extending a "professional" powerwall...?

owitte

owitte

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Oct 19, 2016
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Hi all,

what if you bought a PV system with integrated battery storage and realize you need more capacity? I friend of mine has 6kWp solar and an inverter with integrated 2kWh LiIo battery (SMA Sunny Boy 5000 Smart Energy) since last year. PV produces almost 3 times more than they consume and most of the energy they produce is fed back to the grid, because the battery is way too small (it even doesn't last overnight).

My friend said they paid around 7.000 EUR just for the battery and I was ROFL. After I recovered from that, I told him that my powerwall has 15kWh, just for a few hundred bucks:cool: . And after he finished crying, we began thinking about how to extend his battery...

Has anyone done this before or at least thought about it? Don't know what kind of cells they use (the specs sheet just says LG Chem LiIon, 150V, 12.5A charge/discharge rate), but maybe he can start collecting laptop batteries soon...:D
 
Hi owitte,

This is probably not exactly what you're looking for, but I had the same "problem". Even though the kWh to price ratio was way not as bad as the one mentioned and we already have 9kWh I am right now also expanding the the storage.

The Problem is, that with the system I have, I would loose 10yrs warranty If I opened it. I don't know if you can easily access the batteries in the SMA ? My approach right now is to get a second inverter which handles the laptop batteries and will feed back into the original inverter through its AC generator input ( Idk if the SMA has one?). This way I can extend the capacity without loosing warranty.
 
Sohax said:
Hi owitte,

This is probably not exactly what you're looking for, but I had the same "problem". Even though the kWh to price ratio was way not as bad as the one mentioned and we already have 9kWh I am right now also expanding the the storage.

The Problem is, that with the system I have, I would loose 10yrs warranty If I opened it. I don't know if you can easily access the batteries in the SMA ? My approach right now is to get a second inverter which handles the laptop batteries and will feed back into the original inverter through its AC generator input ( Idk if the SMA has one?). This way I can extend the capacity without loosing warranty.
Click to expand...

thanks for your response. Of course I know about the warranty problem. SMA gives only 5 years, so there're still 4 years remaining. We first wanted to think about the technical issues, it's then up to him if he wants to take this risk.

Your approach is a very good idea, too bad that the SMA inverter doesn't have AC input (according to the specs). It's a hybrid inverter that mainly powers the house and feeds energy back to the grid. They just added a small battery as a sales argument and to generate more profit, if you ask me :dodgy: . It's not very effective: They used around 500kWh from the battery so far this year while taking about 10 times more energy from the grid in the same period... and winter is still to come.

But I wonder how you charge your powerwall? And what about injecting the AC current from the second inverter? As far as I know, the inverter needs to synchronise with the existing AC phase... I have one that automatically switches between battery and grid on the input side, but it needs a grid connection in order to do that without interruption.

Well, in the end maybe my friend needs to set up a second system with a bigger battery, including charge controller/inverter and just split up the PV input. But I first wanted to check out if there's no easier/cheaper way...

Have sun!
Oliver
 
I am looking to use the SMA Sunny Island, it is there battery inverter series.

It has 2 AC in/out puts, so it is easy to keep the battery only supplying loads.
 
Where I live new legislation has been introduced forcing You to register/get permission from Your utility vendor to use, any battery that will be able to feed the grid.
This rules out any "home made" Power Wall.

Only way out is a totally isolated Island Unit, no mains whatsoever, not even for charging.

ChrisD
 
**IF** his 150vbattery is effectively a 42s (3x14) LiIon setup, would it not be possible to simply piggyback some extra capacity in parallel with his branded battery? Of course it would need its own bms, which ought not to be any concernofthe branded battery. An isolator for the additional battery, fuse and extreme care in matching voltages before connecting, would represent minimal prudence!

Checking the actual workingvoltage range of the branded battery would seem to be the starting point.
Working with ~150v dc is the obvious hazard of this route.

ChrisD5710 said:
Where I live new legislation has been introduced forcing You to register/get permission from Your utility vendor to use, any battery that will be able to feed the grid.
This rules out any "home made" Power Wall.
Click to expand...

Chris, we don't know where it is that you are referring to!
 
dougal said:
**IF** his 150vbattery is effectively a 42s (3x14) LiIon setup, would it not be possible to simply piggyback some extra capacity in parallel with his branded battery? Of course it would need its own bms, which ought not to be any concernofthe branded battery. An isolator for the additional battery, fuse and extreme care in matching voltages before connecting, would represent minimal prudence!

Checking the actual workingvoltage range of the branded battery would seem to be the starting point.
Working with ~150v dc is the obvious hazard of this route.


Click to expand...


yeah, that's exactly what I have in mind, just extending the capacity of the existing battery by adding more cells in parallel. And of course you need to be careful with 150V. Don't know if it must be a seperate bank with own BMS, depends of the existing design... I would prefer just adding more cells to the exiting seriesses, if possible.

