Solar installtion review request - numbers check - solar install on a boat

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Windarra
Windarra Registered Users Posts: 11 ✭
in Solar Beginners Corner #1
Hello folks,

I've been lurking and reading for a bit now, seems like there are some very knowledgeable folks here, so I'd like to run some install specs and see if anyone has any comments. I also have a few questions regarding wiring runs.

This is actually an install on a 43' trawler style boat. We're planning to do some extended anchoring this summer, and we do not want to run our generator unless we absolutely have to.

Our electric budget we way way overestimated at about 215 ah/day, just replaced our house batteries with 6-6v wired as 12v lifeline GPL-4CT for a 660 ah bank. We're getting ready to install 4 sharp 230 watt 24v. solar panels with a MorningStar TriStar MPPT 60 charge controller. We're going to set up a series/parallel install to get 48v. to the controller.

Mr. Ohm and I have a passing aquaintence, and running the numbers it looks like this config should work so we could run for a few days if we have cloudy weather, yet still be able to keep the batteries topped off most of the time. Hopefully, cuz the stuff arrived yesterday

Does this seem to match up with enough power to keep the batteries topped off, but still allowing for 2-4 days of inclement weather?

Even more important, we ran the morning star calculator, and all seems well, but still wondering if we're over/under powering the panels/controller/batteries.

On to the wiring questions...I have the ideal location for the controller, but I don't think I can get the wiring to work to place it there.
When combining the panels, here are the amp specs..
Short Circuit Current (Isc): 8.48 Amps
Maximum Power Current (Ipm): 7..67 Amps
Series Fuse Rating: 15 Amps
So if I'm understanding Mr. Ohm correctly, I should be budgeting for (on the generous side) 20 amps.
The panels utilize MC4 connectors, and the largest wire I can find is #10, which would mean that the longest run I could do from the panels to the controller with a 2-3% voltage drop would be 30 feet (one way)? Does this seem correct?

Thanks in advance for any input y'all could provide.
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #2
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    Re: Solar installtion review request - numbers check - solar install on a boat

    Welcome to the forum. Your plans look pretty good from my experience on the ground. Sounds like a fun project. Reading this forum I have learned that boats may have issues with shading and/or maintaining optimal orientation of the panels. As far as the charge controller, I recall seeing some threads here by boaters and ham radio operators discussing charge controllers and RF noise... You might want to research that. Another thing... you are planning to have three parallel strings of batteries. More than one string is workable, but less than optimal. Get yourself a digital clamp ammeter and use it regularly to monitor the current flow in each of the strings. if they begin to deviate during charging or discharge take corrective action quickly.
    Windarra wrote: »
    Does this seem to match up with enough power to keep the batteries topped off, but still allowing for 2-4 days of inclement weather?
    not sure about 2-4 days of inclement weather... why do you think you can draw 215 ah per day for four days from a 660 ah bank?
    Windarra wrote: »
    The panels utilize MC4 connectors, and the largest wire I can find is #10, which would mean that the longest run I could do from the panels to the controller with a 2-3% voltage drop would be 30 feet (one way)? Does this seem correct?
    Once you get to the combiner box (mounted at the panels) why limit yourself to #10 wire?

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #3
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    Re: Solar installtion review request - numbers check - solar install on a boat

    i'll toss in a few cents worth here. the pvs will be outputting close to the max of the controller with the possibility of exceeding the 60a limit so it would be held to that 60a. if the pvs get shading or aren't optimally aimed then this could degrade it some so it most likely will not be exceeding the controller limit. also note it shouldn't hurt the controller if it hits that limit and holds back the current.

    with a 215ah draw per day on a 660ah battery bank this would normally be seen as 660ah/215ah=3.07 days, but that would be to drain the batteries to 100% dod which you don't want to do. it is recommended that you not exceed 50% dod so you will be able to have 1.5 days autonomy. you may need to try to conserve some power in order to gain more time. also keep in mind that the 50-60ah you will get from the pvs in a day may be close to the amount of current you are drawing off of the batteries in that same 24hr period so it is kind of a wash there, but throw in a cloudy day and you may struggle to bring the batteries back up as well as keep up with the loads for that the following day.

    now if that is 30ft on the + wire and another 30ft for the - wire then you have 60ft of pv wire total. with #10 and 15.34a at 48v this is around 2.44% and that does not include the wires from the controller to the batteries and all of the interconnections for the batteries. some feel up to 3% v drops are ok and some prefer up to 2%. i just remembered you have to include the series interconnects from the pvs as well. it may well pay for you to go to a larger wire. i think you are using the calculations ok, but you need to include those other wires i mentioned as it does not just pertain to the wires going from the pvs to the controller.
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  • Windarra
    Windarra Registered Users Posts: 11 ✭
    #4
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    Re: Solar installtion review request - numbers check - solar install on a boat

    Still working on the replying with quotes.... :)
    Thanks for the heads up on the RF interference, we don't currently utilize ham frequencies, only VHF, so I'll definetly keep that in mind.

