Solar panel

Discussion in 'Boat Design' started by Ron Skelly, Feb 27, 2014.

  1. Ron Skelly
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    Ron Skelly RonS

    Does anyone have experience and feedback utilizing a small electric trolling motor with a battery and solar panel on a boat?
     
  2. Fanie
    Joined: Oct 2007
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    Location: Colonial "Sick Africa"

    Fanie Fanie

    Sure Ron, not sure if this is for sea or fresh and what kind of distances you had in mind.

    The idea would be to calculate the motor life on the size battery, so you can get there and back safely, the solar panel always add some life, as well as keep the battery from getting drained as much, so yes, the solar panel makes a huge difference but this also depends on the size panel.

    Draining any battery reduces it's life cycles (amount of times you can recharge it), the less you discharge the battery in every go the more you can charge it, it's not linear.

    The best way to use a trolling motor is when you want to cruise softly around the fish and of course catch them all. You know, like when you catch one this side of the boat, you throw it back at the other side of the boat, it swims back to the other side and you catch it again.
    When you get tired of fishing you put the fish in the live well, when you're rested you throw the fish back and it starts all over again :D
    Ok so we normally get there on a fuel motor, then use the trolling motor. Wind an boat size and a lot of things play a role here.

    It helps when you give a little bit more about what you plan to do. Worst case is it can give every one a good laugh - even that is better than not catching any fish.
     
  3. Ron Skelly
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    Ron Skelly RonS

    Thanks Fanie. The solar panel, small motor and battery will be used on a small boat in freshwater and just slowly cruising small lakes and quiet rivers. I'll research some panels and batteries to see how much effect the panel will have, to see whether it is worth designing it in. Any feedback appreciated.
     
  4. Fanie
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    Fanie Fanie

    Panels are terribly inefficient for their size, on small boats they may be more of a nuisance than anything else.

    It is always better to have a fuel motor as well as an electric, the fuel has lots more power for longer cruising and the electric gets you around the quiet places. You'll appreciate this when one of the two has a slight problem.
     
  5. portacruise
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    portacruise Senior Member

    I converted a one man inflatable pontoon fly fishing boat to run on an electric motor with solar assist, many years ago. I don't use the solar part because I don't stay out long enough to make it worth the trouble. Still use the electric part for slowly cruising and trolling on a weekly basis.

    Trolling motors are too inefficient for solar use. Here is a very efficient electric testbed design by Rick W. that includes video links at the bottom of page : http://www.rickwill.bigpondhosting.com/V4_Electric.htm
    The pontoons can be fitted with a platform if you need more room, and will be more efficient than a flat barge for slow cruising. His more complex tri designs are faster and more efficient, but not needed for slow cruising.

    Porta


     
  6. Skyak
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    Skyak Senior Member

    You can certainly build a boat that charges it's batteries via solar, but if you are expecting to build a boat powered real time by the sun you will build a custom motor and prop. Trolling motors are not optimized for power efficiency -more like low cost thrust. In the UK there have been some very talented hobbyists building and comparing solar electric pleasure boats. give them a look;

    http://www.electric-boat-association.org.uk/solar.htm
     
  7. Ron Skelly
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    Ron Skelly RonS

    Really appreciate everyone's advice. I have decided "No" to solar, at least not for now. One less thing to worry about.
     
  8. BertKu
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    BertKu Senior Member

    Ron, my apology, but I like to ask Skyak, why are trolling motors so inefficient?. Is it that they don't use a controller with a pwm (pulse-width modulation) driving the motor or do they use some resistors in series with one of the windings and thereby reducing speed? Bert
     
  9. Skyak
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    Skyak Senior Member

    Hi Bert,
    my statement was based on knowledge of economics, company behavior and general experience with electromechanical system design. In short, no company wants to produce the most efficient trolling motor sitting on the shelf because it costs more and everyone wants to produce the cheapest motor with the right number that motors are purchased by -thrust and voltage. To conclusively make such a statement I should know all about the trolling motor market and the engineering that goes into them -but I don't. BUSTED! That said I am 99% confident that trolling motors do not offer power efficiency sufficiently high for the cost of power generated by solar panels -it is cheaper to get a better motor, control, and prop than it is to buy more solar panels and mount them. I could increase my confidence by searching, comparing charts, comparing technology... but you know what, no vendor gives any of this important info. Based on this fact and what I know about how much can be done to improve efficiency of a small electric drive I will add another 9 -Corporate Rule 1-if customer doesn't know and value something, don't spend more money on it than competitors, spend less.

