48V LFP Battery Recommendations? Planning an Energy Storage System - House Battery

team teri on 22/09/2024 - 19:27
Last edited 23/09/2024 - 10:05 by 1 other user

Feel free to keep discussing, but I've had to put things on hold, see comment below

I'm currently designing a battery storage system for my house. Something that does similar things a Tesla Powerwall can do, but going the DIY design route. A lot more flexible, open interfaces, and a lot cheaper (we're on ozBargain after all!).

I'm planning to get a 48V LFP (Lithium Iron Phosphate) battery bank.

Reasons to go higher than 12V or 24V: much lower currents, and as a result much smaller wire sizes, cheaper active components, etc. A Victron Multiplus II 48 costs heaps less than a 12 or 24 with the same output.

Reasons to not go even higher: 48V is ELV, meaning it is legal for me (not a sparky) to work on the DC side myself. Plus there are plenty of battery options around.

I picked up 2 of the 100Ah 12V Voltx batteries from this deal, for $159 after cashback. Probably a pricing error, but it was honoured and the cashback tracked. They are specified to allow up to 6 in series. I wish I had 4, that would give me my 48V LFP bank. 5kWh would be sufficient.

Would be a bit 'cheap and cheerful'. I'd assume the cells would go out of balance at some point, perhaps get permanently damaged, and I'd have to rely on the 5 year warranty. As things are: no point getting another 2 at current retail price ($600 each or so), so unless the price error (with cashback) happens again: not an option. If anyone else bought the same deal that I got and not doesn't really need them, PM me and we might work something out.

Voltx sell a 48V version, since they are all on one BMS, I'd hope they stay properly balanced. $1960 though at the cheapest supplier I found. Not really enticing. Maybe another pricing error will bring that into 'acceptable' territory. There's hoping, but unlikely.

Leaves my preferred solution: a 48V server rack battery. Plenty of those on offer. But I find it hard to know which suppliers that can be relied on to supply a battery that will either "just work" for close to a decade, or to be still around to honour a 10 year warranty…

Any good value recommendations?

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  fantombloo on 22/09/2024 - 19:43

  They are specified to allow up to 6 in series

  I don't understand this. Surely the overall BMS determines how many batteries you can series. Maybe they are working on some figure based on how matched they are, therefore sharing load equally, but that's a recipe for longer term disaster.

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  SBOB on 22/09/2024 - 19:55

  48V is ELV, meaning it is legal for me (not a sparky) to work on the DC side myself.

  but how are you interfacing this 48v battery pack into a grid tie inverter?

  all power to the 'diy', but it would want to be a very friendly or risk tolerant sparky that's going to wire that side up for you and certify your battery setup :)

  • 

    netjock on 23/09/2024 - 10:15

    Some inverters have BMS and battery plugs so it is behind the inverter and not tied to AC side.

    Growatt hybrid inverters have these plugs so you can wheel in a battery and plug & play.

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      SBOB on 23/09/2024 - 10:41

      Pretty confident a licenced electrician still needs to certify the battery/48v side being connected to such equipment, if it's not an already certified/ticked device

      • 

        netjock on 23/09/2024 - 11:35

        if it's not an already certified/ticked device

        There you go. Unless you buy it from aliexpress and get it through customs undetected or someone hasn't already reported it.

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  JIMB0 on 22/09/2024 - 21:07

  Sounds like an interesting project. Have you found a sparky that will actually hook this thing upto the grid for you or are you just going to plug appliances directly into it?

  I'd assume the cells would go out of balance at some point, perhaps get permanently damaged

  Can you individually charge each cell to balance the battery?

  • 

    Naigrabzo on 22/09/2024 - 21:32

    HE means day to day, not just first use and it would not be practical.

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  whitepuma on 22/09/2024 - 21:32

  +1

  Just thinking about what's theoretically possible at a cheap price. salvaged & written off EV's are getting very cheap…i saw a completely pummeled model 3 sell just last week for under $3k, and the battery visible looked completely in-tact.

  Would be pretty cool if you could strip the battery out of an EV and use it for the purpose you're looking at.

  I say theoretically because i have never done it myself and am unsure of what practical hurdles you may encounter.

  • 

    netjock on 23/09/2024 - 10:16

    Problem with EV is they are different voltage. Plus check tear down of Tesla packs and it is pretty hard.

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    team teri on 23/09/2024 - 10:18

    Unfortunately (from what I read years ago, maybe they changed back) Tesla in particular is useless: they glue their battery packs together in a way that the only way to recycle them is to put the whole thing into a big shredder and recover base metals. No repair of the pack, or swap or reusing of individual cells.

