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Age: 5
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Date: 2000-2001


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 watt-hours of electricity per hour. Well designed, modern power plants can make one killowatt-hour (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 kilowatt-hour, or 926 watt-hours. 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 watt-hours of electricity per hour. Well designed, modern power plants can make one killowatt-hour (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 kilowatt-hour, or 926 watt-hours. 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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