12.5: Generating Current Electricity pg. 518

Transcription

1 12.5: Generating Current Electricity pg. 518 Key Concepts: 1. Electrical energy is produced by energy transformations. 2. Electrical energy is produced from renewable and non-renewable resources. 4. Electrical energy consumption should be reduced. - Electric generating stations produce electrical energy by using external energy sources, such as; water, steam, or wind). Generating Electrical Energy Using Moving Water: Hydro-Electric Generation - Falling water has been used for thousands of years to do work, water wheels and grain mills the first hydro-electric generating stations was built at Chaudiere Falls on the Ottawa River. Hydro-electric generation was one of the first methods of electric generation. - Fast moving water (waterfall, river, or a water reservoir) is used to turn a turbine, and generator to make electrical energy. - There are 180 hydro-electric generation stations in Ontario, 58 connected directly the electrical distribution grid. - The network of transmission lines and towers that provides electrical energy to our homes and business make up the grid. - Hydro-electric generation is considered to a renewable energy source. The water cycle is continuously replenished.

2 Figure 1: Hydro-electric dams divert and control the flow of water so that it flows past a turbine connected to a generator. Renewable Resource: natural energy resource that is unlimited (for example; energy from the Sun or wind) or can be replenished by natural processes in a relatively short period of time (for example; biomass). The Pros and Cons of Hydro-Electric Generation - No air or water pollution is created. - Water flow is altered. Reservoir dams cause problems up stream and down stream. - The ecology is altered, watershed, fish migration, terrestrial ecosystems may become flooded. - Large scale dams cost a lot to build and cause the most damage. Using small scale dams has less impact on the environment. Generating Electrical Energy Using Moving Water: Tidal Generation - using the moving water of tidal changes can rotate turbines and generate electricity. - Tidal cycle occurs twice daily, and the generation of electricity occurs as the tide comes in and goes out. - The station is on for 5 hours and off for seven. -Tidal changes in inland lakes is very small and can not be used to generate electricity.

3 - Tidal changes along Ocean shorelines are ideal. (Bay of Fundy) - Tidal generation is renewable, cycled over time. The Pros and Cons of Tidal Generation - There is no pollution generated. - Location is the limitation. Suitable Ocean coastlines need to be found. Generating Electrical Energy Using Steam: Thermal Generation - Thermal generation is responsible for heating water into steam. The steam is used to rotate the turbine and generator, producing electricity. - Thermal energy is created by burning fossil fuels, and radioactive energy to heat water to produce steam. - Biomass, Geothermal energy, and Sunlight energy are alternative sources to produce heat tot create steam. Using Fossil Fuels in Thermal Generation - The fossil fuels used to create thermal energy are; Coal, Oil, and Natural gas. - Fossil fuels are not renewable resources. They take millions of years to produce, using dead plants and animals, decomposing deep below the Earth s surface. - These sources are large contributors to greenhouse gases and pollution. - Mining for fossil fuels also leads to the destruction of ecosystems. Non-renewable resources: a resource that cannot be replaced as quickly as it is consumed.

4 Using Radioactive Materials in Thermal Generation - The use of Uranium in nuclear reactors to generate heat to boil water, creating steam to produce electricity. - Uranium rods are placed within the Nuclear Reactor, neutrons collide with the uranium, breaking the nuclei of uranium atoms. - When the nuclei break, a large amount of energy is released. - The energy is used to create steam from water, which then turns a turbine and generator to generate electricity. - Uranium is a non-renewable resource because it is of limited supply. - This form of electricity production does not produce pollution but it does produce nuclear wastes. Using Biomass in Thermal Generation - Plant and animal matter is burned to generate heat to create steam. - Biomass is a renewable resource. - Biomass is a large contributor to green house gases (CO 2 ) Biomass: any biological material (including plants and animals). Using Geothermal Energy in Thermal Generation - uses thermal energy found deep within the Earth s surface. - Thermal energy is transferred from the ground to a liquid. - The water in pipes is then pumped to a central tower to heat water to generate steam.

