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Very Simple 4kW "Off-Grid" System $7,000 (Any Advice?)

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  1. #1
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    Default Very Simple 4kW "Off-Grid" System $7,000 (Any Advice?)

    I am doing two separate (but identical) 4kW "off-grid" simple systems (one for upstairs, and one for downstairs), each having 16x 250W 12V (22.5Voc, 18.9V, 13.41A) panels in series, which run directly into each MPPSolar 5048MG inverter http://www.mppsolar.com/manual/PIP-M...l-20211006.pdf or https://mppsolar.com.au/product/u564...high-pv-450vdc (or Growatt 5kW Offgrid SPF5000ES is a similar inverter that I could swap out for if need be). Each 48V battery bank is 4x 300Ah 12V LiFePO4 in series, which also plugs directly into inverter. Each battery has internal BMS built-in apparently. Optional backup generator/grid AC bypass can also plug directly into each inverter supplying grid power if there are cloudy/rainy days.

    Across both $7k systems ($14k total cost), we would have total 8kW panels, 28.8kWh batteries, 10kW total power draw capability, 30-50kWh daily generation (winter-summer). No combiner box, no complex wiring, no charge controllers, no BMS, no displays. Just panels, inverter, and battery bank. I think I still need PV isolator, battery DC disconnect & fuse, and inverter AC breaker, but that's about it maybe? Keen for any advice if I missed something. Haven't set it all up yet, but have already bought the batteries/inverter/panels a couple years ago all still unopened in boxes. I would prefer to keep the two systems separate, and also the wiring is so much simpler I think.

    Cheers,
    Ryan

  2. #2
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    Quote Originally Posted by countrybloke View Post
    which run directly into each MPPSolar 5048MG inverter
    This is the exact 5048MG inverter that I bought 2 of a couple years ago (https://www.aliexpress.com/item/32864019448.html). That exact version is no longer sold, but that listing still shows the exact specs of it. Their newer versions are very similar specs anyway. MPPSolar is the only genuine brand of these style inverters. There are plenty of look-alike knockoff inverters that look similar, but to get the genuine MPPSolar brand you should buy directly from them as I did. Btw they don't sell on Aliexpress anymore, only on their website now (https://mppsolar.com.au/product-category/inverters/).

    I also have one of these 4-battery cheap balancers $55 (https://www.aliexpress.com/item/32643622608.html), but amp transfer is so tiny. To do away with a BMS completely, I guess I would need to buy a better balancer, like maybe a couple of these $119 ones? (https://mppsolar.com.au/product/maxx...y-balancer-t2/)

  3. #3
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    Quote Originally Posted by countrybloke View Post
    but have already bought the batteries/inverter/panels a couple years ago all still unopened in boxes.
    Get some charge on those batteries before they turn in to useless bricks. Especially with an inbuilt BMS that is likely drawing a small amount of current. While lithium is better for storage they still discharge over time and can be damaged if get too low.

    While it will be extra work I personally would recommend setting them up for operation in parallel which that MPP unit seems to support. Greater capacity for solar to charge battery while each set is facing sun, better load spread etc.

  4. #4
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    Yes you're right, I'll try to get the batteries set up asap before christmas. I checked one of them recently, and it's still at 13.2V (70% full), almost the same reading as when it arrived nearly 2 years ago. Kinda hard to believe it has held perfect charge, but anyhow I should still get them up and running asap.

    With the 5048MG inverter, I'm only powering a single 240V 10A outlet (which supplies a surge-protected 8-outlet powerboard). It's a lot more complex to join both systems together and might also attract electricity company attention, especially hooking up AC grid bypasses on both inverters, and paralleling that - I don't even know how that would hook together? For a single inverter, I would simply hook up the AC bypass to a single household outlet to pull 2.4kW max. When parelleling to pull 10kW max, how would I even do that unless somehow dual-wiring them from the main house electrical box or something? A lot of off-grid parallel tutorials are for US 120V inverter units, and there is not much out there that applies to paralleling AU 240V inverter units, (especially when trying to use grid bypass as backup when batteries are low). It needs to be completely separate from the main house electrical box, to avoid interferring with current feed-in rates or requiring connection/installation approval.

    I figure it would be pretty difficult for any household to use more than 57.6kW daily, which is the max output from one single outlet (240V x 10A x 24 hours). And the surge board (https://www.bunnings.com.au/arlec-8-...board_p0272240) has 8 individual switches, so if you need to use a high-powered appliance, like a toaster, you can temporarily switch all others off if need be. Stove and hot water are still grid powered. To make those run on the inverter (or parelleled inverters) along with other household loads, would seem to be a pretty big job, and I'm no electrician, I would have to learn so much to even attempt that.

    I guess down the track in the future, if we do away with the electricity company entirely, then maybe both systems could later be joined, and also connected to the main house electrical box. But would probably need some kind of off-grid specialist to help then. Most electricians shy away from these installations.

    I do have a concern about start-up surges from multiple fridges/freezers on a single outlet. I'm intending to get some of these to help fix that issue: (https://www.aliexpress.com/item/32835631088.html). After a blackout, I could set each fridge to auto-start consecutively within 15 seconds of each other, instead of them firing up all at once and tripping the surge board. What do you think?

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