best solart panel for 24V boat lift

jack99jack99 Posts: 6Registered Users ✭✭
Been having issues with expensive soalr panels that have a built in charge controller.
Batteries were draining....
Now ready to get the latest good stuff with separate charge controller.
Batteries are 2 x 12V lithiums 35 Ah , using the boat lift 3 - 4 times over weekends only.
Pump is a 3KW hydraulic pump.

What wattage is enough to charge those batts and do i get away with a PMW controller or MPPT needed?

Thanks !



  • EstragonEstragon Posts: 2,944Registered Users ✭✭✭✭✭
    Making assumptions, but:
    - 3000w load for 2min/lift 3000/30=100w
    - 8 lifts (4 up 4down) 100×8=800w/weekend.
    - 800w/12v nominal=67ah.

    Essentially, 100% of battery bank capacity is being used over a weekend (subject to assumptiins above), but the bank is likely charging to some extent over the weekend.

    You could check for average insolation for boating season months in your location at:

    Assuming you get 4hrs of full sun equivalent per average day, 67ah/4hrs=~17a @ 18Voc panel =
    306w. This, very roughly speaking, would get you fully charged on the monday following a really gloomy weekend - a bit more than you likely need.

    A minimal system would be more like a 5% charge rate; 70ah @5% =3.5a @18Voc = 63w. So somewhere in the 100-300w range for pv.

    IMHO, a pwm controller would do fine, but check the charging requirements of the batteries. I think most are designed as drop-in replacements and work with regular lead acid charging, but ...
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • mcgivormcgivor Posts: 2,307Solar Expert ✭✭✭✭✭
    The hydraulic pump would draw around 125A at 24VDC, without actually knowing the specs, this seems exceedingly high for a battery rated at 35Ah, mathematically the consumption based on short running times may seem ballenced, but the ability of the batteries to supply this current without voltage drop would be something to look into. The conductors feeding the motor would need to be sized appropriately, ~ 2 AWG  to avoid voltage drop as well as being as short as possible. Assuming this is the only load, as well as being power up, gravity return, 4 times per weekend is relatively low, my rough calculation would be around 20Ah, therefore the PV would need to be capable of replacing this plus an additional 50%, a 300W 24V nominal panel  or 2×100 12V nominal panels  in seriesl would probably be ample, with a PWM controller. Without battery details, all is just speculation, do you have a link to the specifications for the battery? That would be extremely helpful, as well as location to determine how much solar insolation is available.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 

  • jack99jack99 Posts: 6Registered Users ✭✭
    Hi All ,

    Thanks for input.
    As you may have gathered I am not very familiar with the technology.
    Initially the SUNSTREAM boat lift came with the 24V DC motor and after looking up the model of the motor it states 3KW.
    The (upward) lift draws a huge amount I believe as my boat is close to 12.000 LBS , the downward launch is obviously not that much of a deal I believe , so technically I am lifting 2 x over a weekend and then a week (5 days) of rest in ...Hong Kong.
    The strange thing is that the lift originally came with 2 relatively small 12V solar panels wired in series , it came that way from manufacturer in 2012 along with lead acid batteries of 80 Ah.
    I could lift boat 2 x a weekend but by the next week it would struggle , I then replaced the original lead acids (105 Ah) x 2 with fresh ones but the same thing would happen after a few weeks.
    I figured smaller Lithium batteries which I am using now would solve the issue as I believe they can be drawn very deep without problems and are much lighter and smaller to fit in the battery box , but the same issue still happens after a few weeks , to me it means batteries are not charging fast enough.
    I have then upgraded to a large 24V solar panel from Solbian (72W model supposedly the go to brand for boating industry) which has a built in charge controller , but its definitely not working for me , 3-4 weeks later the batts die half way lifting up the boat.
    Someone told me it is a charge controller issue , but as the current one is built in I might as well get a new proper solar panel for my needs with an MPPT charger ( read it is better then PWM)
    If I look online there are boat lift solar sets which come with a 20V 30W or 20V 40W solar panel and PWM charge controller , supposedly for boats over 10.000 LBS , thats why i figured anything over 40W should do it for me.
    I am based in the candy store with regards to solar panels as I am next door to China and get anything , anywhere anytime but need to know what I am looking for.
    Also there is space on top of the battery box to put a solar panel (flat mounted to the battery box cover facing straight up) but ideally  it can't be over 4 feet length /width.
    I am confused about the 60 cell and 72 cell differences , I would definitely prefer a smaller more power solar panel but don't know what specs to follow.
    All help appreciated very much , thanks

