Mike, check out

https://en.wikipedia.org/wiki/Nickel%E2%80%93iron_battery

that's the Edison iron battery, or nickel/iron

Thanks for this, Dave.

I'm certainly no Chemist, and 'tis a long time since I was messing about in a school chemistry lab too.

That Nickel-Iron battery sounds interesting. Any idea why it is deemed expensive to manufacture?

As far as I remember, car brake lines are nickel placed steel, which could potentially provide a ready-made electrode.

The reasons the (Acquion style) salt water battery grabbed my attention are that it is a proven technology, can provide precisely what I need - 100W for hours at a time, thereby halving my grid electricity usage - is robust, safe (fire/explosion), non-toxic, long-life, seems to be relatively simple...

But perhaps real-life - as distinct from demonstration - DIY batteries are outside the capabilities of the ordinary guy.

Aquion has that "DIY salt water battery" on one of the links, but you're not going to make a battery capable of delivering 100W out of copper wire and nails and keeping it in your garage. 

So from the way they describe that DIY rechargeable battery, it's a copper/zinc salt water battery. First thing I'd try with that after following their directions would be, what's the charge that such a battery could hold? If you use copper and zinc sheet and a thin separator, how much more charge could the battery hold and how many cycles could it do?

It's fun to try a DIY rechargeable battery, but nails and wire in a big jar of salt water does not lend itself to a lot of energy density for a battery.

Apologies I missed the link you provided to the aquion DIY instructions at first.

Hi Dave.

Can't seem to respond to your last message, so placing a response here.

I think that DIY battery is just the efforts of that particular web site team, and not the actual Acquion battery technology, which seems to use Manganese Oxide as the cathode and Carbon Titanium Phosphate as the anode.

Anyway, thanks for the time you have given me, and for the effort in trying to explain complex matters to an old guy like me.

Take care.

Mike!

Totally with you on giving a hearty f u to Russia. I have friends in Ukraine, but even if I didn't, my grandfather moved from there to the US in 1905.

Yeah looks like aquion has gone under.

When you think of rechargeable aqueous batteries, the oldest type of course is lead-acid. These days nickel metal hydride is another success story.

As far as a roll your own DIY rechargeable battery...I don't know of an easy one off the top of my head. I poked around on the internet this weekend because I should at least see what might be out there. I was thinking of the canonical Daniell cell, copper/zinc, from long ago. It's not rechargeable afaik, but with some playing around perhaps it's possible to get it to recharge a bit.

The thing that one wants to avoid when recharging a battery is breaking down the solvent, so in this case it's water. 

in the case of a Daniell Cell, when it's discharged, copper sulfate in solution plates out on the positive electrode (acting as the cathode now) and the zinc that the negative electrode is made of oxidizes to zinc ions in solution (negative electrode acting as an anode). To recharge it, you'd reverse the process, with the negative electrode becoming a cathode and hopefully plating zinc, while the now copper coated positive electrode becomes an anode and oxidizes the copper to copper ions back in solution.

We know that Daniell cells weren't used as rechargeable batteries, but...you can plate zinc out in an aqueous solution. One of the big competing reactions there would be evolution of hydrogen/breakdown of water, and this would slowly but surely increase the pH of the electrolyte as hydroxide gets left behind when the hydrogen goes.

I worked on iron/chromium flow batteries, but I wouldn't recommend playing around with a lot of chromium chloride and hydrochloric acid, but they were rechargeable. 

There might be some iron chemistries out there that would work. Edison had an iron based battery...I think it was rechargeable.

If I was going to DIY a rechargeable battery, I'd start small and see how things go- I have a friend, ham radio operator, who asked me a similar question a few months ago.

