storing thermal energy over long periods of time is a pretty lossy process, and that 75% efficiency number will be out the window if one tried to use this system for seasonal storage. this system fills the same space as battery storage, which it is also marketed for (over night storage for solar power).
here is a more detailed post on the matter: https://www.rechargenews.com/energy-transition/new-co2-batte...
citing from this: "In Energy Dome’s system, carbon dioxide is compressed at a pressure of 60 bar which heats the gas to 300°C liquid. The heat is then extracted and stored in “bricks” made of steel shot and quartzite for later use, cooling down the CO2 to an ambient temperature. The gas is then condensed into liquid form and stored in carbon-steel tanks.
‘Our lithium-ion battery will have double the energy density of standard Li-ion for same price’
When electricity is required, the liquid CO2 is run through an evaporator to turn it back to a pressurised gas, which is then warmed up back to 290-300°C causing the stored heat."
Lastly, it's worth remembering that not everything is competing against an "optimal" solution. This may be a _very_ viable system for infrastructure that simply sheds excess energy. Shedding of excess energy results in 0% efficiency gains. Additionally, this type of storage potentially offsets the need to run a secondary system for peak/off-cycle loads. That in itself can be a massive energy savings.
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Finally, it seems that power plants are actually terribly inefficient at converting an energy source to electric. Coal - 33%, gas - 42%, and combined cycle - 60%.
http://needtoknow.nas.edu/energy/energy-sources/fossil-fuels....
They're not storing heat. They're dumping the heat, and store liquid CO2 near ambient air temperature. Here's some analysis of CO2 liquefaction cost, from an unrelated project.[1] You can have multiple stages of compression, with heat exchangers between them to get the temperature down. How to set this up is a good homework problem in thermodynamics.
It's not clear if this is profitable, but it's a lot better than some of the other ideas. Ones such as the crane and concrete block thing, or the electric trains full of rocks on a hill thing, or the giant rock cylinder with water underneath thing.
[1] https://www.researchgate.net/publication/293044124_Simulatio...
The mine shaft things are not obvious losers, but suffer by inability to re-use the expensive part for multiple mineshafts. There are undersea methods that do better, sharing the expensive, onshore equipment among as many simple undersea units as you like.
The scheme described in TFA has the advantage that the tankage needed for an unlimited amount of storage is cheap, with only the total wattage rate in and out limited by initial investment. Tankage underground (e.g. in salt domes) could store the CO2 and the heat in the same place, without losses; earth is excellent insulator. They specifically say in TFA they are storing the heat of compression by pumping it into iron.
The Chilean project storing energy in liquified nitrogen is similar. They also say they are banking heat, even though boiling the nitrogen with ambient air on the way out, in a "warming tower", seems to me more practical.
75% round-trip efficiency is absolutely fine. Pumped hydro is not better, that way.
There is an unfortunate habit in the energy sector of promoting ideas in absurdly expensive form, just because that makes it look more "hi-tech", to be taken more seriously by investors attuned to look for that. The form of each idea actually built and used by utilities will be whichever form is cheapest, which will seem too boring for the press to pay it any attention.
or did the source simply explain their process incorrectly?
Also the same reason elephants can't have metabolisms as fast as mice, or else they would spontaneously combust.
I mean, the process is simple, clean, does not require special materials, provides lots of jobs and really seems long term.
The holy grail of energy storage will ultimately be a similar form (compressed gas, fuel generated with solar power, heat reservoirs, etc).
No matter how much you root for batteries, they will not provide grid scale power.
Beyond a week, burning liquified ammonia imported from tropical solar farms wins. Probably you keep a week's worth of that on hand to burn while you wait.
There is no need for storage (beyond use for load-leveling and peak shaving) until after renewable generating capacity is overbuilt enough to charge it from. (The alternative would be to recharge storage by burning NG: You would better burn that NG and deliver the power to users instead of drawing down and then recharging storage from it.) Until then, capital is better spent building more renewable generating capacity itself, displacing more coal, than on storage.
