Upgrading solar from 200 watts to 1200 watts

deegoredeegore Registered Users Posts: 8 ✭✭
Hi, I've been running my 200 watt setup for years and am attempting an upgrade. I'm getting all new components. I have 12 100 watt renogy rng-100p panels, 12 6volt 235 amp hour Duracell golf cart batteries, and 3 60 amp powmr mppt charge controllers.
My plan was to connect 4 panels together parallel into each charge controller, and connect the batteries in series in pairs to get 12 volts, then connect the pairs of batteries together parallel. The panels will be on the roof about 40ft from the charge controller. It looks like I need 00 gauge wire for this which will be very expensive. Also, The charge controllers won't accept anywhere near that large of wire.
Would I be better off connecting the panels in series to get 24 or even 48 volts? This is where I'm having a hard time.
If I'm figuring right, wiring the panels for 48 volts would keep the amps down to about 40 for all 12 panels. 
If that's the case, I could hook up all the panels to one controller.
So here are my questions,
1. Should I connect the panels in series for 48 volts and use only one charge controller?
2. Can I have 48 volts going into the charge controller, and still have the batteries wired for 12 volts.
3. How do I figure wire size for connecting the batteries to each other?
Thanks so much for any help

Comments

  • EstragonEstragon Registered Users Posts: 3,043 ✭✭✭✭✭
    If you already have the controllers, you could split the load between them. Do you really need 12v battery bank that size? That would be 6 strings for ~1400ah. 1200w of panel ÷ 14.5v charging is ~83a out to the batteries. In most locations you likely won't often see that, but it might be a bit much for a single controller. Better to split the load if you can. It's the output current that counts. Wiring in series does save wiring cost though. Mppt controllers buck higher input voltage to lower charging current. 48v to 12v nominal should be fine, but check the manual.

    Depending on loads, it may be wise to consider a 24v battery system. This would be a more manageable 3 strings of batteries.
    Off-grid.  
    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
  • deegoredeegore Registered Users Posts: 8 ✭✭
    I would like to keep the batteries at 12v because I already have an inverter and a couple 12v appliances.
    The charge controller manual says for 12v battery: pv array open circuit voltage, 20v-80v.
    The panels say open circuit voltage 22.4.
    I take that as meaning no more than 3 panels in series per controller.
    So, what if I did 6 panels per controller, a pair of 3 in series, and used two controllers?
    That would give me 36v, and voc of 67.2
    Please correct me if I'm figuring wrong.
  • mike95490mike95490 Solar Expert Posts: 8,033 ✭✭✭✭
    I'd put no more than 2 panels in series, if possible.   The higher the PV voltage, the harder (hotter) the MPPT circuit has to work to downconvert to the battery voltage.
    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 ,

  • PhotowhitPhotowhit Solar Expert Posts: 4,769 ✭✭✭✭
    Wish you had asked questions before buying anything...

    Here are a couple things you need to know;

    Solar panels put out about 75% of their rated wattage in normal operating conditions.

    Charge controllers are rated at their output current. 

    Most MPPT type charge controller NEED to have 30% higher voltage coming in that they are operating at. So to charge a 12 volt system usually about 14.5 volts you need to have  20+ volts coming into the charge controller.

    Most MPPT type charge controller can be 'over paneled' without harm. 

    So...
    A 60 amp MPPT type charge controller can handle an output of 60 amps at 14.5 volts or about 870 watts of incoming current. 1200 watts of array are likely to produce about 75% of 1200=900 watts. 

    The problems you are facing with voltage drop are some of the reasons to run a higher system voltage once you find the need for a larger system.

    Your questions;
    1; I would likely run 4 strings of 3 panels and use 2 charge controllers. It's nice to have a bit of redundancy, and you already have the controllers. It's a compromise between higher voltage and less voltage drop and lower conversion rates for the charge controllers, which should keep them form higher losses due to higher conversion rates.
    2; Yes with MPPT type charge controllers this shouldn't be a problem.
    3;I would limit my self to 3 strings of batteries max and use larger batteries or a higher system voltage to achieve this...
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • PhotowhitPhotowhit Solar Expert Posts: 4,769 ✭✭✭✭
    deegore said:
    I would like to keep the batteries at 12v because I already have an inverter and a couple 12v appliances.
    The charge controller manual says for 12v battery: pv array open circuit voltage, 20v-80v.
    The panels say open circuit voltage 22.4.
    I take that as meaning no more than 3 panels in series per controller.
    So, what if I did 6 panels per controller, a pair of 3 in series, and used two controllers?
    That would give me 36v, and voc of 67.2
    Please correct me if I'm figuring wrong.
    No you have the right idea.

    What charge controller is this? That's a pretty low VOC. I guess I would agree with Mike and just run pairs of panels.

