how to expand a battery system over 3-5 years

European Guy

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Hi you all! I struggle with the following. Currently I have 2 AGM batteries 12V, 200 Ah, for a 24V storage. In the coming years, the aim is to expand to a total of approximately 15-20,000Wh. So say 8 of these batteries. But I want to get away from lead/acid and from AGM and gel simply because of the cycle life. The current batteries are 1.5 years old but have been used for about 15 weeks because it is still a holiday home. In 3-5 years we will live there permanently and retire at that location, so hopefully I will make a choice now for the next 20-40 years. Then we need that greater capacity.
Question 1: can I simply use 2 batteries from SOK (LifePo) in parallel? Or discharged than the better batteries in the older ones. My idea is to use the AGM completely before I renew it. (I think they call it sustainable. )
2: And how will that go in a year or more if I want to add 2-4 again etcetera.
Currently my system consists of 8 panels of 310 Watt with an inverter/charge controller of 3000 Watt. I will also have to replace it, but that will come later :)
Thanks for your thoughts, Carl (Netherlands and Spain)

Ohw, and this is just a temporary set up, we are rebuilding all the time.
 

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Don B. Cilly

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Well, if you want to go 15-20 kW (of batteries?), you should really aim for 48V.
Meantime, you can stay 24, and then put another 24 of the same capacity in series. Not ideal, but it can be done.

About lithium... I would switch to it as soon as possible. If you do... those AGMs, can't you use them for "something else"? Like power a shed?
The best thing would be, get a 48V LFP battery, change your inverter to 48, use your 24V one for the shed or re-sell it.
With that, it's easy enough to "grow". Add more batteries, inverters (most AIOs have "parallel" capability), panels.
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European Guy

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Hi Don, yep 20kWh of battery power. Which is not that much if you need to live a full life of that for maybe 3-5 day with low sun in the winter time.
Why do you advise 48V? My plan is to have 24V as there are many aparatus available for 24V. As in my current system my water presure pump is 24V. Which is extremely efficient in energy. My outdoor (and some indoor) lightning will be in 24V also. On this way I do not lose much in conversion, can use more efficient motor for a pump. Plus as long as I have battery power some things in my home will work. as for example the charger/inverter will blow up I will still have water for some days. And reading these forum posts there things will happen :-(. So why 48V?
 

Don B. Cilly

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Just for amperage, really. I myself am just fine with 24V, but I have 5kW of batteries, and I really don't draw much.
You can actually use 24V if you go for multiple parallel inverters.
As an example, if you plan to draw 5kW from a single inverter for any extended time - say more than five minutes - that's ~200A (not something you'd want to do). If you don't plan to do that, or you use multiple inverters, 24V should be just fine.

My water pressure pump is also 24V, BTW, and for lights I use 12V LED bulbs in pairs (series).
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European Guy

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That I do understand. No, I will take all the Amps and Watts in consideration for the entire system. I am thinking of installing 3 Victron Energy Multiplus 24/3000 to create a 3 fase system as I do also have a 3 fase generator which kan kick in al all times. On this way power can be spread and I can even use 3 fase equipment as a sawmill. Okay, so 24V should not be the dealbreaker. Moving to LifePo4 is a wise thing as I do understand you. and should find a second owner for my current AGM's.
 

Don B. Cilly

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Moving to LFP is... life-changing :·) The "no-worries", peace-of-mind factor alone is priceless.
Since you're planning Victron, which is top-tier, you might consider server rack batteries.
You can find a price comparison discussion here.
Of course, if you feel a bit more adventurous and trust your abilities, you can save quite a bit of money and still end up with very good equipment by assembling your own. A very interesting thread on the subject is here.

I have two Pylontech 24V 220 Ah paralleled, and very happy with those.
Probably the best course would be buy one already assembled to start with, and consider DIY builds for subsequent ones.
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European Guy

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Great reply, thanks! A pitty that there are hardly any european traders in this business. I would like to build a set of my own. What about used Nissan Leaf cells? These will be widely available in the future. The only issue is the voltage I presume, 7.6 V is a bad starting point.
 

houseofancients

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Great reply, thanks! A pitty that there are hardly any european traders in this business. I would like to build a set of my own. What about used Nissan Leaf cells? These will be widely available in the future. The only issue is the voltage I presume, 7.6 V is a bad starting point.
plus, combustible chem....
 

Don B. Cilly

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If you'd like to build your own you pretty much have to get the cells from China.
There are some reputable vendors, even on Alibaba/Express. Try a search here. Buying the cells is still the hardest part...

Server rack batteries, I don't know about Holland, but in Spain most major home appliance stores (Leroy Merlin, Bricomart...) sell them. And autosolar.es do fast and reliable deliveries, in my experience.
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Don B. Cilly

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Yes, Lithium-Ion is a bit dodgy. The main (just about the only) reason why it's used in automotive over LiFePO4 is "energy density" (weight and volume). Otherwise, I would say LFP is vastly superior, and definitely for home energy storage.

Also, I would think... if they sell used car batteries cheap... what other reason would there be for it other than they're depleted/End-Of-Life?
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European Guy

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accident vehicles. Currently is for sale a number of cells with 99% SOH.
But combustion...... will they starting to get on fire by itself or only trough external reasons?
 

joanna_lannie

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In your case, it's just resorts at the moment, so AGM batteries or gel batteries would be great since you don't need to use that often. But after you retire, it's a good time to replace the LiFePO4 battery, because you will be able to enjoy the benefits of the LiFePO4 battery for a long time. Question 1 is ok, but paralleling seems a little weird? Your ideal system is 15~20kwh, I think a bigger voltage would be better (like 24V or even 48V). Sok's batteries allow you to do series and parallel. But if you want a cheaper and more flexible battery, you should be required to do a DIY battery. Of course, it is recommended to choose a well-known brand of battery cells. Cheap LiFePO4 battery cells often have many traps, and you need to carefully identify them.
 

European Guy

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Hi all, thanks for all comments. I have decided to buy LiFePo4 cells and build my own battery pack. Doing a lot of research and reading your answers , and checking YT channels as Will and Andy, convinced me to make this step. wish me luck :)
 

Shimmy

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Feb 22, 2022
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Just a point to your original question-- nothing wrong with having a 48V battery bank and a 24V distribution system fed by a DC:DC converter. You can even keep the AGMs in place as long as they last on the 24V side as a buffer.
 
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