Charging time for a 100Kwh system? - theoretical question

[asder]

Just a random question for now, theoretical if you wish. Let's say I install a 100Kwh LifePo4 battery backup. Using the winston 1,000Ah cells. I was looking at the inverter dc charge and discharge. They usually are rated between 50a ~130a. I believe 16 in series will get about 51kwh, having two such packs in parallel will get the 100kwh mark? I was thinking for a stationary home system.

What kind of inverter, panel size (total kwh) and such would I require to charge the battery in 5 hours, at a 0.2C charge rate, which is safe for all components? Assuming the batteries are at 5% and charging to max at 95% (10% to 90%, if that makes the calculations easier). If the inverter maxes at 120amps charge and discharge for dc, that would be a scary situation for long term usage?

How would I go about solving this problem? The battery bank is big, but the charging side is small? what features would I need to look for in an inverter? If a single inverter can not do it? how would I make it work with 2~4 inverters (if possible)?

Below is how I understand the calculations work, correct me please if I am wrong somewhere. I have no background in these details, I learn as I go along.

If my understanding is correct. If i have 16 cells, LifePo4, 280ah. I have a 48V system. I would get about 14.3Kwh if I form the cells into a 16S battery? Let's say 12Kwh for a 83.7% usage(12 is easier to work with ). If my inverter and panels are working at full capacity, my inverter has a max charge current of 80A (i checked the settings for it). I set it at 60A for safety consideration. I would be getting 48V x 60A = 2,880 watts (let's round it up to 3,000 watts ) of energy into the battery for charging?That would mean it would take me 4 hours of charging at 3,000 Watts to get the battery to max capacity again?

I was just thinking, if I got a 100Kwh back up, how amazing that would be, than I thought, would I even be able to charge it up on the current 5Kwh setup I have for panels and inverter. Past 3 days have been rainy with heavy cloud cover and no sun. We have used roughly a total of 50Kwh in the past three days, that is where this fantasy came out from.

 

[John Frum]

2000ah@51.2 volts = 102400 wh

2000ah * 0.2c = 400 amps recommended charging amperage gives ~5 hours charge time.
If one string goes offline the remaining string gets charged at 0.4c which is within spec.
Check the specifics for the cells, I'm just going by dead reckoning.
400 amp@51.2VDC = 20480 watts.
20480 watts * 1.15 conversion factor = 23552 ac watts
23552 ac watts / 240VAC = 98.133333333 ac amps.?

 

[John Frum]

Here is an idea.
Make 3 independant systems of 3-400ah@51.2VDC
Peer them only at the ac side.
Design to run on 3 out of 3 optimally and 2 out of 3 for maintenance and fault tolerance.

 

[asder]

2000ah@51.2 volts = 102400 wh

2000ah * 0.2c = 400 amps recommended charging amperage gives ~5 hours charge time.
If one string goes offline the remaining string gets charged at 0.4c which is within spec.
Check the specifics for the cells, I'm just going by dead reckoning.
400 amp@51.2VDC = 20480 watts.
20480 watts * 1.15 conversion factor = 23552 ac watts
23552 ac watts / 240VAC = 98.133333333 ac amps.?

It's like magical numbers appeared, things that I did not even know existed. Thank you @smoothJoey .

400amps = check the open circuit voltage of the panels? or 400 amps = check the charge C rate in the documentation? The spec sheet says 0.5C is fine for 1,000ah cells. I didn't know 2,000ah cells are made, would have asked for that spec sheet.

Here is an idea.
Make 3 independant systems of 3-400ah@51.2VDC
Peer them only at the ac side.
Design to run on 3 out of 3 optimally and 2 out of 3 for maintenance and fault tolerance.

That would mean I get 3 inverters, set up a battery bank with each inverter?

 

[John Frum]

400amps = check the open circuit voltage of the panels? or 400 amps = check the charge C rate in the documentation? The spec sheet says 0.5C is fine for 1,000ah cells. I didn't know 2,000ah cells are made, would have asked for that spec sheet.

I'm not really following you but the first numbers were for 2x strings of 100ah@51.2VDC.
Even though the batteries so .5 c is ok I'm always concerned about the batteries bloating from heat stress.

That would mean I get 3 inverters, set up a battery bank with each inverter?

Yes.
I will say it again.
3 discrete systems that are very very close to independent and therefore fault tolerant.
The only integration is ac waveform synchronization.
The units have to coordinate who will keep the beat and who will become the beat keeper in case the beat keeper disappears.
This way you can still run with 2 out of 3 offline, of course at reduced capacity.

 

[BiduleOhm]

Make 3 independant systems of 3-400ah@51.2VDC
Peer them only at the ac side.
Design to run on 3 out of 3 optimally and 2 out of 3 for maintenance and fault tolerance.

That would mean I get 3 inverters, set up a battery bank with each inverter?

3 discrete systems that are very very close to independent and therefore fault tolerant.
The only integration is ac waveform synchronization.
The units have to coordinate who will keep the beat and who will become the beat keeper in case the beat keeper disappears.
This way you can still run with 2 out of 3 offline, of course at reduced capacity.

I plan on doing something like that but with a common DC bus so I have an even better redundancy and I can have a dissimilar number of batteries, inverters and SCC (like 4 batteries, 3 inverters and 2 SCC for example)

 

[John Frum]

I made a couple of thinkos earlier.
3 * 700ah * 51.2 nominal volts * .8 depth of discharge = 91056 watt hours.
As BiduleOhm own says you can add the capability to re-route things for even more fault tolerance at the cost of some added complexity.