    Our house (boat) system is 12 volt, so with storage constraints the 6-6volt was the way to go for that install. We just replaced those, the previous batts were Deka 6v floor scrubbers so the footprint for replacement was spot on without redoing our whole bilge/battery compartment.

    And yes, good point about the draw over 4 days. We did over estimate. We're pretty frugal, so we're not going to be running full throttle on the electronic gadgets if we know we have weather moving in. And again, we can use a back up system if push comes to shove, but would prefer not to. Our biggest draw will be our freezer/fridge at 40 ah per day.

    And regarding the #10 wire, that's the biggest we can find that is both UV resistant & tinned stranded copper (USCG & ABYC should be ok with those in marine applications) with the MC4 connectors.
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  • Windarra
    Windarra Registered Users Posts: 11 ✭
    #5
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    Re: Solar installtion review request - numbers check - solar install on a boat
    niel wrote: »
    i'll toss in a few cents worth here. the pvs will be outputting close to the max of the controller with the possibility of exceeding the 60a limit so it would be held to that 60a.

    Will the Controller throttle down or will we have to think about limiting the input?

    if the pvs get shading or aren't optimally aimed then this could degrade it some so it most likely will not be exceeding the controller limit. also note it shouldn't hurt the controller if it hits that limit and holds back the current.

    with a 215ah draw per day on a 660ah battery bank this would normally be seen as 660ah/215ah=3.07 days, but that would be to drain the batteries to 100% dod which you don't want to do. it is recommended that you not exceed 50% dod so you will be able to have 1.5 days autonomy. you may need to try to conserve some power in order to gain more time. also keep in mind that the 50-60ah you will get from the pvs in a day may be close to the amount of current you are drawing off of the batteries in that same 24hr period so it is kind of a wash there, but throw in a cloudy day and you may struggle to bring the batteries back up as well as keep up with the loads for that the following day.

    Ok great point, thanks. Then we may be on the right track...Our probable usage will be more likely in the 120-150 ah/day, we just over estimated incase we want to throw a monster party, fire up the 110 powered blender on an inverter to whip up margaritas for an hour or two and not worry about still having enough juice to run the water pumps to wash after ;):D

    now if that is 30ft on the + wire and another 30ft for the - wire then you have 60ft of pv wire total. with #10 and 15.34a at 48v this is around 2.44% and that does not include the wires from the controller to the batteries and all of the interconnections for the batteries. some feel up to 3% v drops are ok and some prefer up to 2%. i just remembered you have to include the series interconnects from the pvs as well. it may well pay for you to go to a larger wire. i think you are using the calculations ok, but you need to include those other wires i mentioned as it does not just pertain to the wires going from the pvs to the controller.

    The 24 v runs will be max 16' one way to the combiners, where the post-combined 48v run will be right around 30 feet one way direct to the controller. From there it's less than 10' one way to the batteries, so from the controller to the batteries I think we're looking at about 4 gauge wire.
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #6
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    Re: Solar installtion review request - numbers check - solar install on a boat
    Windarra wrote: »
    And regarding the #10 wire, that's the biggest we can find that is both UV resistant & tinned stranded copper (USCG & ABYC should be ok with those in marine applications) with the MC4 connectors.
    Buy a cable with MC4 connectors and cut it in half. Use the cut end to get into your combiner box. After the combiner box use heavier wire (no more MC4 connectors) to make the run to the charge controller. If you can't find UV resistant wire, put the wire in conduit (to meet NEC it should be in conduit anyway).
    Windarra wrote:
    Thanks for the heads up on the RF interference, we don't currently utilize ham frequencies, only VHF, so I'll definetly keep that in mind.
    Its not just an issue for ham frequencies. Research the issue! On a boat it may be more of a safety issue than a nuisance. Use the search function on this forum. There is a lot of good info on the subject. Do you know how to search this forum on Google? Type your search terms followed by "site:wind-sun.com" (do not use the quotes).
    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #7
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    Re: Solar installtion review request - numbers check - solar install on a boat

    i can tell you right now that you need at least #2 from the cc to the batteries, but i think i'd go #0. this is not just due to the losses in the run, but also the losses in the interconnecting battery wires. it is also important that losses be kept low in this stretch because of the lowered voltage in it, but also due to v drops fooling the cc into thinking the battery is charged when it isn't. this particular controller i believe has a remote battery sense for voltage and can compensate for the v drops presented by the wires to the batteries only to keep the cc from being fooled into thinking the batteries are charged when they aren't. it will not stop v drop losses from occuring though so good heavy wire is still needed.

