I would like to respond to the what Steven Harris said about the nickel iron batteries:
Questions 1. "Steven Harris just sent me this email: I own NiFe batteries, I have since 1994. I know them well. The BIG reason to NOT buy them, they are incredibly expensive, they are charging you 9x the price of a lead acid and guarantying you only 5x the life.
Answer 1: In reality, a nickel iron battery cost about double the price of a good lead acid battery. For example, a 12V, 263Ah Sun Xtender Sealed AGM Lead Acid Battery cost $650.00 online. This battery is rated at 1,850 cycles @ 30% DOD, which is 5 years. A comparable Nickel Iron Battery would be the Iron Edison 12V, 100Ah battery. The Iron Edison Battery is rated at 7200+ cycles, which is 20+ years. This battery will cost you $900.00.
So, if you are off grid and using your battery everyday, over a 20 years period you would have to replace that lead acid battery bank 4 times. With Nickel Iron you will never have to replace the battery, so over a 20 year period, you would have definitely saved money.
Questions 2: NiFe batteries are VERY inefficient, which means a significant fraction of the energy you put in, does not get stored, something like around 25%.
Answer 2: I am going to break this answer down into 2 parts. First, we are going to talk about Nickel Iron Battery efficiency, and then we will talk about Lead Acid Battery efficiency.
Nickel Iron Batteries are about 75% Efficient. We tested the cells at the National Renewable Energy Laboratory, and below are the results. Overall at normal temps, the out performed their rated capacity between 75-80% efficiency.
http://ironedison.com/images/Spec%20Sheets/Test%20Results/NREL%20TEST%20RESULTS%20-%20Amp%20hours%20capacity.jpg
Lead Acid Battery Efficiency - Below is a link to the Sandia National Laboratories results on Lead Acid Battery Efficiency. According to this document, they found out that when you are only using the top 20-30% of a battery, it really only has a charge efficiency of 55%.
http://ironedison.com/images/Spec%20Sheets/Test%20Results/Sandia%20Labs%20Lead%20Acid%20Efficiency%20Test.pdf
So after looking at the actual data - the nickel iron battery is more efficient than a lead acid battery in daily off-grid charging.
Question 3: They are VERY VERY gassy, that is why there is such a huge head space on them to hold SO MUCH extra water, which MUST be distilled water ONLY.
Answer 3: Nickel Iron Batteries do off-gas a little more than a lead acid battery, but this is because of the differences in the batteries chemistry. Both a wet lead acid and nickel iron battery require to be put in a battery box and we recommend using a vent fan.
The Nickel Iron Battery produces hydrogen when the battery pushes the oxygen from the water molecule to increase the oxygen concentration on the nickel plate. The head space is not huge on a nickel iron battery, but you do want an area for the electrolyte so you are not having to fill the battery with distilled water all the time.
A wet lead acid battery produces hydrogen through inefficient charging, when the electricity not used from charging is spent on splitting a water atom.
Both a wet Lead acid battery and Nickel Iron Battery uses distilled water only. A sealed lead acid battery does not need water and does not off-gas, but has a shorter life if cycled everyday.
Question 4: They have a high rate of self discharge, so if you just leave them there, they can loose 10% or more of their charge PER DAY.
Answer 4: Nickel Iron Batteries have a 1 % self discharge rate. If you are wanting a battery that will just sit there and not be used, then you might want a sealed lead acid battery. Sealed lead acid batteries are good for people that are not using their battery and want it to sit and hold its power in case the power goes out once a year or so.
If you plan on using your battery every day, it really does not matter if it discharges 1%, because you are going to charge up the battery and use the batteries power that day.
Steven Harris has said these type of statements before to others, so we have actually reached out to him directly to talk to him about his system. We think his equipment settings are probably not set up appropriately. He did not want to talk to us about his equipment or equipment settings.
