AC coupled battery system

[nowty]

If as you say, ignoring the cost, then it’s a no brainer and go for the max because it will give you an number of advantages.

• You could be more conservative on the cycle depths and therefore (as Tinbum says) place less strain on the batteries so you get longer overall life from them.

• Over time batteries will degrade, so a bit more than you need to start with will still give you enough capacity later on.

• I'm not convinced battery prices are going to come down much more with inflation like it is and the sheer global demand for the product.

• If you want more of a fit and forget system like you say, then that points to the larger stack.

But I'm a bit biased with such a large pack, I could get by with a smaller one but not much smaller in winter, I personally get capacity anxiety when I'm down to my last 10 kWh which is more than many people have to start with.

[Joeboy]

If as you say, ignoring the cost, then it’s a no brainer and go for the max because it will give you an number of advantages.

• You could be more conservative on the cycle depths and therefore (as Tinbum says) place less strain on the batteries so you get longer overall life from them.

• Over time batteries will degrade, so a bit more than you need to start with will still give you enough capacity later on.

• I'm not convinced battery prices are going to come down much more with inflation like it is and the sheer global demand for the product.

• If you want more of a fit and forget system like you say, then that points to the larger stack.

But I'm a bit biased with such a large pack, I could get by with a smaller one but not much smaller in winter, I personally get capacity anxiety when I'm down to my last 10 kWh which is more than many people have to start with.

I would add that if you are on a reasonable TOU tarriff and have as previously discussed caught all the power vampires & time shifted the heavy load use into the TOU tarriff window (EV's washing machines, dishwashers, storage heating etc) where possible and are continuing to deplete 6 US3000C's then yes if money is not a problem, why not?

Someone posted on the other place a few years back and it stuck with me. Basically he was saying that due to the technological advances in RE available at home we run the risk of looking through the wrong end of the scope when consuming power. His point and far more eloquently put than I can manage was that we should always try and reduce the amount of power we use first via more power efficient machines and switching off what we don't need or use and insulate, insulate, insulate. I post this up more for those coming through later or new to the journey. I personally cannot wait to see a pic of a 9xUS3000C stack if the previous works have been carried out. If they've not i'm still looking forward to seeing the stack!

[martinW]

Hello All,

I've been reading this post with much interest as I am looking to go down the AC coupled battery route myself. I had been considering the Solax Ac coupled system, but the 18kWh max battery and what seems a closed ecosystem on the battery front had me pause.

Now I've found this post about the Sofar system which seems better (for my needs) with potentially a 8 x 3.5kWh storage battery 28kWh. Also I could make my own battery if I wanted (but I don't think this is as cost effective as a US3000C).


Quick question, can you limit the max charge and discharge of the battery pack, i.e. max volts and min volts. I've had a look at the manual (well user sheet) and it seems to say you can, just wondering if you have tried it out. Just thinking on Li-ion systems (I know this is Lipoe) if you reduce max cell charge by 0.1v or more and and increase min voltage at discharge you can make the batteries last a hell of a lot longer (at obviously a reduced storage capacity).

Also where you talk about having 9 US3000C batteries, I though the Sofar MP3000SP could only use 8 batteries

[Stinsy]

Hello All,

I've been reading this post with much interest as I am looking to go down the AC coupled battery route myself. I had been considering the Solax Ac coupled system, but the 18kWh max battery and what seems a closed ecosystem on the battery front had me pause.

Now I've found this post about the Sofar system which seems better (for my needs) with potentially a 8 x 3.5kWh storage battery 28kWh. Also I could make my own battery if I wanted (but I don't think this is as cost effective as a US3000C).


Quick question, can you limit the max charge and discharge of the battery pack, i.e. max volts and min volts. I've had a look at the manual (well user sheet) and it seems to say you can, just wondering if you have tried it out. Just thinking on Li-ion systems (I know this is Lipoe) if you reduce max cell charge by 0.1v or more and and increase min voltage at discharge you can make the batteries last a hell of a lot longer (at obviously a reduced storage capacity).

Also where you talk about having 9 US3000C batteries, I though the Sofar MP3000SP could only use 8 batteries

A few points:

• Both Solax and SoFar are compatible with Pylontech batteries.

• You can now put 16x Pylontech batteries in a “stack”.

• The inverter will concern itself about charge/discharge voltages. Some let you override but many don’t because the risk of damage is too high. Most inverters choose charge/discharge voltages that are very conservative in any case.

• If you want to research voltages, Pylontechs are a 15S LiFePO4 configuration.

[Oldgreybeard]

We now have 6 Pylontech US3000C batteries up and running with 3 more arriving in a week or two I hope. Looking at the charge voltage it does seem as if this is kept to below the maximum for LFP cells of about 3.65 volts per cell. The packs are as already mentioned, 15 cells in series, so if they were being charged to the maximum cutoff voltage then that would mean a pack voltage at 100% SOC of around 54.75 volts. In practice the voltage doesn't seem to get that high, and I think that this may be because the Pylontech BMS is set to a lower voltage per cell, perhaps to extend the cycle life (they do have a guarantee).