  • jack99jack99 Posts: 6Registered Users ✭✭
    I can only find the below specs on the DC motor

    1. Type: ZD2973D

    2. Voltage: 24V

    3. Power: 3KW

    4. Speed: 3100RPM

    5. Rotation: CW

    6. O.D. : 127mm/5'

    7. Insulation: F

    8. Protection Class: IP54

    9. Operation Mode: S2

    10. Torque 10 Nm

    The lithium batts (12V in series) are 35Ah , but I still have the 12V 105 Ah Royals (lead acid)

  • jack99jack99 Posts: 6Registered Users ✭✭
    Here are some pics of the lift , one of the pics shows the tiny 12V solar panel on one of the boxes as well as the large 24V solar panel from Solbian which I my opinion should easily match what the 2 original 12V panels are giving out.

  • EstragonEstragon Posts: 2,944Registered Users ✭✭✭✭✭
    The difference between a 60 and 72 cell panel generally boils down to 2 things; size (72 cell tend to be larger ~1m x 2m), and voltage (72 cell higher ~37V under load). A single 60 cell panel may not provide enough voltage for a 24v nominal bank, especially if the panel is hot and/or used with mppt type controller.

    The main advantages to mppt are the ability to wire multiple panels in series (less voltage drop / smaller wire), and somewhat more production particularly in cold climate. In your climate with panel(s) nearby, neither really applies, so pwm is probably a better choice.

    Lithium does have a wider range of usable capacity, and generally have a fairly flat voltage curve in the usable range. They vary a bit by chemistry and construction, but in general they can handle decent heavy surge loads. That said, there are limits (eg maybe 2x capacity so 70a in this case - you'd need to check spec for your batteries). As Mcgivor noted, you're pulling some big current and need battery and wiring capable of supplying it.

    I have a pair of 150w Renogy panels that are about 1m (39") square, but unfortunately they're 12v nominal, as most smaller panels will be. You'd need a pair of them in series, or a "boost" type charge controller (most are "buck" controllers, which convert higher voltage / low current pv to low voltage / higher current for charging batteries). Maybe boost controllers or small 24v panels are available there?
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • jack99jack99 Posts: 6Registered Users ✭✭
    Thanks Estragon , it still puzzles me why original lift supply would include 2 tiny 12V panels , the 72W solbian panel (24V) is way bigger and is capable (under ideal circumstances) to deliver 3A , I don't think the 2 tiny 12V panels dated 2012 can match that.
    I can literally get any solar panel that is available worldwide from around the corner but need to know the minimum wattage I need.
    I have both the lithiums and large 105aH deep cycle batts so I can try both on the new panel.
    will follow your advise on the PWM charge controller , at least I get see if they are charging....Thanks for your input.
  • mcgivormcgivor Posts: 2,307Solar Expert ✭✭✭✭✭
    edited May 11 #9
    Think of the boat lift as a weight lifter, which ironically it is, as opposed to a marathon runner, or a normal off grid  system, both need tremendous amounts of energy but over differing periods of time. The boat lift needs high capacity for a short duration, the only way to achieve this is with capacity, battery capacity that is, as there are long rest periods between lifts, there is time to replenish what is taken out. Naturally there needs to be sun to achieve this, Hong Kong sun on a flat panel averages between 3 and just under 5 hours on a flat mounted panel, but this has to be without shadows, even small ones can reduce output dramatically. The advantages of MPPT over PWM are negligible in a situation where temperatures are relatively stable on the high end of the scale, but Hong Kong has its cooler periods, but as space is an issue it must be considered that MPPT needs a higher voltage ~48V in the case of a 24V nominal system , which may mean a larger panel footprint. Essentially 60 cell panels can only be used with an MPPT controller, 36 or 72 can be used with PWM or MPPT, due to the voltage at maximum power, so 2 × 100W 36 cell panels in series will produce ~160W in normal conditions, which should be sufficient given the rest periods between useage. Understandably there is lots to digest, but I believe the key is a larger battery capacity along with a means to sufficiently replenish what is taken out.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 

