it is transmitted easily over distance, through electricity cables it can be used in many ways, for example electric lamps, heaters, motors etc

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1 of 12 1/24/2013 9:01 AM Science Generating electricity Electricity is a convenient source of energy and can be generated in a number of different ways.

1 1 of 12 1/24/2013 9:01 AM Science Generating electricity Electricity is a convenient source of energy and can be generated in a number of different ways. You will need to weigh up the advantages and disadvantages of other ways of producing energy, such as the use of nuclear power stations. Electricity Coal, oil and natural gas are primary energy sources. Electricity is a secondary energy source because we use primary energy sources to produce it. These primary sources can be non-renewable or renewable. Electricity itself is neither non-renewable nor renewable. Electricity is convenient because: it is transmitted easily over distance, through electricity cables it can be used in many ways, for example electric lamps, heaters, motors etc Process of using electrical energy Generating electricity Generators are the devices that transfer kinetic energy into

2 2 of 12 1/24/2013 9:01 AM electrical energy. Turning generators directly Generators can be turned directly, for example, by: wind turbines hydroelectric turbines wave and tidal turbines When electricity is generated using wave, wind, tidal or hydroelectric power (HEP) there are two steps: The turbine turns a generator. Electricity is produced. Turning generators indirectly Generators can be turned indirectly using fossil or nuclear fuels. The heat from the fuel boils water to make steam, which expands and pushes against the blades of a turbine. The spinning turbine then turns the generator. These are the steps by which electricity is generated from fossil fuels: 1. Heat is released from fuel and boils the water to make

3 3 of 12 1/24/2013 9:01 AM steam. 2. The steam turns the turbine. 3. The turbine turns a generator and electricity is produced. 4. The electricity goes to the transformers to produce the correct voltage. Efficiency of energy transfer "Wasted" energy Energy cannot be created or destroyed. It can only be transferred from one form to another, or moved. Energy that is "wasted", like the heat energy from an electric lamp, does not disappear. Instead, it is transferred to its surroundings and spreads out so much that it becomes difficult to do anything useful with it. Electric lamps Ordinary electric lamps contain a thin metal filament that glows when electricity passes through it. However, most of the electrical energy is transferred as heat rather than light energy. This is the Sankey diagram for a typical filament lamp. Sankey diagram for a filament lamp Modern energy-saving lamps work in a different way. They

4 of 12 1/24/2013 9:01 AM transfer a greater proportion of electrical energy as light energy. This is the Sankey diagram for a typical energy-saving lamp.

4 4 of 12 1/24/2013 9:01 AM transfer a greater proportion of electrical energy as light energy. This is the Sankey diagram for a typical energy-saving lamp. Sankey diagram for a typical energy-saving lamp From the diagram, you can see that much less electrical energy is transferred, or "wasted", as heat energy. Calculating efficiency The efficiency of a device such as a lamp can be calculated using this equation: efficiency = (useful energy transferred energy supplied) 100 The efficiency of the filament lamp is = 10%. This means that 10% of the electrical energy supplied is transferred as light energy. 90% is transferred as heat energy. The efficiency of the energy-saving lamp is = 75%. This means that 75% of the electrical energy supplied is transferred as light energy. 25% is transferred as heat energy. Note that the efficiency of a device will always be less than 100%.

5 5 of 12 1/24/2013 9:01 AM Efficiency of power stations The energy produced by burning fuel is transferred as heat and stored in water as steam. The energy in steam is transferred to movement in a turbine, then to electrical energy in the turbine. Energy is lost to the environment at each stage. Here is a Sankey diagram to show these losses. Sankey diagram Note that only about a third of the energy stored in the fuel was transferred as electrical energy to customers. Different kinds of energy sources Renewable energy sources Our renewable energy resources will never run out. Their supply is not limited. There are no fuel costs either. And they typically generate far less pollution than fossil fuels. Renewable energy resources include: wind energy water energy, such as wave machines, tidal barrages and

6 6 of 12 1/24/2013 9:01 AM hydroelectric power geothermal energy solar energy biomass energy, for example energy released from wood Wind farms are noisy and may spoil the view of people who live near them. The amount of electricity generated depends on the strength of the wind. If there is no wind, there is no electricity. A wind turbine Non-renewable energy sources There is a limited supply of non-renewable energy resources, which will eventually run out. They include: fossil fuels, such as coal, oil and natural gas nuclear fuels, such as uranium Fossil fuels release carbon dioxide when they burn, which adds to the greenhouse effect and increases global warming. Of the three fossil fuels, coal produces the most carbon dioxide, for a given amount of energy released, while natural gas generates the least. 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 or store radioactive waste, which is a dangerous health hazard. Nuclear power stations The main nuclear fuels are uranium and plutonium, both of which are radioactive metals. Nuclear fuels are not burned to

7 7 of 12 1/24/2013 9:01 AM release energy. Instead, heat is released from changes in the nucleus. Just as with power stations burning fossil fuels, the heat energy is used to boil water. The kinetic energy in the expanding steam spins turbines, which drive generators to produce electricity Advantages Unlike fossil fuels, nuclear fuels do not produce carbon dioxide. Disadvantages Like fossil fuels, nuclear fuels are non-renewable energy resources. And 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. Nuclear waste is given different categories. Nuclear waste categories Category Examples Disposal Low level Intermediate level Contaminated equipment, materials and protective clothing Components from nuclear reactors, radioactive sources used in medicine or research They are put in drums and surrounded by concrete, and put into clay lined landfill sites. They are mixed with concrete, then put in a stainless steel drum in a purpose-built store.

