Renogy Panels for a 12V System

Hi!

I have four Renogy 150W panels installed on the roof of the shed that we are turning into a full time office. We're finishing up drywall right now and are moving onto wiring. I was hoping that I could parallel each of the four panels since there is a tree in my neighbor's yard that starts shading the panels around 2PM, but after reading about how panel voltage drops when the panels heat up I am a little unsure (I live in Phoenix where ~120F ambient is possible).

My setup:
Four Renogy 150W panels (Voc 22.5v, Isc 9.05A, Vmp 17.9v, Imp 8.38A)
Midnite MNPV6 Combiner Box with four 150v 12A DC breakers
Midnite Classic 150 Charge Controller
Five 100AH AGM batteries
AIMS 2000W cont/6000W peak Low Frequency Pure Sine Wave Inverter Charger (not using the charging portion of it)
Siemens Load Center with 60A backfed main and three 15A circuits for the office

The load center has a bonded neutral setup and all grounds lead back to it with a 4 gauge wiring running directly below to an 8ft grounding rod. I have the panels grounded at the combiner box grounding bar which then has a grounding wire running to the load center.

Can I get away with all the panels paralleled? Will the Vmp-hot be too low to successfully charge my bank? (No equalize, 14.4V absorb, 13.4V float)? My wire runs are approximately eight feet from the furthest panel to the combiner box (10 gauge), six feet from the combiner box to the charge controller (4 gauge), five feet to the buss bars (4 gauge), and two feet to batteries (1/0 gauge). I have a few more questions, but I would like to figure this one out first. Thank you!

Comments

  • Raj174Raj174 Solar Expert Posts: 754 ✭✭✭✭
    Hi dirtbikr,

    Looks like a nicely balanced small system. I would suggest wiring the panels as 2 strings of 2 in series. That should work well with the Classic and produce maximum power from the panels. Max amperage to battery about 40 amps.

    Rick
    3600W PV, MNE175DR-TR, MN Classic 150, Outback Radian GS4048A, Mate3, 54.4V 195AH LiFePO4, Kohler Pro 5.2E.
  • PhotowhitPhotowhit Solar Expert Posts: 5,226 ✭✭✭✭
    edited October 2016 #3
    You need 2 in series to meet the minimum requirements for an MPPT type charge controller. It likely would NOT work properly, even in colder climates.
    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
  • BB.BB. Super Moderators, Administrators Posts: 30,651 admin
    edited October 2016 #4
    [been fixed, thank you. -Bill] Photowhit do you mean two panels in series for Vmp-array to meet the charge controller/battery bank minimum voltage requirements? In any case, while I would suggest an MPPT controller with a 2series x 2parallel array, Vmp-array~18 volts for a 12 volt battery bank should work OK.

    For "dirtbkr1", I, personally, am not a big fan of 5x 12 volt batteries in parallel. Each should have its own fuse/breaker (to protect battery wiring from shorts) and parallel batteries can have issues with poor current sharing. Plus a bit more difficult to catch bad batteries/cells/debugging battery problems.

    http://www.smartgauge.co.uk/batt_con.html

    -Bil
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • PhotowhitPhotowhit Solar Expert Posts: 5,226 ✭✭✭✭
    BB. said:
    Photowhit do you mean two panels in series for Vmp-array to meet the charge controller/battery bank minimum voltage requirements?
    -Bill
    Yep, changed it, up too late...
    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
  • dirtbikrdirtbikr Registered Users Posts: 7 ✭✭
    BB. said:
    For "dirtbkr1", I, personally, am not a big fan of 5x 12 volt batteries in parallel. Each should have its own fuse/breaker (to protect battery wiring from shorts) and parallel batteries can have issues with poor current sharing. Plus a bit more difficult to catch bad batteries/cells/debugging battery problems.

    http://www.smartgauge.co.uk/batt_con.html

    -Bil
    Hi Bill,

    What you're saying is that your recommendation is 2S2P regardless, even though the ~18 Vmp may work? That seems to be the consensus from the others and it sounds like a plan if we all agree.

