Nickel Iron Batteries For Off Grid Energy Systems
Daniel Mark Schwartz
October 12, 2019
Nickel iron batteries are a century old technology that has profound potential impact for off grid energy systems. The weakest point of renewable energy production, batteries systems are typically expensive, fragile, toxic, and fail relatively quickly. Iron batteries, however, once the darling of famous inventor Thomas Edison, solve many of these problems and seem to be prefect for off grid energy systems.
What Are Nickel Iron Batteries?
Like pretty much every form of battery, nickel iron batteries are differentiated by the chemical reactions that occur on their two electrical plates. These Edison batteries use an iron to iron oxide conversion on the positive plate, and a nickel oxide-hydroxide to nickel hydroxide reaction on the negative plate. (source)
Swedish inventor Waldemar Jungner appeared to have first invented the Nickel Iron battery, along with many other batteries with various chemical makeup.
Thomas Edison was the first to produced nickel iron batteries commercially in the United States. He patented the product in 1901. His Edison Storage Battery Company produced nickel iron batteries out of New Jersey from 1903 to 1972, when they were bought up by the Exide Battery Corporation, a major producer of the competing lead acid battery, who discontinued production of iron batteries in 1975.
When Thomas Edison first started mass manufacturing his iron batteries, he was hoping that they would be used in electric vehicles (more popular at the time than internal combustion engines), and then later as engine starts. However, the relatively slow discharge rate limited their popularity as car starters. They did find wide spread use in the railroad industry, as well as in forklifts and standby power applications.
Why Are Nickel Iron Batteries Good For Off Grid?
Now that modern photovoltaic panels (solar panels) have taken power production world by storm, Edison’s old design looks like it could be revamped as the battery of the future. They use inexpensive and commonly available materials, can withstand extreme use that would junk your common lead or lithium batteries, are relatively non-toxic, and have been know to last for decades. Further, the downsides, relatively high weight to charge ratio and slow discharge rate, aren’t a problem in the lightest for stationary off grid energy applications such as running your off grid cabin, or modern homestead.
Nickel Iron Batteries Have Extremely Deep Discharge Depth
Most modern battery chemistry’s, like lead acid and the various lithium varieties, start to eat themselves if they are over-discharged. A sealed lead acid “deep cycle” battery cannot be safely discharged below %50 of it’s max capacity, before you risk destroying the entire bank and throwing 1,000s of dollars worth of lead and acid in to the trash. Further, lithium batteries are known to be even more finicky in some situations, have even been know to overhead and start on fire if driven out of their specific charging profile.
Nickel, iron batteries, however, are extremely resilient. They can be discharged almost completely without any ill effect to the battery. Although you should probably follow correct charging procedure, they are known to withstand almost any abuse without a fuss.
No matter if you are a homesteader who depends on their batteries as their only power source, or a prepper who wants to make sure that their equipment will be ready to go when the time comes, even it was neglected for a few years here and there, nickel iron has a lot to offer in term of dependability.
Nickel Iron Batteries Are Low Cost and Have Incredible Longevity
See my article on the Total Cost of Off Grid Solar Systems for more detailed analysis, but the gist of it is that nickel iron batteries are more than 10 times cheaper than the second best competing battery when you factor in battery lifetime. While they currently have larger up front costs per kilowatt hour, this is likely due to the relatively low volume at which they are currently manufactured. Like solar panels a few decades ago, as interest in nickel iron batteries increase, so will their price decrease.
Nickel iron batteries are know to last decades, with anecdotal evidence that some railroad installations used the same Edison batteries for more than 50 years without replacement. Although modern production of these batteries is too new to tell yet, it could be that a set of nickel iron batteries you buy now could be your lifetime battery bank, and even an investment that you pass on to your children.
Even as time goes on, it is likely that nickel iron batteries will become more cost effective than high tech modern designs, because they use cheap, abundant materials. Mostly iron and nickel.
Modern high tech battery designs almost always have complex cocktails of chemicals, dominated by the rare earth variety. However, as the name suggests, these metals are hard to find, and we are already anticipating shortages in supply. Perhaps it is time we spent less money and effort as a society on finding the next new thing, and focus instead on perfecting the technological gems of the past.
