What's your favourite energy storage tech?

[Fat Rooster]

Just came across this video, about using calcium oxide <> calcium hydroxide as a reversible energy store and think it may be my new favourite. It's cheap, scalable, and uses largely existing tech (ancient tech even!). The round trip efficiency is the biggest downer, being not particularly great, but the charging can be either completely waste thermal or heat pumped waste thermal, mitigating that in some circumstances. The initial CO2 creation is the next biggest concern, as calcium is mostly carbonate naturally and turning that into oxide liberates CO2 no matter where the energy comes from. That can at least be effectively captured though, as CO2 should be the only major outgassing. You can compress and cool the gas without having to worry about water icing up everything.

I just love that it is a chemical reaction in the sweet spot of hot enough to go fast and be worthwhile, cool enough to be reversible, and using commonly available materials. The mass to energy ratio is better than current gen batteries, never mind the price to energy!

Anyone else got anything they particularly like the look of? Even if it will never be viable, plain old cool is fun too.

[Misereor]

Just came across this video, about using calcium oxide <> calcium hydroxide as a reversible energy store and think it may be my new favourite. It's cheap, scalable, and uses largely existing tech (ancient tech even!). The round trip efficiency is the biggest downer, being not particularly great, but the charging can be either completely waste thermal or heat pumped waste thermal, mitigating that in some circumstances. The initial CO2 creation is the next biggest concern, as calcium is mostly carbonate naturally and turning that into oxide liberates CO2 no matter where the energy comes from. That can at least be effectively captured though, as CO2 should be the only major outgassing. You can compress and cool the gas without having to worry about water icing up everything.

I just love that it is a chemical reaction in the sweet spot of hot enough to go fast and be worthwhile, cool enough to be reversible, and using commonly available materials. The mass to energy ratio is better than current gen batteries, never mind the price to energy!

Anyone else got anything they particularly like the look of? Even if it will never be viable, plain old cool is fun too.

Mechanical batteries are fast becoming a thing.
Mostly on ships for now, but once they get the technology matured a little, it should provide an inexpensive energy storage platform for green energy.
Once costs are lowered enough for ordinary civilians to play, I could imagine buying your own battery and add a controller that had it charge up during low cost hours and spend during high cost hours.

[Ibrinar]

One that doesn't exist http://eduard-heindl.de/energy-storage/index-e.html basically cut out a giant stone column, like with a km diameter, lift it a few hundred meter by pumping water under it and you have lots of energy stored. I like it because of the sheer size of the thing.^^ No idea whether that is actually doable though.

[Mastikator]

Pumped-storage hydroelectricity is a pretty clever way of building an enormous city powering battery. Goes really well with solar, since solar is only on half of the time any excess electricity goes into the water reservoir.

[Lord Torath]

Molten Metal batteries. These are obviously not for individual devices, but mass storage. They are large tanks of liquid metal. One major benefit they have is reusability. Most rechargeable batteries have a fix number of times you can use them before they stop accepting a charge. These molten metal batteries do not. Their cathodes don't degrade, and they've been tested to have (IIRC) over a million charge/recharge cycles with no degradation to capacity. They do need to be kept rather hot, though, so no one's going to carry these around in their pockets.

I do not know how much energy is required to keep them hot relative to the amount of energy they can store.

Disclaimer: I am not affiliated with either the news site I linked nor the company making the molten batteries.

[Yora]

I really like the idea of giant flywheels held up by magnetic bearings inside a sealed vacuum. You can spin them up like an electric motor and then get the energy back into electricity by using it as a dynamo. (Both are the same device and can be used as either, depending on if you turn the spiny bit or send electricity to the cables.)
Wouldn't be a portable solution, but sounds really good for storing power generated during the night, in theory.

[halfeye]

I really like the idea of giant flywheels held up by magnetic bearings inside a sealed vacuum. You can spin them up like an electric motor and then get the energy back into electricity by using it as a dynamo. (Both are the same device and can be used as either, depending on if you turn the spiny bit or send electricity to the cables.)
Wouldn't be a portable solution, but sounds really good for storing power generated during the night, in theory.

