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Chapter 17

Chapter 17.docx

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Monika Havelka

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Chapter 17: • Hydro, nuclear, biomass are conventional alternatives • Canada’s energy is hydropower • Fossil fuels combined provide about 81% of world’s energy! • of the remainder of the energy supply: ~1/2 provided by biomass; ~1/3 by nuclear energy; ~1/10 by hydro and the rest by “new” renewables Hydroelectric power: the kinetic energy of moving water is used to turn turbines and generate electricity Modern hydropower uses two approaches: • Kinetic energy of water in two major ways: 1. large dams 2. run of river technologies Large dams: • most hydropower today comes from impounding water in reservoirs behind large concrete dams that block the flow of river water and then controlling the flow of water through the dam • Reservoir, storage or impoundment approach: water held in reservoirs behind dams • Process: 1. Water flows from the reservoir through the dam 2. Flowing water turns the turbine 3. Turbine turns the rotor, which consists of a series of magnets 4. Electicity is produced as the rotor spins past the stator, which is the stationary part of the generator made of coils of copper wire 5. Electricity generated in the powerhouse of a dam is transmitted to the electic grid by transmission lines 6. Water is allowed to flow into the riverbed below the dam to continue downriver • The amount of power generated depends: 1. On distance the water falls 2. Volume of water released Run-of-river/diversion approach: • Generates electricity without water impoundment and without greatly disrupting the flow of river water • This approach sacrifices the reliability of water flow that the storage approach guarantees • Can use various methods • Diverts a portion of a river’s flow through a pipe or channel passing it through a powerhouse and then returning it to the river • The pipe or channel can be run along the surface or underground • Another method involves: river water flowing over a dam small enough not to impede fish passage, using the water to run turbines and then returning water to the river • Run-of-river systems are useful in areas from established electrical grids and in regions without the economic resources to build and maintain large dams • Run-of-river is often called small hydro or micro-hydro Hydropower generates relatively little air pollution: • Two advantages over fossil fules: o Renewable o Cleanliness • Fossil fuels are used to built dams • Recent evidence – large reservoirs release the greenhouse gas methane as a reulst of anaerobic decay in deep water • Creates a small fraction of the greenhouse gas emissions typical of fossil fuel combustion • Hydropower is efficeient with EROI (energy returned on investment) of 10:1 or more • Fossil fuels had a higher EROI in the past, but as the cost of reaching remaing deposits has increased Hydropower has many negative impacts: • destroys habitats • disrupts natural cycles of flooding and sedimentation – sediments trapped behind dams • causes thermal pollution because water downstream may become warmer if water levels are kept unnaturally shallow = that can eliminate fish populations and other creatures • reducing biodiversity • blocks passage of fish! • has geological impacts (e.g., earthquakes)! • displaces people Nuclear Power: usable energy extracted from the force that binds atomic nuclei together – occuoes a conflicted position in our modern debate over energy • Nuclear energy = the energy that holds together protons and neutrons within the nucleus of an atom • Nuclear fission = the splitting apart of atomic nuclei • Nuclear power comes from processed and enriched uranium • Electicity is generated from nuclear power controlled fission in nuclear reactors, facilties contained within nuclear power plants • Nuclear fuel cycle: begins when the naturally occurring element uranium is mined from underground deposits • Uranium minerals are uncommon and unranium ore is in infinite supply • Radioisotopes emit subatomic particles and high-energy radiation as they decay into lighter radioisotopes, ultimately becoming stable isotopes • Fissison tak
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