lecture 18 chapter 10 electricity. ohm’s law & power resistance behavior in metals,...
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Lecture 18 Chapter 10
Electricity
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• Ohm’s Law & Power
• Resistance behavior in metals, semiconductors, superconductors
• Series vs. parallel resistances
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Restructuring the Electrical Utility Industry• First commercial power plant in 1882 by Thomas Edison• Electric companies were “vertically owned”
– Production– Transmission– Residential meters
• 1978, Public Utility Regulatory Policy Act– Cost comparison between buying or building– Must buy the least expensive ( ~&0.06/kWh )
• 1996, Federal Energy Policy made transmission lines available to anyone, like a toll road
• Restructuring first began in 1997– Broke the utility up into separate companies– Allows consumers to purchase power from other sources
• Still out as to whether cost will go up or down.• But so far, Ameren has given us a big rate hike, from $0.08 to
$0.11 /kWh• Then again June 1, 2009 Ameren reduced rates due to cheaper
wholesale cost of electricity. Then rates will go up again in 2010.
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Pricing Electrical Energy Use
• Review of computations– Energy Used is watts expended times period of
use
• Savings at home begin with the proper appliance selection
– Domestic oven uses 12,000 W– Microwave oven uses 1450 W
Requires shorter cooking timeHeat only the food and not the container
• Peak pricing (time of use pricing)– Cheaper rates between 9 p.m. to 7 a.m.– Higher rates at all other times
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Fig. 10-12, p. 342
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Fig. 10-13, p. 343
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Fuel Cells
• Explaining fuel cells– Fundamental working principles
• Different types of fuel cells– Proton Exchange Membrane (PEM)
Advantages & Disadvantages
– Solid Oxide Advantages & Disadvantages
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Explaining Fuel Cells
• Electrochemical device where fuel and oxidizer (oxygen) chemically react (not combustion)
• This occurs catalytically at the 2 electrodes, the anode and cathode
• Electrolyte separates the electrodes and allows ions formed during the reaction to pass
• Electrons released during the reaction cannot pass through the electrolyte– Instead they travel through a wire and generate
electricity
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Explaining Fuel Cells• With no combustion (which is inefficient compared to reaction in fuel
cells) fuel cells can achieve greater efficiencies than existing methods of electricity generation
• Fuel cells also:– Do not operate on thermodynamic cycle– Therefore 2nd law of thermodynamics that gives max. efficiency
between 2 temperature reservoirs does not apply
• Fuel cells are expensive and difficult to build and operate; that is the main reason they are not more common
• Some fuels (H2) are not naturally occurring
– difficult and expensive to produce the fuel & lowers overall efficiency
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Proton Exchange Membrane (PEM)
• Hydrogen ions (protons) and electrons are:– Produced at anode– Consumed at cathode
• Products of the reaction– DC electrical power– Water
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Proton Exchange Membrane (PEM)
Advantages– Relatively lightweight and can be used for
Transportation (e.g., cars, buses) Portable electronic devices (e.g., radios, laptops,
cell phones)
– Highly researched; much information is known about them
– Once you have hydrogen the only products are DC electrical power and water
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Proton Exchange Membrane (PEM)
DisadvantagesHigh water content is required in electrolyte therefore:
• Operate below boiling point of water (60 – 100°C; 140 – 212°F)
• Active cooling (fans, etc.) is needed to remain at this temperature during operation
• Expensive and very active catalysts (platinum) are needed to continue the reaction at this low temperature
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Solid Oxide Fuel Cells
• Oxygen ions are transferred through electrolyte
• Electrolyte is solid oxide ceramic
• Operate at high temperatures (800–1000°C; 1472–1832°F)
• At this high temperature:– No catalyst is needed– Many fuels can be used
(methane, butane, propane, possibly diesel)
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SummaryCurrent fuel cell technology challenges:
– Large number of fuel cells needed for appropriate amounts of power
– Expensive catalysts sometimes needed– High temperature fuel cells need long time to heat up– If H2 is used for transportation; new infrastructure
needs to be developed (H2 stations, etc.)– Fuel cells in cold weather need time to heat up
(This has been improved to less than 15 sec)
– Produce DC power; inverter is needed to make AC power
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Table 10-3, p. 346
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p. 348
Anchorage - 1 MW