'Freeze-thaw battery' stores electricity long-term for seasonal release | Hacker News Reader

'Freeze-thaw battery' stores electricity long-term for seasonal release

eandt.theiet.org

122 pointsOJFord100 comments

For more on the general problem of storing thermal (rather than electrical) energy on a seasonal basis see

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

I was especially surprised to learn that serious attempts at storing heat in soil and rock have been made

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

which in the winter is able recover >40% of the energy stored in the ground through boreholes in the summer ("BTES Efficiency")

https://www.dlsc.ca/reports/swc2017-0033-Mesquita.pdf

Furthermore, we have a real problem with the soil storing heat: https://citymonitor.ai/transport/londons-tube-has-been-runni...

Stupid question: can we harness this 100 year old heat to power something today?

You can't exactly harness heat; what can be harnessed is a temperature differential, to convert into some form of mechanical motion or electrical potential. You'd need some apparatus that connects the hot mass and some cold sink with thermocouples. Whether that's possible or feasible on the scale of the London Tube, I don't know.

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

Instead of that, probably a more feasible way to make use of heat is just as heat, by some way of circulating it into buildings in the winter. One interesting angle of looking at this would be that it's really an artificially created geothermal source.

An additional dumb question. If all the expense was undertaken to build all the piping to functionally turn the tube into a heat source for buildings, how long would it take to sap the stored heat from the soil to the point where the temperature differential doesn't work anymore? At some point would they have to switch from having it be a heat source in winter to making it a heat dump in summer?

Heat is energy, so I find it surprising that it can't be harnessed. Is it really not possible to take some of the energy out of a system and use it for something?

Not all heat is useful. If there was a magic device that could take any heat and convert it into electricity, global warming could be trivially reversed.

There is the Seebeck effect, where you run a Peltier junction in reverse. Efficiency is, to put it mildly, low. [1]

[1] https://en.wikipedia.org/wiki/Thermoelectric_generator

This still works from a temperature differential, not just a quantity of heat.

furthermore you could prevent the heat death of the universe :)

Air conditioning is really silly when you think about it. It takes a ton of energy to move some energy outside. It feels like it could be self powered.

It's actually forcing the energy apart. The energy wants make this one big mess where every bit is the same temperature as every other bit.

Your AC is working hard at pushing all the heat outdoors and making a pocket of cool inside.

Self-powered evaporative air conditioning is an ancient technology.

Air conditioning as we understand and use it today is a gold-plated band-aid over bad design. It's so entrenched you almost can't get a house built any other way.

If it got hot enough you could use a geothermal-type generator for reasonable efficiency, but that is (of course) still exploiting a temprature differential (a place where water remains liquid, and a hot place where it becomes high pressure steam to drive a turbine). However sadly that is unlikely to happen before the tunnels become unlivable :)

Yes

https://www.newcivilengineer.com/innovative-thinking/harness...

Pump cold air down, suck warmer air up, heat buildings in winter. Same idea lots of passive houses use to regulate temperature.

Storing heat in rock is very natural. It's how geothermal works, after all.

The basic idea is that the thermal time constant of a uniform sphere (or other shape of fixed aspect) is proportional to the square of its radius. So, for a sufficiently large sphere, the time constant can become very long, >> 1 year. Rock is a good choice because it's very cheap.

The other thing one can do is store cold. This is useful not only for cooling, but for increasing the efficiency of storage of work, since one can generate heat and cold via a heat pump, then reverse that cycle to recover the work. An efficiency of 65% or so may be reasonably achievable with the high temperature in the temperature range of ordinary steel.

> The basic idea is that the thermal time constant of a uniform sphere (or other shape of fixed aspect) is proportional to the square of its radius.

Shouldn't the thermal mass go like volume (radius cubed) while the power conducted away go like surface area (radius squared) so the time to cool should go like mass/power ~ volume/area, so linearly in radius?

The rate at which heat conducts out is also affected by the temperature gradient, which is inversely proportional to radius.

It doesn't sound like the improvement of cost is enough the justify using it only for few cycles a year as the title says rather than every other day. That said, I see nothing in this article saying why it would be limited to seasonal release, I'm guessing it just has a lower self-discharge.

The title made me thought of an idea my father had, for which I'm still totally ambivalent:

Freeze water in the cellar (speaking of like 30m^3) using thermal pomp during winter to heat house and when electricity costs little, and use that ice in summer to cool down the house. I didn't run the numbers, but I'd guess that if it was even remotely not a pure energy loss some other people would have already proposed such things.

