Optimal distance between batteries

[Bob Smith]

Hi all,

I am struggling to find enough space to fit the batteries. Even if I am buying 2 to start with, I want my system to be modular and be able to cope with more batteries without having to redesign it.
The brand I am looking at is Solax with their HV batteries. The standard installation go with up to 4 batteries (1 master and 3 slaves) but someone on the forum (sorry I forgot his name) mention the BMX Parallel box which allows not to have any master and have up to 8 batteries.
Now I can comfortably fit 4 batteries in the area shown in the picture (two on the wall and 2 on the floor). Unfortunately, it will be a squeeze 6 on the floor.

In the specs I have found that they recommend a distance of 25cm between the batteries but their illustration only shows the batteries installed one next to the other on the wall. I do not have the luxury.
I am wondering if I were to install the 4 more batteries about 2m to 3m away (ie behind the position I took the photo from which is at the hatch). I suppose I will need to purchase longer cable but apart of this, Will there be issues that some batteries are close to the BMS and the others 2 to 3 meters away?

Alternatively I could have an extension built especially for the new PV system but misses will probably give her veto lol and I won't blame her. It is going to be expensive enough!!



for info it is 170cm height by 270cm wide

 

[bladerunnerpv]

Hi Bob, is this the tp3.0 or tp5.8 system ?

If it's TP5.8...
Looking at the user manual for TP5.8 (section 4.6) it shows all four of them to be installed side by side in a row, and says (section 4.4) separation > 300mm

parallel box :
https://shop.krannich-solar.com/de-...lutions/accessories/14855/bms-parallel-box-ii
The X1 (single phase I think) can take a max of 6 batteries arranged in two groups (see the datasheet download), I think you can have 2, 4 or 6, but not an odd number?
so arranged B-B-B-box-B-B-B
or arranged B-B-box-B-B
or arranged B-box-B

The parallel box user manual says "The recommended installation distance between the box and the battery module is 300-600mm, and the distance between the modules is 250mm."
(which contradicts the T5.8 user manual !)

"Will there be issues that some batteries are close to the BMS and the others 2 to 3 meters away?"
The parallel box user manual would suggest so yes...

So if you have space you could have two rows of three batteries, and the parallel box above them

hmmm, TP5.8 Dimensions: 474 x 193 x 708 mm

So min width for 3 batteries is 3 x 708 + 2 x 300= 2724mm which is marginal for the wall
or
So min width for 3 batteries is 3 x 708 + 2 x 250= 2624mm which is marginal too

If you're planning to get 2 on wall and 2 on floor, I don't think this enables you to expand as not enough space to put 3rd on the wall?

Looks to me like parallel box on the wall, then the two battery chains on the floor along the loft (from wall towards shadow in your pic) is the way to go?

Hope you've got strong joists, at 70kg per battery, and ideally you don't want something like a water pipe underneath a battery methinks.

I hope this helps in some way, but I suspect not, perhaps it will trigger a thought from someone else

NB I have no installation experience, just looking at the manual!



I looked at the TP3.0 too...
Looking at the user manual for TP3.0 (section 4.5.4 p26ff) it shows them in two columns, with 2 batteries in each column, BMS on top of one column, arranged thus

BMS
|
Slave1 -- Slave3.
|
Slave2 -- Slave4

Page 30 for four batteries has some measurements but it's not entirely clear what they refer to, A1..3, B1, B2 ??

BMS to Slave1: B+ to B+ (C:120mm); COMM to COM1 (E:200mm);

BMS to Slave4: B- to B- (A3:1.2m),
Get the cable through corrugate pipe.
Slave1 to Slave2: B- to B+ (A1:690mm); COM2 to COM1 (B1:600mm);

Slave2 to Slave3: B- to B+ (A2:1.2m); COM2 to COM1 (B2:1.2m);

Slave3 to Slave4: B- to B+ (A1:690mm) and COM2 to COM1 (B2:1.2m).
Get the cables through corrugate pipe.

