nickel based batteries for off grid.

Both nickel iron and nicd batteries seem to be able to last a long time. Much longer than lead based batteries. Nickel iron batteries are pretty hard to get and hold less of a charge for their size than lead acid. They do not have the current capabilities either. nicd (AKA nicad) batteries have a great current capability and a nice level output over discharge. I have worked with them for portable power for electronic news gathering use back when I was doing broadcast work (in analog days). I would not have said they lasted longer than lead acid and of course they were sealed and once failed not repairable. However there are flooded nicd batteries. They are designed for 25 year plus life times... same a nickel iron batteries. What has changed since the late 90s when other chemistries started to replace them for rechargeable batteries, is the ease of making and designing smart charging solutions. Thinking back to my ENG repair days, the battery belts did not have smart chargers at all and sealed nicd batteries do not take over charging well. It seems that they absorb heat for most of their charge cycle until near the end when they start to heat up and their internal resistance goes down so they charge faster, heat faster and finally boil off. Most nicd chargers either charge at a 16 hour rate and time for 16 hours then shut off. If the battery is not flat, it gets over charged, but the current is quite low and the battery doesn't die from it, but just sees a shorter life. One of the chargers I worked with tried testing the charge state then charged at high current for a time before shutting off for a bit and then testing again before going on. It is hard to tell how well that worked though as ENG crew are hard on equipment, their performance in getting there first shoving through whatever is happening damages things.

So back to flooded nicd batteries. These may be a better solution for off grid storage than lead acid while still being cheaper and lasting longer than some of the other alternatives. When they do finally fail, they are rebuildable too. The main thing would be to build the right charger. Flooded nicd are more robust than the sealed ones and can stand more charge mistakes, but would still benefit from a charging style other than what lead acid uses (I might suggest that most lead acid charging solutions are lacking too). They would do best only receiving 110% of whatever power was removed. That is using a power use meter and only allow that much power plus a bit more to be reintroduced. What to do with extra? Dump it into other forms of storage. filling a water bucket till the water runs over and then continuing to fill it makes no sense anyway, same with batteries.

The extra power from pv or micro hydro or whatever, can most easily be turned into heat, great in the winter but the sun shines most in the summer when it is already hot. Heat can still be used to cook or even to warm up the ground mass in a PAHS home to be used months latter, place the heating coil 6 or 9 feet away from the house for some delay.

It could be used to chill an ice cube even colder so it can last the whole night without requiring the use of batteries.

It could be used to charge a capacitor booster pack that can take care of surge requirements for loads where the average load is still within the PV panels output instead of bouncing the battery.

The thing is, it is becoming easier to get the needed equipment to control these things. There are so many small computers around with various io on them. Many of them use very little power and almost all of them have some sort of networking built in so they don't need a screen and or key board to run. They can be controlled from any android (maybe even one of those even more over priced Iphones) or laptop. (actually an old DX100 could probably do a lot too) Monitoring power in and out should be quite easy (though current measurement at both low and high rates could be a challenge), and diverting power intelligently could be done too.

Power use from pv should do:
- direct use first.
- charge batteries and capacitor boost pack only till full.
- keep an ice block super frozen for food preservation only till chiller has gotten things as cold as it can.
- keep a fly wheel going if there are stationary rotary uses, like shop work or laundry... in some cases the original power may be coming from this flywheel (diesel, steam, gasifier gen)
- add other energy storage ideas here
- dump what is left over to heat in some useful way (or not useful if the source is wind)

Playing with the power that comes from a pv to make the best use of it will have some efficiency loss, but can be better than just charging the battery and letting the battery run things, once the battery is full energy is wasted.

I've been using a set of NiFe (Nickel Iron) coupled with a AGM Lead Acid bank for about a year now, and I will never go back to the LA batteries again. They are able to discharge to a much lower level (70% vs. 20% DOD) so you can get away with a much smaller Amp/Hr battery bank. I was able to utilize my existing (lead acid) charge controllers, and inverters with the new batteries, and I even used my old batteries in a hybrid battery bank (NiFe and AGM). I think with the current availability of technology to integrate with the NiFe battery charging requirements, and their inherent robust nature (rebuildable, durable, high depth of discharge(DOD), and less toxic electrolite) makes them a perfect fit for alternative energy use. There are only a few suppliers here in the states, but they are worth the investment for me. These things are reported to last for generations vs. a decade or two....how could you go wrong with this technology....I love 'em.

