jonescg's home battery storage system

[jonescg]

I figure since about 95 AEVA members will be about to install an 11 or 23 kWh battery thanks to the AVASS clearance sale on LFP cells, I might as well jump in with a thread about how I used lithium cells to store energy. I have about 2 kW of second hand Gumtree solar on the shed roof. Nothing wrong with them - previous owner did an upgrade and it was cheaper to sell it for $1100 with all the kit. So I bought it and put them on the roof. We'll be moving house before November, so nothing is really too permanent - it can all come down in a few hours.

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Years ago, there were these E-max sport scooters which were really crap. They came with lead cells which were heavy and lousy, and failed after a fairly short period. Patrick Finnegen and the guys at EV Shop in Balcatta had a few which I converted to lithium, as well as a WA branch field day where we took a dilapidated scooter under our wing and treated it to some lithium.

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They went better, but really, the scooters themselves were still pretty ordinary. The wheels were too small to handle any bumps, a tall person would accidentally turn the scooter off by bumping the key with their knee, and they wouldn't ride out of sight on a dark night. So I bought all three scooters which had under-utilised 20 Ah LFP cells and decided to make a home energy storage system. The three scooters gave me 96 cells, and I ended up buying some new ones from EV-Power to bring this up to 144 (~9 kWh).

If one gets paid 7 cents a kWh to export, it makes sense to use all your power when the sun shines; charge an EV or run the hot water system. If you can't do either of these because you live in a rental and ride your EV to work, well, you really need a battery.

I decided to make the 'power cabinet' as universal as possible. Starting with a steel frame cabinet to fit cells on the lower and middle shelves, and enough room for the charger/inverter in the upper shelf. The top is clear for me to pile crap on top of.

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The cells were terminated using laser cut 5000-series aluminium. I made the holes 6 mm to account for the invariable irregularities, despite the bolts being M5. Also, since the busbars were touching aluminium terminals below, I didn't put any conductive grease on them, but perhaps I should have? Anyway, the wooden shelves made it easier to terminate with a torque setting on the drill, and then I could lower the battery trays onto the shelves.

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To join the two 8s9p shelves, I used 8 parallel lengths of 8-gauge wire. This ensures the current path is evenly distributed across the cells, rather than having one cell at the end taking all the current at its terminal.

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There is a main isolation switch, 125 A fuse, busbars for running any 48 volt loads should you want to (lights, fridge etc) and a shunt for measuring current. Two DC leads come from the battery - one for the charger which is a 1600 W 48 volt lithium charger and one for the inverter @bga kindly loaned me. The inverter is an PIP4048 which has a maximum DC input from solar of 120 volts - too high for two panels in series, and too low for three in series. I believe the later models now use 145 V as the maximum MPPT voltage.

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The charger is set to charge from mains when the GPO timer ticks over to 10 am, and ticks off at 3 pm. This is more than enough time to fully charge the battery. I'm using 16 EV-Power battery balances to ensure the cells never go over 3.55 V per cell. I will eventually put a more detailed BMS on, but for now the PIP4048 inverter is set to shut off at 46 volts which is pretty much empty give or take some safety margin. I never let it run that low anyway.

So now I can come home at night, plug the scooter charger in to the inverter and put some bottled sunshine into the bike. Never any more than about 4 kWh on a big day - typically 3 kWh. I can do this once every couple of days. The timer ensures that it's only charged while the sun shines. It doesn't tun the house or anything like that - but it would be able to handle an 8 kW load if it needed to.

So, how are you going to set your battery up?

[coulomb]

Anyway, the wooden shelves made it easier to terminate with a torque setting on the drill, and then I could lower the battery trays onto the shelves.

How did you lower the battery trays to the shelves? Perhaps you could remove the upper shelves and lower using an engine crane.

To join the two 8s9p shelves, I used 8 parallel lengths of 8-gauge wire. This ensures the current path is evenly distributed across the cells, rather than having one cell at the end taking all the current at its terminal.

Were all the cables the same length?

The inverter is an PIP4048 which has a maximum DC input from solar of 120 volts - too high for two panels in series, and too low for three in series.

Even the earliest PIP-4048MS models could handle 145 V of solar input. Was this a PIP-4048KS model? It's slightly cheaper, and comes with a non-MPPT (PWM only) solar charge controller.