As an example (although not rechargeable), I often do an aluminum-air battery as a demonstration. If I use a 10x10 piece of foil as my anode and some copper mesh/battery graphite for the air cathode, I can get enough potential and current to run a small hobby motor- about 0.5V at 100 mA, or 50 mW. Sounds nice, but...if I want to charge my phone, I'd need 5V and 1A, so I'd need an Al/air battery 100 times bigger, so a square meter of aluminum foil, and that's just to charge my phone. These demo batteries I make will last maybe half an hour to an hour.

malone.a.mike:  Ah yes, I was forgetting about the problem in Europe.  Our electricity here is $0.17 per kwh if we stay below 256kwh/month.  Most of the US is paying far less than that.  As for lead-acid batteries, it sounds like you're thinking of car batteries which are optimized for starting, rather than deep-cycle ones that are made to handle 1500 or more deep cycles and last 20 years or more if you take good care of them.  It only takes about five deep cycles to kill a car battery.  I have four 232AH 6V deep-cycle Interstate GC2 lead-acid batteries, meaning about 5kwh capacity (although I hope to never have to discharge more than 50%).  They're about seven years old.

Our refrigerator takes about 110W when the compressor is running, but several times that much when defrosting, which I think takes about 15 minutes four times per 24 hours, or something like that.  I had thought that if things get really bad, it'd be good to have one of those small office refrigerators that takes a lot less energy, and then just forego the luxuries like ice cream.  OTOH, if the food supply gets bad too, you'd want to be able to keep more on hand.

The problem I've had is that modified-sine-wave inverters are so easily destroyed, apparently by reflections off the ends of long connections, because of the fast edge rates of the waveform.  When you see people demonstrate them on YouTube, even with very heavy loads, they only have the 6-foot (2m) cord on the equipment, not 50 or 100 feet (15m or 30m) like it takes to get the power from our detached garage to the far end of the house.  We went through a lot of them; and although most were replaced under warranty, I say the best warranty is the one you don't have to use.  At the recommendation of another engineer friend, I finally spent the money on a Renogy pure-sine-wave inverter that's supposed to be able to do 2kw continuously and 4kw for a few seconds (not just a couple of cycles).  It's only been in service three months so far.  Hopefully it will last many years.

Hi Garth.

In my researches I had determined that a micro grid tie inverter - one little inverter per solar panel - would be the most suitable for my needs, and was in the process of designing one when I tripped across some already available via the usual Chinese outlets, and I bought a couple.

https://www.aliexpress.com/item/1005003313764414.html?spm=a2g0o.store_pc_groupList.8148356.1.79e974ccu0WNrt&pdp_npi=2%40dis%21EUR%21%E2%82%AC%2042%2C64%21%E2%82%AC%2031%2C98%21%21%21%21%21%402100bddd16710152561525805ebb94%2112000025161597691%21sh

I already had a 100W polysilicon solar panel from a few years back that I got with the intention of sometime experimenting with it or putting in into service.

The Russians got my enthusiasm for that fired up and I hooked it up to one of the above little grid-tied inverters, while also acquiring a second 100W (monosilicon this time) solar panel.

I was surprised to discover that half of my average daily usage was that fridge-freezer. I *can* buy a newer model that would halve that, for maybe €800. I estimate it would take over 13 years to pay back that cost, even at the current - temporary? - elevated cost of electricity.

I think lead-acid might have a similar cost and payback time.

https://batteriesdirect.ie/product/trojan-j185h-12v-225ah-deep-cycle-battery/

All to save in the region of 375Wh (0.375kWh, €0.16 ) per day.

Hence my interest in a potential DIY solution.

Although it might seem like madness to continue to pursue this when I have already cut back so much, nonetheless if I can halve my electricity usage yet again it is worth it psychologically to me. (And a few extra bob that I can send to Ukraine.)

Wow, I didn't know those micro grid-tie inverters existed.  That Trojan you linked to though is about twice what I paid for similar capacity in my Interstate batteries seven years ago, with no trade-in.  (It's cheaper if you trade in old ones.)  My main purpose in doing my solar was to have power if the grid goes down long-term because of social unrest, political unrest, EMP, whatever (as things weren't looking good at the time), but it would be nice if it paid for itself eventually too.  We have had some brief outages of a few hours since then, and it was nice to have.  I have wished the refrigerator had the intelligence to take an input from the solar to turn its thermostat a little colder when there's sun and a little warmer when there's not, and to bias the defrost-cycle timing to when there's sun.  As you may know, the fridge takes a lot more power in the first second of startup.  Ours takes over a thousand watts for that first second; so it takes a sizable inverter.

Hi Garth.

Replying here, as cannot reply to your most recent post.

Yes, if you need a standalone system then a sizeable inverter is required to accommodate motor startup currents, but for a grid-tie system then the grid provides for those momentary surges.