Man, that takes me back to first reading "The stainless steel Rat", there was one planet in that that used those for vehicles.

[factotum]

Pumped-storage hydroelectricity is a pretty clever way of building an enormous city powering battery. Goes really well with solar, since solar is only on half of the time any excess electricity goes into the water reservoir.

Yeah, I'm a fan of that tech as well, although the slight disadvantage is that you do really need a nice mountain to build your power station inside so you get a decent head of water, like at Dinorwig in Wales:

https://en.wikipedia.org/wiki/Dinorwig_Power_Station

[jayem]

Yeah, I'm a fan of that tech as well, although the slight disadvantage is that you do really need a nice mountain to build your power station inside so you get a decent head of water, like at Dinorwig in Wales:

https://en.wikipedia.org/wiki/Dinorwig_Power_Station

There was a form of underground hydro with a heavier fluid and building up pressure pressure (so a bit like the concrete load idea). I'm not sure I like the idea.
Classical Hydro/Battery has an elegant simplicity and it looks after a water supply, although it of course can still be dangerous.

As a partially cheating answer, I'm going to suggest a lifestyle/usage one. Economy 7 used to be cheap in the night, expensive in the day, and washing machines and immersion heaters would go at night. Swapping it over isn't going to be perfect (you do need lights after all, winter is cold and dark) but every kWH that can easily be shifted is energy you don't need to worry about storing electrically in the first place.

link found
Also while looking for it, i have a new favourite form. You build your lower reservoir under the sea and empty it
link

[sktarq]

probably some of the Vanadium series ROx Solution batteries.

Very high cycle system, quite cheap, hugely scalable, the solutions change colour depending on charge state in some of them (like pink, yellow, green, blue...its quite visually striking), the system holds charge without bleeding very well...are already being used in some places (large building or complex/facility) and so have proof of concept done...does not need the constant energy input that molten metal batteries do (which would be my second favorite-and why the use of them to backup a heat producing server farm amuses me)

[erikun]

There is something about an iron and water battery that sounds really neat. However, there isn't much information about it working so I'm not necessarily on-board, just curious about it. Although from their website, it looks like the battery using FeCl₂ and FeCl₃, which would probably not quite count at "just iron and water" or "safe enough to drink", despite what the video claims.

[Eldan]

My university's engineering department built some kind of complicated heat exchanger with ground water and geothermal heat that cooled the building in summer and heated it in winter, with the same water. It sounded pretty ingenious, I have no idea if it turned out to be practical. But they did integrate it into at least one campus building.

[Rydiro]

I'll second flywheels.
And jam.

[Yora]

There is something about an iron and water battery that sounds really neat. However, there isn't much information about it working so I'm not necessarily on-board, just curious about it. Although from their website, it looks like the battery using FeCl₂ and FeCl₃, which would probably not quite count at "just iron and water" or "safe enough to drink", despite what the video claims.

Chlorine, like fluorine, is extremely aggressive in its pure elemental state and will bond to pretty much everything immediately. Much more so than oxygen, our well known great corroder. But this also means that once it got hold of another atom, it really doesn't want to let go, so chlorides and fluorides are very stable and unreactive. Basic everyday salt it a chloride and we constantly throw lots of that stuff into our bodies, and really need it to live. Fluorides are in a lot of toothpastes and I think added to the water supply in many places.

Iron chloride is still pretty toxic even as a stable molecule. Wouldn't want to drink water that has chips of that stuff floating in it.

[Fat Rooster]

There is something about an iron and water battery that sounds really neat. However, there isn't much information about it working so I'm not necessarily on-board, just curious about it. Although from their website, it looks like the battery using FeCl₂ and FeCl₃, which would probably not quite count at "just iron and water" or "safe enough to drink", despite what the video claims.