  • BB.BB. Posts: 28,067Super Moderators, Administrators admin
    edited May 12 #10
    In general, the starting suggestion is 5% to 13% rate of charge--5% can work for weekend/sunny season usage (cabin). 10%+ is better for full time off grid home/usage (9+ months of the year). Obviously, in your case, it is not a typical home system... For Flooded Cell Lead acid batteries, 5% is pretty much the minimum suggested rate of charge. And 10% is the actual minimum rate of charge some Mfg require for their batteries:
    • 105 AH FLA battery * 29.0 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 198 Watts array minimum
    • 105 AH FLA battery * 29.0 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 395 Watt array nominal
    • 105 AH FLA battery * 29.0 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 514 Watt array "typical cost effective" maximum
    Note that Li Ion batteries (in general) do not really have a minimum charging requirement. However, if you take them near dead, they will fail. And depending on the battery chemistry, a failing Li Ion battery can catch fire pretty easily if over/under charged (LiFePO4 -- Li Iron Phosphate batteries tend to be the "safer" Li Ion chemistry).

    In Hong Kong, you will have something like this many hours of sun per day (fixed array):

    Hong Kong
    Average Solar Insolation figures

    Measured in kWh/m2/day onto a horizontal surface:
    Jan Feb Mar Apr May Jun
    Jul Aug Sep Oct Nov Dec
    So, if you go with a minimum 198 Watt array, roughly you will have (assume don't use boat much December through February):
    • 198 Watt array * 0.61 DC flooded cell end to end system eff * 3.08 hours of sun per day = 372 WH  Watt*Hours per day
    • 372 WH per day / 24 VDC battery system = 15.5 AH per day @ 24 volts

    Really need to know the time of the lift (and drop), and the current draw during the operation of the lift. Also, you need to diagnose how well the charging system is working (is it working to specifications, or is it not).

    You need a DC Current Clamp DMM (digital multi meter). Here is an example (note there are AC only current clamp meters, an AC/DC current clamp meters--AC only meters are perfectly good meters, but will not work for your DC power system--You need one that measures DC Current--Both type will measure AC and DC voltage--So check the specifications carefully). Here is an example of inexpensive AC/DC Current Clamp DMM:

    You want to see at what voltage the battery bank is charging. When actively charging, you want ~29.4 volts (~14.7 volts for "12 volt" system) (note that if the battery is discharged, the voltage will slowly climb to ~29.4 volts from ~26.0 volts). Once the batteries are fully charged, you want the charge controller to hold ~ 27.2 volts (~13.6 volts for 12 volt bank) while the sun is up and the batteries are fully charged. At night the batteries should be around 25.6 volts resting (~12.8 volts).

    If you have flooded cell batteries, you can get a hydrometer and measure the specific gravity (the "gold standard" for determining state of charge for flooded cell lead acid batteries).

    And use the DC current clamp to measure the current from the solar panel(s) and into the battery bank. A 70 Watt @ Vmp~36 volt solar panel (72 cell) would be rated around:

    • 70 Watts / 36 volts = 1.9 Amps

    And on a reasonably sunny day at noon time with a discharged battery bank, anything >~1.0 amps (50%) means the system is probably working OK.

    You probably do not need an MPPT charge controller--It will not really be more efficient than the proper "24 volt" solar array + PWM (Note, Vmp-array should be somewhere around 35-40 volts--For example, 2x "12 volt panels" in series will work fine ( 2x 18.0 volt Vmp = 36 volt array).

    If you do use a MPPT charge controller, the Vmp-array will need to be over ~40 volts (3x "12 volt" panels in series) to work properly (MPPT controllers need higher Vmp-array voltages for full charging current).

    Li Ion batteries certainly can supply very high current from a small/light weight battery pack. However, the small AH capacity still means that the bank will "go dead" very quickly if loads > solar charging (Your 105 AH Lead Acid battery bank has 3x the amount of stored energy vs the 35 AH Li Ion battery bank). Your 105 AH battery bank may operate the lift all weekend without bright sun--And the Li Ion bank may run "dead" in less than a day (for example--Don't know until we get some current/power measurements and timing from your system).


    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jonrjonr Posts: 1,098Solar Expert ✭✭✭✭
    My solution was to install a plug so that the lift could use the boat battery.  A little less convenient, but no lift battery and no lift solar panels (one on the boat to keep the batteries topped off is still useful).
  • BB.BB. Posts: 28,067Super Moderators, Administrators admin
    That is a great idea Jon.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jack99jack99 Posts: 6Registered Users ✭✭
    Thanks a lot for all the info , quite a bit for me to digest (and fully understand) , I will go back this weekend and try and see if I can get some numbers with respect to the current draw when lifting , again really appreciate your help.

    kind regards

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