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advise on design
#11
I would do an n+1 system. Ie 3 strings minimum where it can easily run on 1 string at max load and the last you can remove if needed.

With that in mind beware of that bigger strings = a bit harder to maintain but less strings = cheaper in terms of hardware around them like cables and BMS.

Less strings = equal larger packs to move and work with.
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#12
I watched many youtubes and noticed 80p packs etc. I eventually went with 60p for various non-technical reasons - which happened to be 130ah (average 2166mah per cell). Next I did 7s for 24v nominal for a while... and made sense for smaller (12/24v 60amp range) charge controllers. After a few months I began to understand that this is pretty small in terms of powering a house.

I kept the 60p pack but went 14s in conjunction with upgrade to a Midnite Classic 150s and set of 15 panels and 48v@3000 watt inverter. 48v reduces the amps (e.g. half as many as 24v) and matches the more serious (15-30 panels) and 80a + charge controllers etc. However, 48v requires city permit/conduit etc. When you get above 12/24v (depending on jurisdiction) you get into enough volts/amps to be 'more dangerous' and for my location that was 48v level.

Then I went Batrium which requires longmons. Longmons can handle 260ah (or even larger) packs so I still kept the 60p pack design... but doubled them up so effectively I now have 120p 14s and 3 of them which is about 40kwh. So making the packs modular is good! However, I now need 1,680 cells per '48v battery' - to add a 4th battery I have to buy/process 1,680 cells.

I happened to make my packs using 4 of those 4x5 cell holders - with blank spots on each end to protect the +/- pack connection posts. This allowed me to vary the number of cells but keep the same physical pack size and connection posts so they are all interchangeable. Some cell were 2900mah and others as low as 1900mah... so some packs have 45 cells (for 130ah) and some have 68 cells (for 130ah). Also, by leaving blank slots in your pack design, you can add a couple of cells to week packs later on once Batrium exposes them.

I like the comment about going with Nissan Leaf G1 batteries - price competitive to 18650 and so much less work that soldering up 5000 cells and I would have gone that way knowing what I know now... and prices now.

However - decisions can kind of lock you in. For example I could add Nissan Leaf cells to my 18650 bank OK but I would need a 2nd Batrium as these are 2s2p 'units' so they have different longmon/cellmon settings. So my 60p 18650 original decision is core to my battery system. Similarly, going with Tesla car batteries puts you in the 6s / 12s relm.. which limits inverter choices a little bit as the 7s/14s is more aligned with mainstream 24v/48v systems.
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