Dave Redvalley wrote:I've been using a set of NiFe (Nickel Iron) coupled with a AGM Lead Acid bank for about a year now, and I will never go back to the LA batteries again. They are able to discharge to a much lower level (70% vs. 20% DOD) so you can get away with a much smaller Amp/Hr battery bank. I was able to utilize my existing (lead acid) charge controllers, and inverters with the new batteries, and I even used my old batteries in a hybrid battery bank (NiFe and AGM). I think with the current availability of technology to integrate with the NiFe battery charging requirements, and their inherent robust nature (rebuildable, durable, high depth of discharge(DOD), and less toxic electrolite) makes them a perfect fit for alternative energy use. There are only a few suppliers here in the states, but they are worth the investment for me. These things are reported to last for generations vs. a decade or two....how could you go wrong with this technology....I love 'em.

Interesting. How are the two banks coupled? How do you get the NiFe bank to discharge farther without discharging the agm bank at the same time? Are they on a separate controller? I know the cell voltage is different between the two as well, what total voltage do you end up with on the two banks? With how many cells?

It's a little goofy, but I'll see if I can explain it and have it make sense. So here goes...
The banks are coupled parallel, so they draw down to the same voltage. The AGM bank was abused and on its last legs so I don't feel bad running them down as low as I do. The AGM's are there basically to dump amps on a heavy draw (like well kicking on). So here comes the goofy part....the NiFe cells will take and hold voltage at such a high rate (without damage) that the AGM's are setup in three parallel 30 volt banks and the NiFe's are nominally at 24 volts. The NiFe cells are 1.2 volts so I have 20 cells (24 volts). The AGM's are 3 sets of 15 cell strings (5 six volt cans). I know it sounds weird, but it works. We use the back-up generator about half as much as the previous home owners and our family is three times the size, so not bad stats in my view.

Dave Redvalley wrote:It's a little goofy, but I'll see if I can explain it and have it make sense. So here goes...
The banks are coupled parallel, so they draw down to the same voltage. The AGM bank was abused and on its last legs so I don't feel bad running them down as low as I do. The AGM's are there basically to dump amps on a heavy draw (like well kicking on). So here comes the goofy part....the NiFe cells will take and hold voltage at such a high rate (without damage) that the AGM's are setup in three parallel 30 volt banks and the NiFe's are nominally at 24 volts. The NiFe cells are 1.2 volts so I have 20 cells (24 volts). The AGM's are 3 sets of 15 cell strings (5 six volt cans). I know it sounds weird, but it works. We use the back-up generator about half as much as the previous home owners and our family is three times the size, so not bad stats in my view.

I see, so the AGMs are being sort of like a capacitor bank. They don't hold much charge, but because they are being kept partly discharged all the time, they don't leak (charge not fluid) much either. That was one of the things I didn't mention is that the NiCds aside from lasting a long time, allow more current draw than the AGMs. It seems to me the more I look at DC storage, that a composite storage solution is probably ideal.

Exactly!! One of the reasons I'm so sold on the NiFe (don't know about the NiCd)is that they are so robust and resilient that you can really experiment with them and find what's going to work the best for you. Couple that with the compatibility with existing charging technologies (though not totally optimized) they are the most appropriate alternative energy storage option out there. If a cell shorts or goes bad, just replace it with a new one, it won't harm the battery. If you need more capacity, just add another bank, they won't be drawn down or reduced in life expectancy like the LA batteries. Already have LA batteries....just run a hybrid bank best of both worlds. Can't go wrong!

for long term stationary battery systems there are some interesting things coming down the pipeline. i spent a long time researching vanadium redox flow batteries. the problem with them is the cost of the PEM membranes. until some other that dow starts making them cheap they will stay out of reach.
there seem to a few companies working on rechargeable zinc air batteries. i have asked one of them for some basic information about them. still waiting for a reply. if they survive thier estimated costs are around the same as lead acid, but without knowing a bit more about them i am not holding my breath. the world of battery storage is littered with companies claiming to beat lead acid on price and longevity.

not many survive past the start up stage. the vanadium one i was dealing with is now chinese owned and only dealing with megawatt size units. this seems to be where all the interest is. the problem is the way the wholesale electricity market is set up there is not incentive to invest in storage as they can make a lot of money from selling peak electricy. i did read the USA has spent more in the last year on off peak storage that the rest of the world put together. wheather that down to us mere mortals remains to be seen.

i think the most promising electrical storage system may be thermo electric. one lab is claiming a efficiency of up to 80% once all the bugs are ironed out. that would be a game changer. use your solar and wind to power a heating element and you wouldn't need anything better than lead acid. still waiting for them to get out of the lab.. been waiting about 6 years since they first said they were working on them. check out power chips for the latest updates.

bob golding wrote:for long term stationary battery systems there are some interesting things coming down the pipeline. i spent a long time researching vanadium redox flow batteries. the problem with them is the cost of the PEM membranes. until some other that dow starts making them cheap they will stay out of reach.
there seem to a few companies working on rechargeable zinc air batteries. i have asked one of them for some basic information about them. still waiting for a reply. if they survive thier estimated costs are around the same as lead acid, but without knowing a bit more about them i am not holding my breath. the world of battery storage is littered with companies claiming to beat lead acid on price and longevity.

not many survive past the start up stage. the vanadium one i was dealing with is now chinese owned and only dealing with megawatt size units. this seems to be where all the interest is. the problem is the way the wholesale electricity market is set up there is not incentive to invest in storage as they can make a lot of money from selling peak electricy. i did read the USA has spent more in the last year on off peak storage that the rest of the world put together. wheather that down to us mere mortals remains to be seen.

