Nickel Iron vs. Lead Acid - Off Grid battery debate

[johnpearcey]

So, time for an update. I've been using my NiFe cells since Feb and they're performing very well. I did not bother with the initial forming charge. I decided to let the daily usage take care of that. You can tell I'm a bit of a maverick I've attached a graph for the past few days. You can see I use about 30% of their capacity each day and not all days top them up. See my previous post for graph colours. (Ignore orange). We've had great sunshine this year in Ireland and the panels are giving us plenty of energy. The only downside I can see with NiFe is that the charge/discharge efficiency is around 60% (grey line). But a couple of extra panels sorts this out. And to be honest, I haven't noticed it at all. Compared with lead-acid, these babies are a game changer. And if they last as many years as the manufacturer says, then the total cost of ownership is going to be orders of magnitude less than lead-acid. NiFe do gas slightly. I've had to top them up once since Feb (10ltr). I'm using deionised water for half of them and condensed water from a dehumidifier for the other half. We'll see how things compare in a year or so.

[inetdog]

Are you filtering the humidifier water? Straight from the coil there may be significant amounts of dust and organic contaminants.

[johnpearcey]

Are you filtering the humidifier water? Straight from the coil there may be significant amounts of dust and organic contaminants.

No. The dehumidifier has a set of air filters before the coils. And after 2 years of constant use, there is almost no perceivable residue in the container. So I really don't think I'd be able to filter it any better. I'm a little concerned about carbonic acid though. But the pH is 7 so it can't be too bad. I'll be checking the SG as I go.

[inetdog]

Mike, is it about time for another update on your system?

[Mike90250]

Mike, is it about time for another update on your system?

After installing the auto watering system, which is more efficient in that i can overfill 6 cells at a time when the stupid floats stick, there's not much else to report. 2 years ago, I replaced the fluid (electrolyte) in the cells ( a week long process with mixing, cooling, dumping old, refilling and bolting the bank into place )

I've purchased and am configuring new Schneider PC charge controller 150-60 and a new XW6848pro inverter, to replace old (still working, 10 year old gear), hopefully installing in the next 2 weeks. Keeping the old gear as "hot" spares. I figure better to replace when I can plan, instead of in a panic when something fails.

[inetdog]

Thanks, Mike. Just curious how you dumped the old electrolyte, which was not particularly toxic except for its pH.

[Mike90250]

I turned it into fertilizer to both neutralize our acid rain and add potassium to the soils.

[inetdog]

I turned it into fertilizer to both neutralize our acid rain and add potassium to the soils.

Sounds like really expensive Chinese fertilizer....

[Mike90250]

Just worn out electrolyte.

[nwdiver]

I'm currently using NiFe off-grid. Just changed over from lead-acid. Lead-acid are not actually cheaper despite what people keep saying. The capital outlay is more for equivalent *quoted* Ah. The problem with lead-acid is that you can't effectively use more than 20% of the quoted capacity. But with NiFe you can use all of it.

I had considered either industrial or NiFe batteries due to their longevity until I remembered the time value of money. I bought 415Ah of L16 batteries for $3k. 200Ah of NiFe would have cost me $9k. The ~$6k I saved will be ~$12k by the time the L16s die and I can just spend $3k on more L16s (or hopefully something even better in 10 years) and send the old ones to be recycled. And on and on and on.

[johnpearcey]

I had considered either industrial or NiFe batteries due to their longevity until I remembered the time value of money. I bought 415Ah of L16 batteries for $3k. 200Ah of NiFe would have cost me $9k. The ~$6k I saved will be ~$12k by the time the L16s die and I can just spend $3k on more L16s (or hopefully something even better in 10 years) and send the old ones to be recycled. And on and on and on.

Surely a fairer comparison of 415Ah of L16 would be more like 80Ah of NiFe?

[nwdiver]

Surely a fairer comparison of 415Ah of L16 would be more like 80Ah of NiFe?

No; 80Ah wouldn't get me through some nights. 200Ah would. Even cycling the L16s to ~50% DOD sometimes they should last ~8 years. I've been running mostly off-grid since March using L16s to get a feel for the challenges. Maybe half of my cycles are to ~50% and ~30% are only to ~20%. With that kind of use I should get >8 years out of the batteries. Makes more sense to spend $3k every 8 years than spend $9k once due to the time value of money.

[SunEagle]

As I have always stated you have to do the math. Basically how many kWh will a battery system provide each cycle and how many cycles it provides over it's life. That gets you a value that you divide into the cost. That produces a $/kWh which is easy to compare to all battery systems or a POCO.

[nwdiver]

As I have always stated you have to do the math. Basically how many kWh will a battery system provide each cycle and how many cycles it provides over it's life. That gets you a value that you divide into the cost. That produces a $/kWh which is easy to compare to all battery systems or a POCO.

Yep; There could be a magic perfect battery that will last 1M years, smells like roses when it charges and spits out a grill cheese sandwich when it ends it's absorption cycle but if it costs $1,000/kWh I'm not going to be interested. I'll buy the one that costs <$200/kWh, lasts ~8 years, invest the difference and use the dividends to replace the battery every 8 years and still have plenty left over for a panini press.

[SunEagle]

Yep; There could be a magic perfect battery that will last 1M years, smells like roses when it charges and spits out a grill cheese sandwich when it ends it's absorption cycle but if it costs $1,000/kWh I'm not going to be interested. I'll buy the one that costs <$200/kWh, lasts ~8 years, invest the difference and use the dividends to replace the battery every 8 years and still have plenty left over for a panini press.

+1. Works for me.