To Store Renewable Energy, Try Freezing Air

https://www.scientificamerican.com/article/to-store-renewable-energy-try-freezing-air/

by fortran77 • 7 years ago

125 109 7 years ago

aurizon9• 7 years ago

You might get away with pissing on Carnot's grave once - but twice - never. By that I mean the energy of compression is lost. A compressor is an analog to an internal combustion engine - in reverse. You put in energy via amotor and compress the air. Unless you can use that heat of compression it is lost. Then you run another analog to an internal combustion engine - in reverse. https://www.google.com/search?ei=jFgWXoCkI474-gTJspPoDQ&q=en... Extract:- • Is compressed air free? No, compressed air is not free. Although "it's only air," compressed air is actually very expensive because only 10 to 20 percent of the electric energy input reaches the point of end-use. The remaining input energy converts to wasted heat or is lost through leakage. For example, to generate 5 CFM it takes 1 HP.

So 10-20% for the compressor.

Then the expansion:- https://en.wikipedia.org/wiki/Pneumatic_motor

sir motors are in the 60-65% efficiency range. Then the electric motor to drive the generator is about 93% efficient (some as high as 95%)

This string of 10-20% plus 60-65% plus 93.95%

Gives a net range of 5.58% efficient all at low end of range to about 12.35% at the high end. At best you lose 87% and at worst you lose 94.5%

But this is wasted energy anyway, but it has to pay for manitanance and staff etc, so in the worst case it is terrible and the best case is sub-marinal. Looks like a free energy racket to me?

p1necone• 7 years ago

Are there many downsides to just lifting weights/pumping water up hills? What if you connected a lot of very large weights and electric motors to the grid and intelligently wound them up/let them down based on demand?

Maybe a two tiered approach combined with capacitors for fine tuning?

petschge• 7 years ago

The main downside is that you need a place to store the water at the top. Favorable geography is most likely already in use. And building new lakes on hill tops alters the ecosystem quite a bit.

SailingSperm• 7 years ago

This startup is stacking concrete blocks as a 'battery'

https://qz.com/1355672/stacking-concrete-blocks-is-a-surpris...

opencl• 7 years ago

Pumped hydro is by far the most commonly used utility-scale energy storage in use today. Efficiency is in the range of 70-80% so it's a lot better than compressed air in that regard, the main downside is that you just need a really large amount of water and a place to put all of it.

Lifting weights for energy storage is not really very conceptually different from pumped hydro (both store gravitational potential energy), water just happens to be vastly cheaper per ton than pretty much anything else. Concrete is something like $50 per ton and water is more like $0.50.

kerkeslager• 7 years ago

Vast size.

wahern2• 7 years ago

They're using a different process: https://en.wikipedia.org/wiki/Cryogenic_energy_storage Not particularly efficient, but doesn't seem to be as fundamentally broken as compressed air storage.

robocat• 7 years ago

Text from link: "In isolation the process is only 25% efficient, but this is greatly increased (to around 50%) when used with a low-grade cold store, such as a large gravel bed, to capture the cold generated by evaporating the cryogen. The cold is re-used during the next refrigeration cycle.[8] Efficiency is further increased when used in conjunction with a power plant or other source of low-grade heat that would otherwise be lost to the atmosphere. Highview Power claims an AC to AC round-trip efficiency of 70%, by using an otherwise waste heat source at 115 °C."

rklaehn• 7 years ago

There are lots of ways to get better efficiency for this process. One is to store the heat of compression in a gravel bed for use when evaporating the liquid air again.

Another way is to use waste heat from an industrial process to evaporate the liquid air.

It is also possible to use the cold to increase the efficiency of a combustion carnot process such as a natural gas turbine.

jp572• 7 years ago

It's not compressing the air, though, it's liquifying it (presumably only the nitrogen), and then using the force of the expanding gas as it boils later to drive a turbine. (I don't know why the author uses the strange phrase "freezing to liquid").

