Aquion Energy batteries

[RedDenver]

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.

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.

[Sunking]

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.

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

[northerner]

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.

[inetdog]

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.

[northerner]

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.

[Amy@altE]

Hi Amy, could you also request specs with regards to charging if possible?

What specifically are you looking for?

[northerner]

I'll see if I can get the official specs from them. Stand by.

Hi Amy, could you also request specs with regards to charging if possible?

[Amy@altE]

I'll see if I can get the official specs from them. Stand by.

[Sunking]

Their specs have been a moving target. If you find the internal resistance published, please let us know. There was an Aquion person lurking here - maybe they would be kind enough to post it.

Easy to figure out, simple Ohm's Law from discharge curves.

[Living Large]

However, if all the specs they post hold true, especially considering cycle life and predicted cost reductions, then they may just be the best option. That is yet to be seen.

I am concerned with more than predicted cost. Inhaling fumes from my backup generator and listening to it and maintaining it, for starters. I wouldn't be using solar electricity AT ALL if my decision was based solely on cost - I would find a location on grid.

Their specs have been a moving target. If you find the internal resistance published, please let us know. There was an Aquion person lurking here - maybe they would be kind enough to post it.

[northerner]

I am a newbie, but I think you are on the right track. northerner believes firmly that the AHI will fit his off-grid application. Just as firmly, I believe it will not fit mine.

The belief that it will work for me is based solely on specs that Aquion has released about their batteries. I have yet to see real feed back from users of this battery.

However, if all the specs they post hold true, especially considering cycle life and predicted cost reductions, then they may just be the best option. That is yet to be seen.

The best option is the one that costs less in the long run! At the same time the AHI batteries are environmentally friendly and require no maintenance.

[Living Large]

Back to Aquion - from the start they never intended these batteries to be EV or even general purpose replacements. The major market seems to be grid-stabilization, and perhaps we are shoe-horning it into our application.

I think it is pretty neat - but like LFP, you've got to really understand and want those battery characteristics to fit your application.

I am a newbie, but I think you are on the right track. northerner believes firmly that the AHI will fit his off-grid application. Just as firmly, I believe it will not fit mine.

I find the flat charge curve of LFP very attractive, but others don't. There isn't a lot to think about, other than staying away from the two ends. I need the fast charge time for my location. I like the low weight. The cost, as long as it isn't way out of whack, isn't so much a criteria for me. I agree totally with your statement of "understanding and wanting particular battery characteristics," and it applies across the board for all chemistries, from what I have seen so far. Of course, there is another route of just going out and buying large batteries at WalMart, if you like to fly by the seat of your pants.

[inetdog]

Back to Aquion - from the start they never intended these batteries to be EV or even general purpose replacements. The major market seems to be grid-stabilization, and perhaps we are shoe-horning it into our application.

But for grid stabilization you really need to be able to deliver a significant portion of the battery energy in a few hours, at most 12 hours, and recharge on that same time scale.
Unless the battery bank is so massive that you are only ever using 1/40 of its capacity per cycle, I do not see the point.

On the other hand, if you do not care much about cyclic energy efficiency, you could choose to pull higher current from the battery bank and accept as much as a 50% voltage drop provided you care most about short term stabilization and have output conversion equipment that can tolerate a wide range of input voltages.
That is, if you are willing to accept a voltage sag of 40% instead of 2%, you would be able to use a C/2 discharge rate. That is probably good enough for a voltage stabilization application. For the charging process you could limit it to C/12 or even C/20 and have a useful recharge in the stabilization application.

For comparison, I have seen statements that pumped water storage has a cyclic efficiency of 50% or lower, so there may be a place for a storage system that can be deployed anywhere, with the option of a relatively small and inexpensive system size.
Maybe.....

[PNjunction]

I got a reply back from my contact at Aquion. He said" SEI growth is a phenomenon associated with organic electrolytes. We do not have an organic electrolyte, so there is no concern."

Good to have a definite answer. The AQ in aquion is basically water as the electrolyte, so no SEI growth like there is with LFP. Makes sense since Prof J. Whitacre moved beyond LFP, where the organic solvent is a highly guarded corporate secret in most other LFP batteries. Note that GBS says that their LFP electrolyte is the least toxic of all, what little there is of it in the cells.

Back to Aquion - from the start they never intended these batteries to be EV or even general purpose replacements. The major market seems to be grid-stabilization, and perhaps we are shoe-horning it into our application.

I think it is pretty neat - but like LFP, you've got to really understand and want those battery characteristics to fit your application.

[Living Large]

OK Amy here is my issue. Internal Resistance is way too high. Using the product sheet for the M100-L082 which is a 48 volt 540 AH battery we can determine Ri from the Voltage vs Capacity curve of 75 milli-ohms. I know to most folks that means nothing to them, but that is significant. For low voltage systems one of the design goals is to limit voltage sag at the battery post to 2% of less. Using a nominal voltage 48 volts and 540 AH capacity means you can only draw .96 volts / .075 ohms = 12.8 amps. On a 540 AH battery that is a miserable C/40 discharge. That is unusable. Basically means you got this huge battery that can only supply a 650 watt load.

Now take something like a Rolls 4CS17PS a 4 volt 540 AH battery. It has a Ri of 1.03 milliohms. It would take 12 of them in series to equal 48 volts giving you a total of lets just say 13 millohms. Using the same 2% design goal you can draw .96 volts / .013 ohms = 74 amps or roughly C/7 discharge current. Using the Rolls equivalent you can supply a 3500 watt load.

Now here is where it really gets ugly. If you can only discharge at a maximum of C/40 means you can only charge at a max of C/40. Again most folks are clueless what that means. But in essence makes it completely unusable because there is not enough Sun Hours in a day to recharge. Bare minimum winter sun hours for a FLA is 3 Sun hours before you exceed a C/8 charge current. For these batteries bare minimum is 16 sun hours. No place on the face of the planet gets 16 Sun Hours. In the lower 48 states Tuscon has the best in summer at 7 Sun Hours.

Sorry I do not see any application these batteries can be used for other than extremely low power application for telemetry in extremely remote locations where is cost is not a factor. Good grief if ever fully discharged would take two full days of commercial power to recharge. On solar more than a week on the equator, 2 or 3 weeks anywhere else. Heck even FLA batteries are a challenge with their relatively high Ri, but these are outrageous now that I see the real data. No wonder they hide it.

Based on Sunking's post, and the discussions elsewhere here of my consideration of AHI, then FLA and finally LFP batteries for my off grid design, I decided to create a chart comparing the key statistics of these chemistries. Some of the data is estimated, some is a range for that particular chemistry if the spec was not available, etc, as noted. If you see errors, please comment. Personally, the data in this chart helped drive my decision to go with LFP from these three options for my needs. Your application may vary.