Aquion Energy batteries

What specifically are you looking for?

Curves showing voltage and currents at various states of charge. I see they have posted plenty of discharge curves, but I haven't seen any for charging.

At first guess, I would say that the internal resistance should be pretty symmetric between charge and discharge (not all chemistries do this, of course. Non-rechargeable batteries in particular ).
That means that you can just take the difference in voltage between the zero current line and the current you are interested in and add that difference to the zero current line instead of subtracting.
In the case of flooded lead acid cells, this method is reasonably accurate as long as the terminal voltage does not go above the gassing voltage. At that point another parallel current path becomes available which is not present during discharge.

That makes sense, but I don't see any zero current lines on any of Aquion's discharge curves for the S20 stack. I guess one could try to estimate it by examining current discharges at 2,4,6,8, & 10 amps.

It would also be interesting to see how the charge acceptance tapers off as the stack approaches full charge, and to see what the recommended "absorb" voltage is.

No guessing about it. Got the link and I will tell you. Ri does not change from charge to discharge.

Section 6.3 of the operations manuals for the L stack and M module have several figures that might be what you're looking for, including the recommended charging profile.

Not sure that I totally agree with the logic/math here Sun King. Internal resistance is a big deal, but what I do not believe that you can draw some of the conclusion that you are. Internal resistance directly correlates to how hot you can expect these puppies will get (i2r). I do not think that you can say that it will limit their C-rate. But it is really beside the point because I am in agreement about the practical use of these batteries. You will end up needing a huge of amount of these to do anything real. Two things should stand out immediately with these guys, first, 3,000 cycle life claim from a company that is 4 years old? Really? Show me a startup battery company that doesn't claim 3,000+ cycles and I will show you honest people. It has become standard boilerplate for newbie battery companies wanting to get funding unfortunately. It hurts green tech and renewables when people make up outrageous claims and really grinds my gears. And the four years is the company's age, not their latest product. Which leads me to the second stand out, they have put out 3 products within one year of starting production, each obsolescing its predecessor. This is a huge red flag. Cell phones companies can't compete with this act of...marketing genius or "I'm not sure what I'm doing but as long as I tell you version 2.0 is better you should buy it". In today's society of throw away product, I don't blame them for trying. Seeing and handling the batteries in person and you walk away at best with the impression that these are early stage prototype. 12 gauge wire connected oddly to batteries in storage bin plastic? And I think there is a fuse for each stacking. Try finding the bad one when the lights go out!

I have no problem with that. By limit I mean over gassing on charge side, or voltage sag on discharge side. Ri is the direct contributor to those two items. Bottom line is the Ri is way to high to be of any use other than running your cell phone. Imagine dragging around a 500 pound battery for your cell phone.

I think you meant dishonest people??? Even battery companies that are trusted and been around 50 years lie like politicians and drunken sailors. Will say anything to get in your pants, err I meant pockets.

I like you but you just crossed a line some folks here are not going to like one little bit. Users like Dan, Don, and Ian do not like facts or anything that shines a bad light on Renewable Energy. They believe anything Green they are told and could careless what is real or imagined. They believe batteries have 8000 cycles and have a positive EROI.

I didn't even think about gassing. Yikes! Don't they claim to be self-balancing as well? Can anyone say electrolysis? I assume it is because they can overcharge their batteries like lead-acid. But yeah...gassing, good point.

I am glad to hear that you appreciate where I am coming from guy. I hope the users you listed don't get too offended. But we have to be more critical about the companies that sell snake oil and that are more concerned with their next series of investment instead of being focused on making a product that works. They will do (have done) more harm to green tech than you or I pointing out technical concerns. That is the beauty of science. You and I could be 100% wrong (doubt it ) . All you have to do is show and explain the data that supports your claims...to people who understand it. Unfortunately, a lot of green tech enthusiast have more good intentions than technical understanding.

And there is this:

S20P stacks

I have a small 1kw* install w/ a pair of Aquion S20P stacks which have been in steady use for about a month now. The purpose of the install is emergency power with the option of running day loads, during which the batteries work to buffer load mismatches.

*1kw STC / 780w NOCT. Even under full orthogonal sun and a few % from mpp I only get ~NOCT w/ full load.

The stacks match well to my 48V system; by the time low voltage shutoff on my SK1500 kicks in at 42V there isn't much left in the stacks, as can be shown in the curves given in the Aquion literature. My CC is set to float them at 57V, the SK1500 throws a high voltage warning but has never shut off on me.

The manual does not allow the 8-layer stacks to be disassembled; they are clamped so they are under constant pressure. I am not not yet sure what the procedure is for failed cells or the risk factor of a failed cell.

They are rated to push a maximum of 450W each, though no voltage is given for that figure. They do not noticeably heat up under heavy load. I measured a trivial 2F degrees increase. They do dip a bit under load but not terribly. I am able to run a freezer, a fridge and fishtank with heater/lamp. I would expect a more serious install of 8+ stacks in parallel to be fine unless doing something out of the ordinary.

I am using them with a Midnite Solar combiner; the Aquion manual wasn't very clear as to which direction to wire the DC breakers: Current could be flowing in either direction depending on charge state, which could compromise the arc-breaking mechanism of the DC breaker. I used fuses as cheap placeholders until I get a better picture of the situation in terms of bidirectional breakers. In the meantime I am in a potentially-awkward position if I ever have to disconnect-reconnect either of these stacks.

The figures given by Aquion are based on accelerated tests. I understand that as a startup they need to get a product out ASAP and that there is some risk of accelerated tests vs real-world results. The fact that I only got two stacks is a response to this risk.

There are a few concerns:
The stacks are 260lb each, have a tilt limit of 15 degrees and cannot be disassembled.
Min. operating temp is 24F, min storage temp is -4F. Manual says violating this limit could result in damage. The -4F figure is familiarly close to freezing point for brine.

I live near Canada and have encapsulated the stacks in an insulated shell. They aren't supposed to casually vent like LA, but the manual states they can vent CO2, CO, and H in modest amounts. Needless to say, when I open the shell all doors and windows are wide open in preparation for concentrated vent gasses.

First off welcome to Solar Panel Talk

Thanks for posting data on your Aquion system. Yours is the second non commercial system that we are learning about. Hopefully it will perform for you as advertised.

Keep us in the loop on how it does over the winter. Thanks

Cool. Tell us more as you learn it. I was looking at these for awhile. Good luck.

Correction

I mistyped: I have the S20Ps in absorption at 57V, float at 54V.

Also, the S30 is out now with a little more capacity, removed the fuse, and better warranty.

The float is below the absorption voltage? Are you sure?

Yes. You may have gotten them mixed up like I did earlier.

aquion-pg17.jpg