There's not a compressor. Well, there might be one in the refrigerator that "freezes" the air, but the air that is being used for energy storage is not, itself compressed.

In any case, as with any other energy storage, I don't think they're claiming it's lossless, but rather that the liquid nitrogen has a much higher energy density than compressed air. It sounds plausible, given that the gaseous to liquid volume ratio for nitrogen is something like 600:1, but I don't actually know. Might still have very high losses, I guess.

hinkley2• 7 years ago

I was under the impression that liquid nitrogen was typically created using a compressor. Is it more efficient to produce it cryogenically?

aurizon9• 7 years ago

The energy cost to freeze is similar to that of the multistage compression/expansion cycle. All the solid state cooling mathods are even less efficient, and you need a cascade. The only way this works is when the excess energy has to be sold at a loss due to baseload excess, and this would allow the power to be time shifted. This, as would other ways of load shifting, would work. Vertical storage via a gravity pond is far better as all stages have high efficiency. Battery storage also works well at high efficiency. https://www.csemag.com/articles/implementing-energy-storage-...

dredmorbius7• 7 years ago

Boyle's Law says that compression and temperature reduction are equivalents: PV = nrT

That is, increasing temperature is equivalent to increasing pressure, and vice versa: decreasing either is equivalent.

The problem with liquifying -- cooling -- a gas, is that:

1. You're removing thermal energy. Which itself cannot be usefully stored. So you're losing that unless it can be applied to some local low-quality heat process.

2. Re-gassifying the liquified air requires energy. If you've managed to store (some of) the removed heat, you can apply that. Otherwise, whatever you're using to introduce heat to the liquified air will itself get very* cold, very quickly, and eventually reach thermal equilibrium. Alternatively, you could apply a fuel-based heat source sufficient to boil off the liquid, but that's going to cost you energy.

Depending on the temperature of the freshly-generated gas, you're also going to be chilling whatever generating process you've got (probably gas turbine), which means both metal embrittlement and potential for frosting if there's any degree of water vapour in the air.

The more usual form of air-based energy storage, compressed air energy storage (CAES) likewise has problems with both heat loss and chilling on expansion. Compressing a gas heats it, and that heat will tend to escape to the environment, similarly to the case for chilling. On the energy-recovery side, expanding the gas to run a turbine will cool it (and the turbine) rapidly. Many CAES designs incorporate natural gas simply as a heating function to heat the freshly-expanded gas, meaning the storage system is not a no-fuel system, though it requires far less fuel than a conventional natural-gas generating plant.

The biggest issue I have with the system as described is that the re-expansion of liquified nitrogen isn't free, and requires a source of external heat. Given the phenomenally cold temperature of liquid nitrogen, any passive heating design will rapidly approach thermal equilibrium with the stored medium, limiting the rate of net energy release.

ramses0• 7 years ago

How would you power a weed-whacker via non-traditional methods?

AFAIK there are three main technologies in use today: gas, battery, and plug-in electric.

Assuming that gas is on the way out, chemical batteries have contamination/recycling issues, and plug-in electric isn't appropriate for all use cases (definitely less convenient).

I can't think of anything other than those technologies which comes remotely close to power a small engine for ~30 minutes at a time, once a week.

Will we ever get to "nuclear-powered" weed-whackers?

Wouldn't it be Great(tm) if there were the equivalent of AA/AAA rechargeable batteries but for larger devices? Maybe the 6-cell laptop format is the winner (but look at the variation in that use-case)...

kortex2• 7 years ago

I have an electric weed wacker, and for my purposes it works great. But even for more industrious weed wacking demands, I don't think small gasoline engines are contributing that much to global carbon.

Pollution and smog, otoh, two strokes are notorious for polluting.

Mirioron2• 7 years ago

Will we ever get to "nuclear-powered" weed-whackers?

