The different electrolyte is no problem; they use potassium hydroxide plus a bit of lithium hydroxide, much less dangerous than acid. These chemicals are provided, in our case, by the manufacturer in powdered form, one must mix them with distilled water. The powder is included in the price.
The batteries are not as readily available. I decided, ultimately, to order the ChangHong version, which a co. here in Colorado deals and has sold and set up quite a few.
There is a co. in Montana building them, but their prices, since about October, have almost doubled. So...I felt I had no choice but to go with ChangHong, who at least do have a track record. I did not want to deal with China, but ultimately I found no alternative that would work for me. I did communicate with a couple of people who are and have been using ChangHong nickel iron batteries, and they both are pleased with them. Plus, the co. has several different "models" of nickel iron batteries, each designed for a particular use. One of these designs is specifically geared toward photovoltaic systems. [Whether this is hype, I shall have to ascertain once I have my batteries.]
Another consideration is physical size. Since the cells are 1.2 volts each, rather than 2.0 v for lead/acid, you need ten cells per 12 v. set rather than six. A bank will take up more space. However, my lead acid cells weigh 330 lb. each, and the new ones I'm getting weigh around 70 lb. Huge benefit for me.
The benefits are, for me, numerous, if these batteries turn out to work as I expect. They are not damaged if there's an unusual spell of cloudy weather, for example, and we are not able to charge them up fully. This does not happen often if one's array is properly sized, but it can happen to the best of us every few yr. or more often. There is very little maintenance and no acid mist or leakage to worry about. There are some of these that have lasted nearly a century and still work well. Meaning, one can buy a bank and perhaps use them all their life. You can add to the banks more batteries if you need to expand and it's fine, no problem mixing old and new cells. If one cell should go bad, you can simply remove it and stick a brand-new one in its place and be just fine.
And so on.
I thought of two potential problems with NiFe while I was contemplating them. They must be charged to a higher voltage than lead acid. Around 15.5 volts seems to be good, with the occasional 17 v. charge.
The first potential problem from this is that some of us have 12 v. appliances, etc., and some of those things are limited to a voltage high of less than 17 v. My Sunfrost 'fridge and SF freezer both have spec's saying upper voltage limit 15.5 volts. A call to Sunfrost tech. dep't said they can go much higher. So I think we are ok there. My other 12 v. stuff is lights and fans. I think they will be ok.
The second problem is with electronic equipment, particularly inverters. I just switched to an Outback 12 v. to 120 v. inverter and the spec's say they can handle 17 volt input. So, that should be ok. Our old inverter was limited to 15.6 volts, but I was kind of looking for an excuse to upgrade to a pure sine wave anyway, so I did.
I have not heard of anyone having problems with either DC appliances or inverters or anything else, using nickel iron batteries. I just realized I'd be dealing with a bit more voltage [while the batteries are at their upper voltage during charging cycle] and it occurred to me this might be a problem. But now I am thinking it may be no problem.
Time will tell whether our current PV array will adequately charge our new bank of NiFe batteries. It could be we have to add another panel or two. The dealer of the batteries feels we are right at the lower limit of what might work, so we'll see.
The batteries are on order, but I expect it to be two to three months before we get them, so actual experience and reports of such will have to wait.
Edit 3/27...I have been using Hydrocaps for many years on my lead-acid banks. I spoke with the co. last week and they told me their caps, same exact caps, work great with nickel-iron batteries. I add maybe a gallon a year of distilled water to my lead-acid bank [1875 amp. hr.] so these caps have been a benefit for me.
Last edited by SteveH
on Thu Jun 09, 2011 6:55 pm, edited 7 times in total.