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Homework Help: Electricity Cost Help me

  1. Mar 3, 2008 #1
    Electricity Cost Help me :(

    1. The problem statement, all variables and given/known data
    A solar-cell installation that can convert 15.5% of the sun's energy into electricity has been built. The device delivers 1.0kW of power. If it produces energy at a cost of $0.080/kw*h, how much energy must the sun provide to produce $1000.00 worth of energy.

    2. Relevant equations

    3. The attempt at a solution

    ? = energy

    given: cost of energy = $0.080/kw*h
    cost = $1000


    $1000.00 = (energy)($0.080/kw*h)

    Sun's Energy = 12.500kwH

    I don't know how to do this! Help Please!
  2. jcsd
  3. Mar 3, 2008 #2
    Looks like you got it right; 12.500/12,500kWh of energy.
  4. Mar 3, 2008 #3
    the teacher gives us the answer.

    It Is:

    =2.9*10^11 J

    I i need help trying to get there.
  5. Mar 3, 2008 #4
    Hrm, 81,000 kW/hr as the answer? Well, either way you need to convert to joules, which I'm guessing the 'relevant equations' section gives you what you need to do. Assuming you were the one that put the question marks, and your sheet doesn't actually say that....
  6. Mar 4, 2008 #5
    Oh, right, you need to divide the 12,500 by 15.5% (meaning divide by 0.155), which gives 80,645kW/hr, or 8.1x10^4kW/hr.

    For converting from kilowatt hours to joules;

    1kW/hr = (1 kW)(1 hour) = (1000 J/s)(3600 s) = 3.6x10^6J.

    So basically multiply kilowatts by 3.6x10^6 and it'll give you joules.
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