I wanted to say "probably not", but I looked some stuff up and now I'm unsure. Essentially all small scale "nuclear power" uses a Radioisotope Thermal Generator. You essentially have a radioactive rock that generates heat and the heat difference is used to generate electricity through the Seebeck effect. The fuel that's typically used for this is Plutonium-238, because it almost exclusively decays as alpha particles (helium-4 nuclei), it has a half life of 87 years while being the most (of the long half life ones) energy dense at around 0.57 W/g. This is what's used in space flight missions and has actually been used to power pacemakers in the past with essentially no ill effect on the patient.

Pu-238 is still too heavy for the amount of power it generates for a weed-whacker. What changed my mind though is that apparently Polonium-210 also almost exclusively decays as alpha particles, but it has an incredible 140 W/g power density. The problem is that it has a half life that's only about a third of the year. It still could technically be used for a weed whacker though.

From a practical standpoint though, small scale "nuclear power", through RTGs, is way too inefficient for it to be used by regular people. Even if you eliminated all the risk of contamination, it would still only make sense for things that need to be running 24/7 that you couldn't swap out the battery on. Fission and fusion, so far, require a far larger plant to generate power.

fulafel• 7 years ago

You could just burn the whacked weeds as fuel and power a microturbine, micro steam engine or other something.

kragen• 7 years ago

As I understand it, they're refrigerating air, not compressing it. If so, your calculations are entirely inapplicable. Carnot efficiency approaches 100% as your cold reservoir approaches 0 K, so it's plausible for such a cryogenic system to get very high efficiencies from an air motor, much higher than normal.

oh-4-fucks-sake2• 7 years ago

Seems like you're pretty knowledgeable on the topic!

I'd be super interested to see an efficiency comparison between the frozen air approach and the "concrete (or any other cheap, heavy thing) battery approach" For the uninitiated: the process of using excess energy to drive motors to lift/stack heavy objects tethered to a pulley. Consuming that energy is by slowly lowering them down as they drive an engine/turbine.

As a rider, I'd be equally interested in the realistic energy density between the two methods: how many MWH can you store per acre.

Thirdly, I would guess the concrete battery would require less maintenance--but I'd love to see a comparison of that too.

Thank you for your comment and getting me thinking about this.

nine_k2• 7 years ago

Motors efficiency, an generators efficiency, can easily be 0.95, and even 0.98.

So overall the lift approach must be pretty efficient, even when we subtract losses for friction in the rope and of the air.

The energy density isn't great, though, you need really much mass, and large elevations, to store anything interesting.

Pumping large amounts of water uphill is more feasible, even if less efficient, and is actually done.

aurizon9• 7 years ago

Yes, pump motors and generators. so 96% motor and 96% pump up = are in the 95-7% efficiency, pumps about the same up or down. So .96 x .96(up) and .96 x .96 (down) = 84.9% and friction drops that a little. It is quite good if you hacve a handy high dam pond to use as many places do. To build a high dsm pong may not be economic unless you have a topographic valley you can dam and fill (and murder all the locals and flying snapping turtles) Dams have many objectors, so new ones are hard to build, except for China.

natmaka• 7 years ago

The 'concrete'-based approach (gravity storage) is pursued, for example by a firm named Heindl Energy https://heindl-energy.com/

There are offerings and deployed energy-storage systems based upon flywheels https://en.wikipedia.org/wiki/Flywheel_energy_storage

Taniwha3• 7 years ago

Remember that peak power is much more valuable than non-peak power (in some places non-peak renewable power has a negative value) so buying it at a discount, wasting most of it in the process, and selling it at peak time can still be economical.

Mirioron2• 7 years ago

If the numbers in the parent post are true, then you'd probably still be better off just pumping the water high up with that energy and letting it fall down when the energy is needed. On the other hand nabla9 quoted numbers that look very good.

Bendingo• 7 years ago

A compressor is an analog to an internal combustion engine - in reverse

A compressor is not the reverse of a IC engine.