It doesn't [r]un the house or anything like that - but it would be able to handle an 8 kW load if it needed to.

8 kW for about 10 seconds; 4 kW continuous. Neat system, and a good fit to your circumstances.

So, how are you going to set your battery up?

I have an existing 320 Ah system in which the battery is now about 9 years old. It also has a few cells that are ex-EV (not mine), where something went crazy with their BMS or the wiring thereof and about half the cells were ruined. But they are (mostly just) capable of running a solar energy system. So now its true capacity is down to less than 70% of nominal; I tell my LyteFyba BMS that it has a capacity of 220 Ah (this setting is used to get the State Of Charge meter correct). So that's conveniently (at present) the same as the nominal capacity of the new cells.

My original idea was to try and buy one of the other 11 kWh batteries and make a 440 Ah system. But it would be a bit of a squeeze into the existing grey monolith cabinet, which is 940 mm wide (for easy transport in typical cars). It happens that I still have the original battery cabinet half a meter away from the main monolith cabinet. So I'm considering paralleling the new 220 Ah battery with the existing ~200 Ah battery. Depending on how I do it, it would add some resistance to the total battery, and flickering lights is already a consideration. While it's just a barely noticeable thing for most people, I have one family member that is particularly sensitive to flicker. I'd end up with two battery management systems, which I'd have to integrate. The LyteFyba system is all open source, so this should be no problem, after a bit of thought and design.

[ Edit: the existing battery is 9 years old, not the whole energy system. ]

[jonescg]

Bruce is popping over this morning so I will ask the owner of the inverter directly ☺.
Could you not put each 220 Ah cell in parallel with the existing cells? Saves on an extra BMS but the wiring would be a bit of a hassle.

[coulomb]

Could you not put each 220 Ah cell in parallel with the existing cells?

That's another option I'm considering. I could pick the best of my existing 160 Ah cells (presently buddy paired), put a spacer under each 160 Ah cell so that the terminals are the same height, and parallel with the new 220 Ah cells. The old cells are many mm less wide, so it should fit (all 220 Ah cells is very tight). It's not clear to me that paralleling cells of very different capacity (220 Ah and ~110 Ah) is a good idea. I do it now for just two cells, wasting some of the nominal capacity of the cells.

Splitting the battery between the main and auxiliary boxes is yet another option, but then I'd end up with hybrid triples (220 Ah in parallel with 2 x 110 Ah). Cabling for both of these options is daunting. However, the existing wiring is pretty daunting as it is...

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At the right end of the top row in the photo, two of the 100 Ah ex-EV cells are paralleled with one 160 Ah cell, to form a hybrid triple of nominal capacity 360 Ah. The outside two are paralleled with the outside two of the bottom row, forming a nominally 400 Ah buddy quad. The odd arrangement of cables (not terribly clear, sorry, but a new photo is not convenient at present) is to ensure the best current sharing possible. Thanks is due to Weber for coming up with that design. The thinnest wires are BMS communication wires. Those celltop Battery Management Units are old Rev 61 boards; the latest boards use pre-made and inexpensive radio control cables to connect the monitoring units much more neatly.

[jonescg]

So how do you power the house @coulomb ? I assume you have a PIP4048 or similar with a built-in changeover relay which flicks over to mains when the battery voltage drops too low? And the inverter is set to PV priority? Otherwise I assume the mains will attempt to charge the battery as soon as it drops out.

Oh, forgot to reply to your earlier query - I slide the shelves in like drawers then wire it up. I didn't leave enough space for more convenient wiring, so once the two shelves are connected, they're kind of set.

[coulomb]

So how do you power the house @coulomb ? I assume you have a PIP-4048 inverter.

Yes. One PIP-4048MS.

or similar with a built-in changeover relay which flicks over to mains when the battery voltage drops ...

It's quite sophisticated. There are many settings to control the behaviour.

I slide the shelves in like drawers then wire it up. I didn't leave enough space for more convenient wiring, so once the two shelves are connected, they're kind of set.

Do you slide the shelf in with tens of kilos of batteries, or did you undo the metalwork and move the batteries over one by one?