> Freeze water in the cellar (speaking of like 30m^3) using thermal pomp during winter to heat house and when electricity costs little, and use that ice in summer to cool down the house.

Unless I misunderstood, the Toronto Zoo has or had such a system setup for one or more of the food pavilions.

What's interesting about this is that the storage grows with the volume (n^3), but the heat/cold loss grows with the surface area (n^2). So you're ability to 'store cold' gets better as you get bigger.

Just the same, you could also use it backwards in the winter time. On hot, sunny days at the end of the summer, warm up the water stored.

> On hot, sunny days at the end of the summer, warm up the water stored.

Phase change stores/requires much more energy than simple temperature change. 0°C Ice to 0°C water transition is 334J/g, 0C water to 100C water is ~400J/g (ie 4J/g per degree C), 100C water to 100C steam is 2260J/g.

To store heat from the summer for winter warming (say best case 40C summer temp) you'd be looking at least 3x as much material for heat storage vs ice storage for summer cooling (at say -10C)

This is a useful thing: storing energy in a phase change makes it easier to keep the energy stored for a longer period of time compared to if there was no phase change. The difficult part is that steam is much farther from ambient temperatures than ice is (and also that it is far less compact). Newton's law of cooling means that the larger the temperature difference, the faster the heat loss, so steam would require much more insulation than ice would.

Besides insulation, there's no hope of storing thermal energy as steam because the density is 1000 times lower than ice or water while the specific heat is similar, so the heat capacity per unit volume is about 1000 times lower.

Storing heat as steam is actually very good and efficient - as long as you're storing the heat for location shifting, not temporal shifting. It's regularly used in combined heat + power plants

(Yeah, I know I'm being both pedantic and off topic, since the discussion here is specifically about seasonal storage)

Doesn't the word "storing" already mean temporal shifting?

The cube/square law also applies in the opposite direction, this is why it takes longer for lakes to freeze and why the Great Lakes never do.

I believe at least one university on the Great Lakes does heating and cooling with pipes deep under the lake.

The Great Lakes do occasionally freeze over significantly, though never completely. 2013-2014 was one such winter, when ice coverage reached 92% across all five lakes. That's quite unusual though.

And the city of Toronto uses lake water for cooling. Heat from a downtown cooling loop is dumped into the city's drinking water supply, bringing the temperature up to around 13° from 6° (if I remember correctly).

Not just drinking water. The cool water is pumped into buildings to work as the air conditioner for a lot of the big buildings.

How does this compare to hauling ice down from a local mountain lake?

Feels like 0-18th century tech. Doesn’t mean it’s bad though.

Don't forget that, until the invention of refrigeration, people used to harvest ice in northern climates. They would store it in hay, and then sell it throughout the year.

Ice was even shipped internationally.

(And, if you're a fan of Disney's Frozen, this is exactly what Sven did.)

Congratulations, you just invented geothermal heat pumps. :) They’ve been the preferred way of hearing single family houses in the Nordics since the 90s.

This exists and is actually used in Germany, it is called "Eisspeicher" (ice storage). It is utilizing the effect that it takes a huge amount of energy for the water to go from solid to fluid, about the equivalent of heating water from 1 to 81 degrees.

MGAThermal does this with a range of materials, allowing heat storage at very high temperatures. https://www.mgathermalstorage.com

Similar systems are actually being build, but with a bigger scale (like big office buildings). There is no freezing involved, just heating the office space with warm water in the winter (cooling the water to ~10°C) and cooling it in the summer (heating the water to about 40°C).

During the rebuild of Christchurch, NZ they used this technique for a number of buildings, basically pumping out water with one well, then re-injecting it with another as I understand.

Essentially exploits the ground water remaining a constant temperature year around, warmer than the surface in winter and colder in summer

Your father's idea is a good one. Here is a thermal heat pit which is being used to store heat for the winter:

https://stateofgreen.com/en/partners/ramboll/solutions/world...

> some other people would have already proposed such things.

Geothermal heat pumps. Been around for decades. Expensive to install due to drilling the well or laying the field, but very efficient.

Geothermal energy is risky AF though. Even with shallow drilling depths, you risk hitting anhydrite and, in combination with water, massive damage like in Staufen [1].