IC engine is a heat engine, and the reverse of that is a heat pump (not a compressor).

Furthermore, Carnot efficiency refers to heat engine efficiency.

extrapickles• 7 years ago

They are referring to an internal combustion engine as a device that coverts heat/expanding gas->work, where the reverse is work->heat/compressed air.

aurizon9• 7 years ago

I beg your pardon. A Carnot engine is indeed a heat engine. The heat of combustion creates hot compressed gas - on which it runs by expanding that gas. A compressor is also a Carnot engine, you compress the gas and you must extract the heat from the hot gas or your air tank will fill with hot gas. As this cools, unless you can use that heat for other tasks, it is wasted. A carnot engine is not reversible. If you run it backwards you must submit to the equation and take your losses. They have been hard at work for almost 200 years trying to beat Carnot - he won them all, no survivors, but he gained immortality...

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

The Carnot cycle is a theoretical ideal thermodynamic cycle proposed by French physicist Sadi Carnot in 1824 and expanded upon by others in the 1830s and 1840s. read the wiki for more

nabla9• 7 years ago

https://en.wikipedia.org/wiki/Cryogenic_energy_storage#Effic...

In isolation the process is only 25% efficient, but this is greatly increased (to around 50%) when used with a low-grade cold store, such as a large gravel bed, to capture the cold generated by evaporating the cryogen. The cold is re-used during the next refrigeration cycle.[8]
Efficiency is further increased when used in conjunction with a power plant or other source of low-grade heat that would otherwise be lost to the atmosphere. Highview Power claims an AC to AC round-trip efficiency of 70%, by using an otherwise waste heat source at 115 °C.

aaron695• 7 years ago

Such energy storage technology could help relieve congested transmission lines in places like Vermont

Normal garbage form Scientific American.

It's either a good battery or it isn't.

What does Vermont have to do with it?

If anything it's an awful test, they obviously will have to update the congested transmission lines, then you have a expensive plant that's useless, if the congested transmission lines don't factor in then why are we talking about them?

CRYOBattery is being sold as a long term payoff battery that has a small footprint. Land is cheap around power stations, creating a dam and turbine is simple tech that works, I can't see why this is better and SA is not helping.

gwbas1c2• 7 years ago

No mention of efficiency...

Anyone know the efficiency? Batteries are in the high 90s, but are so expensive that they don't make sense for stockpiling. (Charge in the summer when days are long, discharge in the winter when everyone needs to turn on the heat.)

philipkglass• 7 years ago

They claim 60% in the basic configuration, or 70% if coupled with a low grade heat source:

https://www.highviewpower.com/benefits/

When I searched Google Scholar, I found this 2016 report from their first 350 kilowatt pilot plant at the University of Birmingham:

https://www.researchgate.net/profile/Adriano_Sciacovelli/pub...

That pilot project claimed less than 25% efficiency, but the authors seemed confident efficiency could be raised. A 5 megawatt demonstration plant has been running in the UK since 2018:

https://www.greentechmedia.com/articles/read/highview-power-...

I presume that the 0.35 MW and 5 MW projects worked reasonably well if they are now trying to develop a 50 MW project.

oever• 7 years ago

There's some recent videos about the Highview system.

Animation https://www.youtube.com/watch?v=Nu9zLOBi0-E

Interview https://www.youtube.com/watch?v=4hbyzuES5J0

Recent article https://www.theguardian.com/environment/2019/oct/21/uk-firm-...

timoth3y• 7 years ago

Efficiency needs to be viewed with target storage times in mind. For example, the reason batteries are not used for seasonal storage is not just because of their cost, but the fact that they lose their charge pretty quickly. They are 90%+ efficient in the short term, but that drops pretty quickly.

