Solar charged small boat evaluation

Discussion in 'Electric Propulsion' started by alan craig, Jun 16, 2018.

  1. alan craig
    Joined: Jul 2012
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    Location: s.e. england

    alan craig Senior Member

    I've been attempting to evaluate the use of solar charging on my electric/rowing skiff to make it independent of shore supply. The pictures show my setup in the garden. There were a few problems to overcome:
    Programming the MPPT correctly
    Finding that, once the 24v 110Ah battery was fully charged, I could no longer measure electric power generated from PV!
    Using the motor as a load in air caused the motor to get rather hot - 81 deg. C measured after two hours, which could have been resistive heating but also direct solar heating of the stainless steel can covering the motor.
    A dummy load in a bucket of water solved the motor heating problem.
    P.S. If you click on a picture you get a short description and a full size picture (no description for first picture).
     
  2. BlueBell
    Joined: May 2017
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    Location: Victoria BC Canada

    BlueBell Ahhhhh...

    You're not going to see much return on your investment on that MPPT with only one solar panel.
     
  3. alan craig
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    Location: s.e. england

    alan craig Senior Member

    The panel itself is used, 260W peak and only £99. Briefly, the most power I saw was 150W and the most daily energy was about 500Wh. I am optimistically hoping for 1000Wh per day on a sunny river less shaded than my garden. The 10A 12/24v MPPT and programmer/display were about £90.
     
  4. BlueBell
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    BlueBell Ahhhhh...

    I guess you had to buy a controller anyway, might as well get a MPPT.
     
  5. Will Fraser
    Joined: Feb 2014
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    Location: South Africa

    Will Fraser Senior Member

    Any suggestions for controlling a direct solar-to-motor set up? I.e. no batteries. I will just have to use the paddle when the sun disappears.

    We have an annual solar boat race where each boat can use 4 x 320W panels. Last year the winning team averaged around 10kt over 4 hours using a directly coupled 1kW brushed motor, via belt and pulley reduction to a home-made prop from stainless steel plate. They used a volt meter and simply tweaked the prop pitch with a pair of pliers to get them onto the max power point.
    They managed to beam a team with a brushless motor and lots of clever electronics. As the winner jokingly said, when all those little resistors and other magoodies on a circuit board cannot keep the smoke in any longer, it is game over.
    This year I am sure they will enter the fully electronic fray, but for my own humble aspirations I believe there is merit in keeping things simple, especially where salt is involved.

    At this stage I have available a 12V cordless drill motor (incl gearbox and speed-control ) as well as a Johnson 775-size motor from some industrial powertool. I would imagine it is 18V.
    I have characterised both motors from their respective spec-sheets and the 775 looks very promising. At 6V the motor is at or near maximum efficiency from 15-35W, just what I need to glide along at 3kts in my 12ft canoe.
    Can the PWM speed control of the drill somehow be used to optimise maximum power from the panel as well as supply the correct voltage for best motor efficiency?
    (I have yet to buy a panel, but would like to go as small as possible.)
     
  6. BlueBell
    Joined: May 2017
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    Location: Victoria BC Canada

    BlueBell Ahhhhh...

    Hey Will,

    WOT!
    I'd try wiring it directly to the motor through an on/off switch.
    Just be sure you don't burn out the motor.
    Zero control. Size your prop accordingly.
    There are a number of German R/C, adjustable pitch, airplane props on-line which are ideal in this application.
    Sea-trials will be your winning ticket Will.
    The more prior to the race, the higher your chance of winning!
    K.I.S.S principle.
    Cheers
     
  7. alan craig
    Joined: Jul 2012
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    Location: s.e. england

    alan craig Senior Member

    Bah, Bluebell beat me to it.
    How many watts can you expect from your panel? I assume you are not using 4 x 320W panels on a canoe! 15-35W from a 700 size motor sounds very low, 100W at least should be possible. A means of measuring speed, and a wattmeter (from a model 'plane shop) are what you need to analyse and tune along with several different props. I humbly suggest giving in to common sense if you are not actually in the competition you describe, and fitting a battery.

