Solar powered cat-again

Discussion in 'Hybrid' started by Ting, Apr 13, 2013.

  1. Ting
    Joined: Apr 2013
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    Location: Caribbean

    Ting New Member

    (This is a variation on questions asked before. I searched for similar subjects but didn't find anything directly addressing my question. Technology also progresses quickly in this field, so previous info is likely to be outdated. On to the subject...)

    I'm thinking of building a solar powered passenger day charter catamaran for use in the tropics. We would do 8-hr sightseeing and snorkeling trips in inshore waters, but would spend only 2-3 hrs/day underway, assuming a range of +\-20 miles maximum, cruising speed of 8 kts. We would be operating in maximum 15-20 kts of wind, 2-4' seas, and would return to the same port each day, so equal parts upwind/downwind. If we did 5 trips/week with 30 people per day I'd be happy.

    The platform would be a converted 50-60', 50-75 passenger day sail catamaran with the mast and (2x60hp) outboards removed. I'm considering a pair of 48v, 20kw electric DC motors powered by 2 separate 48v Li ion battery banks. They would be charged by +\- 1000 sq ft of solar panels, or approx 20kw of solar. (shhhh...we'd also have a backup generator to run at night if needed so the show can go on...but you didn't hear it from me). For house loads we'd have 4 D400 wind gens (1600w) charging a typical 12v DC system (refrigeration, stereo, toilets, water maker, lights).

    Based on nothing but my opinion, limited experience, and guesses, I'd assume a 55' cat could do about 8 kts at 2/3 power with 2x20 kw motors, or a consumption of 50-80 kwh/day. The 20kw of panels would produce 50% output for 8 hrs/day, or approx 80 kwh/day, and two days per week would be reserve charging days.

    Those guesses are arrived at by having run day sail cats with 2x60 hp motors. We can do 10+ at nearly full throttle with inefficient outboard props. 1/2 throttle on a 60hp gets you about 8kts. On a 62' 16t cruising cat we get 8 kts@1800 rpm with 56hp yanmars. That's less than 20 hp from each motor at that rpm. As for solar, we get a maximum of 100+ amps @12v out of a 1600w array at midday. We're charging at 30-50 amps at 8am and 4pm (we also have quite a bit of shade from the boom and rigging reducing output significantly. Presumably there would be no shade on the solar cat, other than limited cloud cover). Our 1600w of solar currently run 4 fridges, an ice maker, watermaker, etc. Presumably for house loads 1600w of wind would surpass 1600 kw of solar in the tropics. Breeze is usually 24/7, solar is 12.

    To summarize:
    55' passenger cat
    2x20 kw electric motors
    100 kwh 48v bank, Li ion batteries (2000lbs)
    20kw solar array, 80x250w solar panels (3000lbs)
    Charge controllers
    Cabling
    4xD400 wind generators
    1 kwh AGM 12v house bank

    What are the technical obstacles to the above?

    What should I expect for speed from 2x20kw motors pushing reasonably efficient 55' hulls?

    What should I expect for discharge and charging inefficiencies?

    What's the system weight going to be? Weight will be an obstacle, but day sail cats are built with lots of load carrying ability. Ditch the mast, sails, and rigging as well as the 2 outboards, motor sled, etc and you aren't really a wash weight wise, but maybe 1/2 the system weight, right?

    What else am I missing, before I open my checkbook?
     
  2. FAST FRED
    Joined: Oct 2002
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    Location: Conn in summers , Ortona FL in winter , with big d

    FAST FRED Senior Member

    What are the technical obstacles to the above?


    BATTERIES.
     
  3. groper
    Joined: Jun 2011
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    Location: australia

    groper Senior Member

    You have to make your battery bank from something like these ; http://evworks.com.au/index.php?product=BAT-WB-LYP1000AHC

    dont pay attention to the price as you will do better with a bulk buy for a large bank like you need, maybe 10-20% cheaper... so 15 of these cells in series gives you your 48v and 1000ah = 48kw/h so you wanted double this, drop another set in the other hull and you end up with 96kw/h. A problem will be a parralell link across the hulls, thats a very large link pair of cables, so its probably better to keep 2 seperate sets, one to run each motor in each hull and then you also have redundancy if something goes wrong... so 1221lbs in batteries alone in each hull, dont forget to add link bars and other heavy guage cabling - they are quite heavy and expensive aswell. You need to oversize your battery bank by 30% more than your useage as you cant cycle the battery 100% DoD without damaging it and you will blow a huge chunk of change replacing your $30k battery bank in your first week of operation. Lifepo4 cells can only be cycled to a max of 80% of their rated capacity without damage, 70% depth of discharge is better and will last much longer. At 70% DoD cycling you can expect around 3000 cycles before the capacity drops to 80% from nominal - you need to figure this into calculations also allowing more capacity for when the cells degrade overtime. So from your initial calculations, i think you need to add more cells and increase the motor bank capacity 40% more than the kw/h you will burn through in a single day of average operation. - which means more cost and more weight.

    Your solar collection rate seems about right. From a decent set of panels ive seen, a 250w panel is 1.65m^2. So thats 165m^2 for 25kw/h of collection. This equates to 1796sq ft. So your initial estimate of getting 20kw/h of panels onto 1000sqft is a bit optimistic, where did you get these figures from? Do you have a link to a more efficient, yet still affordable solar panel? Using the panels im looking at i could only expect to fit 13.9kw of rated solar panels on that 1000sqft area...

    As to losses and efficiency, if you use large enough guage cabling, and keep the cabling length short and with good electrical design, you should have minimal / negligible problems. Buts theres a whole lot of information and application that needs to be considered in the electrical design to acheive this.

