Off Grid Home Forums Technical Discussion Light from bottles filled with water.

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    The idea is basic but ingenious. You take:

    1 . Get 2 liter soda bottle (clear plastic)

    2. Fill it with clean water and add a cap full of bleach (so it stays clear)

    3. Attach it to a similar piece of your roofing.

    4. Cut a hole big enough for the bottle and seal it into place.

    5. Enjoy


    When it is bright you have a light. You can build cases around them with a door to make it so you can control when it comes in also.



    Here is an article about it and some pics:



    Who says you can’t bottle (and distribute) genius? Developed in Brazil to address under-illuminated slums, this simple design idea has been adopted by MIT students and expanded to other developing areas where many low-income homes lack access to either daylight or electricity.

    The physics of the concept are straightforward: the bottles are placed in roofs – half outside, half inside – and their lower portions refract light like 60-Watt light bulb but without the need for a power source. A few drops of bleach serve to keep the water clear, clean and germ-free for years to come.




    In total, one of these do-it-yourself lights takes maybe an hour to install, cutting an appropriate hole, inserting a bleached-water-filled bottle, and resealing around the resulting gap. Even where clean water is rare, a little can generally be spared for a half-decade of lighting.



    We take for granted our electric lights, windows and skylights to access the sun’s glow, but for those living in close-together shacks with corrugated-metal roofs, a stray ray is welcome, and something that can spread light to the darkest interior corners can be a dream come true.


    I’m thinking of adding these to the tin roof of my “old 45′ truck trailer” storage. But I’m wondering just how I seal it against water penetration. I’m sure I could use silicon caulking probably. But I’m wondering if heat and cold will cause the 2 liter bottle to come loose from the caulking. Also I may need a wire basket or hanger to hold the bottle in place. Anyone have any ideas?




    Caulking eventually breaks down.  Will not work with anything but thin roofs in non-freezing areas.  It would need a some support wires.   Why not just cut the clear plastic bottle in half lengthwise and cut holes slightly smaller and caulk them on with adhesive caulk?    How about putting them high on the walls, instead, for no leaks.


    Here are a couple of videos on this subject, the weak point IMO is going to be sealing it in the roof/ceiling so that it will not eventually leak around the bottle. And you would need to put something in it to keep it from freezing when the temps drop low enough to freeze, a bit of alcohol might work, anything to lower the freezing temp of the straight water, they call for adding a cap of bleach to keep the water clear, one would have to be cautious about mixing bleach and alcohol, I am not a chemist and do not know if that would cause harmful fumes or not, perhaps just adding alcohol without using bleach would be enough to keep the water clear… it’s something that would have to be tested of course, you don’t want to find out that your bottles are growing stuff AFTER you have them installed and sealed in the ceiling.



    Alcohol would work if its about 20% to keep it clear. Ok I didn’t think about adhesive caulking, good idea. And yes I like the idea of putting it in the side instead.


    There are different types and grades of caulk, I like one called “Big Stretch”, it stays flexible

    It won’t crack—it just stretches.

    Big StretchWindow frames move away from the siding or doors shift against the brick. They move when the temperature changes, the wind blows, or the ground swells. Big Stretch provides the adhesion and flexibility to handle the movement.

    Big Stretch® is a 100% acrylic latex, high-performance caulk with powerful adhesion and elasticity. Big Stretch will stretch and compress to absorb just about any movement a home can dish out. It spans gaps up to 2″ wide and stretches up to 500% of the original joint size without cracking.

    Features & Benefits

    • Super elastic—moves instead of tears
    • For interior and exterior use
    • Highly durable
    • Low VOC
    • Superb paintability
    • Freeze-thaw stable
    • Limited Lifetime Warranty
    • Stop-flow plunger
    • Paintable with exterior latex paints/stains after 4 hours
    • Paintable with interior latex paints/stains after 24-48 hours
    • Soap and water cleanup
    • Available in 13 colors → View Color Chart
    • Available in 10.5 oz and 29 oz. cartridges *

    * 29 oz. cartridge is only available in white.


    It’s perfect for many interior and exterior applications, including:

    • windows
    • doors
    • siding
    • vents
    • soffits
    • eaves
    • baseboards
    • crown molding
    • sound-proofing interior walls

    It adheres to most building materials, including:

    • aluminum
    • brass
    • nylon
    • steel
    • anodized windows

    A variety of plastics and other surfaces, including:

    • ABS
    • acrylic sheet
    • Plexiglas
    • PVC
    • fiberglass
    • urethane
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    • tile
    • wood
    • glass
    • mortar/stone/cinder block
    • stucco/brick/concrete
    • EIFS
    • drywall / fiber cement


    Yeah, I just put up a big ol’ commercial for Big Stretch… ;) It’s what we use out here in far west Texas, it does hold up to the sun, wind and monsoon season, I get it from my local hardware store.



    I guess thats what all these ideas are about. As for the caulking i personally would have no issue caulking once a year if need be. tarring it after caulking might help it last longer ?

    as for freezing alcohol here are some temps:

    24 proof liquor freezes at -6.7°C (20°F)
    64 proof liquor freezes at -23.33°C (-10°F)
    84 proof liquor freezes at -34.44°C (-30°F)

    I think it would certainly be worth testing it out one winter on a sample piece and should it hold up then maybe investigate it further.


    Jennifer Kelly

    Can you use glass bottles, or do you have to use plastic?


    a couple old glass quart jars with the openings superglued togather should work
    just have to figure out how to keep water in them while gluing

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