[jonescg]

Nope, just slid the drawer in. I was originally planning on having someone help but end the end I just picked up the shelf on my own and slide it in. It was heavy but I could lower it onto a milk crate first.

[mark_hetho]

We have an existing Grid tie hybrid inverter with solar and storage, and I'm thinking along the lines of adding another hybrid inverter and potentially more solar.

One of the things I noticed was that the 23kwh packs are going to potentially be difficult to completely charge in the sunlight hours - some hybrid inverters are limited to a 50-65A charge rate. The batteries are limited to 100A, so 4.8kw. Having a quick look around the models I've come across in with a charge/discharge in the >75A ballpark are the SolaX X1 Hybrid 5.0T, Fronius Symo Hybrid 5.0, Redback SH4600 and the Selectronic range. I'm leaning in the direction of a Batrium BMS and have noticed Batrium have documentation on connecting their Watchmon BMS to the Solax or Redback inverters.

The other path to explore are DC coupling options, but I haven't really investigated that at this stage.

[jonescg]

Depending on what you think you might use your stored sunshine for, it may be possible to run say, the light circuits and one GPO circuit from a battery-inverter. It's going to be a fairly predicable load year-round and probably well within the battery's storage. In my case I know I will never need to draw more than 4 kWh from the storage battery to charge the scooter, so the timer approach works reasonably well.

I figure it would get to be more complicated to use a PIP5048 with a changeover relay if your home is three-phase - and you only export on one of them.

[dgh853]

I'm looking to use an existing Goodwe 3600SBP battery inverter - see details at http://www.goodwe.com/Public/Uploads/pr ... er_SBP.pdf. These Goodwe battery inverters are ~$1500 RRP for the 3.6kW and ~$2100 for the 5kW model. I think that's excellent value and they are on the CEC accredited list. The 5000 model is 100A continuous charge and discharge which would be a perfect match for these packs.

I've had my Goodwe 3600 for over a month and it works well although the WiFi/app connection telling you what the inverter is doing isn't 100% reliable. My current setup is lead acid so I'll be looking to use a Batrium BMS with the 23kWh AVASS pack.

That should make for a very low cost battery retrofit setup (~$5k total cost including AVASS battery, Goodwe inverter, professional AC/DC wiring/install, DIY pack build and Batrium BMS).

Will look to share how the AVASS/Goodwe/Batrium setup comes together on this forum. Excited!

[mark_hetho]

The Goodwe 3600SBP does look like a great fit. I suppose if you wanted to add solar you could still DC couple to the pack with an solar charge controller. I'm not sure I'd DC coupling to a device that isn't expecting that might throw it's state if charge measurements out of whack.

Depending on what you think you might use your stored sunshine for

Wouldn't you want to use it for everything?

23kwh is a pretty good amount of storage. Especially if you don't use it during the day when you can use the solar directly. Optimistically this amount of storage and our existing solar would see us grid independent for 9 months of the year, and probably 90% of the year if we exclude some heavy loads that we can put off to a sunny day.

[Richo]

I'm not too keen on your wiring panel at the top of the rack being made out of wood.
It looks like at least one line is actually mounted to it through your brass bar.
Wood absorbs moisture.
I'd replace only that part with acrylic or polycarb or use another iso mount bar.

Otherwise very nice

I had a blackout on Monday for 8 hours.
Seems W.P. didn't tighten a line clamp properly on a new pole they replaced 2 months ago.
There is only so much I can do with a candle

I wished I had a setup like yours

Stoopid W.P.

[nuggetgalore]

I'm not too keen on your wiring panel at the top of the rack being made out of wood.
It looks like at least one line is actually mounted to it through your brass bar.
Wood absorbs moisture.
I'd replace only that part with acrylic or polycarb or use another iso mount bar.

Otherwise very nice

I had a blackout on Monday for 8 hours.
Seems W.P. didn't tighten a line clamp properly on a new pole they replaced 2 months ago.
There is only so much I can do with a candle

I wished I had a setup like yours

Stoopid W.P.

I am one of the lucky ones who got a set of AVASS cells.
As I am not home at the moment ,a friend picked them up and stored them in my garage laying them flat on a bench.As it will be a nearly a couple of months before i am home, is that detrimental, should they be standing vertical?
Thanks for any advice.