Could have a place, though the energy density and power are quite low. The low power may mean large initial investment in the electrodes, particularly as they both will be oxidative at some point in the presence of chloride. There are few materials suitable, and they are mostly relatively expensive. Mercury electrodes are possible I think (chemistry problems are mostly overcome by self healing), but come with the down side that your battery ends up quite toxic. Cleaning out the mercury shouldn't be too hard though, as there should only be trace amounts. It would be a case of remove the initial mercury from the cell, and then throw in a lump of copper that you leave for a few months, pulling it out and clearing out any mercury that has come out occasionally. You could do that in-situe. The accident risk is there, but there is nothing inherently dirty or difficult to recycle about it.

As I see it there are two possibilities with the chemistry. The first is that it is actually using the potential between the two different ion makeups for energy. Don't know you would get much energy out of that at all (could be very wrong though, anyone know this better?). The second is that iron doesn't actually contribute much energy storage at all, instead acting as an oxidative buffer on both sides for another reaction, with an acid base reaction being the first that jumps to mind. The actual battery chemistry would be H⁺ + OH^- <> H₂O. One side would be as basic as possible, the other highly acidic. To charge it you pump H⁺ across the membrane into the acid side (making it more acidic). The electrode reaction requires something to be reduced, which is where the iron comes in. Fe³⁺ is reduced to Fe²⁺, while staying in solution. The excess chloride effectively becomes hydrochloric acid. At the other electrode the opposite reaction occurs, but the difference in pH should give you a difference in potential.

Unfortunately iron falls out of solution in basic conditions, so keeping things working would not be trivial. It would probably still work with one side relatively neutral, but not sure. You might get better results with chelates, but then you are increasing costs by orders of magnitude. Still, organic chelates such as EDTA don't require any uncommon elements, so are very scalable. They are also already well studied and widely produced.

If you could get this working with sulphuric acid you might be onto a real winner, as you could probably use mine tailing waste water (considered toxic waste) as your feedstuff. Managing the oxidative state while using an oxidative acid might be tricky, but you could get access to lakes of the stuff, with people actually paying you to take it.

Iron chloride isn't a molecule, it is a salt, and only really relevant as a solution. When salts are in solution you can generally consider the ions separately, with their behaviour only really coupled by their effect on pH. Eating solid iron chloride is definitely a bad idea, as your stomach acid can keep the iron in solution, but if you dilute it with water outside the body most of the iron drops out as hydroxide, leaving an acidic solution. This is extremely bad for fish, and the environment in general, but mostly because it the effect is similar to dumping a comparable amount of hydrochloric acid.
Basically it cannot be floating around in tap water. If there is enough that your tap water is very acidic you are probably going to have much bigger problems than the iron, as it would leach all sorts of things out of all sorts of places. If not, or if the water is neutralised somehow, worst case is that you have a bit of rust floating in your water, which is harmless.
As I said, the stuff is similar to mine tailings, after significant dilution, which are well understood and produced in vast quantities. The toxicity is important because of those vast quantities, rather than because it is particularly toxic (this isn't, mine tailings are worse because of other heavy metals). It is a pollutant that can safely be diluted away.

I wonder if this could be integrated into a dilution system for mine tailings, producing energy from them directly. It would essentially be a flow battery that you get charged liquid for from somewhere else. You might even be able to strip out some heavy metals at the same time. That would be cool.

[erikun]

I think the purpose of the iron-water battery is to have something that can repeatedly be charged and discharged without wearing down, and without using extremely rare, toxic, or hard-to-process materials. They mention using it to store solar or wind energy and releasing it onto the grid when the demand is actually there, for example. I think having one in the back yard with a solar panel would be interesting, either to provide power during the evening for lowered energy bills or as an emergency backup in case of a blackout. I would just want to know more facts like how much power it could provide/how long/how long to charge it up, and how dangerous the chemistry mix is if something goes wrong and it starts leaking.

(Although it's probably an iron-water-NaCl salt battery, now that I think about it.)

Interesting points about other options. It's probably not what they are going for, but reusing mining runoff into similar batteries would certainly be a better solution than just letting it flood and drain out into streams. Sadly, owners of abandoned mines probably wouldn't let you just collect such water for free and it's not as if just buying a mine is a cheap thing to do.