20-Jan-2012
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20-Jan-2012
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Energy Usage.
• My house is electric plus natural gas
• From my electric bill
– Dec 7, 2011 to Jan 10, 2012 (34 days)
– Electricity used: 1165 kWh
– Gas used: 159 therms
• Conversions:
–
–
–
–
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1 therm = 100,000 BTU
2.74 m3 natural gas (CH4) = 1 therm
CH4: density 656 μg/mL, 1000 L/m3
1 BTU =1055 Joules
1 kWh = 3.6MJ
– 2.2 lbs per kilogram
– Gasoline 42,000 J/gram
– Gasoline: 6.1 lbs/gallon
• Questions:
20-Jan-2012
– What is my average electrical power usage?
– What is my average power usage from natural gas?
– How much gasoline would be needed to replace the natural
gas used?
– Estimate: How much CO2 am I responsible for from natural
gas usage?
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My house
• Electricity:
34 days * 24 hours/day = 816 hours
1165 kWh/816 hours = 1.4kW
This is pretty typical for a house.
• Gas:
159 therms*100,000 BTU/therm =15,900,000 BTU
15.9MBTU*1055 J/BTU = 1.7x1010 J=17000 MJ
17000 MJ/3.6 MJ/kWh = 4660 kWh
4660 kWh/816 hours = 5.7 kW
About 4x electricity usage.
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Natural gas
• How much gasoline would be needed to replace the
natural gas used?
1.7x1010 J for one month.
1.7x1010 J/(42,000 J/gram) = 405 kg
405 kg * 2.2 lbs/kg = 900 lbs
900 lbs / (6.1 lbs/gallon) = 146 gallons of gasoline
That’s about about 29 gallons per week.
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What about CO2?
• Natural gas:
2.74 m3/therm*159 therms = 436 m3
ρ=656μg/mL =656x10–3 kg/m3
so: 436m3*656x10–3 kg/m3=286 kg
Or: 630 pounds.
This is the amount of methane consumed, not
the amount of CO2 produced.
• Natural gas: 13.5 pounds CO2/therm
13.5 lbs/therm * 159 therms =
2150 pounds of CO2!
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Energy Costs
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•
• Fuel
•
•
•
•
•
•
•
•
20-Jan-2012
market cost
cost per kWh
(1000 Cal)
--------------------------------Coal
$40 per ton
0.4¢
natural gas $10 per mil/f3
3¢
Gasoline
$3 per gallon
9¢
Electricity $0.10 per kWh
10¢
car battery $50 battery
21¢
Comp bat $100 battery
$4.00
AAA bat
$1.50 battery
$1000.00
PHYS 199REL
cost if converted
to electricity
1.2¢
9¢
27¢
10¢
21¢
$4.00
$1000.00
7
Who has the energy?
• Billion barrels of oil equivalent
•
•
•
•
•
•
•
•
Country
--------USA
Russia
China
Iran
Saudi Arabia
Canada
oil
---21
60
48
136
260
179
coal
-------1194
754
550
32
natural gas
-------32
280
14
157
9
total
1237
1094
612
293
260
220
• US and Russia have largest reserves of shale.
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