Solar Panels You Can Walk On

Discussion in 'Boat Design' started by justinDesign, Nov 12, 2007.

  1. justinDesign
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    justinDesign Junior Member

    I am currently designing a vessel with a large deck and wish to incorporate solar panels into this deck, however this deck is intended to be walked on. Does anyone know of a solar panel that one can walk on without damaging and do they get hot. Could you walk on them with bare feet if they exist. Please let me know if such a panel exists and the manufacturer if possible.

    Thanks
     
  2. Pericles
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    Pericles Senior Member

  3. FAST FRED
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    FAST FRED Senior Member

    The flexible units CAN be walked on . and are better for a boat as slight shading will still produce some charge.

    Most of the more efficient glass covered units will have almost zero output if even slightly shaded , common on a boat.

    FF
     
  4. DanishBagger
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    DanishBagger Never Again

    That's not necessarily true, Perry. Some are actually rugged enough to be walked on:

    http://www.midsummerenergy.co.uk/buy_solar_panels/spectra_marine_solar_panels.html

    They're of the flexible type, meaning less wattage than rigid types, but I'm assuming you'd need them to be flexible to begin with?


    A bit off topic, but how nice is this:

    http://www.powerfilmsolar.com/products/military/armytents/index.htm


    Do solar cells get hot?
    Well, they're black, so if not properly ventilated underneath, that heat will certainly be radiated into the boat. I guess one could minimise the heat entry by using isolated alu-foil to reflect some of it.

    Also, I guess a deck with solar cells will be pretty slippery when wet. I think it's fine incorporating solar cells into the boat, but not so much so, that work areas become unworkable.
     
  5. longliner45
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    longliner45 Senior Member

    ok once again I am not a designer but,if you intend to incorporate them into your deck,,( and you are doing correct research now),,to walk on and so forth,,,on my boat the deck adds strength to the stucture,so,,, just a thought,,,,,longliner
     
  6. artemis
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    artemis Steamboater

    :idea: My suggestion would be to check out the electric boats forum http://groups.yahoo.com/group/electricboats/ - solar panels on boats is a "hot" topic there and you'll probably get the best info of the kind you're looking for. :)
     
  7. War Whoop
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    War Whoop Senior Member

    I used them deck mounted years and years ago on an open class race boat did a great job keeping the batteries up never had to fight for an outlet for the charger again. Yes they did get hot, But the new stuff who knows? Personally I would not give a second thought about using them again!

    [​IMG]
     
  8. Pericles
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    Pericles Senior Member

    Build them into a bimini.

    Danish, I stand corrected. Have just taken delivery of Issue 7 of Barden catalogue. http://www.barden-uk.com/. Very informative (with price list)!:D

    Thanks,

    Pericles
     
  9. marshmat
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    marshmat Senior Member

    A few quick calculations on the PowerFilm and Spectra units mentioned in post #4, and they become a little less appealing. Example:

    "Quadrant" model is 8' x 9.5' (76 sq.ft, or 7.06 sq.m) and outputs 190 W, that's 27 W/sq.m or about 2.7% efficient.

    "Temper Fly" is 10' x 19' (190 sq.ft or 17.65 sq.m) and outputs 750 W, that's 42.5 W/sq.m or about 4.3% efficient.

    "Spectra 20" is 622x508 mm (0.31 sq.m) and outputs 20 W, that's 64.4 W/sq.m or about 6.5% efficient

    Sunpower's A300, one of the most popular and powerful monocrystalline silicon cells, runs about 215 W/sq.m or 21.5% efficient. Drop that to about 18% for the area of a completed panel including gaps, frames, etc. and you're still looking at more than four times the power per unit area as the PowerFilm flexible units, and three times better than the Spectra.

    When comparing efficiencies for solar photovoltaics, it's normal to assume you're getting 1000 watts per square metre as sunlight (a very, very close approximation on a sunny day in the middle latitudes). The efficiency is the fraction of that 1000 W/sq.m that comes out as electricity.
     