    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • deegoredeegore Registered Users Posts: 8 ✭✭
    The charge controller is a cheaper one off Amazon. Powmr is the brand.
    It looks like wiring the panels for 24 volts and using two controllers will let me get away with using 4 gauge cable.
    That is much more doable.
    I didn't realize you could have too many batteries, should I use less or do you think i I will be ok?
    I really appreciate all the help.
  • PhotowhitPhotowhit Solar Expert Posts: 4,769 ✭✭✭✭
    Many strings of batteries creates difficulties in load sharing and in charging. Require very careful setup to be sure you have equal resistance through each string. Even when well setup, you have a lot more cells to check for electrolyte levels and if you have a problem it can escalate quickly and be a PITA to run down.

    Also in reality you are somewhat under paneled for a battery bank that size. For full time use we like to see a charging current of between 10 and 13% of the battery capacity.

    6 strings of 235 amps = 1410 amps, so you would be looking for a charging current of 140-190 amps. With a 1200 watt array, your normal output of 900 watts will only create about 900/14.5 volts=62amps.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • EstragonEstragon Registered Users Posts: 3,043 ✭✭✭✭✭
    Assuming wiring the panels for 24v means 2 in series for Voc ~40v, Vmp ~36v, Imp ~5a, you have 3 strings in parallel per controller, so ~3x5A=15a. You can plug in numbers using a calculator like:
    https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=2.061&voltage=36&phase=dc&noofconductor=1&distance=40&distanceunit=feet&amperes=15&x=71&y=34

    IMHO, a 6 or 8ga would be an ok voltage drop. If you could do strings of three, so 10a in parallel per controller, 10ga would do? Depending on the local cost difference between 6-8ga and 10ga vs a bit of efficiency loss with higher voltage, at 40' it likely makes more sense to do strings of 2.

    To find the max string size, you need to know the maximum voltage the controller can handle, then calculate the maximum Voc at record low temps for your location adjusted by the temp coefficient for your panels. This can be important in locations like mine that can get to <-40°.

    In addition to the issues @Photowhit noted with lots of parallel battery strings, you should also fuse each string so a short fault in one string doesn't see the fault fed by the 5 good ones. The same is true for having three strings of panels, but you can probably get away without separate breakers/fuses per string there, if the combined current ~10a from 2 is less than the max fuse size for the panels (eg 15a?).

    Going from a 200w setup to 1200, I assume you have a generator and are willing to use it. The pv is a bit small relative to bank size, but if you can/will bulk with generator when needed it could work okay.

    Some info on wiring batteries in parallel:
    http://www.smartgauge.co.uk/batt_con.html
    Off-grid.  
    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
  • deegoredeegore Registered Users Posts: 8 ✭✭
    Ok, thanks for the info.
    It sounds like the way to go is wire pairs of panels in series, and 3 pairs per controller.
    I have been calculating wire size like this, 6 100watt panels at 24 volts=25 amps. I will learn the correct way to figure this before I buy the cable. Thanks for pointing that out Estragon.
    For the batteries, I will wire sets of 4 in series to get down to 3 strings. I will then get a 24 volt inverter and a step down converter for my 12 volt stuff. Sound good?
    One last question, what gauge wire should I use to connect the batteries together and go to the controller and inverter?
    I will keep everything as close as possible, and am thinking a 1500 watt inverter.
  • EstragonEstragon Registered Users Posts: 3,043 ✭✭✭✭✭
    My personal preference is to oversize wire (but not breaker size) for inverter DC and battery interconnections. The incremental cost is generally not huge in the scheme of things as lengths are fairly short, and it minimizes voltage drop and reduces potential issues with parallel connections somewhat.

    The inverter manual should have recommended wire and breaker/fuse size. I'd consider the wire size as a minimum size, and use the recommended breaker size.

    A step down converter should work for 12v loads. A potential mode of failure for converters apparently can expose 12v loads to battery voltage though. Some 12v loads are ok with this, but some not. I don't know how likely that failure mode is. Presumably not very, as converters seem to work for people, but something to be aware of if you have expensive/critical 12v loads.
    Off-grid.  
    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
  • NANOcontrolNANOcontrol Registered Users Posts: 87 ✭✭
    And now for something completely different. I use multiple modified $5 buck converters operating MPPC which allows me to use cheap grid tie panels in series for about 60V.  These supplement the regular PWM charger on 12V to give a "boost" in low light levels.  Their output is set at 13.8V and any excess power goes to heating water.  I'm surprised that this method isn't more common as a cheap way to expand a system.  That is an extra 500W for under $370.
  • mcgivormcgivor Solar Expert Posts: 2,425 ✭✭✭✭✭
    So 500 watts for $370 or $1.35 per watt, am I missing something, current module prices  $0.30-0.50 per watt, can you elaborate on what  MPPC is ?  Multi-Pixel Photon Counter, Motion Picture Patents Company,  the T is close to the C on a keyboard but not next io one another, or was that supposed to ba MPPT? Just curious. 
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 
    900W  3 × 300W No name brand Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal as a backup system. 
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergencies and welding.
  • EstragonEstragon Registered Users Posts: 3,043 ✭✭✭✭✭
    I think it would be $370/500=0.74 $/watt.
    Off-grid.  
    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
  • PhotowhitPhotowhit Solar Expert Posts: 4,769 ✭✭✭✭
    mcgivor said:
     ... am I missing something, current module prices  $0.30-0.50 per watt, ...
    I guess wholesale outside of the US, But inside the US not much below 60 cents.

