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Solar energy design question

  1. Apr 23, 2008 #1
    I am an amateur science/engineering enthusiast (AA electrical engineering), I would like to design/build a solar energy system consisting of a small tracking parabolic mirror heating a steam boiler to drive a small turbine-generator. The mirror I am thinking 3 foot diameter and I have some idea how to go about constructing it. The questions come in on the boiler design, pressure, safety, how to pump in the cold water feed, check valving, turbine construction, cooling the steam, and many phases of constructing same. Any info on any of the above would be appreciated.
     
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  3. Apr 23, 2008 #2

    Danger

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    I am also an amateur, so I can't answer much of that. What I would seriously recommend, however, is that you have your pressure vessel built by a professional shop, with an appropriate relief valve provided by them. Safety always has to come first.
     
  4. Apr 24, 2008 #3

    Mech_Engineer

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    Well, a useful number that you will want to know is this- solar energy incident on the earth at sea level is about 125 W/m^2. With a 3 ft diameter mirror, this means you will only have a maximum power of about 80 W to work with; that doesn't sound like a whole lot when you're wanting to drive a steam turbine and an automatic tracking system...
     
  5. Apr 25, 2008 #4

    Redbelly98

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    Actually it's closer to 1000 W/m^2. You may be thinking of a photovoltaic cell, where the low efficiency results in an output power close to what you are saying.

    See the paragraph under "Solar constant" here:
    http://en.wikipedia.org/wiki/Solar_radiation
     
  6. Apr 27, 2008 #5
    Thanks for the info, I am aware the pressure vessel would need special design cosideration, as far as the area of the mirror, this would be more or less a model. If it worked, something larger could be made.
     
  7. Apr 27, 2008 #6

    Mech_Engineer

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    That would be the amount of power incident at the edge of Earth's atmosphere (still in space). By the time it gets through Earth's atmosphere to the ground, I think it is anywhere from 100-375 W/m^2 average. That's at sea level in North America. The number will rise as you go higher in the atmosphere or closer to the equator, and peak power will incease or decrease depending on time of day and weather conditions.

    http://simple.wikipedia.org/wiki/Solar_energy
     
    Last edited: Apr 27, 2008
  8. Apr 27, 2008 #7

    Redbelly98

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    Well no, that number is 1300 to 1400 W/m^2. According to your link.

    Checked out your link. They are averaging in the time the surface is in total darkness, and cloudy weather, to get those numbers. They also factor in that a horizontal surface is not oriented at a perfect 90 degrees to the sun.

    http://simple.wikipedia.org/wiki/Insolation

    The 1000 W/m^2 figure is more applicable to the purpose at hand: boiling water during daylight hours, where one can aim the setup directly at the sun.
     
  9. Apr 29, 2008 #8
    The part I am afraid will use the most energy is the pump to introduce cold water into the boiler
     
  10. May 3, 2008 #9

    Con

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    The pump you may use you can find it by apply the formoula of the 1st low of thermodynamics.

    Q= m . C .Dt

    m= mass flow rate , c= water heat coefficient 4200, dt= temperature difference between the boile imput and output.

    Q= heat gain you may have.

    Note: the above formula is only valid for closed systems.
     
  11. May 4, 2008 #10
    Before you get to far along on a design, you should get a copy of the ASME Sections 1 and 8 for boiler and pressure vessel code requirements. Also, a copy of B31.1 Power piping would be needed. These are the American Society of Mechanical Engineers code books that govern the minimum design requirements. Also, make sure they are the 2007 editions and for Section 8 you should use Division 1 not Division 2.
     
  12. May 9, 2008 #11
    sngtd, I realize that what you're building is just a model, but you probably won't get much power at all with a 3-foot mirror, so the turbine generator isnt going to be able to be big.
     
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