[1] https://de.wikipedia.org/wiki/Hebungsrisse_in_Staufen_im_Bre...

The large portion of single family homes in Sweden are heated (and cooled) using geothermal heat pumps. The drill holes are 100-150m deep.

Geothermal energy for power generation and heat pumps for heating homes are totally different systems. It's like comparing a fireplace in your house to a nuclear power plant.

I think there is terminological difference between ground source heat pumps and geothermal energy. First is in actuality naturally stored solar energy. Where later is from internal activity of earth.

There's a few large building air conditioning units that do exactly this. Ice Bear was one brand name I think.

Just realized that with a battery intended for seasonal storage you only get one cycle per year so for the same ROI as a battery that cycles weekly or daily it has to be much cheaper per kwh of capacity. OTOH it only needs to last for like 50 cycles.

I like to imagine a system with the different geothermal-like technologies working together in maybe a layered like structure.

Extracting from the winter / summer cycle, the day / night cycle, and the consistent deep ground / surface air temp differential.

Granted day / night might not have enough variation to take advantage of in a lot of places - but surely some cool tech has come out of desert areas right?

Arid locations already enjoy much cheaper cooling via swamp coolers over heat pumps. They're just enough to keep it bearable during the day, then the night comes and clears out all the latent heat.

I wonder what the napkin math is vs something like methane synthesis.

I think you’re on to something with that. With so few round trip conversions compared to something that is charged/discharged frequently, the conversion efficiency doesn’t matter as much compared to the cost of storage.

For a given kwh of storage that is round-tripped daily, a 1% loss of efficiency loses 3.65kwh per year. For a kWh of storage that is round-tripped once per year, you only lose 0.01kwh. At 70% conversion efficiency the yearly storage still loses only 1/10 the energy as a daily system at 99%.

Tangent, but in the seasonal storage context.

Apparently, according to a reported simulation, if you (1) take a ca 15m x 15m house thermally in contact with the ground, (2) insulate the ground outside to a radius of ca 40m, and (3) heat the interior to say 25C, then (4) evenually (50years?) the ground itself under the house will come up to a steady temperature consistent with that.

Even if the simulation was correct, I can only see this being sustainable with solar gain being used for heating, but it makes for an interesting long-term-oriented picture.

One imaginable scale of application could be for a cluster of houses in a larger agricultural setting.

Gradual heating of the ground is definitely a thing; over the decades, certain London Tube lines have drifted from pleasantly cool to sweltering: https://www.wired.co.uk/article/central-line-temperature-lon...

Yes, people are literally dying in the heat from heart attacks because city planning won't allow TFL to knoxk down a house sp they cam build a ventillation shaft

Do the tubes never cross a road? Why knock down a building instead of taking a vent to a street?

I think you're underestimating the size of vent needed.

They'll turn the entire plot into a single giant chimney, and decorate the face to match the houses either side of it.

like this:

https://en.wikipedia.org/wiki/58_Joralemon_Street

Ah I was thinking of the subway vents you see along the street and sidewalks in New York. That is indeed a drastically different scale.

I'd love to read more about this simulation, have any links?

I am unable to find a link, and IIRC this was reported 10 years ago or so. I recall an attribution to German designers or architects. I cannot remember where exactly it was reported, but I remember it as moderately plausible reporting, although not in a journal.

A quick estimate with soil:

Take a specific gravity of 2.7 gm/cm^3, a specific heat of 0.2 cal/gm-K, and 1 cal ~ 4.2J ~ 4.2 W-sec. For a cube 25 m (2500cm) on a side, if I am not mistaken this suggests a thermal inertia of about 3.5E10 W-sec/K.

Now take a thermal conductivy of 1 W/m-K. For a slab of 25m x 25m, also with a thickness of 25m, we get a net conductivity of 25 W/K .

Then 3.5E10 W-sec/K divided by 25 W/K gives 1.4E9 sec . Given 3E7 sec/year, that suggests about 47 years.

Aka a 50 year time scale.

Of course this assumes a low water table.

Is there any examples of using something like a server farm to heat a building in the winter? Removing heat from a server farm through heat exchange with a cold building seems like an efficient combination of two interests (building needs heat, servers need to get rid of heat). Of course this becomes a problem in the summer months...

