DIY solar system with NiFe (nickle Iron) batteries

The system I created was for dry-docking a 30' RV. It included NiFe and lead acid batteries (3 banks total), solar panels, and a custom built charge controller. I'll detail it all here in order.
Why I chose NiFe batteries for my main bank (instead of Lead Acid)
I have to admit, I was hooked on NiFe batteries when I learned their strengths and weaknesses. I purchased these for my solar system knowing I'd build the rest to match the cells. Starting with that decision turned out to be of huge benefit, for I reached hurdles at every step of deployment. Had I known of those hurdles in advance, I would have been scared away from NiFe, and I would not have the system I have today. This thread will detail all I learned starting with the batteries. It's a lot of information, but it will be all in one place. I believe anyone considering a DIY solar backup system will benefit greatly from this thread.
My escapade began with an article detailing Thomas Edison's batteries. Though over 100 years of age, his cells were still operating and in use by one of the museums! Reading about NiFe was a dream. Lead-acid is a great choice for some people, but it wasn't for me. I wanted batteries that could stand considerable abuse, and which I could count on even if I didn't baby them. NiFe batteries fit the bill. Let's look at both benefits and drawbacks.
Benefits that sold me on NiFe batteries

  1. Not damaged by freezing, even if they are fully discharged
  2. Not damaged by repeated full discharge (this enables me to buy less capacity, since I don't have 1/2 the battery capacity unavailable as with lead-acid)
  3. Not damaged by an over-voltage charge (all you have to do in extreme situations is top up the water)
  4. Not damaged by excessive charging (again, just top off the water)
  5. The internal structural components are steel, so they are very durable
  6. Can accept a very fast C/5 charge (compared to a C/20 for lead-acid)
  7. With reconditioning, a 50 year service life is common
  8. Well maintained, 20 year serviceable life between reconditioning periods
  9. Poorly maintained, 7-8 year serviceable life between reconditioning periods
  10. Reconditioning requires only distilled water and pot ash. Lithium, if available, increases efficiency.
  11. The purchaser mixes the electrolyte. Alter the composition to optimize the cells for any temperature.
  12. When NiFe batteries are used for low current applications, they significantly outperform the wattage they are rated for.
  13. NiFe can be directly charged from solar panels, so I don't need a charge controller. This is huge for me because I saw a charge controller as a weakness. The fewer and simpler the parts, the less likely I am to have my solar system fail me. Think economic risk here... if essential parts fail and can't be replaced, you have no power.

Detrimental aspects of NiFe batteries

  1. Price - NiFe cost about a dollar per watt of storage capacity at the time I purchased. This is much more than lead-acid.
  2. NiFe is not as energy dense, so they require more space.
  3. NiFe cannot provide as much current on-demand as lead acid. They can't, for example, provide for the huge current draw of a vehicle's starter motor. They do however, perform very well at a draw of up to one third of their rated capacity. A 4200 watt pack can supply up to 1400 watts per hour. That's roughly a 100 Amp draw.

Myths about NiFe

  1. They discharge rapidly. I have tested my batteries and they hold a charge for about 15 months. So they do lose a bit of power in storage, but not a lot. If I'm relying on my solar array, I'm using it daily. This makes the power loss inconsequential. For optimal longevity, I should charge them at least once per year.
  2. Creating a backup solar system on NiFe is hard. I can't count the number of times I was told this. The only thing that made it difficult was disinformation. After I weeded through that, it was exceptionally easy.