    Other makes: yes, could be an option.

    But then: battery cells are very cheap now. About $140 / kWh delivered for top of the line brand new automotive grade, rated to 10000 cycles.

    • 

      whitepuma on 23/09/2024 - 10:27

      Could it be done by not stripping it apart to get the cells? instead use the whole module itself?

      I think if some company out there can figure this, would be a great way to re-use those wrecked vehicles whilst being profitable.

      • 

        team teri on 23/09/2024 - 12:11

        Yes, that would make sense, and I hope someone will do it.

        It would certainly require licensed workers every step of the way. Now you're looking at 400V DC :-)

        But yes, one of those 50 or 60kWh car batteries would easily take most homes off-grid in conjunction with correctly sized energy sources.

      • 

        netjock on 23/09/2024 - 15:23

        You also need to find somewhere to store the pack. If you store it vertically make it doesn't bring the wall down with it and cost you $20k to fix your house.

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  Naigrabzo on 22/09/2024 - 21:33

  Do you know whether you can ever be certified to use these DIY batteries in a on-grid situation? I reckon it's only legal in off grid. check to be sure.

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  Big Dog on 23/09/2024 - 00:33

  Are you required to list DIY home battery on your house insurance policy?

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  iDroid on 23/09/2024 - 09:30

  What is your motivation?

  If it's to save money then this may not be the best route.

  5kwh of batteries is at best going to save you $2 a day in power use.

  Will you ever get your money back?

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    team teri on 23/09/2024 - 09:48

    I estimated only $400 a year saving in power costs in year 1, rising over time with power prices. I would have expected to make the investment back over the 10 year expected life. (With the exception of the battery the rest of the setup should last a lot longer, and batteries are only getting cheaper to replace)

    Not considering 'cost of capital'. That would have been compensated for by having UPS for all essential appliances, plus knowing I reduce my carbon footprint, not using coal and gas power over night. In any case it would have worked out a lot better than any off-the-shelf battery solution.

    The big kicker would have come at an unknown point in time that can happen any day now: when my current PV inverter packs it in. I know when that happens now I will have to throw away the existing panels too and get a complete new system. No installer would integrate the old panels with a new inverter, since they aren't certified to current standards (meaning simply that, since they are not being sold anymore, no one has applied for certification, the panels are not bad or unsafe in any way).

    With the ESS in place, I could have just re-configured (part of) the array to ELV voltage and used some MPPT chargers to directly top up the battery. Adding some extra battery capacity along the way to make it worth my while. That's the flexibility the intended setup would have given me.

    Alas, it's not to be, see my update just below.

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  team teri on 23/09/2024 - 09:32

  To alleviate concerns: maybe DIY was the wrong term.

  When I wrote this post I was merely trying to contrast things with the typical, and currently rip-off priced, 'all in one' packages like the Tesla Powerwall or similar products from BYD or LG at similar prices.

  Several of the server rack batteries (the technology I asked for recommendations for) are CEC approved. For example this one here

  Where I hit a serious snag is when I looked closer at the Victron Multiplus, the incredibly flexible Swiss army knife at the heart of the whole plan. It appears in Australia we have some additional rules that don't apply elsewhere that mean it is currently certified only for off-grid. Even though it looks likely that will change very soon (new software to comply with AU rules has been available for a few months), it seems to require a $2000 extra piece of hardware.

  Bummer. That puts a stop to the original idea for now. Back to the drawing board.

  I might have to take my shed off-grid. Following the lead of a Youtuber.

  Or maybe I'll take the whole house off-grid. The $400 yearly supply charge goes a long way into paying for a lot more batteries to make that possible…

  Watching Andy's videos had indeed spurred on the idea of a DIY battery from individual cells. ;-)

  Anyway, to summarize why I find this a deeply unsatisfying situation (from a bargain perspective):

  Cost of Tesla Powerwall with Gateway: $13,600 for 13.5 kWh

  Cost of Victron Multipus with 3 CEC certified 5kWh server rack batteries (with unknown quality cells): $6,500 for 15 kWh

  Cost of Victron Multiplus with DYI battery (using the best available cells and BMS): $4,000 for 15kWh

  All these are plus installation. Yes, installation costs will be higher for options 2 and 3, but nowhere near where the excessive hardware cost places option 1.

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    theangryman on 24/09/2024 - 19:40

    +1

    Looking at the CEC website the 48V/5000 was recently approved - https://cer.gov.au/document/cec-approved-inverters

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  Protractor on 23/09/2024 - 09:32

  Do you reckon they'd honour the warranty if not installed by a certified trades person?