Residential Electric Power Bill

$145.6/1948 kWh = $0.0747/kWh

Avg. Power: 1948kWh/31day.24h/day = 2.6 kW.

Commercial Power Costs

Energy cost estimates for a project out at IUCF: use (i.e. energy) charge: $3105/(360hr*575kW)=$0.0147/kWh peak use (i.e. maximum power demand) charge: $13.11/kW Why is this different from the residential calculation?

Energy Conversions (Table 2.2)

AutomaticallyHappens!

digestion

thermal

A key question to consider is with what EFFICIENCY can each of theseConversions be accomplished (Useful energy output/ total energy input)

Efficiencies of typical DevicesDevice Transfer effected Efficiency

Generators Kinetic-Electrical 70-99%

Elec. Motors Elect.-Kinetic 50-90%

Transformer Electrical-Electrical 95-99%

Gas Furnace Chem.-Thermal 70-95%

Wind Turbine Kinetic-Electrical 35-50%

Power Plant Nucl/Chem-Elect. 30-40%

Fuel Cell Chem-Electrical 50-60%

Solar Cell Radiant-Electrical 5-28%

Fluoresc. Light Electrical-Radiant 20%

Incandescent light Electrical-Radiant 5%

Energy Losses in a Carhttp://www.fueleconomy.gov/feg/atv.shtml

NOTE: only 13% gets to the wheelsand ALL of that goes to thermalenergy (eventually)

http://www.fueleconomy.gov/feg/hybrid_sbs_cars.shtml

See also:

Efficiency example (H&K p75)

Not all hybrids are created equal!

http://www.fueleconomy.gov/feg/hybrid_sbs.shtml

BMW hydrogen sports car

“Our long-term EfficientDynamics strategy can be summed up with one vehicle: the BMW Hydrogen 7. As the world's first luxury performance sedan with hydrogen drive, it runs on the most plentiful element in the world and emits virtually nothing but water vapor. And because the infrastructure for refueling a hydrogen internal combustion engine is not yet complete, the V-12 engine also runs on gasoline at the push of a button, though emissions will result. “

http://www.bmwusa.com/uniquelybmw/EfficientDynamics?PANELID=4

Efficiencies of typical DevicesDevice Transfer effected Efficiency

Generators Kinetic-Electrical 70-99%

Elec. Motors Elect.-Kinetic 50-90%

Transformer Electrical-Electrical 95-99%

Gas Furnace Chem.-Thermal 70-95%

Wind Turbine Kinetic-Electrical 35-50%

Power Plant Nucl/Chem-Elect. 30-40%

Fuel Cell Chem-Electrical 50-60%

Solar Cell Radiant-Electrical 5-28%

Fluoresc. Light Electrical-Radiant 20%

Incandescent light Electrical-Radiant 5%

Coal-fired Electric Power Plant

Lighting: Overall efficiency

Incandescent light!

The Electromagnetic Spectrum

Black Body Spectra

0.00E+00

5.00E-12

1.00E-11

1.50E-11

2.00E-11

2.50E-11

0 500 1000 1500 2000 2500

Wavelength (nm)

Inte

nsi

ty

Series1

Series2

Light from hot objects

VisibleUV IR

6000K

2500K (x10)

Lighting efficiency comparison

http://www.mge.com/home/appliances/lighting/comparison.htm

LED’s(white)

Light Emitting Diodes (LED)

http://alt-e.blogspot.com/2005/04/energy-efficiency-led-lights-to.html

What is Temperature?

• It is the quantity that determines the direction of heat flow (from higher Temperature to lower temperature) when two objects are brought into thermal contact. (“zeroth law of thermodynamics”)

• For gases under normal circumstances this is related to the average energy per molecule, BUT this relationship is not valid in all circumstances nor for all materials.

Specific Heats• Ice (near 0oC) 2090 J/kg.K=2090 J/kg.Co

• Water (near 0oC) 4186 J/kg.K=1000 cal/kg.Co

• Aluminum 900 J/kg.K• Copper 387 J/kg.K

This is how thermal energy and temperature are related!!

Temperature Scales:• 0oC = 273.15 K ice melts at this temp• 100oC = 373.15 K water boils at this temp• 0 K: absolute zero, the coldest temperature possible.• Note that 1Co = 1 K. The Celsius degree and the Kelvin

are the same size! The only difference in the scales is the position of the origin, hence the two scales are equivalent for talking about temperature DIFFERENCES, but not for talking about absolute temperatures.

Phase transitions in water

Possible Swain journals for Article Summary.

• Scientific American (e.g. Sept. 2006)• Nature (e.g. Nov. 2001)• Science (access through Swain library web

page, they no longer have paper copies)• Science News• Physics Today• The Physics Teacher• Bulletin of the Atomic Scientists