    So I don't know what they are doing for motors and control, but I do know the motors are mounted in cool water to conveniently draw away all the heat from inefficiency. I know there are many ways to make an electric motor more efficient -PWM is better than resistor power control, the motor control circuit can have bigger better FETs, the windings can be larger wire, lower current (higher voltage), they can use better magnets and more precise cores to cut eddy currents or better yet they can get rid of permanent magnets and go to an 'inductive machine' and get rid of brushes altogether. For any solar powered boat you should not consider a motor with brushes. I did find one manufacturer that did make a brushless trolling motor but no numbers or technical specs. Even in brushless inductive motors I think that more complex AC drive can be more efficient than DC but I am not knowledgeable enough to know. Watch the electric car market and the electric plane market for state of the art. Solar electric planes have the highest cost power -therefor the highest incentive for efficiency, and auto's have the biggest high efficiency market.

    http://www.teslamotors.com/blog/induction-versus-dc-brushless-motors

    Another indicator is the difference in price and technology for the all in one battery and motor products and the electric primary drives -roughly 10x.

    http://www.torqeedo.com/uk/technology/lexicon-of-power-ratings/overall-efficiency

    Academic solar competitions are another great indicator of state of the art without investment.
     
  10. BertKu
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    BertKu Senior Member

    Thank you Skyak,
    I was looking at the 86 pounds trolling motor advertised in Australia for 179 to 228 Aus dollar. They are consuming 1 Kwatt. If one take 90% efficiency, it means that the water contact must cool 100 watt. Which is better than a lot of Diesel and petrol engines, whereby one has to cool the engine by using energy from the engine itself. The only problem is that the battery technology is not up to scratch. Bert
     
  11. Skyak
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    Skyak Senior Member

    Where did you get a 90% efficiency number? The last link I listed for torquedo says it is ~20% overall and I would estimate at least half that is dissipated in the motor and that may be generous since the torquedo is two and a half times more efficient. There is quite a bit of battery tech that also costs more, but before you draw conclusion consider that the cheap motor may be a POS.
     
  12. BertKu
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    BertKu Senior Member

    That is what I said . If a trolling motor uses a outrunner brushless motor, the losses in the motor is approx 10%, i.e. 100 watt. The other 10% is indeed the controller with Mosfets. Should one places quite a number of Mosfets parallel in the controller, one can improve the efficiency. However, it makes the controller more expensive. That is a problem for a manufacturer. A mosfet is a resistive product and by placing 10 parallel, this times 6, one brings the efficiency up. But who is going to pay more for such a controller? 80% efficiency, I am quite happy with. Bert
     
  13. Skyak
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    Skyak Senior Member

    You are reversing the loss and output.

    1Kw motor , 20% system efficiency means 800w are lost and I would estimate more than half or 400w and as much as 700w of that is lost in the motor and controler.

    By comparison consider the torquedo's 50% efficiency. So to get the same 200w 86lb thrust you would need only a 400w system. So the POS trolling motor needs 2.5 times as much battery to push the boat as fast and far as the competent torquedo. Still happy? Or do you think you should consider a better motor and less batteries?
     
  14. portacruise
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    portacruise Senior Member

    It is easy to confuse the net overall efficiency delivered to the water with the stated efficiency of a part of the system. AFAIK good outrunner motors and controllers can both be about 90% efficient. Very large, hand made slow turning props like those built specifically for a particular hull shape in HPB can be fairly efficient, maybe 90?%. Fairings on the submerged leg cut losses significantly. For ways to improve efficiency of cheap fishing motors, see McDenny postings on this page, photo in #252 http://www.boatdesign.net/forums/boat-design/efficient-electric-boat-27996-17.html

    AFAIK most fishing motors still use cheap, brushed motors and very inefficient "trolling"/"weedless" props as parts diagram show in their parts manual. The rear bearing is a brass bushing for the ones I have disassembled. The Torquedo motor is significantly better, but the rest of the design is quite traditional and lossy, IMHO.

    Hope this helps.

    Porta
     

  15. BertKu
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    BertKu Senior Member

    Thank you Porta,
    Very soon I will post all my work I have done over the last 4 years with some questions. My experience is very good with indeed a slow turning large prop and a brushless outrunner motor and a controller build with 6 x 4 of 100 Ampere 8 milliOhm parrallel placed mosfets are giving me reasonable success.
    I don't have the equipment to measure overall efficiency, but it is certainly not 20% efficiency like Skyak is suggesting.
    Bert
     
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