P1.4 Methods We Use To Generate Electricity

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GCSE Physics (P1) Mind Map on P1.4 Methods We Use To Generate Electricity, created by killthemoment on 08/09/2014.

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P1.4 Methods We Use To Generate Electricity
1 P1.4.1 Generating Electricity
1.1 Various energy sources can be used to generate the electricity we need. There are advantages and disadvantages of using each energy source.. Electricity is distributed via the National Grid.
1.1.1 In some power stations an energy source is used to heat water. The steam produced drives a turbine that is coupled to an electrical generator. Energy sources include fossil fuels which are burnt to heat water or air, uranium and plutonium, when energy from nuclear fission is used to heat water and biofuels that can be burnt to heat water. Water and wind can be used to drive turbines directly. The main nuclear fuels are uranium and plutonium. These are radioactive metals. Nuclear fuels are not burnt to release energy. Instead, nuclear fission reactions release heat energy. The rest of the process of generating electricity is then identical to the process using fossil fuels. Unlike fossil fuels, nuclear fuels do not produce carbon dioxide or sulfur dioxide. There are disadvantages however: nuclear fuels are non-renewable energy resources; risk of large amounts of radioactive material released into the environment and nuclear waste remains radioactive and is hazardous to health for thousands of years and must be stored safely. The wind is produced as a result of convection currents in the atmosphere, which are driven by heat energy from the sun. Wind turbines use the wind to drive turbines directly. They have huge blades mounted on a tall tower. The blades are connected to a 'nacelle', or housing, which contains gears linked to a generator. 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. Wind is a renewable energy resource and there are no fuel costs. No harmful polluting gases are produced. However 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. Water can be used to drive turbines directly. Machines use the kinetic energy in the movement of waves to drive electricity generators. Huge amounts of water move in and out of river mouths each day. A tidal barrage is a barrier built over a river estuary to make use of the kinetic energy in the moving water. Hydroelectric power stations use the kinetic energy in moving water. The water high up behind the dam contains gravitational potential energy which is transferred to kinetic energy. Water is a renewable resource with no fuel costs and no harmful polluting gases produced. Barrages and HEP stations are reliable and easily switched on. It is difficult to design wave machines producing large amounts of electricity. Tidal barrages destroy the habitat of estuary species. Hydroelectricity dams flood farmland pushing people from their homes. The rotting vegetation underwater releases methane, a greenhouse gas. Hot water and steam from deep underground can be used to drive turbines; geothermal energy. 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 turbines and electricity generators. In some places, the rocks are hot, but no hot water or steam rises to the surface. 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. Geothermal energy is a renewable energy resource with no fuel costs. No harmful polluting gases are produced. Most parts of the world do not have suitable areas where geothermal energy can be exploited. Solar cells are devices that convert light energy directly into electrical energy. Solar panels use heat energy from the Sun to heat up water. You may see 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 energy is a renewable energy resource and there are no fuel costs. No harmful polluting gases are produced. Solar cells provide electricity in remote locations. Solar cells are expensive and inefficient, so the cost of their electricity is high. They do not work at night. 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. 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.
2 P1.4.2 The National Grid
2.1 Electricity is distributed from power stations to consumers along the National Grid.
2.1.1 Electricity is transferred from power stations to consumers through the wires and cables of the National Grid. When a current flows through a wire some energy is lost as heat. The higher the current, the more heat is lost. To reduce these losses, the National Grid transmits electricity at a low current. This needs a high voltage. Transformers are used in the National Grid. A transformer is an electrical device that changes the voltage of an alternating current (ac) supply, such as the mains electrical supply. A transformer that increases the voltage is a step-up transformer and one which decreases the voltage is a step-down transformer. Power stations produce electricity at 25,000 V. Step-up transformers change the voltage to the very values needed to transmit electricity through the National Grid power lines. Electricity is sent through these at 400,000 V, 275,000 V or 132,000 V. This reduces energy losses during transmission but the voltages would be dangerous in homes. Step-down transformers are used locally to reduce the voltage to safe levels. The voltage of household electricity is about 230 V. Electricity from a power station goes to step-up transformers, high voltage transmission lines, step-down transformers and then to consumers.
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