electricity. These propellers always need to be turned towards the wind. Disadvantages: The wind does not blow all the time and if it is too strong the turbine must be shut down. People find them unattractive and they make a noise but only over a short distance. Advantages: Low-cost electricity generated Lack of chemical pollution Not expensive to operate and maintain

The Waves Ocean waves are caused by the wind as it blows across the sea. At a wave power station, the waves arriving cause the water in the chamber to rise and fall, which means that air is forced in and out of the hole in the top of the chamber. We place a turbine in this hole, which is turned by the air rushing in and out. The turbine turns a generator. A company called Wavegen now operate a commercial wave power station called "Limpet" on the Scottish island of Islay,

Disadvantages: Advantages: The waves are not always strong Low-cost electricity generated Needs a suitable site Lack of chemical pollution Some designs are noisy Not expensive to operate and maintain Must be able to withstand very rough weather

The Tides The tide moves a huge amount of water twice each day. A huge dam (called a "barrage") is built across a river estuary. When the tide goes in and out, the water flows through tunnels in the dam. This flow of water can drive huge turbines, generating electricity. Disadvantages: Very expensive to build There are few suitable sites for tidal barrages Extensive damage to wildlife habitats Advantages: Low-cost electricity generated Lack of chemical pollution Not expensive to operate and maintain

The Sun Solar Cells (really called "photovoltaic" or "photoelectric" cells) that convert light directly into electricity. Disadvantages: Doesn't work at night. Can be unreliable Advantages: Low-cost electricity generated Lack of chemical pollution Can be used to get electricity to a remote place. Not expensive to operate and maintain

The Earth (Geothermal energy) In volcanic areas, hot underground rocks heat water to produce steam. We drill holes down to the hot region, we pump cold water down one set of holes, steam comes up the other set of holes. The steam is then used to drive a turbine, generating electricity. Disadvantages: There are not many places where you can build a geothermal power station. Hazardous gases and minerals may come up from underground Advantages: Low-cost electricity generated Lack of chemical pollution Not expensive to operate and maintain Not much impact on the environment.

The Earth (Biomass) Wood was once our main fuel. We burned it to heat our homes and cook our food. Sugar cane is grown in some areas, and can be fermented to make alcohol, which can be burned to generate power in the same way as coal. "Bioconversion" uses plant and animal wastes to produce fuels such as methanol, natural gas, and oil. Disadvantages: Advantages: It makes greenhouse gases. Uses waste materials Collecting the waste in sufficient quantities can be difficult. Less demand on the Earth's resources. Fuels are not expensive Some waste materials are not available all year round.

Hydro-electric dams A dam is built to trap water, usually in a valley where there is an existing lake. Water is allowed to flow through tunnels in the dam, to turn turbines and thus drive generators Disadvantages: Very expensive to build Extensive damage to wildlife habitats Suitable sites are difficult to find. Advantages: Low-cost electricity generated Lack of chemical pollution Energy stored by Dam until needed. Reliable – constant generation Fast start up time.

The advantages and disadvantages of using fossil fuels, nuclear fuels and renewable energy sources to generate electricity. These include the cost of building power stations, the start-up time of power stations, the reliability of the energy source, the relative cost of energy generated and the location in which the energy is needed. Small-scale production of electricity may be useful in some areas and for some uses, eg hydroelectricity in remote areas and solar cells for roadside signs.

Using different energy resources has different effects on the environment. These effects include; the release of substances into the atmosphere, the production of waste materials noise and visual pollution, and the destruction of wildlife habitats.

The National Grid Pylons and wires like this form the National Grid. Distributing electricity around the country, from the Power Stations to consumers. Compare the advantages and disadvantages of overhead power lines and underground cables.

Electrical energy can be transferred across large distances without the movement of appreciable amounts of mass. However, it is sometimes uneconomic to connect small-scale generation production to the National Grid.

For a given power, increasing the voltage reduces the current required and this reduces the energy losses in the cables.

A Step-up Transformer A transformer can be made to increase the voltage across the secondary coil (step up). At power stations, step-up transformers are used to produce very high voltages before the electricity is transmitted to where it is needed through power lines (National Grid).

A Step-down Transformer A transformer can be made to reduce the voltage across the secondary coil (step down). Step down transformer Local transformers reduce the voltage to safer levels before the electricity is supplied to consumers (homes, schools and shops).

Carbon capture and storage is a rapidly evolving technology Carbon capture and storage is a rapidly evolving technology. To prevent carbon dioxide building up in the atmosphere we can catch and store it. Some of the best natural containers are old oil and gas fields, such as those under the North Sea.