

Coal to Electricity
Name: Unknown
Status: student
Age: 5
Location: N/A
Country: N/A
Date: 20002001
Question:
How much coal is needed to generate electricity to run a
60watt light bulb? a tv?
Replies:
You have asked a hard question because there is a lot we must know before we
can even start to provide an answer. Not all kinds of coal produce the same
amount of heat. So, what kind of coal is being used  in other words, is it
good stuff with a lot of energy  or is it poorer quality coal that will not
make so much heat when it is burned? Also, not all power plants are the same
in their ability to convert heat into electrical power. We would have to know
something about that as well.
For now, lets just say that a 60 watt light bulb or a TV set would not take
much coal to run it. However, think about all the light bulbs and TV sets and
the zillions of electrical things that are demanding electricity. Now that
takes a lot of coal!
So, it is probably a very good idea to not waste electricity. Turn things off
when you are really not using them and you can be helpful in saving
electricity for all those jobs where it's really needed.
Regards,
ProfHoff
Assuming all energy conversions are 100% efficient [which is really not a
good assumption], and assuming coal is essentially carbon  here goes:
A 60 watt bulb uses 60 joules/sec. That comes from the definition of the
watt, which is 1 joule/sec.
The combustion of carbon is the reaction C + O2 = CO2 liberates 93.965
kcal/mol. The conversion to joules is: 1cal = 4.184 joules and there are 12
gm of carbon in 1 mol. So stringing those conversion factors out the
combustion of coal liberates about 3.3x10^4 joules / gm coal. If my
arithmetic is correct this means 1 gm coal will keep the light going for
about 550 sec which is about 9 minutes.
Vince Calder
I asked Bruce Salisbury of The Arizona Public Service Company to field this
one......Here is his reply:
"Typically, Coal has a "heating value" of 8,800 to 11,000 btu's per
lb. Lets assume the smaller value of 8,800 btu's per lb. A 60 watt light
bulb uses 60 watthours of electricity per hour. Well designed, modern power
plants can make one killowatthour (1,000 watt hours of electricity) using
9,500 btu's of energy from coal. So 1 pound of coal can generate 8,800/9,500
of a kilowatthour, or 926 watthours. In this case, one pound of coal is
enough electricity to run your 60 watt lightbulb for 926/60 hours (15.4
hours)"
Jim Rubin
Typically, Coal has a "heating value" of 8,800 to 11,000 btu's per
lb. Lets assume the smaller value of 8,800 btu's per lb. A 60 watt light
bulb uses 60 watthours of electricity per hour. Well designed, modern power
plants can make one killowatthour (1,000 watt hours of electricity) using
9,500 btu's of energy from coal. So 1 pound of coal can generate 8,800/9,500
of a kilowatthour, or 926 watthours. In this case, one pound of coal is
enough electricity to run your 60 watt lightbulb for 926/60 hours (15.4
hours)
jr
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Update: June 2012

