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A Two Lens Design For A Cheap Solar Thermal Collector
  • Vote Up0Vote Down
    rajeshbhatsmailbox
     
    May 2011
    Here is a video of greenpowerscience where the guy shows a water lens.

    It's 3 foot is diameter and gets around 380 degrees farenheit. I guess thats close to 200 degree celsius. He uses an almost hemispherical lens.
    Also note that by using a combination of lens and water bottle he got around 600 degrees.

    I have attached an image that explains the concept. Two spherical water lenses that provide an intense combined focusing power. Tell me if this can drive a stirling engine.
    If we wanted to make a spherical lens how large can we make it? Would using two concentric spheres with water filled in the space between them we could reduce the weight. it is shown in the second image.
    If we can make it large enough, then mirrors would not be required at all. We should be able to get a high enough temperature to drive a stirling engine.
     
    Attachments
    		 Two lens design.JPG 41K
    		Lens.JPG 19K
  • 8 Comments sorted by
  • Vote Up0Vote Down
    rajeshbhatsmailbox
     
    June 2011
    Will a perfectly spherical plastic container deform when filled with water? What are the dangers to a perfectly spherical structure?
     
  • Vote Up0Vote Down
    mjnmjn
     
    June 2011
    Plastic containers filled with water will almost certainly deform under their own weight.  However, this doesn't necessarily mean their optical qualities degrade.  It might just mean a change in focal point.  More research is needed.

     
  • Vote Up0Vote Down
    rajeshbhatsmailbox
     
    June 2011
    The support for the lens will also be a problem. The lens has to be kept at a sufficient elevation and has to be supported by some structure. Care needs to be taken that the support structure dos not block the sunlight in any way and also leaves the area right under the lens free, so that the Stirling engine can move freely.
     
  • Vote Up0Vote Down
    Jason
     
    June 2011
    One idea I was kicking around, rajesh, was giant spheres made out of ice. Of course it would only work in very cold climates.
     
  • Vote Up0Vote Down
    mjnmjn
     
    June 2011
    It would have to be free of dissolved gasses before being frozen, otherwise it wouldn't be clear.
     
  • Vote Up0Vote Down
    gregor
     
    June 2011
    Guys, why not add this to the discussion on the http://opensourceecology.org/wiki/Main_page_for_the_solar_energy_to_electrical_energy_conversion_project  page?

    This sort of discussion is what I am trying to capture.  Although I really don't think this particular approach is practical I won't bother to say why because it will not make any difference to the project.  We need to harness this sort of thing so that it actually adds to the body of design work, in particular the initial lateral thinking stage where we decide what approach to flesh out.

    It happens again and again, the solar accumulator thread, the other thread I think the GF posted on the forum, etc.  let's start using this sort of discussion instead of regarding it as entertainment.

    Pivotal will help with later phases, but I had another look at it, and I don't think it will help with the lateral thinking and the initial exploration of design options phase that these projects seem to go through.

    I emailed Marcin to ask him what he thinks of adopting the approach that I describe in section 4.1 of the development process section of that page, but he has not answered me at all.    
     
  • Vote Up0Vote Down
    rajeshbhatsmailbox
     
    June 2011
    The conventional approach to solar power is flawed. They are using sophisticated technologies like PV and ultra high reflective glass. Its a top-down approach. They are hoping that somehow these technologies can be made cheaper, because it worked for telecom and computers. I don't think it can be done because of net energy limits.
    We have to use a bottom-up approach. We have to trace the same path that fossil fuel industry used. It started with cheap coal that was found just lying around on the ground and slowly demand was created and then more efficient ways of extracting coal were developed.
    I still think that a plastic sphere filled with water is the way to go. The materials are really cheap. Plus the round shape has its own benefits, like protection from strong winds. Even if the plastic degrades, it can be recycled cheaply. Also, the focus is closer to the ground and the collector placed at the focus can be moved independently of the lens. I'm hoping i can see  a small prototype, to see if the concept works. Starting with a plastic sphere 1 meter in diameter. See if it can boil water.
     
  • Vote Up0Vote Down
    mjnmjn
     
    June 2011
    @rajeshbhatsmailbox
    Why not create a wiki page to describe it and your results?
    - Mark

     
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