It's not very clearly written, and although a picture paints a thousand words I don't think they've been to art classes!

It looks like a connect of (up to ?) 1.2m between columns, (slave 2 to 3)
but that includes the width of the battery which is 482mm wide, so a gap of around 700mm is implied.

But elsewhere (section 3.1.2 seems to suggest a gap of 200 to 250mm between columns.

ugh

 

[Bob Smith]

Thanks for your detailed response. ,

I had read those manuals but it was not clear to me if the recommended length/distance were just recommendation or minimum requirements or something to strictly follow

I realized I have missed an information!!! Thank you for bringing it to my attention.
The inverter specified is X1 and therefore this will only be 6 batteries and not 8. Well I guess this should still be enough kWh of storage!! (I know it is very tricky to see how much you'll need in the future, so I know I'll start with two 5.8 batteries but I want to make sure I can comfortably add to it).

6 batteries instead of 8 gives more room
This will give something like this




I need enough space in between the left and right raw to be able to get close to the wall and access the inverter, BMS and whatever else...

The width of the floor is only 90cm because then I have the atch of the attic.

 

[bladerunnerpv]

You're welcome Bob, at least there was one bit of usefulness !

"I had read those manuals but it was not clear to me if the recommended length/distance were just recommendation or minimum requirements or something to strictly follow"

It's not clear if it's hard and fast is it?
Just conjecture, but I guess if the cables are too long then there might be too much voltage drop involved, taking it below the operating voltage range of 100-131V? Not done any sums to see if that makes sense tho.

Looks quite snug in there! Might be worth roughing the units out in cardboard boxes and connecting string, will give an idea how much elbow room there really is to access the inverter.

If I'm visualising it correctly then the fronts of the floor mounted batteries, being daisy chained, will all be facing the same direction due to the cable exit points of the wall mounted batteries being on the right hand side IIRC, so then as you walk up the middle, some of the walkway gap will be be taken up by the depth of the right hand side set of batteries? So the walkway gap would be 474+250-depth of battery?

Separately will the hybrid inverter make enough 'juice' to fill 4 or 6 batteries? There have been quite a few previous threads, I expect that's been covered already.

Hmm, just for my own curiosity... the recommended charge current is 25A for the TP5.8 at 115.2V = 2.88kW ?

So 4*5.8kWh/2.88kW = about 8hrs for 4 batteries, and about 12hrs for 6 batteries? A bit less due to limit on depth of discharge

hope this helps in some way, enjoy!

 

[Bob Smith]

Thanks @bladerunnerpv
This is exactly what I have started to do. Build some boxes to the dimensions of the devices. I start to be used to it. I have done something similar for the PV Panels for the flat roof (space and shade) lol.

As for the charge/discharge you are correct for one batteries but not for more. Here is the data

The more batteries the more power, so the batteries will not end up being the bottleneck.
It will either be the inverter or what the DNO allows me to have when I want to charge them from the grid.

 

[bladerunnerpv]

Thanks for putting me straight Bob

OK just getting my head around this and 'thinking aloud' if you'll bear with me...

6x battery case... the recommended charge current is 25A for the TP5.8 at 345.6V = 8.64kW ?

But presumably this may not be achieved and will be limited by the inverter spec or the parallel-box, whichever is least?
T-BAT H 17.3

parallel box quotes two options for NOMINAL CHARACTER (Battery Pack), T-BAT-S 17.3 and T-BAT-P 17.3, presumably the P version is the relevant one (P=parallel ?) for 6x batteries

T-BAT-P 17.3
Nominal Voltage V 345.6
Operating voltage V 300-393
Total energy kWh 34.6
standard power kW 8.7
max. power kW 10.5

I don't know enough about this to be certain, but I would presume the standard power as being the number to look at, 8.7 is close to 8.64, so looks about right.