The system I have been putting in place has other driving factors, brought on by my desire not to give the Russians a penny, rather than being able to operate independently of the grid.

It would be really nice if I could have employed one of those Acquion type batteries as that would potentially have eliminated my fridge-freezer as a grid consumer, and halved my grid consumption at the same time.

(Maybe I'll come across on old forklift battery that I could use for the same purpose. That would probably even do my cooking too :)  ).


Hope you have a good Christmas.

Take care.

Mike

Edit

By the way, there are probably some things about those micro grid-tied inverters that you should know, just in case you are interested in them.

1) The enclosure is NOT waterproof, and there have been reports from some users that theirs have blown as a result of getting wet (inside). I have mine positioned on the underside of their respective panel and this seems to work OK, although I am only half way through the winter as yet.

2) They can get hot when operating near maximum power. Hotter than I would like. Heat is the enemy of electronics. Daily summer temperatures here rarely exceed 30 Celsius (86 F) so it you live in a warmer clime then that might be something to prepare against. (Maybe mount it on a metal plate, or stick the heat sink from the CPU of an old scrapped PC onto it.)

3) There are advantages to micro inverters, i.e. 1 inverter per solar panel.*

a) The power rating of the inverter can be better matched to the panel, possibly increasing efficiency

b) As each panel is operating at different solar and temperature conditions, the MPPT in the individual inverters will be better able to keep their panel at the maximum power point (e.g. if part of 1 panel becomes shaded that will not affect the operation of the other panels as 1 single large inverter would, and the inverter for that single panel will still maximise the power from that shaded panel)

c) The length of the low voltage heavy current cabling is reduced, reducing losses in turn

d) Easy to install - IMO - and easy to add extra panels to the system

* There does not HAVE to be 1 inverter per solar panel. Panels can be connected in series or parallel and share an inverter of the appropriate rating. E.g. 2 x 200W panels could be connected is series and make use of a single 500W inverter (I like to overrate a bit - I use 120W inverters for each of my 100W panels)

Indeed, the use of series-connected panels - which give a higher output voltage - could potentially increase low light (morning and evening) output, if the inverter can kick in at 'low' panel output voltages and the MPPT is reasonably well implemented.

There may be other things that I cannot think of right now.

TC

M

Re: Battery HackChat

Has there been any advances in simple to make DIY batteries that could be used to extend the usefulness of solar PV systems? Batteries such as the salt water type, for instance?

During the summer, my 100W fridge-freezer is my single greatest consumer of electricity on a daily basis. My small 200W - soon to be 480W - peak solar PV system would be able to be the source for most of this daily energy requirements IF there was a storage system that could source 100W for hours at a time, as salt-water batteries are claimed to be able to do.

Hi Mike, you have linky to the chemistry of the salt water batteries of which you speak? It would help to know what the typical energy you need for your fridge through the night- hook up a kill a watt and see how many kWh it uses over a 24 hour period, and when the sun ain't shining. 

Also, there's probably some non battery ways of getting your freezer to keep stuff cold longer...

Hi Dave.

The Russians annoyed me. A lot. Near the beginning of this year I decided to cut down on my energy usage. I walk where I can. I cut down on heating. I cut back  non-essential electricity usage (water is just fine, even for this tea and coffee addict).

I began to monitor my electricity usage. To my surprise, my fridge-freezer consumed 0.75kWh/day on average during the summer. It is roughly 95W, and ran for maybe 1.5 hours out of every 4, or even longer on warmer days. (It starts off consuming about 110W, drops to about 100W after about 15 minutes. When running over an hour it had dropped to 90W or a bit less).

I live in Ireland.

By the end of the summer, I had got my electricity consumption down to 1.2kWh/day of which the fridge was still around 0.7kWh-0.75kWh.

I have 2 small (100W) solar panels than I got into service during the early summer for one and middle summer for the second. These were giving me about 18kWh per month by summer's end, with surplus going to the grid at no benefit to me.

If I had a battery that could supply around 100W for hours at a time then conceivably my solar panels could provide a lot of the energy required by my fridge. (And I could add another panel or two.)