On the other hand, something like pumped hydro is less efficient and takes longer to bring online, but can store the energy for months or even years.

fyfy18• 7 years ago

takes longer to bring online

For anyone wondering how long that is, the largest pumped hydro plant in the UK can be at full capacity in 16 seconds from standby, or 75 seconds from cold.

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

dredmorbius7• 7 years ago

Efficiency is only one measure of a storage system's overall usefulness.

Other dimensions are total capacity, total cost, ramp-up / ramp-down times, storage and delivery rates, and various elements of technical complexity.

Batteries offer moderate-scale, fairly-expensive, moderate density, and relatively low storage and delivery rate, energy storage. They're exceptionally useful for mobile uses (from handheld to vehicular), but may not be as desirable for stationary systems.

There's a spectrum of energy storage options, ranging from capacitive storage (very responsive, but also expensive, inefficient, high-rate but low-yield.), flywheel, battery, physical mechanisms (pumped hydro, compressed / liquified air energy storage), and chemical (electrolysis, fuel cell, fuel synthesis).

If you're storing energy when it's abundant and releasing it when it's highly scarce, net efficiency doesn't matter nearly as much as matching generation and load capacity. Losing energy because you don't have the capacity or capture rates means a theoretically highly-efficient process is actually lower in net efficiency.

The duration of energy storage, ranging from a few seconds (capacitors) or minutes (flywheel) to proven-at-hundreds-of-million-years (hydrocarbon chemical energy storage) also matters. If you're trying to smooth out transients, capacitors or flywheels (mimicking "spinning reserve" or inertia) are your tool. If you're shifting over a period of hours, batteries, CAES, and pumped hydro come into play, with the latter offering long-term capacity of months if needed. Fuel synthesis could in theory allow shifting by years or decades, with very stable storage, though a net round-trip efficiency of ~15-20% (losses in synthesis compounding Carnot efficiencies of thermal energy generation, if used for electrical generation).

I've got concerns over LAES, well reflected in @aurizon's comment: https://news.ycombinator.com/item?id=21996594

Thermal losses in cooling, and the need to supply energy to re-heat the liquified air, make me question this method.

meatmanek• 7 years ago

This Low-Tech Magazine article[1] does a much better job of explaining the complexities of compressed-air energy storage, including different ways to minimize or harness adiabatic heating, though with a focus on home-scale installations rather than grid-scale.

1. https://solar.lowtechmagazine.com/2018/05/ditch-the-batterie...

8bitsrule• 7 years ago

From what I've read, winter heating consumes 40% of American households' energy budget. (A seldom-mentioned part of the big picture.) The heat extracted from liquifying air might be used for home-heating in a place like Vermont.

I recall walking by a city telecom building getting rid of excess heat, in the winter, by opening big vents in the wall. Meanwhile, apartment buildings around it were burning fuel to keep warm. There are many ways we can do this stuff better.

gwbas1c2• 7 years ago

I always wondered if mining crypto currency would be profitable enough to reduce my heating costs!

nkrisc• 7 years ago

Maybe! Just running my computer to game on raises the temperature in my office by about 3°F. My hunch is that a significant portion of that is from my monitor, as well.

dredmorbius7• 7 years ago

District heating and cooling, and seasonal energy storage, are both approaches to an integrated energy system which distributes needs over space (district) and/or time (seasonal).

District heating distributes heating (or cooling) from sites with an excess to sites with a need. Industrial processes are frequently utilised, though in sufficiently dense construction, office cooling can be a source of heating elsewhere. Many office towers have a net cooling load at all times of year, even under cold ambient conditions.

Seasonal energy storage banks heat from warm periods of year for use in cold periods. This may be completely adequate for general space heat, and sufficient for a large portion of higher-intensity heating (e.g., water). Storage may be in geological structures, if those are sufficiently stable (ground-water migration will also migrate out your stored heat), or constructed energy storage facilities, often little more than well-insulated water tanks with vertical thermal stratification.