I guess I am somewhat less impressed with the direction batteries have taken. Off grid living.... well electronics in general could do with a big chunk of built in longevity. This is more true for those who want to be off grid as a life style choice rather than just looking at the cost of running power into where they need it. It seems finding something that lasts "forever" (30 years plus anyway, but 70 years would be better), is getting harder not easier. Lead acid is lasting longer than it used to, much of that being new chargers and care systems. Nickel iron still seem to be better than most and (flooded) NiCd seem to come close. Lead acid seem to be the most accessible. Everything else seems to not last as long. (aside from some very low output batteries that last forever with no charging... not storage solutions) The one storage solution coming... well here now if you have the money, is capacitor banks. A more modest size of cap bank would make a good buffer to handle short term peak loads (who knows, some of the better inverter systems may use such a thing internally).

We have gotten used to lead acid and how it charges, they are a pretty good compromise in the available current too. This is where the nickel iron fall down, they do not have a great instantaneous current availability for bank size. That is where NiCd batteries shine, they seem to be next best to capacitors, beating out just about everything else.battery wise. The big problem with NiCd batteries is that they (especially the sealed type) need a new way of charging to get the best performance/longevity. It is a no brainer to me that NiCd last longer than NiMH and I am seeing Lion batteries if treated well. I have some of those little solar lanterns that charge in a day and discharge over night.... night after night for years... full discharge every 24 hours. Getting a year out of a NiMh is doing good. Lion maybe two years... if reduced performance is ok (like less than half the ah available)

I am thinking what put me off of them was poor charging and low amount of charge for the size compared to AA... But a lot of that was the lower voltage to begin with. Also, I repaired a lot of them that got abused badly, flattened quickly and to a point that some cells were reverse charged and left on the charger too long (or had the charger restarted on charged batteries).

We live in a world of ten year life times for everything. A 10 year old car is worth $1500 as a trade less as an insurance write off. Almost everything that is "long lasting" has no more than a 10 year life. A golf cart is the same thing. These are the place we get our lead acid batteries from. Companies who supply off grid power stuff? There is more of a worry the supplier won't be around long enough to service the warranty or have replacement parts even less than 10 years down the road. There is room for something to emerge in this area... somewhere between DIY and premade.

i think the most promising electrical storage system may be thermo electric. one lab is claiming a efficiency of up to 80% once all the bugs are ironed out. that would be a game changer. use your solar and wind to power a heating element and you wouldn't need anything better than lead acid. still waiting for them to get out of the lab.. been waiting about 6 years since they first said they were working on them. check out power chips for the latest updates.

I look forward to it, though I think I would heat directly with solar rather than convert to electric to chemical to electric to heat to electric. I think more work could go into storing heat as heat than we do now too. Both at warmth temperatures as well as cooking temperatures. (deep freeze ice too, but that is another thread already)

the reason i said solar to electric element to power chips was that solar thermal is a lot more complex in that you need a tracker to get the best out of it. you would be losing a fair bit in the conversion but gain with less complexity. using solar pv to heat water and then attaching power chips to the water tank would a good option. i am not holding my breath that they will get out of the lab anytime soon. they do seem to have a few major advancements in the last few months though. the reason zinc air seem like a potential winner is the fact that zinc is a common metal and they is plenty of it. if i can find it there is a very good independent report that has done all the maths for us. will send a link when i remember where i put it!

bob golding wrote:the reason i said solar to electric element to power chips was that solar thermal is a lot more complex in that you need a tracker to get the best out of it. you would be losing a fair bit in the conversion but gain with less complexity. using solar pv to heat water and then attaching power chips to the water tank would a good option. i am not holding my breath that they will get out of the lab anytime soon. they do seem to have a few major advancements in the last few months though. the reason zinc air seem like a potential winner is the fact that zinc is a common metal and they is plenty of it. if i can find it there is a very good independent report that has done all the maths for us. will send a link when i remember where i put it!