But building the factories that will build the storage that will someday be needed should happen now, because we will need a lot, and making automated factories takes a long time. And that is happening. Some of those may end up idle as cheaper methods replace theirs, but for at least a few decades, demand will be insatiable.
Edit: I clarified that I meant the amount of energy stored not how long the gasses themselves can be stored. "Long term energy storage", to me, should be defined as being able to discharge at max power for like a day or more, and this tech is more "medium term" storage, again in my opinion.
From the article: "many hours up to many days"
> "Long term energy storage", to me, should be defined as being able to discharge at max power for like a day or more,
"Long term money storage" should be defined as storing more than $10 000 - yes, no, or irrelevant?
Your example should be more like “a long term emergency savings is 6 months of your budget” vs. “a short term emergency savings is 2 months of your budget”
> Energy Dome’s novel approach to long-duration energy storage dispenses with batteries altogether. Instead, the company erects enclosures that resemble tennis bubbles and fills them with carbon dioxide gas. Excess electricity can be used to pressurize the gas into liquid form, storing energy; turning the liquid back into a gas releases that energy, turning a turbine and regenerating electricity.
> As detailed in Canary Media’s previous reporting, this approach has a few advantages relative to other long-duration storage attempts:
> It uses off-the-shelf equipment from mature industrial supply chains. That means Energy Dome doesn’t need to build its own factory, a capital-intensive step that other long-duration startups needed to do. It also means Energy Dome doesn’t need to spend years on laboratory science — it just needs to prove that the equipment all works together the way it’s supposed to.
> The dome is supposed to deliver round-trip efficiency of 75 percent, meaning 75 percent of the energy that goes into the process comes back out at the end. That’s less than typical battery efficiency but a lot better than many long-duration storage contenders.
> Carbon dioxide is easier to compress and store at ambient temperature and atmospheric pressure compared to other gaseous storage vehicles, like hydrogen or air.
That's what the dome is for, storing the uncompressed gas. Presumably there is a much smaller metal pressure vessel for storing the liquid CO2.
When people make up stats, they use numbers like 63% or 87%, not 75%.
EDIT I guess compressing to liquid, CO2 can be stable at <31 deg C at 5ATMs which is what they use. Liquid Nitrogen has to be kept very cold, even under pressure.
CO2 phase diagram: https://www.wolframalpha.com/input?i=co2+phase+diagram
Nitrogen phase diagram: https://www.wolframalpha.com/input/?i=nitrogen+phase+diagram
You can see that CO2 is way more reasonable to store liquid at ambient temps.
Insulated low-pressure tankage is cheap.
It will be interesting which will turn out more practical.
It would look like a good idea only if they somehow compel their customers to buy only CO2 coming from a direct-air-capture facility.
Or even better, if they attach a small direct-air-capture device to their "bubble". (it would not need to be extremely efficient, as I understand that the CO2 is then captive of the storage [I'd add... in a normal operation mode... because we never know what can happen with incidents and that's why I push for DAC before it's too late and it's already everywhere])
(I'm assuming here that not all of their emitted CO2 is long-term stored, otherwise of course that also solves another problem)
Can we both fight for the disappearance of the chimneys, and depend on them?
At the very least, we need to be ready for the absence of these chimneys as if it could happen overnight, for the simple reason that we really need for it to happen overnight (it won't, but that's bad, and we need to keep thinking it's bad).
(I precise: I would be completely in favor of a total PSCC, it's just that I think that a partial PSCC for any chimney is a bad path)
Hydraulic hybrid vehicles recapture 75% to 80% of braking energy for reuse, which compares very favorably to electric batteries.
Something like this paired with intermittent sources like solar and wind could make them viable.
Or, in volume, whatever turns out cheapest will. Zero opex will beat mined and transported NG pretty quickly once enough renewables + storage is built out.