    As for my own project with solar PV in this thread, the panel I bought was too heavy to be a solar roof for my little boat so I bought some flexi panels; I'll post about it soon.
     
  8. BlueBell
    Joined: May 2017
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    Location: Victoria BC Canada

    BlueBell Ahhhhh...

    ac,
    Now that you've bought lightweight flex panels, curve your roof...
     
  9. alan craig
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    Location: s.e. england

    alan craig Senior Member

    Just for you Bluebell...
     
  10. Will Fraser
    Joined: Feb 2014
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    Location: South Africa

    Will Fraser Senior Member

    It is not for the competition, so a battery is not out of the question. It would be nice though not to depend on the battery. If I can optimise everything simultaneously (panel, motor and prop) I hope to get away with a 50W panel. It can straddle the gunnels near the stern . It is only a 12ft, 19lb open canoe, so panel size and weight is an issue.
    The motor spec sheet shows 400W max and 200W at max efficiency. The panel specs show Vmpp 17.5V and Impp 2.85A. At 18V the motor can only produce 15W with 2.85A because it falls on the wrong side of the efficiency curve. Its no-load current is already at 2A.
    At 6V the motor will be turning much slower and peak efficiency falls in a power range equal to that of the solar panel. My big assumption is that I can in some simple way do an efficient dc-dc conversion to up the amps. Does a pwm charge controller do that?
     
  11. BlueBell
    Joined: May 2017
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    Location: Victoria BC Canada

    BlueBell Ahhhhh...

    NICE!
     
  12. BlueBell
    Joined: May 2017
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    Location: Victoria BC Canada

    BlueBell Ahhhhh...

    WF,
    I DON'T FOLLOW YOU ON A DC-DC CONVERSION???
    Oops, sorry, didn't mean to yell...
    Do you have room for a 20" diameter, 2-bladed prop?
     
  13. alan craig
    Joined: Jul 2012
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    Location: s.e. england

    alan craig Senior Member

    WF, I think I get it now; yes, a PWM controller will chop the voltage from the panel down to any lower voltage and current will be dependent on load. But a 12v 7Ah battery weighs 2.2kg/5lb and will keep you moving for an hour at your expected power level when there is no sun and will store precious energy when you're not using it (paddling/resting/in the pub). And from my limited testing of panels, the voltage drops substantially when there is shading or cloud.
     
  14. Will Fraser
    Joined: Feb 2014
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    Location: South Africa

    Will Fraser Senior Member

    Thanks for the advice. This project is turning into a very enjoyable learning curve.
    The dc-dc conversion is what you get from a step down buck converter. As far as I can tell this is exactly what is at the heart of a pwm speed control. PWM solar charge controllers apparently do not step up the current to maintain input power, so I suppose it is also not a guarantee that a drill's pwm control will step up the current. More testing to do.
    I have since sourced 4x 50W panels. It will give me more flexibility in mounting options and weight distribution. I have decided to enter the race (solarboatrace.co.za) with my 18ft kayak so now I am busy sketching outrigger arrangements.
    I have hooked up the 18V drill to a single panel and was able to drill a 1/4" hole through about 1" spruce. The motor first needs to be nursed up to speed though. If the trigger is depressed all the way at the start the panel voltage first drops to about 16V (from Voc of 22V) as the motor accelerates. If too much pressure is applied to the wood the voltage obviously drops and the motor stalls, so selecting the drill's low speed/high torque setting and keeping the rpms up helps a lot, while using the volt meter to tell me when to back off on the pressure.


    20181020_093851-1.jpg
     

  15. BlueBell
    Joined: May 2017
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    Location: Victoria BC Canada

    BlueBell Ahhhhh...

    Glad you're having fun Will.
    I've built a 17 foot race boat with an outrigger before and won!
    But that was with a very restrictive set of rules.
    Your race is much more wide open.
    Are you interested in winning or simply participating?

    It would be up to Alan, but you really should start a new thread.
     
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