# Kilowatt hours question

1. Mar 5, 2016

### theone

1. The problem statement, all variables and given/known data
1. A flow of steam at 180°C from a geothermal field is supplied to a steam turbine connected to an electric generator. The steam flow has a power content of 150kW. The power system uses a cooling tower to reject heat and the ambient temperature is 15°C.

The electricity is sold at a rate of 6 cents per kW-hour. If the average thermal efficiency of the actual power plant is 18%, what is the total revenue generated in one year (assuming that the plant operates continuously).

2. Relevant equations

3. The attempt at a solution
is the net work 150kW * 0.18 = 27kW

and so the revenue is $6\frac{cents}{kW-h}*27kw*(365*24)h$

2. Mar 5, 2016

### Staff: Mentor

The 18% efficiency are not relative to the steam flow power. You have to take into account the maximal thermodynamical efficiency as well.

Also, you did not use the temperature values yet. Usually a good sign that something is wrong.

3. Mar 5, 2016

### theone

there was a first part to the question about finding the theoretical max efficiency and I used the values there. But I don't understand this part,
isn't the equation $n_{thermal}=\frac{w_{net}}{Q̇_H}$ with $Q̇_H$ = 150kW and $n_{thermal}=0.18$?

4. Mar 5, 2016

### Staff: Mentor

Hmm, now I'm not sure how "thermal efficiency" is meant.

5. Mar 5, 2016

### theone

in the textbook, the thermal efficiency of a heat engine was defined like that, so I think i have to use that.
also, if possible could you have a look at my other question : https://www.physicsforums.com/threads/energy-savings-question.860706/

6. Mar 5, 2016

### Staff: Mentor

Okay, then it is fine, but then the problem looks quite easy.

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