# Homework Help: Electrical energy production question

1. Nov 4, 2013

### nwag93

1. The problem statement, all variables and given/known data
If all the solid waste of 230 million tonnes were burned in waste-to-energy power plants that are 20% efficient,

a) how many kilowatt-hours of electrical energy could be produced in a year? Compare this quantity with the total U.S. electrical energy production of approximately 3.8 trillion kWh annually.

b) what would be the equivalent average electric power output from all these waste burning power plants? how many 1-GW coal-fired plants could they displace

2. Relevant equations

im not too sure

3. The attempt at a solution
i dont know how to begin
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Nov 4, 2013

### Simon Bridge

Welcome to PF;
Please start by telling us what "waste to energy power plant" means to you[1]... what does one of these things actually do? What is it? i.e. does it convert matter into energy by E=mc2?

How much energy is represented by so many tonnes of solid waste?

What does "efficiency" mean?

Sort out those questions and you should be able to answer your own question.

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[1] by "you" I mean in the context of the course that this hmework has been set for ... if you don't know off the top of your head, you will have to go back over your coursework for clues.

3. Nov 5, 2013

### nwag93

I am just confused. I don't know where to start. Is there an example I could use?

4. Nov 5, 2013

### haruspex

To answer this question you must make use of other facts that are not in what you posted. Specifically, how much energy can be obtained from burning, say, 1kg of waste? Maybe there were earlier parts of the question that gave this information, or perhaps it should be in your course notes somewhere. If not, you'll have to make some assumption about what the waste consists of chemically. Or maybe just research the subject on the net.

5. Nov 5, 2013

### nwag93

It is around 20 MJ/kg. does that help?

6. Nov 5, 2013

### Staff: Mentor

Please check your PMs. You must show more effort toward solving your schoolwork problems here. That is an important part of our Homework Help rules (see Site Info at the top of the page).

7. Nov 5, 2013

### haruspex

Of course it helps!
So how many J will you get from 230 million tonnes?

8. Nov 11, 2013

### nwag93

9.6x10^18 joules

9. Nov 11, 2013

### haruspex

Do you have a typo in there?