    I am making a busbar out of 1.5 x 0.25 x 6 inch grade 110 copper bar and will connect all batteries, the Midnite Classic, and the load to the bar. I also have a clamp ammeter so I can fiddle with arrangement and wire length to get the most even resistance characteristics possible. I will inspect the setup once a month and adjust accordingly. I also plan to fuse all the positive connections with 60A ANL fuses as close to the positive terminal as possible. The battery bank will be grounded via the Midnite Classic from my understanding; is there a need to run the DC negative busbar to the ground/neutral bar in the load center?
  • BB.BB. Super Moderators, Administrators Posts: 30,651 admin
    Two different issues... One is the Vmp-array minimum voltage of ~18 Volts Vmp for a 12 volt lead acid battery bank. If you have shading problems... If you have two panels in series and one is even partially shaded, the current from that string will drop to zero amps.

    So, if you have shadows creaping across your 4 panels, one at a time--Your best harvest would be if each is in parallel and no series panels.

    If your panels are in a (for example) 2x2 array--And two panels are shaded about the same time, then putting them in series is not going to affect your harvest--And for an MPPT controller, 2x in series would save you one wiring costs (lighter gauge wiring, longer distances, lower voltage drop, no series fuses/breaker needed as array is not 3x or more parallel connected panels/panel strings).

    However, the issue I was talking about was the use of (I think) are 5x 12 voltage batteries in series. I would highly suggest a larger battery or using 6 volt/lower voltage, higher AH batteries in series parallel (2x6 volt, 3*4 volt, 6*2 volt large AH rated batteries/cells).

    The "ideal" bank is usually a single string--Although some folks prefer to parallel strings of batteries--If one fails, they can disconnect the bad string and limp along on the 1/2 size bank until it is fixed.

    Personally, I would suggest 3x parallel strings is what I would suggest as maximum (and I really do not like paralleling 12 volt cells into 12 volt battery banks). You can go more parallel strings, but you do get more maintenance issues and have to be very careful that the design/installation is done correctly if you do go >3 parallel strings of batteries.

    Clear as mud? :p

    -Bil
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.BB. Super Moderators, Administrators Posts: 30,651 admin
    Yes, it is generally a good idea to ground the battery bank negative lead (especially if in a home with plumbing or to the chassis of an RV). You want a short to ground to pop a protective breaker/fuse. However the system will work without grounding.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • dirtbikrdirtbikr Registered Users Posts: 7 ✭✭
    I do in fact have a 2x2 grid, so I will be sure to wire the panels that match on longitudinal lines in series.

    I hear you loud and clear on the 12v bank. I will have to play this one out though and see how it goes as I no longer have a choice until this bank bites the dust. Beyond ensuring that amperages are as close as possible between all the batteries, is there anything else that I should look out for? If the office runs out of power it's not a big deal, I can run an extension cord out there for the necessary items, so this is more of a getting my feet wet in solar and energy storage than a whole house endeavor. If you were going to purchase 500-600AH worth of batteries to make a 12v bank, what would you buy? My budget was ~$500.
  • BB.BB. Super Moderators, Administrators Posts: 30,651 admin
    6 volt @ ~200 amphour batteries are hard to beat at around $100 each for flooded cell.

    Plan on 3-5 year life (unless you live in a very cold climate) or buy "better" name brand (5 to 7 year life?).

    6 of them would give you a 12 volt @ 600 amphour bank.

    Any larger, go with 24 or 48 volt battery bank.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • dirtbikrdirtbikr Registered Users Posts: 7 ✭✭
    Awesome, thank you for your help, I really appreciate it. When these give up or I get tired of shuffling them around to maintain them I will definitely do more research on 6v or lower batteries. Look forward to talking more with all of you soon!
  • BB.BB. Super Moderators, Administrators Posts: 30,651 admin
    Let us know how it all works out for you. Always looking for real world feedback and experience.

    Take care,
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • PhotowhitPhotowhit Solar Expert Posts: 5,226 ✭✭✭✭
    edited October 2016 #13
    Here is a link to Midnite's sizing tool;

    http://www.midnitesolar.com/sizingTool/

    Please note at the bottom they say "Most all MPPT controllers will want to see a minimum of 130% of the actual high battery voltage" I thin boB has used 140% in the past... (boB is one of the owners/designer/engineers at Midnite)

    While a charging voltage of 14.4 would want a voltage of 14.4 x 1.3= 18.72volts, but the NOCT (Normal operating cell temperature) values will be less than the VMP of 17.9 volts.

    Strings of 2 would be your starting point, based on this information... IMHO

    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
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