advice re new set up on a boat

jimbob01
jimbob01 Solar Expert Posts: 63 ✭✭
hi guys my first post...
i currently have a small system on my boat...12v with various '12v' panels total about 800w.. a bank of 800ah yuasa endurance batteries and a 2.5kw sterling pure sine wave inverter.
i need more power/storage etc
ok so i bought 6x 235w 60 cell sharp panels
i have in mind to go 24v...
i have the option to use 8x 200ah 12v powersonic batts
the original 800ah yuasa (8x 160 ah@6v)
also i have 12x yuasa 100ah 6v batts
i would have room on my roof for the 6 x 235w panels=1410
also 4 x 80w(12v) panels..........................................1730 total watts
my dilema is how do i get the best from the batteries ie they are not all the same?
and which mppt(s) do i go for?
i currently run a c60 xantrex pwm...
i have a 15kva back up westerbeke.http
i would like to here from those that have experience? thanks for reading .jim.

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: advice re new set up on a boat

    Boats are tough to do solar on... If they are at anchor, you cannot easily tilt the panel to face south at the "ideal" angle. And if it is a sail boat, the lines/masts/booms/sails provide moving shadows that kill much of the output of a solar array.

    If the boat is docked (such as a house boat most of the season/permanent living situation, and you can face the array south (northern hemisphere), it is better.

    If you are looking to run from solar power much of the year (depending on amount of sun where the boat/solar array is located), we can run some numbers and see if they make sense to you.

    Generally, we like to have the loads define the battery bank, and then the battery bank defines the size of the array--As well as the loads defining the array size too.

    In the "olden days" when batteries and fuel were cheap, and solar panels were expensive--People generally installed a lot of "extra" batteries to extend the run time during poor sun/heavy loads.

    Today, with fuel and batteries costs skyrocketing, and solar panels a cheap as they every have been--The better solution is to size the battery bank for about 2 days of no-sun load and 50% maximum discharge. And size the array on the larger side. With lead acid batteries, 1-3 days and 50% maximum discharge it about the best for long battery life--You do not want to have 7+ days of storage--Lead Acid batteries begin to sulfate if they set at lower level of charge for days/weeks at a time and will fail after a few years.

    Another difficulty is lots of smaller AH batteries in parallel. You should wire them per this website, and you need to keep on top of the battery bank servicing. That is a lot of cells to check specific gravity/add water. And you should monitor the wiring/current flow during charging/discharging with a DC Current Clamp Meter.

    My personal recommendation is to aim for one series string of batteries (use larger Amp*Hour rated batteries, and you can get 3/2/1 cell batteries to keep their size small enough for one-two people to move around without a forklift/crane) and, at most three parallel strings of batteries. And, for safety, you should have a series fuse/breaker per string (especially with 3 or more parallel strings) to protect against fire if there is a short circuit--adds costs/complexity to bank). Although, there are many people with more batteries in parallel and very happy with the results.

    So 12x 12 volt * 100 AH battery bank. Two days of "no sun" and 50% discharge and assuming much of your loads are 239 VAC @ 50 Hz:
    • 12 batt * 12 volt * 160 AH * 0.85 inverter eff * 1/2 days of storage * 0.50 maximum discharge = 4,896 Watt*Hours per day loads

    And, we recommend charging at 5% to 13% rate of charge (based on battery 20 Hour Capacity Rating):
    • 12 batt* 14.5 volts charging * 160 AH * 1/0.77 panel+controller derating * 0.05 rate of charge = 1,808 Watt array minimum
    • 12 batt* 14.5 volts charging * 160 AH * 1/0.77 panel+controller derating * 0.10 rate of charge = 3,616 Watt array nomimal
    • 12 batt* 14.5 volts charging * 160 AH * 1/0.77 panel+controller derating * 0.13 rate of charge = 4,700 Watt array "cost effective maximum"

    And, how much sun do you get in your region... In much of North America, we get around 4 hours of sun minimum for 9+ months of the year. In other regions, perhaps closer to 3 hours of sun per day for 9 months--Add mounting to a boat/sail boat, you may even get less.

    Taking a guess at your power usage of 4,896 Watt*Hours per day of loading and 4 hours of sun "break even" day:
    • 4,896 WH per day * 1/0.52 system efficiency * 1/4 hours of sun per day = 2,448 Watt array "minimum"

    So, for my mythical off grid system, I woudl suggest around 2,448 watt to 4,700 Watt array, with 3,616 watt array being a healthy nominal amount of array.

    And for charging your battery bank, you have the 5% to 13% nominal range, and with a genset you can go as high as 20-25% rate of charge (you need to monitor battery bank temperature--higher charge rates can cause thermal run-away and "melt" the bank down). Taking 10% and 20% for an AC battery charger:
    • 12 batteries * 160 AH * 0.10 rate of charge = 192 Amps nominal
    • 192 Amps * 14.5 volts charging * 1/0.80 charger eff * 1/0.67 power factor * 0.10 rate of charge = 5,194 VA generator loading (typical AC battery charger numbers)
    • 12 batteries * 160 AH * 0.20 rate of charge = 384 Amps healthy high current (plus temperature monitoring of battery bank)
    • 192 Amps * 14.5 volts charging * 1/0.80 charger eff * 1/0.67 power factor * 0.20 rate of charge = 10,388 VA generator loading (typical AC battery charger numbers)

    And you see the issue with a large 12 VDC battery bank and why we recommend higher battery bank voltages (24 or 48 volt) as your bank and loads increase... 192 to 384 amps of charging current requires very short/heavy cables to manage that level of current flow--Plus voltage drop (0.5 volt maximum recommended for 12 volt battery bank) is a big problem too.