[coulomb]

The standard advice in the early days of LiFePO₄ was that all cells had to be upright all the time. The reasoning was to do with stratification of the electrolyte.

But there is almost no free electrolyte in the cells, and now it seems that the advice is that any orientation other than vent down is fine, operating or stored. I don't know if the amount of electrolyte in the cells has changed to cause the change in recommendation, or if the manufacturers were simply too cautious early on.

So they should be fine.

[nuggetgalore]

The standard advice in the early days of LiFePO₄ was that all cells had to be upright all the time. The reasoning was to do with stratification of the electrolyte.

But there is almost no free electrolyte in the cells, and now it seems that the advice is that any orientation other than vent down is fine, operating or stored. I don't know if the amount of electrolyte in the cells has changed to cause the change in recommendation, or if the manufacturers were simply too cautious early on.

So they should be fine.

That is what we thought, thanks.
He was more concerned with them falling over until properly restrained.

[nuggetgalore]

Mate of mine told me to place some type of corrugated plastic spacers between the cells(to allow cooling between the cells) and mount them in a strong tight container.
The pictures at the start of this thread show the cells tightly packed but not constrained, any comment on this?
What happens when the cells age and grow a belly?

[T1 Terry]

Mate of mine told me to place some type of corrugated plastic spacers between the cells(to allow cooling between the cells) and mount them in a strong tight container.
The pictures at the start of this thread show the cells tightly packed but not constrained, any comment on this?
What happens when the cells age and grow a belly?

They loose capacity because there is not enough electrolyte to saturate the full surface of each plate to maintain a path through the separator. You can get quite a bit of the capacity back if you don't leave the cells with the beer-belly look for too long, but if you keep cycling them the capacity loss becomes a bit more permanent.
I'm experimenting with a number of cells that bulged after pressing them back into shape and then strapping them and laying the battery on the flat face for a few weeks, then turning it over the other way and leaving it for a few weeks. The idea is to try and get the electrolyte soaked back into the plate material. No idea if it will work or not but if I can get better than 50% capacity back I will at least have gained something, they are paper weights at the moment

T1 Terry

[jonescg]

Yeah compression is a good thing, but you don't need to go overboard. The cells I have are 'constrained' but I wouldn't say they were compressed.

[nuggetgalore]

Yeah compression is a good thing, but you don't need to go overboard. The cells I have are 'constrained' but I wouldn't say they were compressed.

Thanks for the replies. I think I will box mine into two rows of 8 without excessive force ,just hold 'em tight. Allows me to start with 24 volts to use my current setup and later maybe change to 48 V without much rewiring.

[nuggetgalore]

Yeah compression is a good thing, but you don't need to go overboard. The cells I have are 'constrained' but I wouldn't say they were compressed.

Hi all, back in Melbourne after a very warm autumn in Switzerland.

Re my lithium cells ,should I be worried???
I started to assemble my set of AVASS cells and noticed some have already developed a belly, the fattest is nearly 90 mm across the widest part , 5mm each side. They were stored standing up just tied with a strap the last two months never have been connected since I got them (gosh,that's nearly half a year ago).
Another thing I noticed is the voltages of each cell two months ago varied a max of 0.01 V but now some are double that with one 0.03 V higher than the lowest. I was going to parallel two rows of cells similar as jonescg did, but now I wonder if the voltage difference is too much.Do I have to balance them before connecting?
Any advice appreciated, thanks.

[jonescg]

Re: the bulge - most of them had some kind of bulge so I wouldn't be too concerned. I would however recommend a compression jig like this one:

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Not busting tight, just tight enough that you can't move the jig up and down once clamped.

As for the cell voltages, the best thing you can do is put them all in parallel and charge them to 3.5 V. It will literally take days, even at 10 amps. But I suspect they are already at 60% SOC so it mightn't be so bad.

[nuggetgalore]

Thanks Chris.
I will do as you suggest (Not busting tight, just tight enough that you can't move the jig up and down once clamped).
I had a another look at the Brighsun 460 Ah specification ,I thought there was more info than just this
Capacity 460 Ah
Nominal Voltage 3.2 V
Minimum Voltage 2.2 V
Maximum Voltage 3.6 V
Maximum continuous charge current 100 amps
Maximum continuous discharge current 230 amps
Dimensions (L x W x H) 130 mm x 78 mm x 520 mm
Weight (single cell) 10.5 kg

like some SoC graphs etc.I must have been dreaming.lol.

