Seeking Advices to minimize Voltage drop

mjb652mjb652 Registered Users Posts: 2

I am a new comer to off grid solar.

I am gathering information and advises for a small 12V system for my summer home in the Caribbean.

I currently own:

4 300 watt Solarworld panels (VOC 40v, VMP 32.6v, ISC 9.3A, IMP 9.31A)

6 Agm 100Ah batteries

1 MNPV6 Disco Combiner Box

1 MPPT Charge controller Midnite Solar Clasic 150

1 Pair MC4 Solar panel cable Y connectors ( M/FFF F/MMM)

1 3000w Xantrex pure sine Charge controller.

Solar panels combined (series/parallel) using the Y connetors on concrete roof about 25feet from the MNPV6 combiner box.

The combiner box will be located at about 30 feet from the Charge controller. the batternes are at 6feet away. All the cable will be fished thru 1-1/4 PVC conduit on the roof as well under ground to the house.

My questions are the following:

A) size Breaker to use in the combiner box (15 or 20A)?

B) size cable to use from the Connectors to the combiner box? to keep voltage drop below 4%

C) cable size from combiner box to CC

D) do Ineed more battery and or more panels?

This solar system will be used 24/7 for a mid size refriginator/freezer, and a 17 cubic feet freezer. There will 3 or 4 Led 15w lights in use for 3 to 4 hours at night. Also 3 ceiling fans for a few hours when the 8000btu air conditioner (power by a generator) is off. There will be cell phones to charge as well as the use of 2 laptops for about 2-3 hours a day.

All advises or comments are appreciate.

Thank You

BTW: should I be concerned about performance issues due to the additional heat which will be generated by the concrete roof. If so, how to treat this matter? tks

Comments

  • MrM1MrM1 Registered Users Posts: 373 ✭✭✭
    edited April 5 #2

    I think for the loads you describe, a 12v system is too small. You may consider going up to 24v or 48v if possible. also you do not say the voltage input of your inverter. This will determine the system DC voltage. You then connect batteries in series to get the voltage you need to power the system.

    For Batteries:

    12v x 200 Ah = 2400watts of storage

    24v x 200 Ah = 4800watts of storge

    I do not know how you will wire the 6 batteries or what voltage they are ... but at 200Ah and 12 v that is only about 1200 watts of usable storage before recharge is needed. That is not much

    Other than that, it seems you need to do your load calculations letting you know the number of Watt Hours you will use in a day, and then determining how many days you want to be able to go without charging (due to clouds etc). This is the only way to design a successful system that will supply those loads daily, and be able to recharge the batteries in a timely manner.

    Describing your loads (ie. a fridge, freezer and 4 LED bulbs) does not tell you what your daily loads will be. But with a mid size fridge alone, you are probably talking on order of 1800-2700 watts per day (I am guessing). This alone moves into a medium size system from a small system.

    REC TwinPeak 2 285W 3S-3P 2.6kW-STC / 1.9kW-NMOT Array / MN Solar Classic 150 / 2017 Conext SW 4024 Inverter latest firmware / OB PSX-240 Autotransfomer for load balancing / Trojan L16H-AC 435Ah bank 4S connected to Inverter with 7' of 4/0 cable / 24 volt system / Grid-Assist or Backup Solar Generator System Powering 3200Whs Daily / System went Online Oct 2017 / System, Pics and Discussion
  • MrM1MrM1 Registered Users Posts: 373 ✭✭✭
    edited April 5 #3

    You need to use a Kill-O-Watt meter on the fridge and freezer for a few days, Then divide the number of watts used by the number of hours ran then multiply that by 24 hours to get the number of Watts a device or appliance uses in a day. This is the best way to get a true total load calculation.

    You can ball park loads here at this link. They give you suggested loads for various devices

    Then you can determine system size, Batteries needed, charge controller size and number of panels etc here at this link

    These are not exact ... but a good rough estimate.

    But just looking at what you described, I can see needed upwards of 2500 watts (Watt*Hours -BB.) per day.

    REC TwinPeak 2 285W 3S-3P 2.6kW-STC / 1.9kW-NMOT Array / MN Solar Classic 150 / 2017 Conext SW 4024 Inverter latest firmware / OB PSX-240 Autotransfomer for load balancing / Trojan L16H-AC 435Ah bank 4S connected to Inverter with 7' of 4/0 cable / 24 volt system / Grid-Assist or Backup Solar Generator System Powering 3200Whs Daily / System went Online Oct 2017 / System, Pics and Discussion
  • DaangeroussDanDaangeroussDan Registered Users Posts: 23 ✭✭

    You forgot to multiply the amps for your 12 volt system. The wattage is the same, your math is wrong and misleading. The only advantage to running high voltage is the ability to use thinner lines. The power is the same. And with a Midnight controller, he can run his pv in series to 48 volts, into a 12 volt battery bank that is much less dangerous to children or pets.

  • DaangeroussDanDaangeroussDan Registered Users Posts: 23 ✭✭
    edited April 5 #5

    Here is a quick guide I made with some voltage info and examples. You have a very nice "small" system that will probably need more input in the winter months, but be great in the summer. https://www.youtube.com/watch?v=v0eztArZsBE

    This "myth" that somehow high voltage battery bank is benificial to "watts" is just that, a myth. What you want is to run your battery bank to the voltage of your 3000 watt inverter's set voltage. Your midnight will take care of higher voltage from the pv, up to 48 volts I think.

