1 - Why nickel iron batteries?
There is no battery technology available that is as durable as nickel iron. In terms of rated capacity per dollar, lithium and lead acid seem to be cheaper than NiFes, with lead acid in particular looking very cheap on paper. But they will perform as rated the day you buy them, and not much longer. If they are not kept “topped off” by grid power or a generator, lead acid will typically drop to 50% capacity by year two or three, and by year four or five, they are pretty much useless. Lithium doesn’t perform much better- a four to seven year useful life is typical for deep cycled lithium systems.
The ability to use the full capacity of a battery is a big deal for living off-grid. At Living Energy Farm we don’t have a back-up generator, and we cycle our batteries pretty hard. The nickel iron batteries in our Iron Sun Homestead kit are ten years old and performing at 150% of their rated capacity. If we had lead acid batteries, we would have replaced them twice by now; with lithium, at least once.
Our battery supplier considers their NiFes to have a 40 year lifespan, but NiFes have been known to have a useful life far beyond 40 years. To test this claim, we bought an 80 year old NiFe battery- one of the first made by Thomas Edison- which had been neglected for years. We brought it back into service, and amazingly, it is performing at 50% its rated capacity.
There are other environmental benefits of NiFes, beyond their durability. In fact there is no battery technology available that is as safe and non-toxic as NiFes. NiFes are perfectly safe to store in your home because there are no toxic electrolyte or metals. Lead acid batteries are highly toxic and must be stored outdoors. Lead acid batteries used in the US are sent overseas to be recycled because the process is so toxic. Lithium battery disposal is toxic as well, and they also require scarce materials which are causing conflicts around the world.
NiFes are made of iron, which is super abundant, and nickel. Nickel is not as abundant, but there are nickel deposits in several places around the world, so the mining process is not as likely to cause conflict as is mining for the rare earth metals needed for lithium batteries.