[jonescg]

http://www.brighsunauto.com/Ch/ProductView.asp?ID=4
Only official source of specifications I have. There were some discharge curves for the 220 Ah cells in another thread.

[jonescg]

Hi All,
Now that the bank and I share a home, I figure it's time to add solar and storage. My ~8 kWh battery as the subject of this thread is probably not up to the task, and I want to go fully legit. So what's the plan of attack?

The house:

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It's a basic open gable with an east-west split. It's about 15 metres long north to south. The northern end of the house has a beautiful massive Marri tree (green) which shades the roof for several hours in the middle of the day, but the good news is the western roof gets plenty of sun thereafter. The Pepper tree at the SE corner will be pruned away to nothing eventually. So panels will have to be two strings on the east and west, which might well match our load profiles for the most part. The shed has a brilliant northern aspect, but it's a long way from the house and meter box, and only has a single run of 2C+E at 6 mm2. The trees in the yard were removed before this image was taken - it's pretty much un-shaded for most of the day.

The loads:
We are not big energy consumers, but we do have some significant loads. We have a ducted air conditioning system which we use for heating through winter, and about 4 times a year all day in summer. We have a dishwasher which can be programmed to start at any time, and we have a solar hot water collector which is fairly useless for 6 months of the year, so the booster gets about an hour a night (3 units). We have an electric scooter consuming 3 units a day, and will one day have an electric car consuming about 10 units a day. At the moment, on the worst winters day we'll consume about 20 units, and on the best summers day we'll consume about 5 units.

The wiring:
It's pretty good wiring for a 38 year old house. We have a three phase connection with 64 amp boundary fuses. We still have a spinning disc meter, but any upgrades will result in a replacement 'smart' meter. The aircon is the only three-phase load, and I think its only 15 amps per phase.

The goal:
To effectively reduce our energy consumption from the grid to zero, but still have the option of importing and exporting power when needed.

So what are the options? Three-phase hybrid inverters are a pest because they are all high voltage and call for very specific batteries - I hope to salvage old bus cells for this project and keep it at 48 volts (although if there is a compelling case to go high voltage I'm open to ideas).
I can easily fit 5 or 6 kW of solar on the roof, but the total generation will be limited because of the east-west split and the big tree. If I bias the panels to the southern end of the house it won't be so bad. SO an inverter with two MPPT inputs makes sense.

How about this? Move all household loads to one phase (the same phase as the single phase hybrid, DC-coupled battery inverter) and leave the aircon as a three phase appliance. The shed has it's own 32 A supply, but since it's only ever running about a 1kW of lights for a few hours 3 days a week, I'm not fussed if it goes on a different phase. Charging an EV at 7 kW will drain even the biggest battery in short order, but I'm loath to power it from the grid if I can help it, especially if it's not on the same phase as the inverter.

Any ideas?

[T1 Terry]

we should have talked about this while we were there. we fitted up a semi off grid set up very similar to what you are suggesting a bit over 2 yrs ago and it works great. they also have grid tie feed in so that offsets the power they use and the grid connection fee and they still get a bit of money back now most of the house runs off grid.
We use 24v rather than 48v, just much easier to work with as there are far less cell balance problems and the whole battery capacity can be used rather than limiting the upper charge voltage so no cell goes near the upper knee. safe for the battery pack but greatly reduces the useable capacity.
You can even set 3 of the inverters up to provide 3 phase power if you want and double up on the number of inverters on the single phase you want to power the rest of the house from, so a mix and match approach is quite possible. Each inverter has an 80 amp max output MPPT controller built in and additional 60 amp output controllers can be added as required. We built a system with 10kW of solar that uses this method but it is only single phase .... at the moment. They were conned by the evaporative air con people into believing the swampy used a lot less power than a good quality inverter split system. They discovered the truth the first time they turned it on full power, a continuous load greater than the peak load of the inverter split system. There is every chance the swampy will go back to the installer after a battle with consumer affairs and a split system unit will be installed. then we will probably be back there to re arrange the inverters to create a 3 phase output from the same set up.

T1 Terry