Thorstein Chlupp of Rienna LLC designs zero-net-energy homes in Fairbanks, AK, utilising seasonal thermal energy storage. His videos run long, but are exceedingly comprehensive and explain in detail design and construction decisions.

Seasonal storage is covered here beginning at about 1h18m, to about 1h30m:

https://invidio.us/watch?v=AtHkvpRI6fc

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

kardos2• 7 years ago

Storing heat in a big water tank is certainly an option but it has drawbacks. I'm looking forward to developments in thermal storage in phase change materials and also storage via endothermic reactions.

im3w1l• 7 years ago

Maybe in the future we could use desalination/resalination for power storage. There is a lot of sea out there.

peteretep• 7 years ago

How would that work? Is resalination exothermic?

caf• 7 years ago

To the contrary, dissolving sodium chloride in water is slightly endothermic.

thaumasiotes• 7 years ago

In desalination, you're taking a substance that is literally worthless and turning it into something valuable (though cheap).

It seems unlikely that once you've got the water, the best available use for it would be dumping it back into the sea. (Which would be the easiest way to resalinate it -- since you're already desalinating, we can safely assume you're next to the sea.)

adrianN• 7 years ago

Perhaps they want to use https://news.ycombinator.com/item?id=21721049

ChuckMcM• 7 years ago

It is a fun idea, I tried to convince a large internet company to do something similar outside their data centers at one time, they chose not to bite.

A much better solution is this one: https://www.heindl-energy.com/wp-content/uploads/2017/10/Bro... it stores energy by pumping water into a tank to lift up a giant concrete piston. When you want the energy back you just let it down by running the turbo pumps.

The nice thing about gravity storage like this are that it doesn't need anything but a hole in the ground and existing hydroelectric technology. The down side is that it can freeze at low temperatures, you get some back because at the depth these cylinders would be dug there is significant below ground heating but there would be days when it would be too cold to run these things without warming them (and thus impacting your efficiency)

ul5255• 7 years ago

It's a nice idea but are there implemenatations yet except prototypes? I'm only aware of activities in Weilheim/Bavaria in Germany: https://www.haustec.de/energie/wie-pumpspeicherkraftwerke-im... and http://gravityenergyag.com/demoanlage-weilheim/ but this still looks like it will take a while to complete

gorgoiler• 7 years ago

Dinorwig in (under!) Snowdonia is another implementation of the idea, at a large scale:

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

rob74• 7 years ago

@gorgoiler: that's a "classical" pumped storage facility, not the concrete (or stone) piston version proposed here.

According to this press release https://www.stawm.de/energie/strom/speicherung.html, in April last year they were hoping to be able to start building the Weilheim prototype by December. The seal technology was undergoing trials near the Baltic Sea (translating from the press release).

While this sounds interesting, building the "cylinder" and the "piston" to fit exactly at the huge dimensions they are envisioning, and getting the seal to work at these dimensions and in the long term sounds like a pretty big challenge...

japanuspus• 7 years ago

Except recouping the CO2-expenditure of the concrete piston will take a long time. A simpler solution is to use the gravitational potential energy of the water directly. Pumped hydro, as this is known, is super simple if you have a mountain and maybe even an existing hydro-power plant to take the energy back out.

I have never checked this, but a Swiss friend of mine once explained the Swiss energy system as being centered around pumped hydro using free surplus power from the French nuclear power plants.

omegabravo• 7 years ago

that does look like a lot of concrete. I suppose ideally it would be a shell filled with the dirt removed to create the hole, even then it would be substantial at 150m in diameter (the smaller one)

InternetOfStuff• 7 years ago

Except recouping the CO2-expenditure of the concrete piston will take a long time.

