Comment by Manuel_D | Hacker News Reader

Comment by Manuel_D | Hacker News Reader

Parent Full thread

Note that none of these exotic storage systems have ever actually been deployed commercially. Yes, liquid nitrogen is used for things like cooling. But no one has deployed a grid-scale storage system using liquid nitrogen. Liquid hydrogen has been used in rocket launches, but has not been used for energy storage. These technologies are mature in applications besides energy storage. They are not at all mature in the context of energy storage. Grid-scale storage systems using these technologies remains the stuff of prototypes and white papers.

This commenter is also incorrect in the claim that there is not enough renewable capacity to charge up storage. California , Hawaii, and other energy markets often hit days of excess renewable production. Proponents of energy storage promised that companies would swoop in to store and resell this excess energy. But this has not materialized, because energy storage is not nearly so simple or cheap as this commenter claims it is.

You can insist until you are blue in the face that these are all untried and exotic, but you will be wrong throughout. And you know you are wrong as you say it.

If in fact they were exotic and untried, billions of dollars would not already be committed to factories to produce them in industrial volume. The processes involved are used industrially billions of times worldwide every day.

You only wish they were exotic because you imagine it would make nukes more appealing. But nothing can make nukes appealing. They get less so with each passing day.

> If in fact they were exotic and untried, billions of dollars would not already be committed to factories to produce them in industrial volume. The processes involved are used industrially billions of times worldwide every day.

Yes, for purposes different from energy storage. The massive amounts of ammonia synthesized through the Haber process for fertilizer production does nothing to demonstrate ammonia's viability for electric grid storage.

Likewise the hydrogen used in space rockets has no bearing on the feasibility of electrolyzing water, storing the hydrogen, and converting it back to electricity. If anything, the fact that most hydrogen is produced through steam reformation highlights the difficulties of electrolysis at scale.

We have plenty of experience with flywheels. Almost every car has a flywheel in it. Does that mean it's guaranteed to be extremely cheap and scalable to store electricity by spinning a bunch of giant flywheels? That's the kind of leap you're making here.

When someone actually builds and operates a facility that takes in electricity, produces ammonia, and then taps that stored ammonia to produce electricity later, then we can actually measure real-world cost of such a storage system. Until then, it's just optimistic predictions. And optimistic predictions don't actually store any energy.

Every air separation plant (you know, the kind used to make oxygen for steelmaking) employs expanders for recovering energy from cryogenic nitrogen. This is an off the shelf technology.

It's off the shelf technology for chemical processes. It's not off the shelf technology for energy storage.

We have plenty of experience with flywheels. I bet there's millions of cars built every year that have a flywheel in them. Does that mean energy storage using giant flywheels is guaranteed to be insanely cheap and way cheaper than the existing storage systems?

Just because we have plenty of experience using a given technology in one application doesn't mean it's guaranteed to be a smash hit in a different application.

Air separation is not a chemical process. It's a physical process, involving compression, heat exchangers, and expanders. You know, just like an energy storage system using cryogenic gases. None of this is magical unknown technology. The components are literally in use today and have been for years.

Now, whether LN2 (or LAir) energy storage is practical is another matter. The efficiency seems poor unless you have a source of waste heat to juice the process.

Air separation is mostly used for chemical processes [1] to isolate certain gases like oxygen or nitrogen. This is what I wrote in my previous comment:

> It's off the shelf technology for chemical processes. It's not off the shelf technology for energy storage.

The while point I'm making in these last few comments is that just because a certain technology is effective for one application doesn't guarantee it's effectiveness for a different application.

1. https://en.wikipedia.org/wiki/Air_separation#Applications

So what if it's used for chemical processes? To make it efficient, there is careful transfer of heat from the input stream to the outgoing streams, with compression/expansion to convert the heat energy back to work. Making this efficient involves just the kinds of components that are needed in a cryogenic energy store.

You correctly point out that air separation is made efficient by transferring the heat from the output stream to the input stream. After cooling air enough to isolate whatever chemical is needed (like nitrogen) the cold output stream is run back through the warm input stream to help cool the input stream. This also has the effect of warming the output stream back to ambient temperature. This is fine if you're separating out oxygen to use in a smelter, or nitrogen to be used in the haber process.