Choosing a supplier
If you want to buy new NiFe cells you can buy from China or from India. New NiFe cells are not produced elsewhere in the world, period. Now before you say 'Chinese crap' let me tell you that China produces the NiFe batteries used by almost all military establishments around the globe. The Chinese electric rail system runs on these batteries, as do the backups for many remote cell towers, pumping stations, and other essential services.
There is a US remanufacturer of NiFe batteries in Montana. They do not build new cells, but rather clean existing cells and ship them with new electrolyte. I didn't want used cells at their price, which was 60% higher than Chinese suppliers I reviewed. Reconditioned cells should have the same lifespan as new, so if you want to buy US cells period, remanufactured it is.
The supplier I chose was New Taihang Power Company. They work closely with Changhong and apparently the batteries are virtually identical. New Taihang will not sell small quantities, while Changhong does. When I reached out to the New Taihang factory to buy a small number of additional cells, they recommended Changhong, and so they are the focus here. Changhong has considerably better documentation that New Taihang.
Completing the purchase
I reached my supplier through Alibaba. First, I confirmed that the supplier was bonded and had a high reputation. Then I obtained my quote, sealed the deal, and sent a bank draft to the institution. That part freaked me out a lot, but the bank information was very clearly for the right place. I did some looking into Chinese bank accounts and found out that one cannot open a fraudulent account in the name of the Chinese government under penalty of death. Talk about a wow moment there. Anyway, I sent off the money, and one week later had confirmation the batteries would move to production.
The representative I worked with was exceptional. She sent me regular updates on the status of my order. It was delayed because the Chinese government ordered a HUGE supply of cells from Changhong and New Taihang factory was helping to fill the order. I was presented with the choice to wait an extra 3 weeks or to cancel for a refund. I waited of course, and the cells were in the container after that delay.
It took several weeks for the shipment to arrive in Canada. Prior to the arrival, I was asked for the contact information of my receiver, which I did not have. I've never ordered anything from China direct. I asked my rep if they had worked with any Canadian receivers before, and she recommended one. All customs clearing papers were emailed to me in advance, and the order cleared customs without a hitch. It went into storage at the brokers. I went to the customs office 3 days later and cleared the batteries, then showed up and paid the $150 storage and transfer fees. Storage adds up fast, so don't leave your shipment too long!
Transporting the batteries
It was a 5 hour trip to the port so I could bring my batteries home. They could not be couriered like most case goods, because they are considered hazardous due to the potash in the container.
I was a might shocked when I saw the batteries. They were created in a wooden box, and exceptionally well packaged. They came complete with a bag of dry potash, a bag of lithium, safety goggles, a rubber apron, gloves, a hygrometer... everything needed to make them serviceable.

The cables to connect all the cells were also included... along with spares.
Because all goods were dry, I was able to simply load them into a car. 11 batteries totaled about 500 pounds. I needed 10 cells for the battery bank and figured on one extra for emergency replacement. Having seen the durability of these cells first hand, I don't think I'll ever need the replacement. They are rock solid, but as previously mentioned, they are built for military and other intense industrial use.
Building the electrolyte
The electrolyte is nothing but distilled water and potash. You have to put the water in a large jug, to which you add the potash. The water will heat up as the potash dissolves and chemical bonding occurs. VERY IMPORTANT... you cannot add water to the potash. To do so would cause an intense chemical reaction, building a base of extreme concentration strong enough to dissolve flesh on contact. Add potash to the water and you are rather safe. Wear all protective gear.
Lithium hydroxide is included to help increase battery performance. It only adds 5-8% capacity, so it's far from essential, but they include it and you want to add it.
The concentration of the potash and water determines the temperature the battery is best suited to. Plan for winter instead of summer. In the winter, your battery's capacity and efficiency are more important because you have less sun energy for charging. By my calculations, it is better to have less capacity in the summer when you don't need your batteries as much as you do in winter months.
The electrolyte cannot be stored for extended periods outside of the batteries. I tried and ended up with a batch that looked like vomit after sitting a few months. Not sure what happened, but I assume it reacted with my plastic storage container. Maybe it would store in other circumstances, I am not sure. It stores fine dry.
Filling the cells was a simple matter of pouring into a funnel they supplied, and watching until I reached the full line. The casings allow enough light through to see the electrolyte level. I filled all cells to a small bit beyond the full mark.
Charging the cells
Unlike lead-acid cells, the batteries are stone cold dead when the electrolyte is first added. I connected a Mastech variable voltage DC supply to charge the batteries. I set the power supply for 50 Amps variable voltage, and watched closely as the cells charged. It took 14 hours for the cells to fully charge. They bubbled through charging and for 2 days afterwards. The bubbles are explosive offgassing, so you have to do the charging outside. I did it in a garage.
A note about my Mastech DC supply... don't buy the aftermarket leads. Although they are supposed to be rated for 50 Amp 30 Volts, there's no way! I tried and the leads got quite hot at 21 Volts 14 Amps... so hot in fact that I was afraid they'd melt off their plastic shell. I carved an end off a set of jumper cables and used them for leads instead. Worked perfectly and accepted the full 50 Amps. I'm very happy with the Mastech charger. They do sell direct to savvy end users for a 45% discount, so don't waste coin buying a Mastech charger from an intermediary. The model I bought was an HY3050EX. It draws about 14 Amps @ 110 V when charging at the max rate for a 4200 watt battery bank.
That's the end of the basic battery section of the post. I will have to find my formulas for optimal electrolyte strength at different temperatures. I'll post that when it's located. I have a couple manuals I can post too. The next posts will detail choosing the right solar panels, building the charge controller, and testing results.