Fresnel Lenses for heat production

Discussion in 'Designing, building, making and powering your life' started by Carol, Dec 12, 2015.

  1. Carol

    Carol New Member

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    Just thought I'd mention this in case anyone else has tried it or knows about it. I bought some linear fresnel lenses last spring from greenpowerscience.com. Haven't set them up yet but they are supposed to produce heat up to about 400 degrees F with sun shining through them. I have to figure out what kind of frame to build so the sun rays going through them will not touch the frame at all. I'm planning on having them aimed at rocks that will be sticking up just slightly out of ponds, so it will heat the water & I can create a warmer micro-climate outside of a greenhouse.

    If anybody has any thoughts on this that would be helpful, please let me know.

    Thanks,
    Carol
     
  2. songbird

    songbird Senior Member

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    interesting ideas Carol, i would be curious how the rocks work out as i suspect they will not transmit as much heat as they get and then may crack and shatter through time. you may do much better by aiming at the water itself and line the area with the darkest rocks you can find and they will capture any energy the water doesn't and as they'll be submerged the temperature changes and the amount of heat needing to be conducted may not be as great so they'll hold up better.
     
  3. Pakanohida

    Pakanohida Junior Member

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    You will most likely blow up the rocks with a Fresnel lens. I use them for starting fires outside.



    However, I did find this.

     
  4. 9anda1f

    9anda1f Administrator Staff Member

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    What an intriguing idea Carol! Doesn't a linear fresnel lens focus into a bar the length of the lens?
     
  5. Brian Knight

    Brian Knight Junior Member

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    It is an interesting idea but agree it would be an engineering feat to get measurably warmer water. I think you could get better results by focusing on the water itself but the biggest challenge is creating a tracking system that would keep the lens focused with the changing angles of the day and season.

    You might get better results by using more proven forms of solar thermal energy. Do you have any topography to work with? A loop of black poly pipe could be run down hill of the pond and create a natural thermosiphon. I've had success doing this for water heaters in the warm seasons. Of course my newest water heating obsession of compost could work too but you would need to get the compost pile downhill of the pond to thermosiphon without pumps. The advantage of compost is it would work day, night and potentially in freezing weather.
     
  6. Carol

    Carol New Member

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    Will try to answer all the comments in this one.

    Thank you so much for the idea of aiming the lens at the water, rather than the rocks. I had no clue if it would work my way or not, but I believe your idea is much better, so I will try it that way. Didn't even think about the rocks blowing up, but they probably would if they get hot enough.

    As I said I haven't tried anything yet, so not sure how much heat they will produce here in Alaska. I guess it will depend on length of time of sun shining. And also as was commented on, being able to follow the sun. I was going to just try to do it manually at first, occasionally changing the angle & position of the lens. However, I was trying to figure out how to design a holding frame that could be angled to follow the sun. A ball joint wouldn't work because you can't put anything between the lens & the water. So was working on designing a frame that would be in front of the lens that could be angled to follow the sun. If anybody can come up with an idea for that, would love to hear it.

    I do believe the linear lens will make a long narrow line of light, so it will have a large area to cover. The lenses are 20" x 30"..

    Also, this is just one way of heating. Yes, I've already been studying & planning on using compost heat as well as producing methane, and want to build rocket mass heaters for some situations also. You know, they say to use as many methods as possible to handle something, as well as making the methods useful in many ways. Besides bringing the temperature up in the outdoor areas, I will be heating a greenhouse, as well as a cob & straw bale house. Have lots of plans & lots of work ahead of me.

    I appreciate all the responses - they are very helpful
     
    Last edited: Dec 19, 2015
  7. 9anda1f

    9anda1f Administrator Staff Member

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    Hi Carol,
    I found this video showing different fresnel lens types: (very educational)

    and this showing how he built his frames:
     
  8. Topher

    Topher Junior Member

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    Actually this isn't a method of heating. It is a way of concentrating heat. You are moving sunlight from a large area, to a small area. Unless the water area is smaller than the area of the lens, you will just be heating one section at the expense of shading the rest. And actually it is probably worse than that, as the concentrated heat will more readily escape the area (perhaps in the form of water vapor).

    Thank you kindly,

    Topher
     

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