  10. DanishBagger
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    DanishBagger Never Again

    Yes, they are indeed less effective than rigid (ineffective) solar panels. Somehow, I think you have miscalculated somewhat (without me checking the numbers, so there).
    I have seen much more effective "walk-on" solar panels than what you portray, which makes me wonder about your numbers.


    However, there is no doubt that flexible solar panels are indeed even more ineffective than rigid ones, but you might want to show people how inefficient a rigid solar panel is – especially one, that isn't manually adjusted either.


    I'll take flexible, more or less unbreakable, solar panels any day, over rigid ones to be placed on huge struts*–*but that has most to do with my boat and my needs, just like Justin wanted something to walk upon.

    But it's a choice, and a valid point - the relative inefficiency of those things.

    Makes me wonder how come people still use NiMH batteries for certain electronics and much worse: Lead acids for their boats? I mean, those things a very inefficient too. ;)
     
  11. marshmat
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    marshmat Senior Member

    I rechecked the calcs, DB; by the accepted norms for calculating array efficiency, they're correct for the arrays offered for sale at the links above. The only way I can think of to get 2.7% out of an amorphous flexible array is to have enormous dead areas around the edges of the cells and between them, because on an active-area basis these things are usually close to 7%.

    Efficiencies are calculated the same way for all types of cells, and always assume normal incidence (cell pointed straight at the sun). At an angle of incidence, they will all show reduced output, generally according to the sine of the angle of incidence up until you hit the critical angle of reflection of the cell or protective material- at which point power drops off sharply. This happens for both rigid and flexible cells, whether on struts or flush-mounted. And the monocrystalline ones don't have to be placed on struts, although boaters generally do that to get better all-day power out of a small panel (witness http://qsvt.ca/index.php or any other solar car as an example).

    Sunpower A300, around $10 per watt and coming down quickly. 21.5% based on active area, about 18% for a typical completed array.
    Emcore or Spectrolab triple-junction GaAs, often over $100/watt. 25-28% based on active area, up to 30% if wrapped in really good (Gochermann-type) encapsulation. Again, knock a couple points off for a completed array to account for the gaps between cells.

    So still a very long way from capturing all the energy available in the sunlight- and remember, most of what doesn't get converted to electricity goes to heat up whatever's below the panel. And as for all cells, the actual power will be reduced by the sine of the angle of incidence when it's not pointing right at the sun. But a well-designed car can cross Australia using six square metres of those A300s.

    If you want flexible panels, you're going to take a three-fold hit in power compared to the same area of monocrystalline silicon. So it depends what you want them to do. For keeping a battery topped off, that might be an acceptable tradeoff. If you're trying to run the boat's drivetrain on solar, it probably isn't. These things are generally spec'd by individual, specific application, and with good reason.
     
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  12. Pericles
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    Pericles Senior Member

  13. ted655
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    ted655 Senior Member

    They are months away from "solar cell" paints. They exist now, but are working on marketing.
    Things happen on my deck that are nowhere near the "soft soled" shoe provision I've seen on all the sites posted here.
    Good luck with that approach. Also, you do understand these things have a limited "useful" life span?
     
  14. DanishBagger
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    DanishBagger Never Again

    Great explanation and comparison, Marshmat.
     

  15. JonathanCole
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    JonathanCole imagineer

    A couple of important points to remember about solar electric devices are:
    1. whatever part of the light shining on the device that is not converted to electricity is converted to heat. So if you have a square meter of sunlit panel seeing 1000 watts of potential energy and you convert "only" 20% to electricity, then you have a square meter of surface putting out 800 watts of heat. That is definitely not something to walk on in bare feet!

    2. the most durable solar panels are embedded behind a strong piece of glass, because glass gives the most long-lived protection against the ravages of UV light. Most plastics are destroyed withing 5 years in the sun. Glass can last 50 years or more, but it is not the best thing to walk on. But then with that kind of heat being thrown off, You probably don not want to walk on them anyway! In marine applications you would definitely want it on the roof and not the floor.
     
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