Stockholm, Sweden has an open district heating network: buildings can not only buy heat from it for heating, like a normal district heating network, they can also sell surplus heat to the network. At least two data centers (Bahnhof Thule and Bahnhof Pionen) sell heat from their heat exchangers to the network.

https://celsiuscity.eu/wp-content/uploads/2020/06/Waste-heat... pages 7-9

In Amsterdam, the botanical gardens and Hermitage Amsterdam exchange heat in that sort of mutually beneficial way, https://www.cultureelerfgoed.nl/onderwerpen/praktijkvoorbeel....

This is actually one of the use cases that Satoshi Nakamoto spoke about in regards to Bitcoin mining.

The purpose built machines for mining (ASICs) turn electrical energy into heat through performing hashes. If you need electrical heating there's functionally no difference between turning a regular heater on or turning on an ASIC. The benefit of turning an ASIC on instead is you can recoup some of the cost of expending the electricity.

The issue is that modern heat pumps are way more efficient than just a resistor. Not something that was obvious in Nakamoto’s day. Even gas furnaces are more efficient due to transmission losses.

If your house is one of the few that have an electric furnace, there’s no difference. For most people, though, there’s a huge difference. Running an appliance such as a computer to heat a house will cost more and be worse for the environment.

Wasn't it obvious in 2007 (or even 2000)?

A French company made a product along these lines already, but I don’t think it’s been updated since 2018: https://blog.qarnot.com/introducing-the-qc-1-crypto-heater/

It’s true this is as good as resistive heating in terms of heating efficiency, but it is still far less efficient than a heat pump. Unless you are in an area with a large excess of renewable energy it probably doesn’t make sense environmentally to use an asic heater.

One might use a smaller version as a space heater, rather than for primary heating. In that context it isn't really competing with heat pumps; space heaters are usually resistive.

It looks like the same company still makes some products that leverage waste heat from computation (https://qalway.com/fr), just not ones that specifically mention crypto as the source of the computation.

One of Amazon’s buildings in Seattle (Doppler) uses a data center next door to reduce their overall heating costs during the winter.

Source: https://www.aboutamazon.com/news/sustainability/the-super-ef...

This doesn't seem cost efficient at all, my (medium sized) house in Germany consumes about 3000kWh of electricity during winter. This does not include heating, which consumes another 15.000kWh (of heat energy from oil, so around 5000kWh electrical energy with a heat pump).

If I were to use this battery I would need to get 3000(8000)kWh of energy storage at 23$ per kWh which would amount to 69000(184000)$. There are better hydrogen-based solutions for that cost. Also, did I read correctly that I have to keep the battery heated to 180°C during discharge? This is going to waste a lot of energy in winter.

You're assuming that the battery needs to store the total energy requirements of a house for the entire year. Much of the time the energy needs can be met by conventional energy generation (wind turbines, solar, hydro, etc) and the battery is only called upon when there's a shortfall. So you'd only need a fraction of the annual consumption to make it useful. The whole idea is to make renewables more effective by storing the excess. Grid storage will be an important part of the transition to renewables.

But yes, it is expensive, but it's only at the R&D stage. I'm sure could be made cheaper, and the article mentions reducing the cost to $6/kWh.

If you use solar power in a climate like Germany you will get that kind of math.

Let's say you use 8000 kwh per year, and you have the solar capacity to create 8000 kwh per year. Assume you already have a normal home battery of ~14kwh so day/night is not an issue, the solar production during daytime charges the battery and all night time power comes from the battery.

Now your big problem is that 70% of the 8000 kwh solar per year is produced from May to September. You need 670 kwh per month for usage, so in those four months you have just under 3000 kwh too much. Then in April and October the panels roughly produce what you use. And November to March you have a total shortfall of 3000 kwh.

So you need seasonal storage capacity of about 3000 kwh to be able to run an 8000 kwh yearly usage on solar in this climate.

The other option is to buy much more solar panel capacity than you need, then you can use a smaller battery which in total could be cheaper since solar panels aren't that expensive anymore.

> The other option is to buy much more solar panel capacity than you need,

You need the space to install them also. I have a 6.6kW array, and would need 3x that capacity to heat my home using electrically-powered air source heat pumps during the winter months. Even with 0.75 acres / 0.30 hectares, that would be quite a lot of my property covered by panels, and way more than could ever feasibly fit on the roof (the current array is ground mount).