I have tried lead-acid, and find them unsuitable for this. Lead-acid is very suitable for providing large currents for short durations - such as starting a car engine, where it might supply 300A or more for 5 seconds - but I find that even supplying 30W for more than 4 hours kills them (over a period of months).

And they are expensive.

LiIOn would certainly do the job, but would be gross overkill for my needs as well as expensive, and not at all environmentally friendly (as yet).

I came across this
https://www.aquionenergy.com/technology/aqueous-hybrid-ion-ahi/

Acquion manufactured a salt water battery that could supply the 100W for long durations and with a lifetime  in excess of a decade.

But they went bankrupt a few years back.

Water might be cheap and plentiful. But it is heavy and bulky, and therefore expensive to ship.

But this type of battery might be a candidate for the DIYer.

What would need to be known:

Salt type and concentration

Electrode material(s), shape, size and spacing

Any inter-electrode (gap) filler material

Suitable casing material

This type of battery could be located outside in locations where weather conditions permit, or could by built in a form factor that would suit European domestic appliance slot-in locations in a kitchen or utility room.

If able to benefit from time-of-day energy saving tariffs (e.g. night time low cost) then even a location with no renewable energy source could still charge the battery during off-peak and use during the day or other peak times. If with solar, then excess solar could be used to charge and the battery used to supply energy when insufficient solar available, with the possibility of using time-of-day charging as well for those times of the year when little or no solar energy is available.

It might not suit everyone, but it would suit me just fine.

Edit

Another link which might prove useful

https://www.solarquotes.com.au/blog/aquion-salt-water-battery/

I had read of a promising salt battery almost 50 years ago that was supposed to do even better than today's lithium batteries for EVs.  I believe the claimed energy density was similar to that of gasoline.  Obviously it never materialized (like probably so many things in Popular Science magazine).

Whatever kind of batteries you make or buy, be sure to compare the cost of the battery wear to the cost of the utility.  Even here in California where we pay some of the highest prices of the nation for electricity, I find it still comes out cheaper to run things on the utility when the sun is down, rather than using the batteries; so I just have batteries for when the utility goes down, and otherwise try to mostly keep the load from exceeding the PV's output level.  Lead-acid's weight and size make it a lousy choice for EVs; but for the house where weight and size don't matter, their price is still good compared to lithium, and when they're shot, they can be reconditioned for a lot less than buying new, and when they can't be reconditioned anymore, they're still 100% recyclable, unlike lithium.

I don't use a cell phone, and the seldom times I use my laptop computer, it's almost always plugged into the wall, as its battery life is only a couple of hours max, even with a new lithium battery pack.  My 1980's HP hand-held computers OTOH go months or even years on a set of alkalines.  There's no watching videos there, but they still have their place.  What I get most benefit from modern batteries from is my bicycle headlight, due to the combination of better batteries and LED lights being several times as efficient as incandescent lights.  What we had in the 70's was terrible.

Hi Garth.

(Also see my earlier response to Dave.)

My electricity costs at the moment are about €0.43 per kWh (about $0.45 at current exchange rates).

But the primary reason I am doing this is the Ukraine war. I am taking what the Russians are doing in trying to overthrow a nascent democracy and their war crimes personally).

I have a small 2 x 100W solar panel system which has 2 x micro grid-tie inverters. Having cut back severely, these can provide enough energy to power my daytime needs during the summer months, with any surplus going to the grid at no benefit to me.

I hope to add another couple of panels next year.

I have determined that my single greatest use of electricity on a daily basis is my fridge-freezer. This requires a nominal (as determined by me) 100W.

If I could come up with a battery system that could provide 100W nominal for hours at a time and last years then I could potentially eliminate my fridge as a grid consumer, at least during the summer months.

In my researches, I came across the salt-water battery concept, and a commercial manufacturer of these called Acquion Energy, now deceased. (They were reportedly bought out of bankruptcy by a Chinese outfit, and little to nothing has been heard of them since.)

https://www.aquionenergy.com/technology/aqueous-hybrid-ion-ahi/

Most of the information I have come across is of the publicity blurb type, and of no real use.

But the concept intrigues me, particularly the possibilities for the DIYer.

Edit

Another link which might prove useful

https://www.solarquotes.com.au/blog/aquion-salt-water-battery/