3 phase grid tied solar installation

Good day to all here from sunny South Africa.

I need a lot of direction on this installation please but, be kind I am new to the solar installation fraternity although I have done quite a few installations and I have been off grid for some 8 years now but I feel it is a "hacked system" for lack of words as I am not an Engineer or Electrician.
I have installed 6 x 5 Kva (4000 watt) inverters in a 3 phase system (2 per phase)
My biggest concern is damaging the inverters by fitting a too high amperage fuse between inverters and batteries.
The installation is in a Liquor store which runs off mains power but because of load shedding here is SA we need back up power.
The idea is to run off Utility power and when load shedding is implemented the solar system can assist via the panels installed. The battery bank 48 volt 230a/h are merely to get the system "switched on"
So, in the event of no sun the client will use a generator but during a good UV day here in SA I am assuming I can "run off grid" with 54 x 380 watt panels ( 9 panels per inverter which have built in MPPT charge controllers)
Tell me what I need to get for you and I will do so.
I have run the system but the fuse blew when I changed internal settings from (solar charge only to solar and utility charge.
Axpert 5 Kva inverters are what I am using.
Hope to here from somebody soon.
Main items are 1 x 3 phase fridge (walk in fridge)
4 x 220 volt plug in fridges
cash register and LED lighting.

regards

Mikey Schultz

Comments

  • mike95490mike95490 Solar Expert Posts: 9,362 ✭✭✭✭✭
    With such a small battery bank, you have a larger problem than the batteries only lasting a couple minutes, even when running solar.  It's called Ripple.  The small battery cannot supply enough micro peaks for the inverters and that will shift a lot of ripple suppression to the inverter capacitors. That extra work they will be doing, will cause them to heat up and reduce their long term lifetime.  Solar panels have no "surge capacity" - they only put out what the sun puts in.

    Fuses.   The inverters should specificy what size fuse ( I use a circuit breaker on my 6kw inverter ) should be used, along with what size cable.  The fuse/breaker is only to prevent the wiring from burning up.  the machinery is supposed to be able to preserve itself, when you use the specified breaker/fuse.
     Does the fuse blow when switching from AC - DC  ( inverting and load support) or
    when grid restores and switches from DC - AC ( pass thru and charging)

    Inverter/Chargers should have settings for adjusting the battery charge current from the grid. For such a small battery bank AND so many inverters all trying to charge at once, setting that current to something very small ( 10A) might be a good start.   With so many inverters and 3 phases, not all will switch at the same instant and some will still be inverting while others are switching to charging,
    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 ,

  • MikeyschultzMikeyschultz Registered Users Posts: 2
    Thank you so much for your response. So I get your advice about the small battery bank and i will do my best to encourage the client to increase capacity/battery bank. I switched the system on today with two 125 amp fuses (positive and negative) and it seems to be working fine thus far (except for your advice about the ripple suppression) 
    I did some test on the system mimicking a load shedding scenario.
    With power from the utility as stand by and the solar system on I switched off all the fridges except the three phase fridge, lights, cash registers. I then put Utility off as if we were having load shedding. 
    The system handled the switch from Utility to solar very well to this point. I then put the four fridges on in a sequential manner at 5 minute intervals which was also handled easily by the solar system.
    What I am suggesting to my client is a delayed switching of the four fridges if we have load shedding. So, when the Utility drops off the four fridges immediately switch of and the via some circuitry we switch them on systematically, which we mimicked and it worked well. Provided there is solar power coming from the roof.
    Comments are very much appreciated please.

    regards
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