What source for electric energy in a hybrid system?

Discussion in 'Propulsion' started by Magnus W, Dec 20, 2018.

  1. Magnus W
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    Magnus W Senior Member

    For the purpose of lowering emissions it might be a good idea to have some other means of turning prop (or jet) than the main engine during low speed situations.

    While there are quite a few hybrid system designs available for larger vessels there are none (to my knowledge) available for a planing boat. For a boat sized vessel there's also the option of fitting retractable electrical pod engines but I'm currently toying with the idea of having a hybrid transmission with a PTI.

    It seems to me that the best low speed engine would be electric. But batteries are expensive and the energy to weight (or volume) ratio is pretty bad so getting a decent range on batteries alone doesn't seem doable (remember, a planing boat so not too heavy).

    What would be the best way of generating electricity while under way?

    (I'd like to keep it generic but in my specific case we can estimate the power needed to be 10 kW for a speed of 7 knots. It's rough but in the ballpark considering the drag and efficiency of the drive.)
     
  2. Magnus W
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    Magnus W Senior Member

    One possible solution is a hydrogen fuel cell. While being restricted to a single fuel there are hydrogen generators available making you "independent". This is relatively speaking a light installation in the boat.
     
  3. BlueBell
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    BlueBell Ahhhhh...

    I wish there was a reasonable solution Magnus W, but it's not going to happen without considerable weight and cost.
    Unless you can make a tiny nuclear reactor...
    10kw is a lot of power.
    Oh, wait, I know, how about a sail or two?
     
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  4. Niclas Vestman
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    Niclas Vestman Junior Member

    I would say that using biofuel is the most realistic option. FAME, E85 or similar. They have around 20 to 30% the carbon footprint compared to standard petrol and diesel. Not always, but often, possible to make the neccesary adaptions. Biggest problem would probably finding places to refill without having to a car. Propane is more often avaliable in marinas as well as being a clan fuel. But tank installation is heavy and conversion expensive. My guess would be arround 7k€. Maybe cheaper to by a generator for biofuel, than to convert existing engines. That would also make it possible to use a small amount of solar and modest size battery bank.
     
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  5. JamesG123
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    JamesG123 Senior Member

    You still have to power the hydrogen generator, and pump/store the explosive gas.
     
  6. philSweet
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    philSweet Senior Member

    It depends on the size of the prime mover and associated driveline equipment and prop. What are the specs and sizes of things currently on (or proposed for) the vessel, and what is the vessel? Also, what is the annual usage of low speed operation in hours? You can't just ask what source for the power. We need to know a lot of details about the design, operation, and location of the vessel.
     
  7. Magnus W
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    Magnus W Senior Member

    I know that in order to get a more specific answer I need to be, well, more specific.

    But I would like to have a broader discussion about sources for electrical power that are neither too large nor too heavy to be a considerable option in a boat (and by boat I mean not a ship, say 20 by 5 meters tops give or take).

    In my case I would probably be best of with running the large diesel on some kind of biofuel and accept the the low efficiency during low load as still being better than regular diesel and less expensive and less complicated than running an electrical engine from an odd powersource.

    But for the sake of the discussion, humour me.
     
  8. alan craig
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    alan craig Senior Member

    If you forget the electrical option you could have a 10kW I.C. engine to turn the prop at low speeds, connected to the shaft by speed reduction gearbox, belt or chain. It would need a clutch mechanism to ensure that both engines are never connected to the shaft at the same time.
     
  9. gonzo
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    gonzo Senior Member

    When you consider the extra weight and cost, it is only reasonable to install a hybrid system like that in very limited conditions. For example, where regulations do not allow internal combustion engines in certain areas. The only honest way of calculating emissions ( not like sales department do) is to use cradle to grave data. Consider the cost (in emissions) to manufacture the batteries, electric motor, controller, etc. Add the environmental cost of disposing of batteries. Finally, add the inefficiencies of converting one type of energy to another. That will give you the amount of emissions generated.
     
  10. Magnus W
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    Magnus W Senior Member

    The distinct benefits of an electrical engine is noise, vibrations and exhaust gasses. The "green feeling" is thereby increased immensely which – like it or not – needs to be considered as it's something that can be monetised.
     
