Looking for Suggestions on Combiner box setup for 20 panels in a 48 V system

akallenakallen Registered Users Posts: 10 ✭✭
Existing system is twin off-grid Xantrex 5548 setup. Adding another 5x4 array (about 5040 watts actual), so it would be 10 strings with total Imp at about 178 amps. Thinking I should pay extra for breakers so that I can easily isolate the strings, but am unclear on whether one big box or a couple smaller ones. Since its not high voltage, I don't need any of the fancy disconnecting systems afaik. Looked at a basic MNPV16 setup as a possibility since it looks like I can use it as two buses. Anything else come to mind?
The reason for so much power, if you're wondering, is EV charging is like running HVAC. Its not clear to me that 11kW of capacity may be completely adequate, so I'm looking at technology for direct from array to car charger and thus bypassing my house inverters, although the inverters still need to be able to tolerate my arrays when not charging vehicles. Beginning to think I need something quite a bit larger than what Xantrex sells.

My thanks.
Twin Xantrex 5548 (48 V) with two MPPT60 controllers and Rolls batteries, Pre-2008, so the NEC was simple at the time.

Comments

  • mcgivormcgivor Solar Expert Posts: 3,274 ✭✭✭✭✭
    Charging an EV on a system shared by household  system especially off grid could lead to some unpleasant supprises, example bad sun day,  it is also inefficient to convert DC to AC then back to DC. There are systems developed to do direct PV to EV https://www.tudelft.nl/en/2018/tu-delft/direct-high-speed-charging-of-electric-cars-by-solar-panels/ downside of these would be having to charge only during the day when most need the vehicle and when not changing the potential energy goes unused, though with some creative thinking this can certainly overcome.

    The combiner box question, if two separate system are used it's better, in my opinion, to have separate combiners.
    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.
  • westbranchwestbranch Solar Expert Posts: 5,182 ✭✭✭✭
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • PhotowhitPhotowhit Solar Expert Posts: 5,105 ✭✭✭✭
    akallen said:
    Existing system is twin off-grid Xantrex 5548 setup. Adding another 5x4 array (about 5040 watts actual), so it would be 10 strings with total Imp at about 178 amps. Thinking I should pay extra for breakers so that I can easily isolate the strings, but am unclear on whether one big box or a couple smaller ones. Since its not high voltage, I don't need any of the fancy disconnecting systems afaik. Looked at a basic MNPV16 setup as a possibility since it looks like I can use it as two buses. Anything else come to mind?
    The reason for so much power, if you're wondering, is EV charging is like running HVAC. Its not clear to me that 11kW of capacity may be completely adequate, so I'm looking at technology for direct from array to car charger and thus bypassing my house inverters, although the inverters still need to be able to tolerate my arrays when not charging vehicles. Beginning to think I need something quite a bit larger than what Xantrex sells.

    My thanks.
    You haven't described your system, but I see a couple problems currently.

    You suggest 10 strings of 2 panels that are (5040/20=) 252 watt panels. If the panels are 72 cell panels the input voltage isn't high enough for an MPPT type charge controller to work properly.

    If the intent is to use PWM charge controllers, which would work properly with strings of 2 panels, they currently max out at 100 amps, so you need to divide your panels into 2 or more arrays.

    10 strings with an IMP of 178 amps would have a voltage of 5040watts/178amps= 28.3 volts. Some calculations aren't right. In strings the voltage adds and the amperage remains the same, In parallel the amperage adds and the voltage remains the same.
    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
  • HorseflyHorsefly Registered Users Posts: 369 ✭✭✭✭
    edited November 2018 #5
    Photowhit said:
    You suggest 10 strings of 2 panels that are (5040/20=) 252 watt panels. If the panels are 72 cell panels the input voltage isn't high enough for an MPPT type charge controller to work properly.

    My interpretation is a little different. I think he's saying he's adding a new 5x4 set of panels, and this new 5x4 set totals 5040 watts. So I think he's saying his new array will be ten strings of 4 panels.

    I agree it would be helpful to know the Vmp and Voc of his panels.

