To Store Renewable Energy, Try Freezing Air
scientificamerican.com
scientificamerican.com
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)
I love these ideas though, including yours. As the article points out, it's definitely an investment area worth getting into.
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.
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.
Efficiency of around 80% (comparable to pumped hydro), capacity of 8GWh for a 250m diameter piston.
When the idea was described to me it was proposed to carve the piston out of sheer rock (obviously requiring fitting geology).
https://www.spglobal.com/marketintelligence/en/news-insights...
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...
Why is this not being done more?
1. https://solar.lowtechmagazine.com/2018/05/ditch-the-batterie...
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.
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...
They are insulated like a thermos (but more efficiently), and since they are really big, they have small surface area compared to their volume.
It is a VERY efficient way to store heat over shorter periods, like a week or so, and it helps making power plants more cost efficient.
The best way to make it efficient for long term storage (like seasonal storage) is to
1. Make them huge
2. Make them ball shaped
3. Put them underground
There has been talk of tryibg this out in Denmark. Almost all our powerplants (i.e. the not-really-old ones) are combined heat and power plants, and because we use district heating water to create a vacuum behind the power producing turbines turbines (instead of sea water) we go from a theoretical limit on the energy efficiency of around 60% to 98%, as we do not pump out the excess heat into the sea.
Newer combined heat and power plants have an energy efficiency of around 95% to 96%. The trade of is a slightly lower vacuum, meaning less production of power. However, we can scale up heat production to reduce costs of running power plants when energy prices are low (or even negative).
The entire tank is packed within gobs of insulation. Cheap bulk insulation, rather than vacuum insulation, is effective, and additional volume accomplishes what the more expensive though thinner alternative delivers.
I worked for a major Danish power company for 2.5 years, but I mostly did mathematical modelling and implementation of the production planning system.
That more or less puts it out of reach for homeowners, condo dwellers, etc. You need a big expensive coordinated project to get that built.
Meanwhile, as an analogy, solar panels are within reach for a homeowner. Seasonal thermal storage will need to be more modular / modest sized for it to be widely applied. The potential for storing heat by forcing endothermic reactions (where you later extract it by running the reaction in reverse) has a lot more potential to be "homeowner sized".
Retrofits are possible, though with compromises to both extant structures and building envelope and passive energy systems.
Since efficiency of storage scales with size, community-based (neighbourhood-scale) thermal storage is an option. This allocates storage across a number of local structures, at the scale of tens to hundreds of structures per storage structure.
Similar notions apply to electrical storage, e.g., neighbourhood battery facilities. This works well for battery designs (e.g., liquid metal, molten salt), which are too technical and risky for safe household deployments, but could be deployed in clustered units with dedicated technical expertise.
There are phase-change and transformational materials. Most complicate the process markedly, and may degrade (through loss or contamination) over time.
Only liquid-solid phase-chane is likely to be useful as liquid-gas volumetric expansion tends to 1:1000, leading to very large volume, or high pressure, or both, considerations, with corresponding costs and risks.
Aqueous thermal storage is remarkably inert. Small leaks are harmless, large leaks leave no long-term toxic legacy, pressures are ambient, materials are mundane, systems, monitoring, and controls simple, well-developed, and well-understood.
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.)
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.
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-...
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.
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.
(Interesting side note - when I took a tour of Dinorwig some years back, the guide said that when the facility was built it rarely needed to run more than 1 turbine - now they routinely fire up all 6. At some point it will run out of capacity...)
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.
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.
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?
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.
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.
Condensation of the (now gaseous) nitrogen within the turbine would all but certainly result in significant cavitation effects, as well as create a very low-pressure zone on the exhaust side of the turbine, which would probably not be conducive to normal operation.
Heat of vapourisation is not free, and would have to be supplied, somehow.
https://energyeducation.ca/encyclopedia/Carnot_efficiency.
He essentiallt states that you can only get a certain maximum % out of exnapsnio engines if you expand them to absolute zero in a vacuum. Since you expand to room temperature and pressure, the equation determines that efficiency. That is why car engines are 35% or efficient. Specialized constant speed diesels a bit better and turbines close to 60%
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.
There are offerings and deployed energy-storage systems based upon flywheels https://en.wikipedia.org/wiki/Flywheel_energy_storage
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.
BTW one solution is to use existing hydro dams as partners to wind/solar, add extra generation capacity to the dams, share the transmission infrastructure between the wind/solar/hydro and simply let the dams fill when the wind blows/sun shines. That's more efficient than pumped storage
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.
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
How do you mean a Carnot cycle isn't reversible? You can run the cycle in either direction. That's not the same as saying is has 100% efficiency.
>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.
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)...
Pollution and smog, otoh, two strokes are notorious for polluting.
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.
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.
Maybe a two tiered approach combined with capacitors for fine tuning?
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.
On a more general note, I think the issue with these novel storage methods is that even their more optimistic $/kWh targets are barely competitive with existing battery prices. And due to manufacturing scale, battery prices are expected to continue to decline. A similar thing happened in the solar market. Prices were really high, which led to a bunch of startups attempting to bring novel technologies to market (Solyndra was one of them), but once China started flexing its manufacturing muscle, PV prices dropped and the novel technologies had no hope of competing.
Although I suspect for the quantities involved, it still may be impractical.
Favorable geography ON RIVERS is limited. Off rivers, the possibilities are enormous and largely unexploited.
https://qz.com/1355672/stacking-concrete-blocks-is-a-surpris...
Side note, the article has a comment about peak summer power usage that made me laugh out loud:
> For example, Mumbai hits peak consumption in the summer when air conditioners are on full blast, whereas London peaks in winters because of household heating. Ideally, energy captured in one season could be stored for months during low-use seasons, and then deployed later in the high-use seasons.
It seems hilarious to talk about storing power to run AC in order to solve an excess of heat problem. I honestly feel bad for people who die in heat waves in large cities, but it seems pretty absurd that we’re not already running AC cooling on solar like everywhere.
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.
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.)
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.