Magnum 53 Hybrid

Discussion in 'Boat Design' started by John Kane, Jun 8, 2013.

  1. John Kane
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    John Kane Junior Member

    I am under no illusion that a motor sailer would be far more green and economical but that is not what I am building. I am building a sports fish so I am dealing with the parameters around my boat not others. I think people talk about hybrids as a common philosophy however every boat will have different solutions.
     
  2. Jeremy Harris
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    Jeremy Harris Senior Member

    Here's a reality check on just two of those figures:

    30kW of electric power for 2 hours = 60kWh taken from the batteries

    Even lithium batteries have to be kept within a range of about 70% working SOC, so the battery bank capacity needs to be at least 86kWh.

    An 86kWh lithium battery bank will cost around $45,000 (plus management system and fire safety system cost) and will weigh around 1200lbs.

    That leaves you with $25,000 for the electric propulsion motors, speed controllers, cabling, battery management system, fire safety system and solar panels.

    As already mentioned, after 4 or 5 years you will be looking to replace the batteries. They will lose capacity at around 5% per year from ageing, plus another few percent a year from cycle life degradation. If they are in a warm environment then their life will be shorter.

    The classic way to increase battery life is to fit more capacity, as life is non-linearly proportional to depth of charge/discharge. The downside is that this then increases the capital cost and weight of the battery pack, and that is already eating up a lot of your budget.

    I wish you well, and as I've already said this is a good idea in theory. The problem is that it isn't viable economically, and it presents some pretty big safety risks. The safety risks are manageable, but the safety systems needed, and specifically their testing and certification, may add a lot of cost to the project.
     
  3. daiquiri
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    daiquiri Engineering and Design

    I suspect that many of these failures are a direct consequence of the old and apparently incurable belief that 1 electric HP equals X diesel HPs (typically, X=4). For example, see these talks:
    https://www.glen-l.com/phpBB2/viewtopic.php?f=14&t=9367&view=previous
    http://www.forestryforum.com/board/index.php?topic=26986.0

    or even these articles from sailing magazines:
    http://www.masteryachting.com/files/lagoon_elec.pdf (page 6: a 12 HP electric motor is worth a 48 HP diesel engine, they say)
    http://www.electricmarinepropulsion.org/Newsabout/CWMarch05.PDF (page 3: a 6 HP electric motor will replace a 24 HP diesel).

    No wonder that, once the under-powered motor is installed on board, a bitter truth is soon revealed - that boats cannot read the yachting magazines and don't know the math... So for 6 HP power input they will give just 6 HP worth speed, no matter what drive one uses... :rolleyes:
     
  4. El_Guero

    El_Guero Previous Member

    And as already mentioned, 4 years = replacement of system .... or at very least batteries = $45,000

    Most people are finding their solar panels start needing replacement within 2 to 4 years.

    You are married to the idea of having electric. I get that.


    But, this system will cost you money not save you money. So, if you are married to it, admit the cost, and start trying to save some of that $115,000 in 4 years you will spend on electric ....

    $100,000 in fuel is about 20,000 gallons, is about 10,000 miles ....

    You won't break even on your electric. But, it might be enough of a 'green' marketing solution, you will keep the equipment. As already noted, some well-engineered boats have already taken their electric out.

    You will not make 25% per year ROI. Not even if you get government subsidy.

    IMHO. YMMV.
     
  5. El_Guero

    El_Guero Previous Member

    Daiquiri

    From everything I am reading, 10 hp electric provides 6 real hp only on very good days. Are the 'big' motors on boats more honest about their ratings?

    The battery strength is usually 20% to 30% over rated at the start.

    I want electric assist for my recumbent bike, but the cost overruns are insanely crazy.

    I do not mind spending money when I get what is advertised. But, I hate to spend money and only get half of what was advertised.

    Or written differently, for the OP to get the performance he wants, he will have to spend over $140,000 .... and that is an unfair taxation without representation.

    wayne

    PS to get real performance from electrics you really have to go to automotive quality equipment, and that usually doubles or quadruples the 'real' price you are told to expect before you start the endeavor.
     
  6. daiquiri
    Joined: May 2004
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    daiquiri Engineering and Design

    This is not true - you have been misinformed, I am affraid. :)
    PV panels can last very long time, up to 10-15 yrs if properly maintained. The manufacturers are already routinely giving 20 years warranty for their rated output and 3-4 yrs warranty for product defects. When the PV system fails, it is mostly due to electronic parts - inverters and charge controllers. Very seldom will PV panel fail, unless it suffers a mechanical or other physical damage.
     