Don't know exactly about the battery voltage, (german) specs sheet says it's 150V, but the description is more likely to be max. voltage or charge cutoff... seems to me quite high, and if you want make something like this from 18650s with let's say 3500mAh average, you'll need 42 * 572 = 24024 cells. The housing of it is definitely way too small for that...

I Think we'll just open it and measure ourselves.
 
Just thinking loud

0/ Accoring to your feedback, does the battery settings (in particular the DOD) is set to take advantage of it ? If this is not set properly a few % of capacity maybe used (for instance, the installer guy set DOD at the same level as Lead Acid packs)

1/ The installed powerpack seems to be a 40S6P pack used between 120V and 166V (each cell btw 3.0v and 4.15v). Each cell seems to have a 2100 mAh capacity according to the user manual.

Adding more capacity should be do-able by extending the existing pack (not paralleling) in order to use the existing BMS which may have a proprietary communication protocol with the inverter.
  • Openning the existing battery pack with warranty void (check if the warranty is segregated between powerpack and inverter)
  • Transforming the 40S6P pack into a 40s24P to jump from 1,8 kWh to 8,8 kWh.
This should lower the energy sent to the grid.

2/ Adding a second system in parallel seems unrelevant as the 2 need to sync in order to provide the amount of energy requested by the loads.

3/ Adding a second system to feed the first one is an issue as the first one send back energy to the grid.

I only see 2 options :
  • Trying to expand the existing pack with loose of warranty
  • Replacing the whole existing inverter + powerpack by something more relevant and sell the SMA + its powerpack on the second hand market.
My 2 cents
 
ChrisD5710 said:
Where I live new legislation has been introduced forcing You to register/get permission from Your utility vendor to use, any battery that will be able to feed the grid.
This rules out any "home made" Power Wall.

Only way out is a totally isolated Island Unit, no mains whatsoever, not even for charging.

ChrisD
Click to expand...

registration won't really be an issue. First, it's already registered and second, we just take it kind of 'unofficial' hack, if you know what I mean... :rolleyes:
 
Well 500kWh is not too bad, for a 2 kWh battery^^.

Initially I planned to charge the battery from the grid when the other inverter is feeding in to the grid (I've got all the values on a raspberry pi, I hopw to be able to conteol the inverter (MPP solar mpi 4k hybrid) via Modbus; This could also be done easier with a suitable energy meter that is compatible to the inverter). Not ideal, I know. But splitting up the power at the DC solar side is tricky as far as I know because this might interfere with the MPP Tracker. If not I would be interested in such a solution!

I finally ended up with covering the last tiny part of the roof with another 3kW solar. This should - at least in my case - be enough to recharge the batteries, as they are only the second powerwall. AC charging should in any case be possible with your friends setup. The only issue will be the efficiency
 
owitte said:
Don't know if it must be a seperate bank with own BMS, depends of the existing design... I would prefer just adding more cells to the exiting seriesses, if possible.
Click to expand...

My naive thought was that with an additional parallel self-contained pack, there should be no need to butcher the commercial pack.
There would be just two connections to be made to the existing system, and that those could hopefully be arranged to be made without modification/damage to the existing warranted items.
Extending each of 40 or so serial groups is not something that could be done unobtrusively!
 
dougal said:
**IF** his 150vbattery is effectively a 42s (3x14) LiIon setup, would it not be possible to simply piggyback some extra capacity in parallel with his branded battery? Of course it would need its own bms, which ought not to be any concernofthe branded battery. An isolator for the additional battery, fuse and extreme care in matching voltages before connecting, would represent minimal prudence!

Checking the actual workingvoltage range of the branded battery would seem to be the starting point.
Working with ~150v dc is the obvious hazard of this route.

ChrisD5710 said:
Where I live new legislation has been introduced forcing You to register/get permission from Your utility vendor to use, any battery that will be able to feed the grid.
This rules out any "home made" Power Wall.
Click to expand...

Chris, we don't know where it is that you are referring to!
Click to expand...


I live in Denmark and the new legislation I am referring to can be found here:

https://energinet.dk/El/Rammer-og-regler/Forskrifter-for-nettilslutning. :mad:

under 3.1.1.TEKNISK FORSKRIFT 3.3.1 FOR BATTERIANLG (TECHNICAL INSTRUCTIONS 3.3.1 FOR BATTERIES)

file:///C:/Users/Chris/Downloads/Teknisk%20forskrift%203-3-1%20Batterianlaeg%20-%20rev%201.pdf

This file is in Danish, use Google translate. :blush:

This document definethe technical criteria You have to meet to get permission to connect your "power wall" to the danish utility grid.

As I read the document acommercial Tesla Power Wall, will be OK, but I do not have any hope of getting permission to connect my home made "battery unit".

Hope this clarifies the matter :)

ChrisD
 
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