    At the end of teh day, not many people have done this just yet because the costs are still too high- although improving everyday. Wind power is still cheaper but carries its own limitations and hazards on a passenger vessel which i guess your trying to avoid... within 10 years these kinds of projects will really start to move...
     
  4. Ting
    Joined: Apr 2013
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    Ting New Member

    Thanks for the feedback. It's good to get some serious advice. I'm glad you took the time to respond.

    As for the battery bank size, remember that there should be approx 80kwh coming in a day while I'm discharging +\- 65kwh. I figure I'd run from 8am-830 (13kwh out, 5kwh in), then swim for an hour (0 kwh out, 10 kwh in), then run again for a 1/2 hr (13kwh out, 5kwh in), then beach and lunch for a few hrs (0 out, 20 in), etc. I doubt the battery bank would get below 80%. The reserve capacity is there more as a backup for consecutive shady days. One day off would recover 80% of the total capacity, or 100% of my usable capacity.

    As for solar, we have the Sanyo HIT now. Sunpower Corp has comparable panels. They work out to about 19.5kwh per 1000sqft. Not the cheapest panels, but with limited real estate density and efficiency count for more than $/w.

    Any strongly held beliefs about Mastervolt? They offer everything I'd need except for the panels I want. One stop shopping is nice.
     
  5. bman
    Joined: Mar 2013
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    bman New Member

    Same as GROPER said.I would use a string of 16 cells for 48V and agree that 20KW from 1000sqf seems a bit optimistic.For commercial day use overnight charging would go well.If it could be arranged.A nice clean bottom and good conditions should give you the speed.
     
  6. groper
    Joined: Jun 2011
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    groper Senior Member

    here the spec for the sanyo HIT panels - http://us.sanyo.com/dynamic/LinkListingItems/Files/Panasonic HIT 240S Data Sheet-1-1.pdf

    These look like bloody nice panels with a 21.8% rated efficiency, made in the US, but this still only equates to 17.7w per sqft - so your looking at 17.7kw for your 1000sqft area... how much are these panels btw, do you have a price on them yet? The panels i am looking at for my boat cost $1 per watt, but have lower efficiency...

    As to the capacity, i guess you really need to do the sums and get it right, otherwise your dragging around alot of dead weight for nothing not to mention the high capitol investment...

    For the electrical energy conversion, look at the specific motor you plan to use and its KVA rating - not the KW rating which will tell you its electrical energy consumption rather than its mechanical output power. Big differences in motors and prices, such as brushless motors driven by high current variable speed drives (transistors), down to the old school simple mechanical brush commutation etc...

    providing your willing to top up charge overnight from mains power (or diesel gensets etc) then you should have no problems. so i guess you only need to size assuming a worst case scenario of full on heavy cloud and rain all day with virtually zero charging, or an unknown electrical fault preventing it etc... i guess you will still have an auxillary outboard motor in case the whole thing craps out?

    Make sure you get some properly designed propellors for this too, big gains in efficiency to have a large diameter, fine pitch, high aspect ratio prop - similar to a nuclear submarine prop...
     
  7. bman
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    bman New Member

    Yes nice panels.Appears suited to a 36V system.Wont be easy to retrofit 1000sqft onto a 55ft vessel.
     
  8. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    The panels will take the whole deck. Are you assuming people will be willing to stay below decks all the time? In the tropics without A/C that would be very uncomfortable.
     
  9. Ting
    Joined: Apr 2013
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    Ting New Member

    Thanks again for more feedback.

    As far as the array, assume the cat is 55x30. I think an array that serves as a large awning that measures 30x33 or 25x40 would fit quite nicely. Essentially from the back beam to fwd end of the bridge deck. Guests would be sitting below the awning but in open air on benches on deck, and there'd be a bar obviously, too. See the link below for a smaller approximation.

    http://www.transatlantic21.org/boat/

    It's good to see that they made it across the Atlantic. The concept is much the same, just different course.

    Not planning on having an outboard as a backup.

    Solar calculations may have been on the high side. Prices for the Sanyo aren't cheap but acceptable for my purposes. We got the same panels 3 years ago but they were rated for about 10% less (210w). Hopefully efficiencies increase and costs will come down before I pull the trigger.

    Any guesses whether 15kw motors would be enough? I don't want to overwork the motors and run them hot, and don't want to be forced into slow operation because of not enough power. But I also want to keep the system as small as possible. The Mastervolt 15kw runs at 48v, the 20kw runs at 96v. If you look at their specs they recommend a 15m, 8000kg cat run 2x7.5kw motors. That obviously seems undersized for my purposes (17m, 14000kg), but 20 may be too big.
     
  10. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    The solar panels above deck will create a huge amount of wind resistance. Have you calculated the extra power you need to go upwind?
     
  11. Ting
    Joined: Apr 2013
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    Ting New Member

    I disagree Gonzo. There shouldn't be much more windage than a typical deckhouse, and without a mast and related rigging overall windage should be considerably less.

    Thanks for the input though.
     
  12. nimblemotors
    Joined: Jun 2009
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    nimblemotors Senior Member

    That looks great. How much do expect to spend on building it? JackB
     
  13. rwatson
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    rwatson Senior Member


  14. T0x1c
    Joined: May 2013
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    T0x1c Junior Member

    Mastervolt are generally more pricey than Victron Energy. This is top quality material, however more and more of Mastervolt products need their MasterBus to work, making the system more complicated. Also Victron is more represented in the Caribbeans.
    Mastervolt took over from Victron for the Hymar project (see http://www.bruntons-propellers.com/hymar/HYMAR.PDF) to develop 95% efficient DC-DC converters, and the Battery Monitoring system.
     
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