Energy and power
part II
prefixes
Prefix
Symbol
Factor
Number
Name
Scale (distances)
Tera
T
1012
1,000,000,000,000
trillion
Distance to closest
star
Giga
G
109
1,000,000,000
billion
distance from earth
to Sun
Mega
M
106
1,000,000
million
earth-moon radius
kilo
k
103
1,000
thousand
distance across
campus
100
1
height of a human
centi
c
10-2
0.01
hundredth
A bee
mili
m
10-3
0.001
thousandth
Thickness of
fingernail
micro
mu
10-6
0.000 001
millionth
diameter of blood
cells
nano
n
10-9
0.000 000 001
billionth
wavelength of visible
light
pico
p
10-12
0.000 000 000 001
trillionth
Helium atom (31 pm)
femto
f
10-15
0.000 000 000 000 001
quadrillionth
Size of proton
A MWh is a unit of:
A) Charge
B) Energy
C) Current
D) Power
E) Cost
Cost of energy
I burn 2000 light bulbs for 10 hours. How
much does this cost? ($0.10/kWh)
A) $0.20
B) $2.00
C) $20.00
D) $200.00
E) $2000.00
Cost of energy
I burn 2000 light bulbs for 10 hours. How
much does this cost? ($0.10/kWh)
A) $0.20
Flourescent lights = about 4x more efficient!
B) $2.00 That’s why CU uses flourescent lights instead
of incandescent bulbs!
C) $20.00
D) $200.00
E) $2000.00
Cost of electricity
fuel
market cost
cost per kWh
(1000 Cal)
cost if
converted to
electricity
coal
$40 per ton
0.4¢
1.2¢
natural gas
$10 per million
cubic feet
3¢
9¢
gasoline
$3 per gallon
9¢
27¢
electricity
$0.10 per kWh
10¢
10¢
car battery
$50 to buy
battery
21¢
21¢
computer
battery
$100 to buy
battery
$4.00
$4.00
AAA battery
$1.50 per
battery
$1000.00
$1000.00
Energy units
energy unit
definition and equivalent
calorie (lowercase)
heats 1 gram of water by 1 C
Calorie (capitalized), the food
calorie, also called kilocalorie
heats 1 kg of water by 1 C
1 Calorie = 4182 joules ≈ 4 kJ
joule
1/4182 Calories
≈ Energy to lift 1 kg by 10 cm
≈ Energy to lift 1 lb by 9 in
kilojoule
1000 joules = ¼ Calorie
megajoule
1000 kilojoules = 106 joules
costs about 5 cents from electric utility
kWh (kilowatt-hour)
861 Calories ≈ 1000 Calories
= 3.6 megajoules
costs 10 cents from electric utility
BTU
British Thermal Unit
1 BTU = 1055 joules ≈ 1 kJ = ¼ Calorie
Quad
A quadrillion BTUs = 1015 BTU = 1018 J
Total US energy use ≈ 100 quads per year;
total world use is ≈ 400 quads per year
Power
Is a MegaWatt a lot?
A) A horse can output about a MW
B) A Ferrari could output a MW at peak
acceleration
C) That’s about the entire power output of
the sun
D) A nuclear power plant produces about a
MW
Power
Is a MegaWatt a lot?
A) A horse can output about a MW – 1 kW
is about a hp (+34%)
B) A Ferrari could output a MW at peak
acceleration – 750 kW max…
C) That’s about the entire power output of
the sun – 173,000 TW hits the earth
D) A nuclear power plant produces about a
MW – about a GW
Power examples
value
equivalent
example of that much power use
1 watt
1 joule per second
flashlight
100 watts
bright light bulb;
heat from a sitting human
1 horsepower (1 hp)
≈ 1 kilowatt
typical horse (for extended time)
human running fast up flight of stairs
1 kilowatt (1 kW)
≈ 1 hp
small house (not including heat);
power in 1 square meter of sunlight
100 horsepower
≈ 100 kW
small automobile
1 megawatt (MW)
1 million (106) watts
electric power for a small town
45 megawatts
1 gigawatt = 1 GW
747 airplane;
small power plant
1 billion (109) watts
400 gigawatt
= 0.4 terawatts
2 terawatts
large coal, gas, or nuclear power
plant
average electric power use US
= 2 x1012 watts
average electric power for World
Solar power
1 square
meter
1 kilowatt of sunlight
150 – 400 watts electric using
solar cells
1 square
kilometer
1 Gigawatt of sunlight
150 – 400 Megawatts electric
Fossils
Levels (amount in ground):
Coal: 4.4 Tboe
Oil: 1.2 Tboe
Natural gas: 1.2 Tboe
Flows (daily production):
Coal: 52 Mboe/day
Oil: 84 Mboe/day
Natural gas: 19 Mboe/day
Years of production left (using current #s  most optimistic):
Coal: 231  417 years
Oil: 39  43 years
Natural gas: 173  167 years
In 2008, the U.S. energy use was:
84% fossils
9% Nuclear
7% Renewables
Extra clickers…
Didn’t get to these 31 Aug 2010
In Chapter 1, “smart rock” refers to:
A) a kind of low-calorie food
B) the asteroid that killed the dinosaurs
C) a method for shooting down missiles
D) uranium ore
A disadvantage of hydrogen fuel is that:
a) it contains less energy per pound than gasoline.
b) it cannot be made into a liquid, even at low
temperature.
c) it is highly poisonous and corrosive.
d) it can’t be mined, but must be “manufactured.”