But you can't do this for cryogenic air storage. The whole point is to produce liquid nitrogen (or liquid air) that can be stored and then reheated later to drive an engine to generate electricity. If you ran the liquid nitrogen output through the input stream like in typical air separation, you'd warm the output stream and turn it back into a gas. So even though the two systems both involve cooling systems they're actually substantially different processes. One of them is separating air's constituent gases, and mixes the input and output streams to achieve efficiency. The other is essentially a big liquid nitrogen plant.

Unfortunately the only existing cryogenic air storage plant delivered 15 MWh of storage at a cost of 8 million pounds [1]. That's about $650 per KWh, as compared to ~$130 per KWh for battery storage. Like I said, just because a technology is effective in one application, doesn't mean it's guaranteed to be effective in another one.

1. https://en.wikipedia.org/wiki/Cryogenic_energy_storage#cite_...

You tell me: which component of a cryogenic energy storage system is not already in use in some process (air separation or otherwise)? One of the attractions of this sort of thing is it's composed entirely of things that are already quite mature, and that have existing supply chains.

And for the third time, just because the individual components are used in different applications doesn't mean it's going to be cheap or scalable to use them in energy storage. The cost history of existing cryogenic storage plants indicates that no, it's not effective for energy storage it's 4-5x more expensive.

We build plenty of flywheels. Does that mean energy storage based on giant flywheels is guaranteed to be efficient at scale because we have experience using flywheels in other applications like automobiles?

You're changing the subject now. You were criticizing these for lack of maturity, not for being uneconomical. My point is that your criticism that they aren't mature is misplaced, since the component technologies are all well established. Of course, it could be LN2 or LAir storage doesn't compete.

No, my criticism of the lack of maturity of cryogenic air energy storage is still correct. The fact that it shares some components with air separation does not change the fact that cryogenic air storage is not mature technology.

Similar deal with ammonia energy storage. We've got plenty of experience with synthesizing ammonia for fertilizer production. We've got very little, if any, experience using synthesized ammonia as a form of energy storage.

It was you, not I, that started this tangent about air separation in this comment [1]. I was, from the beginning, talking about energy storage systems.

1. https://news.ycombinator.com/item?id=31760980

I.e., you cannot identify any single stage of any of these extremely familiar industrial processes that would make it unsuitable for energy storage or retrieval, so instead invoke ghosts of fear and doubt.

Do you imagine the ammonia knows why it is being synthesized, and would balk at being synthesized and tanked for energy storage or fuel? Do you imagine it will object to being burnt in a combined-cycle turbine?

Your credibility is at zero.

Why are you all of a suddenly replying to a super-deep thread? Is pfdietz your alt? Regardless if you're asking about the technical shortcomings of ammonia and cryogenic air storage I'm happy the enlighten:

Ammonia storage would first require a source of hydrogen. Currently almost all hydrogen is produced through steam reformation which releases carbon dioxide. So this has to be replaced with electrolysis, which is more energy intensive and has issues with corrosion of electrodes. Then there's the issue of heating up this hydrogen and nitrogen to ~400C and compressing it to fix the nitrogen into ammonia. Currently this is done through combustion of fossil fuels. That too needs to be replaced with an electric source. All these changes drastically increases the cost of producing ammonia over existing processes.

Cryogenic storage is essentially producing liquid nitrogen by refrigerating air, and then hearing the nitrogen to create a pressure gradient to drive a heat engine. Cooling the air is a huge energy sink, and releasing the energy often has to be coupled with a heat source in order transition the liquid nitrogen to a gas. It's actually using the heat gradient of the ambient air and the liquid nitrogen to drive the heat engine, and that ambient air often doesn't have the required energy density to produce more than a few dozen megawatts. Existing prototypes often scavenge waste heat from a fossil fuel power plant. But again, not an option if you plan to eliminate fossil fuels.

If heat capacity of air were too low to boil LN2, it would also be too low to condense nukes' operating steam. You don't get it both ways.

You pretend that electrolysis has not been known for centuries. But nobody is fooled.

Reply on news.ycombinator.com