Firstly I got a 15KVA quattro from @Carl for a very reasonable price and sold my 8kva to a client that wanted to upgrade.
I then added 18 x 465watt panels from a deal that went bad and I was stuck with the material. Could not sell the panels as i was convinced that they were not tier one and did not want to install it for a client. After installing them on my roof I found out they were indeed tier on, but Class B panels. So I let them soak up all the sun they can.
Then out of the blue we got a call from a supplier asking us when we will be collecting out 8 x 465 watt panels that were bought more than a year ago but never collected. For the love of it not me or my wife can remember why we bought these panels. We did pay for it, so it landed on my roof as well.
I bought the house with 16 x 365 watt panels on the roof and an 8kw Sunsynk on the wall as a PV inverter. (Sold Inverter) .
Now the picture at 10 in the morning looks like this. 6 of the 465s and 8 of the 365s still needs to be stringed and connected.
Soon, i need to tie up with @TheTerribleTriplet and see what size bank I can build with the expected price on my Pylon bank. I am very close to pulling the trigger on letting my bank go. Its not 19kwh, made a mistake there, it is 5 x US3000’s and 1 x UP5000 = 22.5kwh.
Get the biggest AH rated cell you can. Bigger bank/s, less wires AND cells compared to 22.6 kWh from 6 in parallel.
16 x 3.2v x 308ah = 15.78 kWh bank straight up. Get two and you have 31.56kWh out of 32 cells instead of 22.5kWh out of 90 cells (6 x 15 cell banks).
Cells MUST BE BATCH MATCHED per bank from supplier. Keep matched cells together per bank.
Top balancing before you start is crucial … but there are big effort ways to do it if installed already. IF you have a lot of time onsite.
100ah cells, most BMS’es work fine. Easy. Big AH cells, little bit more balancing amps required compared to the small cells. 4A are comfortable.
JK BMS’es … and they integrate with Victron. @Paul is smiling.
Tried and tested - but outside the box:
Keep the 17/18 cell banks in the back of your mind. Less wires, bigger AH bank.
Volts are super important to note on the equipment and fuses, but long term, you have backup cells onsite.
If that is something you want to try.
Need a 20S BMS though.
I would argue for more of a balance. When you have those big 260Ah cells, it may reduce some parts, but it also means larger and more expensive switch gear. I’m also not a big fan of having just one string/module in a battery. If you develop a problem in that one single string, the entire system goes down. If you have multiple strings, the system stays up while the problematic module goes down.
I would far prefer multiple 100Ah strings over one huge 260Ah string. It will probably work out more expensive though.
I looked at that at the time, ito redundancy, with smaller cells/banks in parallel.
Hence I argue for 280ah and bigger.
Ps. If the day arrives that 600ah cells come out, are tried and tested, I’m upgrading.
For me, what won in the end, fewer cells, fewer connections and because it is DIY, you have spare cells onsite, BMS, it matters none if there is a problem. Hour of so offline to replace a cell IF needed.
More expensive switchgear, if I understand you correctly, same busbar as multiple banks, just thicker cable from batts to busbar. Cost is negligible(?) compared to parallel banks, methinks.
I therefor ague for fewer points of failure, spare parts onsite, to mitigate any and all failures. KISS.
I feel pretty similar about these new 650W PV modules. I get it, it is technically faster/cheaper to install. But now you have panels that make almost 20A peak current, which means it doesn’t work with any of the smaller/cheaper PV-inverters, or any existing equipment you have, and you have to use thicker cabling. I’d rather go with smaller panels (450W to 500W) and have more strings, at least for now.
I would not feel comfortable advising someone to go for the biggest he can find. Got to look at the whole picture. The industry also seems to be standardising on 100Ah modules, maybe 120Ah. Most rack mount units are 5kWh each these days, and probably for good reason.
Agree on the panels, although the comparison is like apples vs pears.
Read once long ago big wattage panels was more focused on large grid-tied solar farms with higher volt MPPT’s.
As it does get interesting to match big wattage panels optimally with a Victron MPPTs.
450v MPPT’s, becomes easier, simpler.
The higher volt/lower amps older 350w Canadians was the sweetest spot for me to max out a 250 MPPT.
Re. the batteries … apples for apples:
I.e. 20kwh bank made up of 4 x 5kwh banks in parallel.
Done more probably to be priced ito affordability for most home users.
So people want bigger banks, what do you do? Parallel them.
vs
1 x 20kwh bank … same volts / same charge amps as a 4 x 5kWh banks.
Apples for apples.
… with vastly fewer overall connections / points of potential failure on 1 bank.
On top of that:
Keeping 16 cells in line in one bank with a 2-4a BMS
vs
4 x 5kw 15/16 cell banks = 60-64 cells to keep in line, using mA balancer per BMS, for ±6000 cycles.
The 4 x mA balancers totaling probably less than the 1 x 2a balancer on the big ah bank.
All of the above what made me considering bigger ah cells.
Fire hazard:
If 20kWh starts running away it is 20kWh of potential energy in both banks.
16 cells to manage/check vs 60-64 cells.
This is a point you and I will simply have to disagree on. For balancing, better to have more strings, because that means you also have more of them balancing at the same time, and you can get away with a smaller balancer. And if you have a high cell in one module that activates a disconnect protection mechanism, you lose one module, not all your power.
Lower current per module means you can switch with a MOSFET (or two), and that means you can have directional control. High current forces you to go with a contactor and you lose directional charge control.
The only reason to go bigger is that overall it ends up working out slightly cheaper. There are no operational advantages to less and bigger cells.
With lead acid it was different. Paralleling caused enough trouble that we frequently told people to have less strings with larger cells.
Two days back it was raining and my guys could not go out to site so i asked them to rearrange my stuff on the wall after the Sunsynk has been removed. Was a bit of a mess and we redid it. Connected the last panels as well.
That old story of a shoemakers shoes and and mechanics car and and and, well this is not the best installation and the walls need paint but here it is.
Was not for the different gear you sport, I would’ve swore that it was my garage! Wall in same sorry state with lots of holes and peeling white paint. Also same cement floor.
But let me seal my roof first. Then the paint will come.