When the idea was described to me it was proposed to carve the piston out of sheer rock (obviously requiring fitting geology).

achow• 7 years ago

Water batteries: Pumped hydro storage 'the unsung hero' of the US grid.

https://www.spglobal.com/marketintelligence/en/news-insights...

imtringued• 7 years ago

The entire point of hydraulic hydro is that energy capacity scales by r^4 (dimensions of the piston + height within the hole). It is possible to just carve out the piston head from existing rock with wire saws. Systems with 1.6TWh storage capacity are not impossible.

andy_ppp• 7 years ago

It seems like such a simple solution and could work extremely well, I just wonder what the downsides are? Could these systems be a maintenance nightmare in 10-15 years? It seems simple enough that we could roll this out today with enough money?

MrBuddyCasino• 7 years ago

Is that Eduard Heindl? He first proposed sawing cylinders out of natural granite mountains some years ago, seems he dropped that.

kitd• 7 years ago

The actual facility is one cost. Others include extending the grid to your new generators, and the benefit of the system in the article compared to those built out of mountains, etc, is that it can be easily built on the sites of abandoned power stations, which have all the infrastructure in place (or at least resurrectible).

I love these ideas though, including yours. As the article points out, it's definitely an investment area worth getting into.

Intermernet2• 7 years ago

Existing, but abandoned, mines also work as prospective sites. They usually have a large vertical drop, and they often have existing energy infrastructure "wiring" them into the grid.

I'd love to see some of the deepest mines in the world turned into gravity storage systems. Some of them are in areas that are amazing for solar, so you could hook the solar up to a motor to lift the weights, and then use the weight to power generators on the way back down.

Are there any motor designs that work close to equivalently as generators? If so then the system can be simple and self switching. If the energy from the solar is strong enough it lifts the weight, if it's not, it generates electricity.

syllable_studio3• 7 years ago

We're sponsoring a company working on a similar solution. We also believe that underground pumped hydro storage holds great promise. https://www.terramenthq.com/

syllable_studio3• 7 years ago

This is a smart solution - it's great that stories like this are getting attention. I'd like to share a similar project that I'm working on called Terrament. https://www.terramenthq.com/

Terrament is building underground pumped hydro energy storage (UPHS). Just like other pumped storage solutions, UPHS is extremely cost competitive (measured by LCOE, levelized cost of energy). It's extremely efficient (80-90% round trip). But unlike most pumped hydro, you can build UPHS anywhere. Just like this liquid air solution, you only need a couple acres of land. Many people assume this would use lots of water, but it doesn't because it's a closed-loop system.

I see that Heindl energy's solution was also mentioned above -- I love that design. Though, our analysis suggests that our design will give us better capacity.

Thanks everyone for your interest in this important field! This is not just a booming business, it's also critical for supporting the sustained growth renewable energy.

rwmj• 7 years ago

Isn't the classic problem with pumped hydro that you can't really store very much energy unless you have a huge amount of water or a large drop?

syllable_studio3• 7 years ago

Yup, though we don't consider it a problem, that's just the simple math. Our solution tunnels down 1 mile deep and excavates an underground reservoir. While this may sound extreme, it's entirely feasible and cost-effective. We can say that with confidence because we're basing our analysis on research from the U.S. Department of energy. We link to that research on our website if you're interested.

hedora• 7 years ago

They should be able to pull liquid CO2 or dry ice out at some point during the cooling process. That could be fed into a carbon recapture system.

I wonder if using this system for both carbon capture and energy storage is more efficient than using wind or solar to power carbon capture and charge batteries directly.

The energy to crack the CO2 into carbon and oxygen is probably the same either way, but concentrating atmospheric CO2 is energy intensive, and direct carbon capture would have to do that anyway — probably by cooling down a bunch of air, then releasing it. Perhaps another way to think about it is that carbon capture will create a large “waste” stream of cooled CO2-free air; perhaps converting that air to liquid is better than wasting the energy it took to cool it in the first place.

Either way, as the price of renewables drops, the problem of stranded/excess capacity will only grow. The atmosphere is way past the point where we need to use that capacity to pull CO2 out of the air.

To Store Renewable Energy, Try Freezing Air

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