  11. Magnus W
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    Magnus W Senior Member

    It all depends on where the money's coming from. I can assure you that over here it would be a distinct benefit for an operator with say a taxi or charter boat business to be able to claim being green. I suppose I could fit a few trolling engines to the transom and a couple of square feet of solar panels on the roof in order to give the customers what they think they need but it would only be virtue signaling. But since I'm stupid enough not to just wanting to profit from the green hysteria I'm more into marking something that actually works. And maybe not in terms of investment vs emissions but in total emissions.

    I totally agree on the cradle to grave analysis being important. That's why I'm not to keen on relying on batteries for more than only a small part of the stored energy. As far as electrical engine, controller and transmission emissions cost goes it should be offset by the larger life span of the main engine and even more if you add maintenance into it (my current enginens get their maintenance on hours with no regard to the type of operation so 100 low load hours equal 1oo high load hours).

    So I'm back to the question of generating electricity. And if a fuel cell won't cut it, perhaps a small multi fuel powered power source will, I suppose a small and highly insulated gas engine could pass undetected from passengers. I have thought about a stirling gen set but the the only experience I have with them are from subs and while being very quiet the one we had weren't exactly small in relation to the output
     
  12. alan craig
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    alan craig Senior Member

    You started the thread with "For the purpose of lowering emissions..." and then asked "humour me".
    If you think you need 10kW for low speeds then you probably have in the order of 100kW to 200kW as the main drive so my suggestion is reasonable to lower emissions. I think we're on the same side though; I have an electric powered small boat and have completed a solar roof but no data yet on the solar, winter stopped play.
     
  13. fallguy
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    fallguy Senior Member

    Why not wind power?

    Let the arrows fly....

    The thing is, technically, you can generate power underway and while standing; save dead calms.

    And you won't get 10kw, but part of it.

    In a powerboat, I am sure running a wind generator while underway looks and seems ludicrous, but is it?

    Just a conversation.
     
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  14. Magnus W
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    Magnus W Senior Member

    I agree that a small IC engine running at load for best fuel consumption is most likely the better way, especially if you run it on some kind of biofuel. But I'm sticking with electric at this point, for reasons mentioned earlier.


    The idea of filling up while still is appealing but then there are the batteries.

    And I suppose a wind generator could do that. But so could solar panels and they are not so heavy and they have no aerodynamic drag to speak of. In my case I have approximately 12 m2 available which on any normal day would equal a 600 W output, not enough to even get the boat moving but for charging batteries absolutely. (Assuming 50 W/m2 on average.)
    I looked at Leading Edge, a wind gen manufacturer, and their LE600 with almost 1,6 meter rotor diameter has a rated maximum output of 750 W but is rated at 160 W at wind speed of 7,2 m/s. And the price tag is higher than for solar panels of the same max and average output.


    I'm still curious about hydrogen. I'm guessing some have heard about freeing hydrogen from sea water by means of solar power Catalyst frees hydrogen from seawater https://cen.acs.org/energy/hydrogen-power/Catalyst-frees-hydrogen-seawater/96/web/2018/03 which to me is appealing. Combine "free" hydrogen with storage in metal hydride tanks (circa 200-220Wh/kg for the larger tanks) and you have fuel for either an ICE or a fuel cell. The storage pressure is by comparison low (20 bar refill pressure) so that takes care of some of the safety problems. Pragma specs 5000 cycle lifetime for their 21 kWh tank and 45 minutes from empty to fully charged. Weight 98 kg. For some reason they haven't listed the price on the website...

    It should be possible to get the necessary power (10 kW) from a package of about 200 kg (which lowers the energy density to 100 Wh/kg) for a tank/fuel cell solution with 21 kWh of stored energy. With an estimated 70 percent efficiency in the fuel cell that translates into about 15 kWh which is roughly what you would get out of lithium batteries with of the same capacity. So all in all you get the same (ballpark figures) energy density between batteries and hydrogen fuel cells.

    The cost of filling up with hydrogen is most likely way more expensive, but in terms of energy containers you get 5 times the life span from metal hydride tanks vs batteries. Filling time is much lower with hydrogen (assuming you have it stored), especially if you want to keep the batteries happy.

    Are any options viable in terms of ROI? Most likely not. But interesting to think about.
     

  15. fallguy
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    fallguy Senior Member


    Isn't burning water sort of the most agriegous offense possible against humanity?
     
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