    now you will only need to consider 1 of the pv strings for the v drop % presented from the pvs to the combiner. if one is longer than the other then use that longer one for the v drop % to be added to the rest of the system losses later. remember all v drop percents add together starting from the pvs and going all the way to the batteries. now each pv has about 6ft of wire to consider too. i don't know the specifics on those pvs as to what gauge number or length is used. if the gauge number is different on the pvs then calculate the v drop percents for that wire and the run to the combiner separately and add these together after calculated. remember that the series string here is only pushing the imp of a single pv and would be at 7.67a and this lower current at higher voltage does help to keep losses down. the 30ft run length from the combiner will have the beneficial high voltage the series strings offer, but being there are 2 strings being paralleled that the current will now be doubled and will double your v drop losses. 2 x 7.67a = 15.34a. you have some flexibility here in that no mc4 connections will need to be present so you can use whatever gauge you will in order to go as low in the v drop percentage as you may prefer. also note that a fuse or circuit breaker is not required, but often this can be used to double as a means of disconnecting the pvs. a good dc switch rated for the voltage and current could alternately be put in here too.

    to summarize the v drop % for each section needs calculated and later added together that should at least be under 3%, but you could opt for under 2% as well if you like. the following are the sections you can individually calculate for.

    the built in pv wires
    the string run to the combiner
    the combiner run to the cc
    the cc run to the batteries (at a lower regulated voltage from here on out)
    series battery interconnections, and like the pvs, only consider 1 of the battery strings and make each other battery string identical with wire gauge and length used so as to keep symmetry.
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  • Windarra
    Windarra Registered Users Posts: 11 ✭
    #8
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    Re: Solar installtion review request - numbers check - solar install on a boat
    niel wrote: »
    i can tell you right now that you need at least #2 from the cc to the batteries, but i think i'd go #0. this is not just due to the losses in the run, but also the losses in the interconnecting battery wires. it is also important that losses be kept low in this stretch because of the lowered voltage in it, but also due to v drops fooling the cc into thinking the battery is charged when it isn't. this particular controller i believe has a remote battery sense for voltage and can compensate for the v drops presented by the wires to the batteries only to keep the cc from being fooled into thinking the batteries are charged when they aren't. it will not stop v drop losses from occuring though so good heavy wire is still needed.

    The largest gauge wire the Morningstar can use is 2, which is what we'll use. One of the other features is a 'sense' wire monitoring of the batteries.

    now you will only need to consider 1 of the pv strings for the v drop % presented from the pvs to the combiner. if one is longer than the other then use that longer one for the v drop % to be added to the rest of the system losses later. remember all v drop percents add together starting from the pvs and going all the way to the batteries. now each pv has about 6ft of wire to consider too. i don't know the specifics on those pvs as to what gauge number or length is used. if the gauge number is different on the pvs then calculate the v drop percents for that wire and the run to the combiner separately and add these together after calculated. remember that the series string here is only pushing the imp of a single pv and would be at 7.67a and this lower current at higher voltage does help to keep losses down. the 30ft run length from the combiner will have the beneficial high voltage the series strings offer, but being there are 2 strings being paralleled that the current will now be doubled and will double your v drop losses. 2 x 7.67a = 15.34a. you have some flexibility here in that no mc4 connections will need to be present so you can use whatever gauge you will in order to go as low in the v drop percentage as you may prefer. also note that a fuse or circuit breaker is not required, but often this can be used to double as a means of disconnecting the pvs. a good dc switch rated for the voltage and current could alternately be put in here too.

    to summarize the v drop % for each section needs calculated and later added together that should at least be under 3%, but you could opt for under 2% as well if you like. the following are the sections you can individually calculate for.

    Great info, thanks so much. That's a bit to chew on, going to go remeasure some runs, and see if there is some way to shorten some wires.

    the built in pv wires
    the string run to the combiner
    the combiner run to the cc
    the cc run to the batteries (at a lower regulated voltage from here on out)
    series battery interconnections, and like the pvs, only consider 1 of the battery strings and make each other battery string identical with wire gauge and length used so as to keep symmetry.

    Thanks again everyone for looking at this. I was concerned about over/under powering the Morningstar, Thanks again.
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