The settings can be manually changed easily enough with the SoFar inverter. I just set ours using the Pylontech preset (there are half a dozen other presets) but there's an option to create your own charge and discharge profile, just means stepping through each parameter and setting them for whatever value you think makes sense. I'm leaving ours on the default settings in the main. When we were only running three packs I did set the discharge limit to the minimum SOC the inverter will allow, which is 15%. For a time I was charging to 100% overnight on the cheap rate and discharging to 15%, but I have changed that now that we have 6 batteries so that it charges to 80% and discharges to 20%. That seems to be alright for this time of the year.

When the last 3 batteries arrive I will probably adjust the off peak rate charging down a bit, perhaps to 60%, to leave plenty of headroom for charging from PV. The biggest advantage we have found from having a bigger battery pack is that there is now no real need to monitor it all through the day and try to manage loads so that we do not run out of charge in the afternoon or evening. With 6 batteries I don't really have to do much in terms of keeping a beady eye on things and with 9 batteries I think the system should be pretty much fit-and-forget, with no need to worry too much about when to use power hungry appliances.

[AlBargey]

The Pylontech's will also talk happily with Victron inverters, and seem to work well in ESS mode (Energy Storage System) https://www.victronenergy.com/live/ess:start but they're maybe not as competitively priced as the others, although they are exceptionally versatile and programmable for various scenarios. I just use ours as an off grid inverter, although I have used it to 'ignore AC' (Shore power) until a programmed limit - when the sun hadn't charged enough, and I'm about to use the programmable internal AC contactor to use excess solar to trigger the secondary AC output to power the immersions in our thermal store.. But that's only gonna happen in another few months when the sun comes back

[billi]

The Pylontech's will also talk happily with Victron inverters, and seem to work well in ESS mode (Energy Storage System) https://www.victronenergy.com/live/ess:start but they're maybe not as competitively priced as the others, although they are exceptionally versatile and programmable for various scenarios.

Was my experiences at the time too , once understood their programmability , i found that there was an enormous "brain" work behind and one is NOT limited to only use Victron parts in addition (fair )

[Stinsy]

We now have 6 Pylontech US3000C batteries up and running with 3 more arriving in a week or two I hope. Looking at the charge voltage it does seem as if this is kept to below the maximum for LFP cells of about 3.65 volts per cell. The packs are as already mentioned, 15 cells in series, so if they were being charged to the maximum cutoff voltage then that would mean a pack voltage at 100% SOC of around 54.75 volts. In practice the voltage doesn't seem to get that high, and I think that this may be because the Pylontech BMS is set to a lower voltage per cell, perhaps to extend the cycle life (they do have a guarantee).

The settings can be manually changed easily enough with the SoFar inverter. I just set ours using the Pylontech preset (there are half a dozen other presets) but there's an option to create your own charge and discharge profile, just means stepping through each parameter and setting them for whatever value you think makes sense. I'm leaving ours on the default settings in the main. When we were only running three packs I did set the discharge limit to the minimum SOC the inverter will allow, which is 15%. For a time I was charging to 100% overnight on the cheap rate and discharging to 15%, but I have changed that now that we have 6 batteries so that it charges to 80% and discharges to 20%. That seems to be alright for this time of the year.

When the last 3 batteries arrive I will probably adjust the off peak rate charging down a bit, perhaps to 60%, to leave plenty of headroom for charging from PV. The biggest advantage we have found from having a bigger battery pack is that there is now no real need to monitor it all through the day and try to manage loads so that we do not run out of charge in the afternoon or evening. With 6 batteries I don't really have to do much in terms of keeping a beady eye on things and with 9 batteries I think the system should be pretty much fit-and-forget, with no need to worry too much about when to use power hungry appliances.

You're bing very conservative as to how you treat your batteries IMO! I charge mine to 100% and discharge to 10% every day in winter!

I do set the max discharge rate to 2kW in winter because it stops the voltage sagging too much when being discharged from 25-10%. In summer I crank the discharge rate to 3kW (the max my inverter can do) because the batteries spend more time at higher percentages.

This is more "what I do" rather than "what you should do".

[martinW]

I had not realised that you could now use 16 batteries in a stack, mine you that's a heck of a lot of storage.

I like the idea of a slightly bigger battery bank than needed so I maximise solar gains and also treat the batteries gently, I want them to last forever

I suppose it will come down to a cost benefit analysis. I personally don't see much likelihood of batteries prices dropping significantly in the near future so when I'm ready to take the plunge, I'll just go for it. Might start with 7kWh of storage and go up from there..

I need to sort out a new consumer unit and move some circuits around, I might go for an additional board or a new larger board. Hopefully I'll get this sorted during January (work allowing)...

[Stinsy]

I had not realised that you could now use 16 batteries in a stack, mine you that's a heck of a lot of storage.

There is also a device you can use to connect 4x stacks into a single stack!