Lecture 18 Chapter 10

Electricity

• Ohm’s Law & Power

• Resistance behavior in metals, semiconductors, superconductors

• Series vs. parallel resistances

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.

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

Fig. 10-12, p. 342

Fig. 10-13, p. 343

Fuel Cells

• Explaining fuel cells– Fundamental working principles

• Different types of fuel cells– Proton Exchange Membrane (PEM)

Advantages & Disadvantages

– Solid Oxide Advantages & Disadvantages

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

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

Proton Exchange Membrane (PEM)

• Hydrogen ions (protons) and electrons are:– Produced at anode– Consumed at cathode

• Products of the reaction– DC electrical power– Water

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

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

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)

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

Table 10-3, p. 346

p. 348

Anchorage - 1 MW