A system like this makes a nice pairing, but then you need double the capacity of intermittent since when it is working it needs to not only feed the load, it also needs to feed the storage.
It's not long term storage, though, like diesel, gas, coal. Those can sit around for a really long time.
EDIT
Actually, since the system is 75% efficient, you will need more than double the intermittents.
Many places don't have a lower and higher reservior needed for pumped hydro. This can be sited almost anywhere.
It will all come down to what is cheapest, overall. That will take time to learn. If opex is cheap, a more expensive will remain equally useful as a method that turns out, eventually, to be cheaper to build.
Because by definition, any long term storage solution will be able to sell energy and make a profit only a few number of times, and won't be able to recoup its CAPEX expenditure.
Let's say that by long term you mean 6 months (the typical period envisioned, i.e. you charge during the Summer months, and sell during the Winter months). Then you'll be able to sell energy once a year. If your system has a lifetime of 20 years, then you need the CAPEX to be only 20 times higher than the annual profit.
Let's further say you charge during Summer at zero cost, and sell during Winter at 40 cents/kWh (this is about 3 times the average cost of electricity in the US for 2021). Then the cost of this system should not be more than $8/kWh. For comparison the cost of a Tesla Powerpack is about $700 /kWh [1].
So for any system to have any hope to be "long term storage solution" it needs to be 100 times cheaper than the Tesla Powerpack.
In reality it needs to be about 1000 times cheaper, due to numerous other factors: less than 100% round-trip efficiency, the high cost of financing (driven by the significant risk of the project, which is driven by the huge uncertainty regarding future potential competing technologies, such as Hydrogen), operating and insurance costs, etc.
There is a way to solve the long term storage system. You need to solve the apparent paradox that if your system is designed to be long term, then you can't buy and sell very frequently. Here's how you solve it: you buy and sell in different markets. You buy (solar) electricity in Morocco pretty much all year long, convert it to Hydrogen, or some other form of chemical storage (ammonia, hydrogen peroxide, methanol, synfuel), and ship that to Germany, where it is converted to electricity, again all year long.
This way, you buy every single day and sell every single day. You are able to recoup your CAPEX costs, and make a handsome profit.
There are no other ways to solve the long term storage problem.
The EU knows that, and this is why it is betting so heavily on Hydrogen.
[1] https://electrek.co/2020/03/31/tesla-powerpack-price-commerc...
A pure storage play using does not need to be viable. Utilities will integrate generating capacity and storage to deliver on service level agreements.
But synthetic hydrogen and ammonia shipped around will be a huge market, not least because they are massively useful for other than for banking energy.
Here's [1] the solar electricity production by month in Germany. It's about 6 times higher in the Summer compared to Winter. The situation is the same everywhere on the planet at similar latitudes. It's worse at higher latitudes. Unfortunately, a lot of the world's population lives exactly at those latitudes.
You could say that you supplement with wind, since wind does not have the same seasonality problem. But then why build solar at all? If you build solar, then you will have a winter deficit, and you will need a Summer to Winter storage solution.
[1] https://www.iea.org/data-and-statistics/charts/monthly-gener...
https://weburbanist.com/2013/06/30/ziggurat-hat-deconstructi...
The headwear and the energy storage company appear completely unrelated aside from the name chosen.
But there are a lot of different costs: capex and opex cost per kWh to store energy, capex and opex cost per kW to bank energy, capex and opex cost per kW to extract energy, cost for conversion losses, cost for banked energy losses, plus extra specific costs and sometimes specific benefits. Some of those costs will change radically with time as circumstances change; cost for conversion losses of all methods will fall as top line generation gets cheaper.
This is why synthetic fuels will be so important, despite low efficiency and high capital cost: the "specific benefits" exceed those.
Operating this thing via captured CO2, and feeding hydrocarbon synthesis and carbon sequestration, might improve its viability.
Also, I would guess that regulations mean these are built in remote locations.