As for the inverter, the Solax X1 hybrid spec isn't very helpful if I understand it correctly,
for "Output DC (Battery)" it just quotes "Max continuous charge/discharge current" as 30A, but no nominal value.

So 6*5.8kWh=34.8kWh, and 34.8kWh/8.64kW = about 4hrs for 6 batteries?
or as per parallel box spec, Total energy kWh 34.6 gives 34.6kWh/8.64kW = 4.0 hrs for 6 batteries?
(ignoring inverter and parallel box efficiency, which would slightly extend the charge time)

Provided there's enough juice coming from the array of course...

Query: Solax X1 hybrid spec
- why is there an "Input AC" section ? Unless it can be also connected to the grid?
Can it be used as either DC or AC coupled inverter ?

I had in my mind that hybrid inverters are DC coupled only and could not be used to charge batteries from the grid as the AC only flows one way from hybrid inverter to the grid in this case.

https://www.deegesolar.co.uk/ac_coupling_vs_dc_coupling_solar_battery_storage/
Did I miss something ?

Thanks for putting up with my ramblings ;-)

 

[Bob Smith]

The inverter that was quote for my to be system

ie
10 new PV panels on an 2 string inverter
11 new PV panels with microinverter
2 x 5.8kWh HV Batteries
Batteries to be charged from the new panels, my existing 4kWp and from the grid

was a X1-BOOST G3 (see attached datasheet)

When I asked to have the BMS Parallel box to have up to 8 (now I know it is 6 because on 1 Phase), the designer said he needed to check compatibility with the BMS Parallel Box with AC coupled batteries. surely, if not a device could be added in between.
Anyway worse case scenario I stick with up to 4 batteries ie having a master and slave and no BMS Parallel Box.
They were supposed to ring me on Friday but did not, I hope I'll know a bit more on Monday.

 

[bladerunnerpv]

Hi Bob, thanks,

my tired brain is a bit confused with how the inverter fits into the overall setup, probably just me getting my wires crossed, I'll have to go back and re-read the earlier threads

Look forward to hearing more on your set up if you're happy to share and hope your project comes to fruition as you wish,

Sorry can't help on you original question about cable lengths, hopefully someone else on the forum can

 

[MHarv]

Discharge is inverter capacity dependent..... My Solax X1 AC 3.6kw inverter will briefly discharge at 4000w
then drop after 30 seconds to around 3000-3680w..... slightly different from specs... for Solax T58 Master plus Slave
11.6kW

 

[MHarv]

Boost for PV Array only and not batteries, you can with Solax hybrid and Solax X1 AC

What Solax inverter will the Batteries be connected to????

 

[MHarv]

If the loft floor is strong and sturdy to hold 70kg of battery fine, the master battery with BMS on top black stripe around it for info.
the top right hand side is the connection from battery to inverter... top left hand side connectors for adding another battery
3 x 200mm cables for interconnecting slave batteries supplied, but not earth cable which is 6mm2 and connects all batteries to inverter earth.

Now if space is limited, and floor mounting which I did, the slave battery had its wall bracket removed and turned 180' and put in front
of the Master Battery, (Master Battery taller than Slave.) and connected with 3 x 200mm cables supplied and 6mm2 earth in black corrugated plastic split sleeving 24mm which purchased as per instructions in manual

 

[johnb2713]

So 6*5.8kWh=34.8kWh, and 34.8kWh/8.64kW = about 4hrs for 6 batteries?
or as per parallel box spec, Total energy kWh 34.6 gives 34.6kWh/8.64kW = 4.0 hrs for 6 batteries?
(ignoring inverter and parallel box efficiency, which would slightly extend the charge time)

You wont charge at a constant rate, as you approach >90% the rate will slow down.

Query: Solax X1 hybrid spec
- why is there an "Input AC" section ? Unless it can be also connected to the grid?
Can it be used as either DC or AC coupled inverter ?