Good roof space may become a sales argument for houses in the future. Mine happens to have a huge flat roof slightly sloped to the south. I have 8 kW solar and that’s less than half the roof covered.

I use 6000/8000kWh between September and May though, because that is when I'm using a Heatpump to generate electricity.

The economics is not great as described, but I wouldn't see this at being an individual level solution. The larger it is, the easier it is to insulate.

You heat you house with oil? I thought Germany was environmentally conscious

Germany is still mining coal but they are environment conscious so they sell it to Poland to burn and buy electricity from them.

That seems like complete bullshit, since Germany doesn't mine anything apart from lignite, which can't feasibly be transported. Do you perhaps have a source on coal export to Poland? Also, Germany exports more electricity than it imports.

It's called "greenwashing". A fair bit of electricity is produced with solar (at a far higher cost than their neighbor's carbon-free electricity) but their gasoline and diesel vehicle manufacturing continues unbounded and their heat primarily comes from fossil fuel.

Unfortunately, Germany has been ruled by a conservative party for the last 16 years and they did everything in their power to sabotage renewable energy so that lignite mining could stay longer.

However, heating in Germany is a difficult problem to solve with renewable energy: You need lots of power in winter, when there is (close to) no power from solar. One solution would be excessive wind power and heat pumps that can be controlled remotely by the power grid operators.

Gosh, it's still coming out of academia. It takes awhile before these kinds of things are economically viable.

The issue with seasonal storage is that efficiency is much less important than capital cost. The cost of inefficiency is proportional to the number of charge/discharge cycles, the capital cost is not.

So, it makes sense to look at systems like ones using hydrogen, since hydrogen can be stored underground as a compressed gas at a storage capacity cost of $1/kWh. Minimizing that capacity cost is crucial. Sure, the round trip efficiency will be poor (maybe 40%?) but as argued above that doesn't matter much.

Sorry to be a killjoy, but $6/kwh is at least 20x too expensive. In 2021, the average price of electricity in the US was 14 cents/kwh. Assuming you charge with free electricity, your charge-discharge efficiency is 100%, there is no capacity loss over the years, and your cost of capital is zero, you need more than 40 years to break even at that price. All the 4 assumptions above and a few others (zero installation and maintenance cost, zero insurance, zero cost of disposal) are super unrealistic.

I think you misunderstood the article - they're talking about the capacity of the battery in terms of kilowatt-hours, not its cost relative to round-trip efficiency. If the cost were $6/kwh, you could build a 100kwh battery for $600, and charge/discharge that many times. I think this is supposed to be interesting both for its relatively cheap materials (and useful level of energy density), and its ability to be 'frozen' in a room-temperature charged state for long periods of time without much loss of charge.

Seasonal storage means you charge in the summer and discharge in the winter. One cycle per year. You need 40 years to sell electricity 40 times.

"Exploring the use of Iron" "Limited by Nickel"

"Limited by Nickel": This is just lithium ion battery storage, it is plainly obvious.

"Exploring the use of Iron": using LFP (which will be 200-230 wh/kg in production later this year)

"Added some sulphur": great, but you're wayyyy behind the current state of the art research in Li-S.

That cost is appropriate for maybe a day or two of storage. Months between seasons? That's ridiculous, even if we had a dirt-cheap 200 wh/kg sodium ion battery which COULD probably hit 6$/kg, unlike their unnamed/unspecified techs they are "looking into". Likely it is since every other battery buzzword was notched in this article.

The use case, providing more energy in the summer, is covered with solar + couple day grid storage and existing nuclear or gas turbine for load leveling.

What we need is to install as much wind and solar as possible to immediately eliminate coal, then add storage and more wind/solar as needed to start eating away at gas turbine. Nuclear should stick around for long-term load levelling until batteries become dirt dirt dirt cheap.

This article is so poorly written that it might as well be unintentional FUD.

Iron flow batteries already exist commercially, are even more non-toxic/safe, and they don't require heating up (and keeping hot, while using) the battery.

https://essinc.com/iron-flow-chemistry/

The utility industry isn't really that interested in storing power for an entire season. Very little ROI compared to a system that allows them to balance minute-to-minute or day/night...or transmission infrastructure improvements. Got excess generating capacity? Send it somewhere that doesn't.

I hope that some day in the near future we see home-scale or neighborhood-scale iron flow battery systems so that homeowners, apartment buildings, and small neighborhoods can go off-grid.

