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new powerwall project
#1
Hi All

My First post here, so hello to all.

Bit of background to start, i have been fortunate enough to get hold of a complete Tesla P85 battery - 16 modules.

I have a small holding, which has a small campsite with 3 16a hookups, my wife has a cattery which during the winter has electric heaters going 24/7, outbuildings that have various loads eg. welding, air compressors, and then our house with general stuff,eg fridge freezer, tv and lastly the big one, a 10kw shower. With all these loads the peak seems to be at or around 13/14kw for around 10/15mins (Its the shower !!!).  

Im connected to the grid (3 phase), and would like to use that as and when the solar/battery is not capable of the supply.

I had thoughts on what i want, but want to ask some advice, thoughts on the best approach. 

One approach is to connect the shower to one phase, and just take that out of the equation, and then run the solar/battery and use the connection to the inverter to one of the phases as the backup reducing the peak load on the inverter to more like 4 kw.

So one concern is with the inverter, and the other is with the BMS.

Option one.
Using a sigineer 15kwh inverter that has been made to cope with Tesla batteries, and a costly BMS by evtv.  But the inverter has a 50 day wait at the moment, and then its got to be shipped from chine, so more time. Not thought what MPPT charge controller i would use, but expect it would be victron.

Option 2
Using a complete victron setup - 15kwh invertor, cerbo GX, bluesolar 120/100 smart charge, victron shunt 500A 50mV, lynx dist board.

BMS is the concern with this setup, can go with the simp BMS, which uses existing tesla slaves, (But lots of build time) or using a Batrium wm5 and swapping out the slaves.

Option 3
using all option 2 but swapping the 15kwh inverter to a 5kwh

So this is where you lot come in, what setup route would you go or would you suggest anything different/better?

Many thanks in advance.
John
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#2
>... but swapping the 15kwh inverter to a 5kwh
Scratching my head a bit with this statement.   Maybe you could explain what you're thinking here? - and might help get better overall comments.     
Specifically - it seems like if you need a 15kw inverter - then how would a 5kw be OK?    Maybe you're thinking 3 x 5kw inverters to get 15kw?  In my experience (I run dual AIMS 12kw inverters) if you can afford it, there are some significant pros to having 1 inverter instead of multiple smaller ones.

BMS - do you plan to parallel the Tesla units for balance/monitor or monitor each unit separately?   I use Batrium WM4 with 84 packs (6 x 14s) and I can attest that it works well.  Depending on how you hook things up - you might find it useful to see/manage into each Tesla unit independently and Batrium would help facilitate that.   I think they are 12s and you have X units...  say 8.   Batrium is well suited to monitor 8 x 12 = 96 'packs'.    I do agree that hookup is some work - but i don't see how you can avoid that no matter what you do Smile
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#3
I think the best first step is to convert the on-demand 10kW water heater to ideally 2 water heater tanks. One always-on tank that is always ready to supply hot water, and a pre-heater tank to dump surplus solar power in.

Your whole equation will change dramatically with the 10kW load gone, no?
Modular PowerShelf using 3D printed packs.  60kWh and growing.
https://secondlifestorage.com/showthread.php?tid=6458
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#4
(09-12-2020, 02:33 AM)OffGridInTheCity Wrote: >... but swapping the 15kwh inverter to a 5kwh
Scratching my head a bit with this statement.   Maybe you could explain what you're thinking here? - and might help get better overall comments.     
Specifically - it seems like if you need a 15kw inverter - then how would a 5kw be OK?    Maybe you're thinking 3 x 5kw inverters to get 15kw?  In my experience (I run dual AIMS 12kw inverters) if you can afford it, there are some significant pros to having 1 inverter instead of multiple smaller ones.

BMS - do you plan to parallel the Tesla units for balance/monitor or monitor each unit separately?   I use Batrium WM4 with 84 packs (6 x 14s) and I can attest that it works well.  Depending on how you hook things up - you might find it useful to see/manage into each Tesla unit independently and Batrium would help facilitate that.   I think they are 12s and you have X units...  say 8.   Batrium is well suited to monitor 8 x 12 = 96 'packs'.    I do agree that hookup is some work - but i don't see how you can avoid that no matter what you do Smile

3 phase grid supply, over all 3 phases i have a peak load of 14k.  The main peak is due to the shower at 10k.  By splitting out the loads over the phases i can separate out different parts.

eg system at moment 
Phase 1 - supplies camp site
Phase2 - supplies garages - including welding
phase 3 - house including shower.

Eg each part has a single phase supply (using part of the 3 phase).

So by connecting shower to phase 1, i isolate that, and also the camp site. (not powered by solar/battery).

This was originally done to try and balance the phases, but having a 15kwh inverter would/could handle all load, but to continue 3 phase, i would still only have one inverter connected to one of the phases, eg phase 3, the other two still on grid power.

I could connect up a 5kwh to phase one, and another 15kwh to phase 2 to cope with welding... but not enough to warrant the spend/costs.

Hope that explains it?

(09-12-2020, 09:06 AM)ajw22 Wrote: I think the best first step is to convert the on-demand 10kW water heater to ideally 2 water heater tanks.  One always-on tank that is always ready to supply hot water, and a pre-heater tank to dump surplus solar power in.

Your whole equation will change dramatically with the 10kW load gone, no?
Hi, Its a shower head unit, not a water heater, no option to change this, unless i put in a less powerful shower, (The boss would not allow that - The wife!!)