Hybrid inverter is capable of charging batteries from the grid and in order for it to be grid tied it will need this connection.

I had in my mind that hybrid inverters are DC coupled only and could not be used to charge batteries from the grid as the AC only flows one way from hybrid inverter to the grid in this case.

Yes they do DC couple the batteries.

 

[Bob Smith]

Hi Bob, thanks,

my tired brain is a bit confused with how the inverter fits into the overall setup, probably just me getting my wires crossed, I'll have to go back and re-read the earlier threads

Look forward to hearing more on your set up if you're happy to share and hope your project comes to fruition as you wish,

Sorry can't help on you original question about cable lengths, hopefully someone else on the forum can

The least I can do is share my experience, so yes I will and will answer all the questions to the best of my capabilities. I have learnt a fair bit or so I will transfer my knowledge as I go along

I am currently waiting for the designer to make the final proposal.

 

[Bob Smith]

Discharge is inverter capacity dependent..... My Solax X1 AC 3.6kw inverter will briefly discharge at 4000w
then drop after 30 seconds to around 3000-3680w..... slightly different from specs... for Solax T58 Master plus Slave
11.6kW

You are right that the bottleneck can be different on the direction of travel and both must be considered.
This said, they must not necessarily be equal.

My point of view is that you want to charge the batteries as quickly as possible because:
-The radiation is intermittent so if your panels gives 6kW of power for 1h you want to make sure this is what goes into your batteries and not be limited by the inverter or the batteries itself
-When charging from the grid during off peak time, you want to make sure you pull out of the bring the maximum power they provide you during the off peak time window

When discharging:
-It depends on your usage. This can be calculated, you want to ensure that when you have enough stored energy (eg 15kWh), and your house needs 5kW, then the 5kW comes from the batteries (via the inverter) and not that your system gives you only 3kW and the 2 remaining come from the grid. This would be a shame because you'll have enough storage.


The above is my understanding of the thing.

For what I am planning to do:
I expect that at best my PV panels will give a max of 8 to 9 kW (for an installed kWp of 14.5kW, this is because they will be facing 3 different directions). So I want the system to be able to reach that level. (7kW is still good enough for me).

Regarding my home usage, if I do not take into account the underfloor heating, 5kW will be enough.

Boost for PV Array only and not batteries, you can with Solax hybrid and Solax X1 AC

What Solax inverter will the Batteries be connected to????

So far they quoted X1-BOOST-G3 but I do not know yet if which one they are considering that this product family goes from 4.5 to 9kW. so based on what I said above, I would expect the high end ie

If the loft floor is strong and sturdy to hold 70kg of battery fine, the master battery with BMS on top black stripe around it for info.
the top right hand side is the connection from battery to inverter... top left hand side connectors for adding another battery
3 x 200mm cables for interconnecting slave batteries supplied, but not earth cable which is 6mm2 and connects all batteries to inverter earth.

Now if space is limited, and floor mounting which I did, the slave battery had its wall bracket removed and turned 180' and put in front
of the Master Battery, (Master Battery taller than Slave.) and connected with 3 x 200mm cables supplied and 6mm2 earth in black corrugated plastic split sleeving 24mm which purchased as per instructions in manual

Not sure I can picture your description.
The floor will be reinforced just to be sure but two adults can stand there no problem (I have not tried with 3 adults yet lol)

 

[MHarv]

Like I Said The Boost will charge batteries from PV Solar.

You can not (no connectors) connect batteries on X1 Boost models

What Solax inverter are you going to use for Solax Batteries?

 

[Bob Smith]

I'll let you know once I know what the designer has decided

 

[arwooldridge]

Thanks for your detailed response. ,

I had read those manuals but it was not clear to me if the recommended length/distance were just recommendation or minimum requirements or something to strictly follow

I realized I have missed an information!!! Thank you for bringing it to my attention.
The inverter specified is X1 and therefore this will only be 6 batteries and not 8. Well I guess this should still be enough kWh of storage!! (I know it is very tricky to see how much you'll need in the future, so I know I'll start with two 5.8 batteries but I want to make sure I can comfortably add to it).