    Off-grid cabin: 6 x Canadian Solar CSK-280M PV panels, Schneider XW-MPPT60-150 Charge Controller, Schneider CSW4024 Inverter/Charger, Schneider SCP, 4 x Vmax XTR12-155 12V, 155AH batteries in a 2x2 24V 310AH bank.
  • VicVic Solar Expert Posts: 2,987 ✭✭✭✭
    Horsefly said:
    Photowhit said:
    You suggest 10 strings of 2 panels that are (5040/20=) 252 watt panels. If the panels are 72 cell panels the input voltage isn't high enough for an MPPT type charge controller to work properly.

    My interpretation is a little different. I think he's saying he's adding a new 5x4 set of panels, and this new 5x4 set totals 5040 watts. So I think he's saying his new array will be ten strings of 4 panels.

    I agree it would be helpful to know the Vmp and Voc of his panels.

    Agree with Horsefly,   looks like the thought would be to double the array by adding 20 ea PVs,   in five strings of four PVs,   each 250 W (nominal) ea.

    Almost all of the 250-ish watt PVs that we have seen,   are 60-cell modules.   So  one would want to be careful about STC String Voc  --  somewhere around 140-ish string Voc  --  would suggest that the Charge Controllers be chosen carefully.

    For MPPT CCs rated for 150 volts Maximum input voltage,   strings of three PVs works well with 150 V rated CCs.

    Although,   the existing array  is implied to be very similar,   or identical to the proposed added array,   SO,   this CC choice may have already been carefully selected   ...

    YES,   more info on the system   seems in order.   5 kW of PV on a single CC  may be a bit much ...   all depends ...

    Two separate Combiners is most probably the way to go,   otherwise  would assume that there would be just too many cables in and out,   etc.

    FWIW,   Vic

    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • akallenakallen Registered Users Posts: 10 ✭✭
    Sorry this took so long. Thanksgiving traveling and whatnot.

    I agree, my sig is not a very adequate description. System is two Xantrex 5548 running in parallel mode with two Xantrex MPPT-60 controllers. The panels are a hodgepodge of Siemens and Solar World of the 60 cell variety, all of which are close to a 33 volt Vmp. They add up to about 5000 W of usable power (rating is higher). The 5040 watts of new panels I'm installing are very close to the same power delivery. The 5040 is usable power from the 280 watt rating panels. Vmp is 31.5 and Imp is 8.78 for the 20 new panels. Whole system is wired up to the Rolls Surrettes in a 48 V configuration. I never rewired the panels to take advantage of the higher input voltage the MPPT-60s allow for. They replaced the old Xantrex PWM charge controllers a few years back. They allow up to 120 V input in the MPPT range, so if I wire the panels 4 in series I would just be a tad over and not throwing too much away.

    So, back to where I started plus some of the good help already provided. Sounds like best to wire into 5 clusters of four panels in series through a couple of combiners and parallel into my existing after I rewire them. The Tudelft unit MCGIVOR cited is what I might be imagining - DC to charger to car. Need to read more about it to get a sense of the particulars. That of course may dictate something totally different if units of that ilk want to see high voltage DC, and then I'm back to the drawing board.

    My thanks.
    Twin Xantrex 5548 (48 V) with two MPPT60 controllers and Rolls batteries, Pre-2008, so the NEC was simple at the time.
  • VicVic Solar Expert Posts: 2,987 ✭✭✭✭
    edited November 2018 #8

    Hi akallen,

    Looks like you are in SoCal,  due to previous references to SCE,   and Edison,   and that perhaps you have a Grid-Tied or Grid Backup system   ...   form an earlier post in the GT Systems Topic,    ... "I have an off grid battery setup because SCE (in my area at least) likes to go south on a regular basis.
    I'm primarily interested in the additional kW because I want to stay a net producer while driving electrically ... "

    The Schneider SCC or MPPT 60 CCs are simply not designed to have an STC Voc of four times approximately 39 V  --  yielding approximately,   a string Voc of 155 V.   Do not know what PVs you are running,   but SW 290 PVs have a Voc,  over 39 V,   IIRC   ...

    Your climate may be moderate,   but  on a 48 V Flooded battery system (assumed,  from  references to "Surrette"),   the ideal strings of 60 cell PVs are are three PVs.   This yields a string Vmp of about 93 V.   This is much kinder to your CCs  --  they will run cooler,  make more power and last longer.

    All,   IMO,   and FWIW.       Vic

    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
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