5 The Pros and Cons of Thermal Generation - A large amount of energy is available from thermal sources. - Fossil fuels and radioactive material has environmental concerns. - Carbon dioxide gases being released from burning fossil fuels is causing climate change and raising atmospheric temperatures. - Most fossil fuels other then coal are expensive to extract and must be refined before it can used. Coal: is inexpensive and easy to mine. Burning coal releases a large quantity of greenhouse gases and pollutants into the atmosphere. The air pollutants can lead to smog and acid precipitation. Health problems such as; asthma, bronchitis, eye and skin irritations can occur. Oil and Natural Gas: produces a large amount of pollution and produces acid precipitation. Other problems are the transportation Oil can lead to secondary environmental problems, such as an oil spill. As oil and natural gas supplies decrease, the cost of discover and removal has increased. Radioactive Materials: Mining for uranium ore destroys the ecosystem. Nuclear reactors are very expensive to build. Uranium used in reactors does not produce pollution, the release of water, leads to thermal pollution in the lakes, affecting aquatic habitats. Radioactive wastes must be store safely for thousands of years. Biomass: Using left over biomass for fuel is a form of recycling of plant and animal wastes. The burning of organic matter does release greenhouse gases. Geothermal: This type of energy does not produce pollution or contribute to greenhouse gas emissions. Geothermal energy is found deep within the Earth s surface, it is very difficult to obtain.

6 Generating Electrical Energy Using Wind - Wind energy is a renewable resource. - Wind energy does not create air pollution. - A wind turbine ahs large blades that turn and is connected to a generator. - One wind turbine can generate electricity to support 250 homes. The Pros and Cons of Generating Electrical Energy using Wind - Installation and maintenance is costly, but it cheaper then our other generating stations. Wind is free. - Only a wind speed of 5m/s is required to generate electricity. - Wind turbines can be located close to sub-divisions, therefore less transmission lines are required. - The best location for wind farms are offshore in lakes where the wind blows continuously. - The only criticism about wind turbines is threat they generate noise, and are dangerous to birds and their migration patterns. Producing Electrical Energy from Light - A photovoltaic cell is used to produce electricity from sunlight without the use of a turbine. - Sunlight is converted directly into electricity. - Sunlight is a renewable resource.

7 The Pros and Cons of Producing Electrical Energy from Sunlight - Solar cells must be installed in areas where there is ample sunlight. - They do not produce air or water pollution. - They can be added to the power grid or function independently. - They last for 40 years with very little maintenance required. - One draw back is that solar cells can only convert 30% of the sunlight energy into electricity. - Solar panels are expensive to purchase. The Future of Energy Production - 26% of electrical energy comes from burning coal and natural gas. - 50% come from nuclear energy. - Therefore 76% of our energy comes from non-renewable sources. Figure 13: This pie chart shows how Ontario s electrical energy was generated in 2007.

8 Evidence of Learning. Students can - identify different methods of generating electrical energy. - discuss the pros and cons of controversial forms of electric energy generation. - compare different forms of electrical energy generation and identify their strengths and weaknesses. - discuss issues that involve renewable and non-renewable ways to produce electric energy. Check Your Learning Questions 1 8, page 528 Summary: - Turbines are connected to generators to produce electrical energy. - Conventional ways to generate electrical energy include hydro-electric, thermal, and nuclear generation. - Alternative ways to generate electrical energy include tidal, wind, biomass, geothermal, and solar energy generation. - Resources used to generate electrical energy can be renewable or nonrenewable. - Thermal generation commonly uses coal, oil, natural gas, and uranium, which are non-renewable resources. - Fast-moving water, tides, biomass, geothermal energy, wind, and sunlight can be used to rotate a turbine and are renewable energy resources. - Fossil fuels and radioactive materials are non-renewable resources used in thermal generation. - Solar cells produce electricity directly, by converting light energy into electrical energy. - Producing energy using either renewable or non-renewable resources has advantages and disadvantages for society and for the environment. - Societies choose which method of electric generation, or combination of methods, to use based on many factors.