6 batteries instead of 8 gives more room
This will give something like this

View attachment 14723


I need enough space in between the left and right raw to be able to get close to the wall and access the inverter, BMS and whatever else...

The width of the floor is only 90cm because then I have the atch of the attic.

Hi Bob, I have the Solax 5.8 batteries. The recommended spacing I think is just to give you more room to get to the terminals on each side.
I put mine a bit closer at 175mm space between which is just enough to get to the terminals. I also have the BMS parrallel box II. Definitely the way to go if thinking of expanding in future, otherwise the T58 master becomes redundant. They only supply fairly short leads for the battery to BMS box (or inverter) one end of the lead is standard MC4 but the other (battery side) is a different make. I use MC4 leads as extension though, Need 10AWG or 6mm2 cable though for the current.the manual puts one string above the other to make the short leads work. But I did not like putting that weight so high.(they should be wall mounted no sitting right on floor) manual recommends impractically short distance to batteries not sure why though. I guess keep the two leads tightly close together to minimise loop magnetics/EMP pulse affecting electronics.
I have 2 strings of 4 (on X3 Hybrid plus BMS box) all in one row so takes up a lot of wall run though.

 

[arwooldridge]

Hi Bob, I have the Solax 5.8 batteries. The recommended spacing I think is just to give you more room to get to the terminals on each side.
I put mine a bit closer at 175mm space between which is just enough to get to the terminals. I also have the BMS parrallel box II. Definitely the way to go if thinking of expanding in future, otherwise the T58 master becomes redundant. They only supply fairly short leads for the battery to BMS box (or inverter) one end of the lead is standard MC4 but the other (battery side) is a different make. I use MC4 leads as extension though, Need 10AWG or 6mm2 cable though for the current.the manual puts one string above the other to make the short leads work. But I did not like putting that weight so high.(they should be wall mounted no sitting right on floor) manual recommends impractically short distance to batteries not sure why though. I guess keep the two leads tightly close together to minimise loop magnetics/EMP pulse affecting electronics.
I have 2 strings of 4 (on X3 Hybrid plus BMS box) all in one row so takes up a lot of wall run though.

PS just read MHarv post about floor standing. As I understand that, alternate batteries front-front, back to back alternately. The short leads will then reach. But things to watch out. 1/not sure if it's recommended re thermal separation. 2/ the weight of potentially 6 batteries like that would be around 350kg in a small space. 3/floor standing batteries are not that stable ie top heavy and could be knocked over unless strapped together somehow. Maybe leave wall brackets on and bolt two back/back giving some space between batteries and making a stable pair then stand next pair in front etc. 4/ I can't recall seeing floor standing in the manual so maybe check with Solax, I guess the problem may be safety re malfunction/ overheat on a wooden floor, maybe they need raising on some (non combustible?) bearers to give airflow. I believe the manual does quote minimum distance off the floor from memory.

 

[Bob Smith]

Thanks @arwooldridge . I read somewhere they have an option for floor mounting. When I know more I'll give you the info.

8 batteries in a raw on the wall must be impressive!! Do you have any photo by any chance?

 

[arwooldridge]

Thanks @arwooldridge . I read somewhere they have an option for floor mounting. When I know more I'll give you the info.

8 batteries in a raw on the wall must be impressive!! Do you have any photo by any chance?

Actually I have or will have 12 batteries in a row! Four on one X3 hybrid 10kw and eight on another X3 hybrid 10kw with BMS box. It's just 4+4 now, I have the extra batteries but haven't connected them yet (waiting for more Sun). Am away from the site so will photo when back. It's a bit work in progress though.
Interested in any Solax approved floor standing recommendations though, it could be a space economic way to go. Same floor area but more compact?