    Oh, and I highly recommend you get a "shunt" https://www.youtube.com/watch?v=Mqz0S8sn45Q

    Here is one from Ebay; https://www.ebay.com/p/100a-Digital-Multifunction-Power-Meter-Energy-Monitor-Module-Volt-Meter-Ammeter/5021158179?iid=132816306007

    and https://www.ebay.com/bhp/ammeter-shunt

    The directions are very clear, the volt, watt, amp, and total power are very accurately tracked, and can be reset at any time, giving you the ability to perform real time diagnostic evaluations on your systems performance and /or deficiencies based on your draw and input seasonally.

  • DaangeroussDanDaangeroussDan Registered Users Posts: 23 ✭✭

    To learn the draw "exactly" from your AC appliances buy this https://www.ebay.com/itm/Power-Energy-Consumption-Watt-Meter-Electricity-Usage-Monitor-Equipment-White-/254139499036

    Watt meter power analyzer will tell you exactly how much your pulling and you can time how frequently it comes on. No guess work, its a must (only 14 bucks) for anyone learning to live off grid.

    visit my youtube site and click on "videos" to see all my tutorials and opinions based on experience.https://www.youtube.com/channel/UCl-G3EJMjjdCKJkJdPTvkgg/videos?view_as=subscriber

  • DaangeroussDanDaangeroussDan Registered Users Posts: 23 ✭✭

    You asked: BTW: should I be concerned about performance issues due to the additional heat which will be generated by the concrete roof. If so, how to treat this matter? tks

    Yes, heat messes up your input, leave a nice air gap, or use solar trackers is even better https://www.youtube.com/watch?v=-6vCpbBpuVY

    But Panels do perform better when running nice and cool.

  • MrM1MrM1 Registered Users Posts: 373 ✭✭✭
    edited April 6 #8

    I dont think you add amps when referring to battery storage (I could be wrong). All I was noting in my math was battery storage. A 200Ah battery bank at 12v will only store half the Power of a 200Ah battery bank at 24v.

    If I could build my system over again, I would go 48v and 8 225Ah Trojan T105 Golf Cart Batteries. This would have been less money in batteries than my existing 4 L16 435Ah batteries, Been easier to move around each battery, and would have had more storage capacity.

    REC TwinPeak 2 285W 3S-3P 2.6kW-STC / 1.9kW-NMOT Array / MN Solar Classic 150 / 2017 Conext SW 4024 Inverter latest firmware / OB PSX-240 Autotransfomer for load balancing / Trojan L16H-AC 435Ah bank 4S connected to Inverter with 7' of 4/0 cable / 24 volt system / Grid-Assist or Backup Solar Generator System Powering 3200Whs Daily / System went Online Oct 2017 / System, Pics and Discussion
  • mike95490mike95490 Solar Expert Posts: 8,193 ✭✭✭✭✭
    edited April 6 #9

    Dan, when constructed to code, PV arrays, wiring and batteries are no more a danger than any tools in a workshop.

    12V systems are poorly suited to large loads like refrigerators, because of the huge motor starting surge, batteries and cables need to pass hundreds of amps without dropping voltage. 24 & 48v banks are much more suited for that

    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • TecnodaveTecnodave Registered Users Posts: 205 ✭✭✭

    I am only going to comment on several aspects of this.......here PVC conduit is not allowed or frowned on on the roof or attic of dwelling.......code in the Caribbean? I don't know if they have code in Caribbean!

    Solar panels and heat. Make sure that air is free to flow behind and underneath the panels. Common use here is 4 inches of space...free air There I would give them more air behind if you can. Don't mount them flat down!

    12 volts with a referigerator and a freezer..........don't think that is a wise choice......I have 2 referigerators and a freezer on my 24 volt system.....BUT......they are super efficient DC permenant magnet motors referigerators specially made for solar use.........these are not cheap for the referigerator but way less expensive for the whole system. They run directly from the battery, no inverter......approx. 200-250 watt hours/day.each! .....$800-1600 each. I could not do that much referigeration on my 4 controller dual bank 24 volt system if I used Costco cheep referigerator's check out the Sundanzer units at wind-sun.....mine are not Sundanzer......there are others....some are vaporware.

  • mjb652mjb652 Registered Users Posts: 2

    I am grateful for the feedback received from several of you. Some of you pointed out of the missing of some information such as the voltage of my system and daily wattage utilization:

    The batteries are 12v AGM 100ah

    The inverter/charger Xantrex 12v Freedom Sw 3000 w

    Daily energy droned about 4kw/h

    Sun availability about 7h daily

    I am really interested at information about cable size for a distance of about 65 feet from the panels Y connectors to the Combiner Box to the Charge controller. This to minimize voltage drop, and also would I need to use 15A or 20A breaker inside the combiner box.

    Thanks for reply

  • mcgivormcgivor Solar Expert Posts: 2,716 ✭✭✭✭✭
    edited April 13 #12

    How are the panels configured, the size of the conductors will be dependent on the voltage, higher voltage = lower current smaller conductors.

    Since you have a MPPT controller it would be possible to series 2, parrallel 2, using 10 AWG the voltage drop would be approximately 2.93%, which is acceptable, 8 AWG would be better at 1.8%. The breaker or fuse for each string would be 15 A, its not essentialto have two, there could be a single 30A, but having 2 is handy for trouble shooting.

    Here is the link to a voltage drop calculator where you can enter information and learn for yourself what the effects of voltage have in relationship to current https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=2.061&voltage=80&phase=dc&noofconductor=1&distance=65&distanceunit=feet&amperes=18&x=26&y=23

    Edit. I made the mistake of using 80V the VOC instead of VMP which would be ~65V, so the percentage values will be lower, here is the revised calculation. 3% or less voltage drop is what is needed.

    https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=2.061&voltage=65&phase=dc&noofconductor=1&distance=65&distanceunit=feet&amperes=18&x=37&y=27

    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
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