BrJohn

(09-12-2020, 02:33 AM)OffGridInTheCity Wrote: BMS - do you plan to parallel the Tesla units for balance/monitor or monitor each unit separately?   I use Batrium WM4 with 84 packs (6 x 14s) and I can attest that it works well.  Depending on how you hook things up - you might find it useful to see/manage into each Tesla unit independently and Batrium would help facilitate that.   I think they are 12s and you have X units...  say 8.   Batrium is well suited to monitor 8 x 12 = 96 'packs'.    I do agree that hookup is some work - but i don't see how you can avoid that no matter what you do Smile

I plan to make a 48v battery but its not quite 48v.  
Two Tesla battery modules provide a nominal voltage of 43.2 volts and 237 ampere- hours for a backup capacity of 10.238 kWh

so 16/2 =43.2v @ 237Ah x 8 = 81.907kWh total (minus degradation)

Also the low end and high end charge point will also reduce the capacity and im not worried about that, as the battery is big enough and should last longer. (eg one of the minus points to victron compared to the sigineer inverter)
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#5
>Phase 1 - supplies camp site
>Phase2 - supplies garages - including welding
>phase 3 - house including shower.
>The main peak is due to the shower at 10k.

I'm in the US with split-phase 120v/240v.  While I understand what you're saying here...   My inverters cooperate with 120v/240v split-phase because I switch back and forth between grid and off-grid using ATSs.    Because of this - I would not plan to have separate inverters to power 'each phase'.  

In your case - I'm guessing the same idea applies.  Having a separate inverter for each phase probably isn't a good idea.   But that's an uneducated guess where I think the key question is...    how do you plan to interact with your grid power?    Do you plan hybrid or 100% off-grid or ?   If you can share your plans on this - I think that would advance the conversation as there are many excellent 3 phase type operators on this site that can give you good advice. 


>I plan to make a 48v battery but its not quite 48v.  
Agreed - 2 Tesla 6s modules in series will make 12s - which is on the lower end of 48v nominal but will work with some inverters.  

But to determine BMS recommendations,  I was asking how you plan to wire the sense leads to monitor the parallel groups of cells.    You said you have 16 Tesla modules - so that's 6s x 16 = 96 groups of parallel cells to monitor.    

It sounds like you're planning a 2s8p Tesla module setup.   You could parallel the sense leads between all 16 modules (of the 2s8p) which would yield 12s parallel cell groups for a BMS to monitor / balance.   Each cell group would be the 8p(s) monitored as if they were 1p.   If you do this, you can't tell directly which Tesla module is the problem as things age.    

I was just pointing out that with Batrium, you have the option to monitor all 96 groups of parallel cells individually - doesn't matter how your arrange them series/parallel for inverter power.     

You could also do 8 individual BMSs on each 2s1p 'battery' of the 2s8p setup.  
 
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Sounds like a fun project!
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#6
dali1972 its kW and not kWh when you talk about inverters.

Splitting a 3phase unit to use to different places as single phase is not really a recommended way. Note that if you break 1 phase then your loosing all 3. For single phase units its better to buy single phase inverters if you ask me.

I would also look at removing the direct heater and add in a smaller tank. I run a 30Liter here. No you cannot shower endlesly but its enough for 2 showers in a row and it only uses 2kW.. Alot cheaper doing that then having a high power unit...
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#7
(09-12-2020, 03:23 PM)OffGridInTheCity Wrote: >Phase 1 - supplies camp site
>Phase2 - supplies garages - including welding
>phase 3 - house including shower.
>The main peak is due to the shower at 10k.

I'm in the US with split-phase 120v/240v.  While I understand what you're saying here...   My inverters cooperate with 120v/240v split-phase because I switch back and forth between grid and off-grid using ATSs.    Because of this - I would not plan to have separate inverters to power 'each phase'.  

In your case - I'm guessing the same idea applies.  Having a separate inverter for each phase probably isn't a good idea.   But that's an uneducated guess where I think the key question is...    how do you plan to interact with your grid power?    Do you plan hybrid or 100% off-grid or ?   If you can share your plans on this - I think that would advance the conversation as there are many excellent 3 phase type operators on this site that can give you good advice. 


>I plan to make a 48v battery but its not quite 48v.  
Agreed - 2 Tesla 6s modules in series will make 12s - which is on the lower end of 48v nominal but will work with some inverters.  

But to determine BMS recommendations,  I was asking how you plan to wire the sense leads to monitor the parallel groups of cells.    You said you have 16 Tesla modules - so that's 6s x 16 = 96 groups of parallel cells to monitor.    

It sounds like you're planning a 2s8p Tesla module setup.   You could parallel the sense leads between all 16 modules (of the 2s8p) which would yield 12s parallel cell groups for a BMS to monitor / balance.   Each cell group would be the 8p(s) monitored as if they were 1p.   If you do this, you can't tell directly which Tesla module is the problem as things age.    

I was just pointing out that with Batrium, you have the option to monitor all 96 groups of parallel cells individually - doesn't matter how your arrange them series/parallel for inverter power.     

You could also do 8 individual BMSs on each 2s1p 'battery' of the 2s8p setup.  
 
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Sounds like a fun project!

Im gonna try make up a diagram with as much detail as possible, as i agree this is the best way to describe what i want...wether its possible is another matter Smile  I can then come back with replies, rather steep learning curve for me ....
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