Another huge benefit of nickel iron design is that it uses relatively safe chemicals to operate. Most of the chemicals you find internally can be locally at a hardware store or pottery supplier. And, while you do want to take proper care around these compounds, they lack the significant corrosive effects of battery acid, or the extreme toxicity of lead and other rare earth compounds. Just the fact that many lithium batteries are listed as especially hazardous cargo should be enough to see that there is a concern when installing a large battery bank in your home, farm, redoubt, or homestead.
Can You Build Your Own Nickel Iron Battery?
Due to the relatively simple construction, and the wide availability of materials, it makes sense that the industrious and craft DIYer aught to be able to craft their own home built battery bank. Here is a sort run down of the materials you would need:
|Pure Nickel Plate||$6.25/sheet|
|Iron Oxide Power||$10.00 / pound|
|Nickel Chloride||$19.00 / pound|
|Distilled Water||< $1.00 / gallon|
|Potassium Hydroxide||$10.99 / pound|
|Misc Iron sheets||-|
As you can see, the price is relatively manageable, and in a situation where your are ready to scale up for a full home or homestead battery bank, most of these ingredients can be ordered in bulk. Most of the iron and nickel powders are available from ceramics supply houses. The rest of the ingredients can be purchased from any hardware store.
On this list, the nickel, iron oxide powder, and nickel chloride and the active ingredients in the design, and form the bulk of the anode and cathodes. Distilled water and potassium hydroxide (aka Lye) make up the liquid electrolyte that flows between the plates of the battery. The bleach and sodium hydroxide are used to prepare the nickel chloride in to nickel oxide-hydroxide, which is the necessary nickel substance used to power the positive side of the battery, but can be difficult to buy in pure form.
There are other suggested methods of producing the nickel chemistry. They are almost certainly easier and cheaper than the synthesis method recommended here, but may significantly reduce the power output of the battery due to possible impurities. More testing is needed on this front.
The rest of the construction is just mechanical holding and electrical connections. The powdered metals are packed tightly in to small diameter, perforated metal tubes, usually steel/iron, which are nickel coated in order to protect the iron from the effects of the battery. These tubes are mounted inside a conductive metal frame to form a tall plates, with four holes in the corners an extra tab on one side to allow for electrical connection. The plates are stacked, alternating nickel and iron contents, with non-conductive spacer washers between each plate and a bolt and through all the plates in each corner, holding the whole stack together.
In order to hold the battery you will need a water tight container. Current commercial designs use a semi-transparent tall plastic box with a lid. You might be able to design a variation of this idea that uses commonly available “Tupperware” containers. Historic Edison batteries used a nickel plated steel box as well, which could be easily fabricated out of thin sheet metal with minimal metal working tools and skills. One modern adaptation might be use aluminum instead of nickel plated steel.
The tops of the containers must have a method of allowing the electrical terminals to exit, and have one-way valve or cap that allows venting of hydrogen gas produced during normal operation, and access for occasional topping up of the water reserves.
The tab of each battery plate should be connected together by type, so nickel to nickel and iron to iron. This is often accomplished by a non-corrosive rod that is ran along the stack of plates, on on each side. Often nickel coated steel.
Perpendicular to the horizontal steel rod, there are one or more vertical rods on each side that connect to the plate bus bar and extend up and out of the container for connection of cell with other cells in the bank. This rod is usually also steel, and can be welded, bolted, or otherwise electrically connected to the bus bar. The bar is usually threaded at the top, so it can be used to suspend the plates in the electrolyte with two bolts, on on each side of the lid. There are usually additional nuts and washers on the part of the rod that extends outside the container in order to power connect wires/bars to the battery.
Electrical Characteristics of Nickel Iron Batteries
Each nickel iron cell has a nominal voltage of 1.2V, so you will need 10 cells to produced a 12V battery bank. The number and size of plates determines the charge capacity of each cell, and thus the overall capacity of the bank.
In order to charge your cell, you would need to apply voltages of 1.6V or higher. Aggressive charging of the bank is tolerable, and even preferred to help maintain the battery.
There is no dangerous under voltage of nickel iron batteries. They can safely discharge 100% empty, but manufacturers recommend a nominal 80% discharge cycle for typical use scenarios.
No charge leveling is required or recommended by contemporary NiFe battery manufacturers.
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