    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • mcgivormcgivor Solar Expert Posts: 2,425 ✭✭✭✭✭
    Estragon said:
    I think it would be $370/500=0.74 $/watt.
    Good catch i reversed the equation, got to appreciate others keeping watch for mistakes.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 
    900W  3 × 300W No name brand Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal as a backup system. 
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergencies and welding.
  • 706jim706jim Solar Expert Posts: 217 ✭✭✭
    Just curious what 12 volt appliances you have. In my case it includes cell phone chargers and a single halogen lamp. My solution was to run a fused 30 watt 120-12 volt power supply and otherwise not worry about 12 volts in my cabin. I ran 12 GC's for 19 seasons charging them with a maximum of 430 watts so I wouldn't be too concerned about being under paneled with 1200 watts. I would also suggest going 24 volts if at all possible.
    Island cottage solar system with 1400 watts of panels, Trace DR1524 MSW inverter, Trace C40 PWM controller 8 Trojan L16's. Insignia 11.5 cubic foot electric fridge. My 26th year.
  • NANOcontrolNANOcontrol Registered Users Posts: 87 ✭✭
    The beauty of two grid tie panels in series is they will produce 60V, more if 72 cell.   Many wall wart chargers will work off that DC voltage at slightly reduced charge rates.  Computer works fine too. It has to be a switching power supply that does not voltage double. There will be exceptions, but I have more than a half dozen running right now. A neat trick to get out of running an inverter.  You can even use one to boost up the voltage of the other wall warts for added performance.  As always, use at your own risk.  No one should be using 12 or 24V panels these days.  I get 280W panels these days locally out the door for $176 without the bother of shipping. So, a couple bucks for the controllers and I am upgraded for $370. That is very cheap for adding panels to an existing 12V PWM system.  MPPC is constant voltage power point.  It doesn't search. Panel voltage only varies with temperature which can be accounted for.  That gets you 90% of what you would gain with MPPT.  The big advantage is that it allows prioritizing loads and efficient diversion of excess power. On average I divert 2.5KWH to heat water.
  • PhotowhitPhotowhit Solar Expert Posts: 4,769 ✭✭✭✭
    edited July 24 #19
     No one should be using 12 or 24V panels these days.  I get 280W panels....
    So what voltage are your 280 watt panels?

    Do you understand that 24 volt nominal panels, panels meant to charge 24 volt battery banks, have a VMP of 35-40 volts?
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • NANOcontrolNANOcontrol Registered Users Posts: 87 ✭✭
    two grid tie panels in series is they will produce 60V, more if 72 cell. I suppose when you are posting to the kiddie table every detail has to be specified.  Don't confuse not caring with not knowing.
  • deegoredeegore Registered Users Posts: 8 ✭✭
    My water pump is 12v, and I've got a 12v mini fridge and some lights. It wouldn't be much trouble to replace it all with 120 to uncomplicate things. I've been looking at more efficient refrigerators anyway.

    Ok, I think I understand the wire size from the panels. I will go with 6 gauge. Same from controllers to the batteries.
    Does 2 gauge to interconnect the batteries sound good?
    The manual for the controller recommends a 100 amp fuse between controller and batteries. That seems high to me considering the panels are only feeding 17 amps.
    Would a 20 amp fuse be appropriate between the panels and the controller?
    Figuring a 1500 watt 24 volt inverter, I get 62.5 amps, so I'm thinking an 80 amp fuse between the batteries and inverter, and 40 amp fuses for each battery string. 
    Does that sound good? 
    Sorry for all the questions

  • 706jim706jim Solar Expert Posts: 217 ✭✭✭
    The system sounds similar to mine. Originally, I used #1 cable for battery interconnects. After replacing the batteries two years ago, I went with 4 gauge wire. Easier to work with and less expensive. Remember with multiple strings your maximum amperage is reduced by the number of strings. 80 amps into three strings means the interconnects might see 30 amps maximum and they will be by design, very short. I certainly have had no problems feeding the occasional 40 amps through those 4 gauge connectors. Your fuse sizes are reasonable too. You might be surprised by the difference in power consumption between your mini fridge and a full sized model.
    Island cottage solar system with 1400 watts of panels, Trace DR1524 MSW inverter, Trace C40 PWM controller 8 Trojan L16's. Insignia 11.5 cubic foot electric fridge. My 26th year.
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