  7. daiquiri
    Joined: May 2004
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    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    I don't know about that issue of e-motors underperformance. Frankly, it is the first time I hear about it. It might very much related to installation errors, like bad ventilation, shaft misalignments or smtg else.

    Regarding batteries, Peukert is the enemy: http://en.wikipedia.org/wiki/Peukert's_law :)
    The most common of all errors is to take rated batery's Ampere-hour value (the one printed on the casing and in product brochures) and use that raw number for calculations. In reality, the Ah will wildly vary with the intensity of the current, and Peukert's law tells us approximately what is the real battery capacity we can expect for a particular application.

    Cheers
     
  8. El_Guero

    El_Guero Previous Member

    Bikes seem to do better on the e-motor performance estimates than some other e-motors.

    But, you will notice bike e-motors focus on distance, not on hp for the reason they are inaccurate.

    But, maybe accuracy will improve as production is brought back to the USA and EU?

    My bike dealer wants me to go 'green motor' over a small engine. But, everything I read about e-motors is simple, "If you want performance near what we promise you the performance will be, you will spend a lot. And we will still over promise."

    Said differently, you can build your own system for around $500. But, if you want a system that actually performs close to what you would like, expect to pay at least $2500.
     
  9. Jeremy Harris
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    Jeremy Harris Senior Member

    Spot on about battery ratings!

    I've been working with electric propulsion (boats, motorcycles and bicycles) for a fair while now, and the Achilles heel of all electric systems is the battery rating and performance. It has become customary for adverts for battery performance to be highly misleading, especially in the electric bike market, where many vendors openly lie about things like range and battery life.

    Even lithium cells, which have a pretty near unity Peukert number exhibit a massive cycle life variation with depth of discharge. A pack that might have a cycle life of 2000 charge/discharge cycles when run at 60% SOC variation (i.e from 30% SOC to 90% SOC) may only have a cycle life of 200 charge discharge cycles or less if run from 5% SOC to 95% SOC.

    In practice this means that, to get good life, you need to make the battery pack at least 40% greater in capacity than you need, then add a bit more to allow for lifetime ageing. If you had, for example, a six year planned life for the battery pack, then you need to add about 25% to the initial capacity so that after five years the pack can still deliver enough energy to meet the minimum requirement.

    Taking the requirement here for a usable capacity of 60kWh (30kW x 2 hours) and assuming a planned battery pack life of 6 years before replacement, then to be able to still get 60kWh from the battery in the 6th year requires that it have an initial capacity of 60 x 1.4 x 1.25 = 105kWh. Such a pack, if made up with long-life lithium chemistry cells, such LiFePO4, might possibly give around 2000 cycles, so may allow the boat to be operated every day for around 6 years, allowing for maintenance periods when the pack won't be cycled.

    Frankly I wouldn't build such a system, as I strongly suspect that the pack would still fail early and add substantial cost to the project, but in theory, with the right level of engineering expertise such a system might work OK.
     
  10. John Kane
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    John Kane Junior Member

    So jeremy in order for me to push my boat at 5 knots as I mentioned earlier in the thread would take 15kw total not each engine this is why it is why the regenerated 30kw represented 2h run time.

    The solar having to be replaced in a few years is also nonsense the high quality panels are very durable and will last at least 10 and should be considerably longer.

    The batteries at 90% depth of discharge will do 2,000 cycles(my example 50 weekends at 10h so lets say 7 cycles or 350 cycles per year so should get 6 years out the batteries.

    The output power of the electric motors is the output not the rating numbers,these numbers do get fudges some times as people would look at the rating of an electric motor for example 25kw and assume this will be its output. This could be possible however when we are talking about power coming from batteries the amp being drawn can be a restriction and in this case coupling to the existing Diesel engine prop shaft will alter these top end numbers but for 5 knots a relatively small amount of power is needed and quickly that scale goes up if I want 6,7 or even 8 knots.

    This is using all the highest quality items of their kind on the market not using stuff made in a shed.
     
  11. Jeremy Harris
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    Jeremy Harris Senior Member

    OK so the numbers seem off again, complicated by the misuse of units for power and energy, I think.

    Power is in kW, and energy is in kWh (for practical purposes with an electric propulsion system).

    In the original spec you say the motors need to deliver 30kW for 2 hours. That's 60kWh. Now you're saying that the motors only need to deliver a total of 15kW, which for 2 hours is 30kWh.

