20KW PV array, 2 x Radian 8048s, Battery Bank Charge Rate Question

[Farlander]

I plan to install a dual outback Radian system for a residential customer with 20kW of PV power (15.5kW max power). Design calls for using 6 charge controllers, which theoretically could deliver 300 amps combined output to the 660Ah battery bank. Batteries charge rate as designed is maximum 200 amps. Question is, if batteries remain at 100% SOC at float voltage, will there be an issue of passing through 250+ amps through from the charge controllers to the inverter? In theory the battery should not be accepting any amp flow, correct?

If batteries were to be used in a grid down situation and needed the occasional recharge, would the 300 amp available charge rate overload the batteries?

Looking for recommendations on a 48V AGM battery bank that can accept 300 amp charge rate if this setup looks problematic.

Thanks,

[AzRoute66]

The controllers don't know if it is battery or 'loads', so they won't care. If the battery remains pretty fully charged it won't care.

If the battery gets drained enough, it could pull all of those amps and be damaged. I would go beefy AGM. Watch your wires.

No idea of which specific AGM.

[NEOH]

I plan to install a dual outback Radian system for a residential customer with 20kW of PV power (15.5kW max power). Design calls for using 6 charge controllers, which theoretically could deliver 300 amps combined output to the 660Ah battery bank. Batteries charge rate as designed is maximum 200 amps. Question is, if batteries remain at 100% SOC at float voltage, will there be an issue of passing through 250+ amps through from the charge controllers to the inverter? In theory the battery should not be accepting any amp flow, correct?

If batteries were to be used in a grid down situation and needed the occasional recharge, would the 300 amp available charge rate overload the batteries?

Looking for recommendations on a 48V AGM battery bank that can accept 300 amp charge rate if this setup looks problematic.

Thanks,

Without parallel strings, something like ...

http://www.sunxtender.com/2_volt.php

[Farlander]

We decided divide up the array into a grid tied portion and a battery backup portion. We'll have 9.9kW max power feeding the charge controllers, which gives us a max charge rate of 188 amps, safely within our 198 amp charging rate limit. The remaining 5kW will be on a Fronius or similar GT inverter.

Thanks for the replies.

[sensij]

Thanks for the replies.

Would you be willing to write more about the thinking behind the 660 Ah AGM battery? There aren't many situations in which that is obviously a good choice, especially if it is constructed with parallel wiring.

[SunEagle]

IMO the entire project sounds like a ticking time bomb.

No one in their right mind would build a 20kw system and using parallel 80 amp CC's that may introduce in excess of 300 charging amps into an AGM battery system.

The OP needs to meet with a certified Electrical Engineer with a PE license to properly design this system instead of trying to get help from an open forum.

[Farlander]

I can get group size 8D AGM 330 Ah 12V for the best price point of any energy storage I've found thus far. Paralleling two strings is not preferred over a single string I understand, but it's better than 3 strings, and we have implemented this solution before with good results. I agree we are a little oversized on the battery charging but the frequency that the batts will absorb that much charge is maybe a couple times every 2-3 years.

It's not my idea to build it this way, I would have sized 8.7 kW solar to a single Radian backup, but customer specifically required 16kW backup capacity with maximum allowable PV input.

[SunEagle]

I can get group size 8D AGM 330 Ah 12V for the best price point of any energy storage I've found thus far. Paralleling two strings is not preferred over a single string I understand, but it's better than 3 strings, and we have implemented this solution before with good results. I agree we are a little oversized on the battery charging but the frequency that the batts will absorb that much charge is maybe a couple times every 2-3 years.

It's not my idea to build it this way, I would have sized 8.7 kW solar to a single Radian backup, but customer specifically required 16kW backup capacity with maximum allowable PV input.

Great. Then have the customer hire a PE to do the design. You would be making a mistake to get that type of engineering help from an open forum even with some of us being professional electrical engineers.

If the system has a bad ending you would be the one holding the bag. Not something I would do even with my experience as an EE.

[Sunking]

IMO the entire project sounds like a ticking time bomb..

Amen and you know it. This guy claims to be a professional here on a DIY site asking what to do.

Sensij deletes my 1st post calling this HACK out. The guy is dangerous, nuke his butt and his thread. Or leave it up and help the guy kill someone.Senji is going to get the site sued to bankruptcy.

[sensij]

Sensij deletes my 1st post calling this HACK out. The guy is dangerous, nuke his butt and his thread. Or leave it up and help the guy kill someone.Senji is going to get the site sued to bankruptcy.

Give it a rest. There is nothing wrong with the questions asked, and there are clearly more people involved in this than just the OP. No design advice was given here, and you know that I (and other mods) are watching for dangerous responses. Asking for the client's name and number as you did exposes the forum to more legal liability than anything you've been theatrically ranting about, and posts like that will be deleted every time.

OP, it seems like you got what you needed, so I'm closing the thread. Please start another for follow-up, if you'd like.