8 8 of 12 1/24/2013 9:01 AM Category Examples Disposal High level Used nuclear fuel and chemicals from reprocessing fuels They are stored underwater in large pools for 20 years, then placed in storage casks in purpose-built underground store where air can circulate to remove the heat produced. High level waste decays into intermediate level waste over many thousands of years. Watch You may wish to view this BBC News item from 2006 about the arguments for and against nuclear power. Nuclear fission - higher only Nuclear power stations use the heat released by nuclear reactions to boil water to make steam The type of nuclear reaction used is called nuclear fission. In nuclear fission: Watch 1. A neutron collides with a uranium nucleus. A uranium nucleus is large and unstable. 2. The uranium nucleus splits into two similar-sized smaller nuclei. 3. More neutrons are released. 4. These neutrons can then collide with more uranium nuclei. These processes are repeated continuously, forming a chain

9 9 of 12 1/24/2013 9:01 AM reactionchain reaction: A nuclear chain reaction occurs when a neutron splits a nucleus, releasing more neutrons, which in turn go on to split even more nuclei.. Rate of energy released In a nuclear reactor, the reaction is controlled so that energy is released at a steady rate. The energy released in nuclear fission is far greater than the energy released in a chemical reaction, such as burning fuel. This means that the power output of a nuclear power station is large. The lifetime of a nuclear power station is about 20 years. Advantages and disadvantages In considering the subject of nuclear power, it is important to weigh up the advantages and the disadvantages. These are some of the advantages: no carbon dioxide is produced when the station is operating, as stated earlier there is a high power output a small amount of fuel is needed, when compared with coal or gas These are some of the disadvantages: hazardous radioactive waste is produced, as stated earlier building the power stations is quite expensive decommissioning, ie taking apart, the power stations at the end of their lifetime is very costly

10 of 12 1/24/2013 9:01 AM Outline of a nuclear reactor The nuclear fuel, usually uranium oxide, is held in metal containers called fuel rods. These are lowered into the reactor core.

10 10 of 12 1/24/2013 9:01 AM Outline of a nuclear reactor The nuclear fuel, usually uranium oxide, is held in metal containers called fuel rods. These are lowered into the reactor core. A coolant, usually water or carbon dioxide, is circulated through the reactor core to remove the heat. Control rods are also lowered into the core. These absorb neutrons and control the rate of the chain reaction. They are raised to speed it up, or lowered to slow it down. Ideas about science - making decisions Scientific applications give people things that they value, but may have undesirable impacts on the environment. Our society uses more and more energy every year, but the carbon dioxide produced by most power stations is believed to be causing serious damage to the climate. Natural resources should be used in a sustainable way. The use of renewable energy sources would guarantee energy for the future. At the moment, renewable energy

11 11 of 12 1/24/2013 9:01 AM sources cannot provide enough energy. There are official regulations and laws which control scientific research and applications. The nuclear industry is regularly inspected to ensure that standards of safety are maintained. Some applications of science have ethical implications. One point of view is that the right decision is the one which gives the best outcome for most people. Another point of view is that certain actions are never justified because they are wrong. Disposal of nuclear waste raises ethical problems: Some people say that we must have nuclear power, or we will not be able to combat global warming and still produce enough energy. Others say that it is unethical to produce waste that will still be dangerous in many thousands of years time. Weighing up the arguments - higher only Before deciding on a course of action, it is important to ask if it is feasible. Can it be done? Then it is possible to consider if it ought to done. If nuclear waste could be sent down into the Earth s mantle, it would take millions of years to resurface. Unfortunately, there doesn t seem to be any way to do this. It is not feasible. Nuclear waste could be sent into space in rockets so that it falls harmlessly into the Sun. Unfortunately, this would be far too expensive, and any accident on take-off would spread dangerous waste over a large area. It ought not to be done. In different social and economic contexts, different decisions might be taken.

12 12 of 12 1/24/2013 9:01 AM Many developing countries insist that they need to burn fossil fuels in their power stations, even if it produces global warming. They need this to allow them to catch up with the standard of living that we enjoy. Now try a Test Bite - foundation. Now try a Test Bite - higher. Back to Revision Bite

IB Topic 8.1: Energy Production, Energy Sources

IB Topic 8.1: Energy Production, Energy Sources World use of energy sources 91% Nonrenewable Only approximate values are needed Energy density of fuels Energy in MJ/kg Uranium 235 90,000,000 Crude Oil