    You won't get close to 2000 cycles with 90% SOC per cycle, even using the very best lithium cells available. To get 2000 cycles you will need to limit SOC variation to 70% per cycle, preferably 60% to be sure, as this boat is in a relatively warm climate, where the cells will degrade faster.

    The cells will have a calendar life degradation of around 5% per annum if they are kept no warmer than around 20 to 25 deg C. Any warmer and the rate of capacity loss with age increases.

    Electric motor efficiency is generally between 80 and 90% in the real world, so that needs to be factored in. For 15kW electrical input you will probably get around 13kW mechanical power output to the prop if the motor and controller are reasonably efficient.

    Looking at the energy budget using these new figures, and assuming you want a 6 year design life, then you need 30kWh of usable energy, but can tolerate a reduction in battery capacity in the last year of life, so that you can only get this capacity by increasing the SOC range. This would be normal practice, and gives a slight reduction in the nominal capacity of the battery required.

    First we look at the nominal capacity needed for no age related degradation:
    30kWh x 1.4 = 42 kWh, to get a battery that will achieve around 2000 cycles.

    Next, we have to allow for the calendar life capacity reduction of around 5% per year for the first five years (we'll let the battery pack get driven harder in the last year of its life):

    42 x 1.25 = 52.5kWh is the lowest battery capacity you can use to just meet your spec. You may want to consider increasing this slightly to give you a buffer for the odd occasion when you run into a problem that means motoring for longer than 2 hours, that's up to you.

    52.5kWh of LiFePO4 cells of a good quality (say, A123 cells) will weigh about 845 lbs without any casing or management system and will cost around $30,000 or so for the raw cells from A123, assuming you can get a decent deal for this large a quantity. The last order I bought cost me around $45 per 20Ah cell, which would work out at about $36,000 for this size of pack.

    To that price you need to add the cost of the battery management system, battery housings, a fire suppression system capable of dealing with a lithium fire and the motors wiring and motor controllers.

    Hope the above helps.
     
    Last edited: Jun 13, 2013
  12. Timothy
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    Timothy Senior Member

    When I worked on the numbers for the solar sail hybrid I am working on with a 4000 watt solar array, I ended up determining that if I wanted the batteries to last 8 to 10 years with a normal discharge of less than 40 % then I needed a 12.5kwh capacity to be able run a 2kw motor for one or two hours a day and three hours on the rare occasions that I expect to run at night. Using commercially available lithium batteries I calculated the weight for the batteries to be about 250lbs and the cost about $12000. I am relieved to see that these numbers seem to be roughly in line with Jeremy’s. For my purposes the weight and initial cost of the entire system as well as the reduced operating costs over ten years seems reasonable compared to a small diesel, high amp alternator, batteries for starting and house loads as well as the maintenance and the fuel to run them for ten years.
     
  13. John Kane
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    John Kane Junior Member

    Jeremy have you ever dealt with lithionics batteries. If you could take a look at them and see what you think. I would appreciate your feedback as I am only going with the figures they provide.
     
  14. Jeremy Harris
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    Jeremy Harris Senior Member

    I've never heard of them, but have just found their website. It's very sparse on technical information though, and makes claims for cycle life that are pretty incredibly optimistic. There's no mention of the cell chemistry, for example, no mention of how the battery management system works or what its limits are, and no mention of the cell manufacturer (virtually all lithium cells come from China or Korea, with a few still made in the USA at A123 I think (which is now Chinese owned) and some smaller cells made in Japan). I'd want to know who makes the cells, what the cell chemistry is and what sort of quality regime the manufacturer (which clearly isn't Lithionics) has in place.

    It's a sad fact that there have been a lot of companies that have been marketing rather poor Chinese cells in nicely finished packages for a premium price. I'm not saying that's the case here, but I do know of at least two US companies and one British company that have pulled this trick. Not really surprising, as China is awash with very cheap lithium cells, many being rejects from the big electric vehicle battery pack manufacturers.

    If it were me, then I'd stick with a reputable company with a proven track record in making long life lithium cells. The best known is probably A123, who despite now being Chinese owned still produce cells of high quality with a good cycle life. The use what's probably the safest lithium chemistry at the moment, LiFePO4, so the fire hazard is significantly reduced over cells like LiCoO2, for example.
     

  15. El_Guero

    El_Guero Previous Member

    Yes, that is what they say. But, they are not meeting and exceeding their MTBF rates. They are greatly missing their estimates.

    It may be because of faulty parts, but it is the reason I would not consider getting PV at this time.
     
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