question

We had a 48V 1p test setup in 2016 made of a Quattro 5kVA and Iron Edison (https://ironedison.com/nickel-iron-ni-fe-battery) NiFe cells to evaluate them as a possible configuration for commercial installations.

In the end, we decided against it, because even at 50% of the price tag of a "comparable" LFP battery (and the Iron Edison batteries were at that time significantly above that mark), the drawbacks were evident in the tests:

• really low retention efficiency. The 80% hold true for both charging and discharging -> 64%
• 1%/d self-discharge, more like 1.3%, really kicks in the bigger your battery bank is and if you have an installation in a region with pronounced winter time. Suddenly you lose 300+Wh per day of your 500Ah battery bank.
• Rate of charge and discharge are abysmal. Sometimes the sun comes out for a short period of time. Like 15 minutes. And your 9kWp PV installation actually does deliver 8kW you will run into trouble pushing all of it (albeit with said .8² retention efficency) into the battery.
• NiFe vendors try to position these batteries as "hassle free", because they do not need to be balanced, can cope with overcharging and extreme DoD. However, you need to take into account H2 gassing and temperature of the battery. When loading a 400Ah LiFePO4 at 200A (0.5C) for one hour, the battery temperature rises from 22°C to 25°C, doing 70A on a 500Ah NiFe did 22°C to 31°C within an hour. Of course - where do you think the other 20% of the efficiency go to?

Summary:

If you can get them really cheap, and I'm talking about 50$ per kWh and you have enough space and a floor capable to cope with the weight (low energy density) and the place you put them in is kept above freezing point (forget performance below zero, -30°C "operating temperature" is a joke - or you live in a well tempered region) and you make sure there is ventilation and you do not have charge/discharge spikes and you are willing to trade less electronics hassle against more chemistry hassle... by all means.

Did you already find a solution, especially for charge/defiition of the battery type and also for the ESS-System?

Regards

Michael

I have been running a Victron Phoenix 3kW inverter for 6 years on 38xLiFe batteries (80Ah). I have a cheap chinese solar controller which has a nickel-cadnium setting which works well with the NiFe. A set of 38 require a charging voltage of about 66v which provides about 20amps. This 66v is too high for the inverter so I have a small voltage dropper before feeding into the inverter. The only problem I have had is finding suitable chargers to run from a 240v generator. I have had to cobble together various DC power supplies. The most successful is a 60v DC supply with a DC-DC booster attached to provide 66v with a setable current limiter. But they do not last very long (chinese crap from Amazon). I have quite a bit of experience now with LiFe, but this charging issue still needs to be more robust. If anyone out there has similar problems, please get in touch.