    Anyway, lots of guesses here--And I make the battery bank capacity larger, with the battery bank capacity at 12 batteries * 160 AH 12 volt batteries (sounds like you were looking for a larger battery bank).

    I am a huge believer in building a "balanced" battery bank to your loads/charging capacity... It usually gives you the best performance for the money. Oversized battery banks may not last a bit longer, but they also cost a lot more to charge and replace. And if you have an "oops" (loads left on, no charging, etc.), you have a ton of lead to replace.

    Your thoughts/corrections to my guesses?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jcheil
    jcheil Solar Expert Posts: 722 ✭✭✭
    Re: advice re new set up on a boat
    BB. wrote: »
    192 Amps * 14.5 volts charging * 1/0.80 charger eff * 1/0.67 power factor * 0.20 rate of charge = 10,388 VA generator loading (typical AC battery charger numbers)

    How does the final result of your calculations stated in "VA" relate to the "WATT" rating I see advertised on generators?
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: advice re new set up on a boat

    Watts vs VA.... This gets into the AC math:

    Power = Volts*Current -- The "generic" AC/DC formula.

    But, Volts and Current are "Vectors" for AC power -- Which means that the Voltage Sine wave may not be "in phase" with the current sign wave (induction motors, the current lags the voltage). So, the "real number" for watts is:

    Power = Watts = Volts * Amps * Cosine (angle between V and A) = Volts * Amps * Power Factor

    Power factor (or Cosine of the phase angle) varies between 0.0 (no power transferred) to 1.0 (100% of volts and current is transferred as power).

    For "ideal" AC appliances (filament lamps, power factor corrected motors/appliances/power supplies, resistance heaters), PF is usually around 0.95 to 1.00 ...

    For many devices, such as induction motors (especially running with light loads), Power Factor can be in the 0.65 to 0.80 Range.

    And for things like "simple" battery chargers, PF can be in the 0.65 to 0.67 range (especially, again, if lightly loaded--Some battery chargers can do >0.90 if heavily loaded--You have to measure the input power to know).

    A problem with many "electronic loads" (CFL lamps can have 0.50 PF) such such as battery charger and electronic power supplies (such as for computers) is that the "phase between current and voltage is not the issue, but the "spiky" nature of the current--The power supplies tend to take a lot of current just at the peak of the sine waves:
    Attachment not found.

    The PF takes account that the self heating of the wiring (I2R) and saturation of transformers (and generator) cores also is sensitive to "peak current" and "circulating" currents (non-60 Hz current in spiky waveforms--One way to look at current spikes is there is a lot of energy in frequencies above 60Hz--which for motors and transformers is usually wasted as "heat"--can be as high as 20% wasted as heat for MSW type voltage wave forms--ie.., MSW Inverters).

    So, what it comes down to--The wiring, transformers, generators, and AC inverters "care" about the RMS Amps (root mean square calculation of the phase issue, and wave form issues)... I.e., the wire gets just as hot at 10 amp if it has a PF=1.0 as it does with PF=0.0 -- It is the current itself that cause the heating.

    So, when you look at consumer grade generators, their maximum output of 1,600 watt is usually also a maximum output of 1,600 VA too...

    Fuel usage by the motor (and energy supplied by the battery bank) will be based (or the most part) on Watts (i.e., fuel flow/DC amps from battery bank) does not depend on VA--Only Watts and Watt*Hours.

    For industrial generators and some AC inverter (such as those designed for computer backup), you may see a VA rating that is greater than the Watt rating.

    For generators, this is because the loads are a mix and PF=0.80 (for example) is a more representitive match to the AC loads (heaters+motors).

    For your computer UPS under your desk... A 1,000 VA UPS sounds "better" than a 750 Watt UPS... They both will last just as long powering your desktop computer (i.e., battery draw to supply 1,000 VA with PF=0.75 is the same as supplying a 750 Watt load).

    Example for charging a battery bank. Say you have two 70 amp 12 VDC power supplies to choose from. Worst case and Best case designs:
    • 70 amps * 14.7 volts charging * 1/0.80 supply efficiency * 1/0.67 supply PF = 1,920 VA load
    • 70 amps * 14.7 volts charging * 1/0.90 supply efficiency * 1/0.95 supply PF = 1,204 VA load

    In theory, the first supply would overload a Honda eu2000i (1,600 Watt/VA) genset, and the second would not.

    We had a long discussion about these issues on this thread:

    Question about battery charger selection with EU2000 generator.


    There is an issue with doing your own experiments... A Kill-a-Watt meter is not designed to accurately measure non-linear wave forms (i.e., current spikes in above scope photo). You need True RMS reading DMM/Clamp/Current meters to measure the actual RMS current (and voltage). And to measure power/watts/phase angle/PF, you need to measure current and voltage at the same time (not cheap meters).

    Lastly, for consumer level gensets--You probably should run a battery charger at ~75-80% maximum ratings (i.e., a 1,600 Watt generator * 0.80 = 1,280 Watts max continuous). Running the smaller gensets at 100% rated power will usually give a shorter life.

    Battery chargers are able to put high/constant loads on their AC input--Most loads that we run do not (running power tools, home appliances, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jcheil
    jcheil Solar Expert Posts: 722 ✭✭✭
    Re: advice re new set up on a boat

    Awesome explanation. Somehow I was thinking that in the generator sense and in your example that the rating was meant to be the same, but I am an overthinker sometimes and wanted to know for sure. Thanks again.
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html