The efficiency of the Power Chip is still a function of Carnot efficiency. The hope of achieving 80% efficiency in their system is referring to 80% of Carnot efficiency. Achieving high overall efficiency in the conversion of heat to electricity in such a system requires both high peak temperatures and high differential temperatures just like traditional heat engines. Gas turbines, combined cycle systems, and large Diesel engines achieve 75-80% of Carnot efficiency and overall thermal efficiencies from more than 40% (for the gas turbine and even better for large Diesels) to approaching 60% (for the combined cycle) - these are overall efficiencies in the conversion of heat to electricity, and high voltage AC electricity at that.

I think a good application for the Power Chip would be micro scale combined heat and power using a fuel. It's hard to beat photovoltaics for solar power generation in the micro scale. It's no good for a battery. Personally, I like the prospect for modern micro heat engines for use in combined heat and power and augmented with photovoltaics for electricity production. Use opportunity loading during the day on the PV array to minimize battery requirements and lessen conversion losses, then use a heat engine primarily for heat, mechanical work (such as a heat pump), and backup electricity. The numbers look very good when a very small unit can sustain a low power for long periods at high thermal efficiency. However, a unit like this Power Chip could do the same without moving parts (except the mechanical power part, but if the efficiency can be sufficiently high, then electric motors will suffice). That sounds very appealing indeed.

For medium scale solar power generation with energy storage, check this out: https://permies.com/t/32176/solar/Solar-Steam-Power-System . All pre WW2 technology.

Have been doing some reading about lithium batteries in cars. They are light for the power stored, and give good current out too. Their downfalls are that the instantaneous current available is still not good enough and that they need very particular charging care and monitoring. In cars I see two things, each cell has it's own charging/monitoring/protection circuit, and a capacitor bank (often as a capacitor per cell controlled by the same circuit dealing with charging etc.) These things are the reason it is only recently they are being used. They are also part of the reason some other technologies have not worked in the past and are still passed up on now. I think it is good to look at the reasons why we use what we use.

lead acid is the most used, they may be big and heavy for the power out, but in a stationary use this is not a problem. What problems do they have?

- They like to be fully charged all the time. This does not seem so bad as normally we have some charging happening all the time. It does mean the solar panels or other charging system probably has to be sized at peak need rather than closer to average need or a genset needs to be available to make sure the batteries are topped off on a regular schedule normally once a week.
- relatively slow discharge rate, fast discharge reduces overall capacity. Banks have to be over rated so they can handle motor starting loads and such.
- low use of available stored power. 50% discharge is a lot for a lead battery and not healthy.

Some people see nickel iron as a solution to many of these things, pointing out that with the right number of cells (10 instead of 6) nife cells use the same voltages for charge etc. but will withstand abuse far beyond a lead battery.... but they have to be bigger for the same AH size storage and bigger yet for the same instant current for motor starting. They cost more than lead acid and are harder to obtain with only one or two companies that make them.

Li-ion batteries are much smaller for the same power capacity. I am thinking they can supply higher instant current too, but am not finding how much. Lead is ok up to 1c, but has problems even with 1.5c as an example. Hmm it says 2c constant is ok though it lowers life, as high as 15c spikes are ok, but the batteries get really hot even at 10c (about 135F)... I can see why the electric car guys use capacitors for acceleration. and of course the charging difficulties mean more complex electronics.

This is the reason I am interested in nicd batteries. Their discharge is limited only by making sure a battery discharges evenly enough that no cell backcharges. They can handle very high discharge rates, 15c is no problem with peaks to 50c, weight and size are smaller than the lead acid. They can be had for only about double the cost (using sealed cells, I would like to find out more about flooded cells which are way tougher) of lead batteries. The big drawback is to not over charge these guys. However, My thought is that this is something modern control should be able to deal with. If we can charge li-ion batteries without blowing them up (most of the time ) then a controller for NiCd batteries should be doable. The flooded variety NiCd batteries have a similar life span to NiFe batteries. I should be able to get over 20 years life even out of sealed units if I limit charge/discharge to reasonable limits.

NiMH - one word with these unobtainium, at least in large sizes that might last any amount of time. 5c is about their maximum discharge, so NiCd beats them there, they seem to be about even with Li-Ion batteries, but a little more robust. These could be the batteries of the future if patents don't kill them.

I have said not much about cost. Lead acid are the cheapest. Though deep cycle are pretty much double what a starting battery is. NiFe are costly. 10 times more than lead acid or more. Li-Ion are 4x or so, but on the decrease, just remember the cost of charge control. In my case I will be building the charger for the NiCd battery pack. I suspect I will keep them slightly undercharged most of the time. I expect to use the right number of cells to make memory less of an issue too. My costs will be in between Lithium and lead. My hope is to have better service/performance than both lead and lithium.