I've never really seen the advantage in going off grid per se, since it increases the amount of wasted capacity in both generation and storage, and running a few wires is cheap enough in urban environments. The most efficient arrangement might be a global grid.

I am not off grid, but the thing that would draw me to it is as an individual sustainability goal. Perhaps it would be more expensive to initially set up and run, but it should be sustainable for 20-40 years. There is the side benefit of reducing the demand on energy to acheive this sustainably. Spending less on technology and energy means working less. In other words, we pay in our own time for the time technology saves us.

To quote Thoreau: 'One says to me, “I wonder that you do not lay up money; you love to travel; you might take the cars and go to Fitchburg to-day and see the country.” But I am wiser than that. I have learned that the swiftest traveller is he that goes afoot. I say to my friend, Suppose we try who will get there first. The distance is thirty miles; the fare ninety cents. That is almost a day’s wages. I remember when wages were sixty cents a day for laborers on this very road. Well, I start now on foot, and get there before night; I have travelled at that rate by the week together. You will in the mean while have earned your fare, and arrive there some time to-morrow, or possibly this evening, if you are lucky enough to get a job in season. Instead of going to Fitchburg, you will be working here the greater part of the day. And so, if the railroad reached round the world, I think that I should keep ahead of you; and as for seeing the country and getting experience of that kind, I should have to cut your acquaintance altogether.' Walden, chapter 1, Economy.

Utilities around the US are working in numerous states to get favorable legislation letting them pay a fraction of what they do now for solar and wind energy fed back into the grid by residential and commercial customers. Once you even out your meter and reach net generation, any further generation into the grid you'll soon be getting bupkus for. Sorry, but I got better things to do than line the pockets of my state's for-profit utility company.

In rural areas, getting connected can mean tens of thousands of dollars...if they even offer it to you at all.

No matter where you are, you have to pay a monthly connection fee. It really adds up, and given how cheap solar and wind are now, you don't really get anything for it. Battery storage systems a couple years ago were very expensive, but prices are crashing and safer tech like lithium iron phosphate are becoming more commonplace. Heatpump systems have gotten so efficient that I'm pretty sure my next furnace isn't going to be a furnace, but an electric heatpump.

In my area, we lose electricity for a day or so in the winter, 1-3x a season. A year or two ago we were without power for 3 days. Everyone has generators; expensive, noisy/annoying (especially given they conduct a weekly "exercise"), wasteful, polluting, and expensive to maintain.

Having at least a large battery backup would mean I don't freeze, I can cook, take a hot shower, do my laundry, and my food doesn't spoil. And I don't need to pay the electric company for a product that just isn't very reliable and is increasingly irrelevant.

> Battery storage systems a couple years ago were very expensive, but prices are crashing and safer tech like lithium iron phosphate are becoming more commonplace.

Unless you live in a mild climate and/or have a full Passivhaus-level construction and/or live in a very small building, there are no current batteries that will get you through a winter of heating.

I live in New Mexico, have some of the best insolation numbers around (outside of Arizona), generate around 93% of my annual electricity use, including heating (air source heat pumps) from a 6.6kW PV array. A battery system large enough to store my winter needs built with any currently available technology would be completely untenable, both in terms of cost and size.

I pay $7.71 as a monthly connection fee, and I get back my excess summer production as "free kW" during the winter, an arrangement I much prefer to being paid directly. The "free kW" are a 1:1 match for my over-production.

Primary batteries based on molten salts ("reserve batteries") have been standard in military applications since just after WW2. They are ideal for munitions (fuzes, missiles) that need long storage life but don't need recharging.

"The freeze-thaw phenomenon is possible because the battery’s electrolyte is molten salt - a molecular cousin of ordinary table salt. The material is liquid at higher temperatures but solid at room temperature. The freeze-thaw battery was shown to retain 92 per cent of its capacity over 12 weeks."

Any relation between this and 'sodium-ion' battery companies like the recently acquired Faradion? (see https://www.youtube.com/watch?v=W2PmRT3akGk )

The electrolyte is sodium aluminum and chlorine, which sounds pretty different than sodium-ion.

https://www.sciencedirect.com/science/article/pii/S266638642...

The PNNL article is somewhat better than the current link.

https://www.pnnl.gov/news-media/freeze-thaw-battery-adept-pr...

molten salt is a form of long term energy storage being used by some companies. One example is below

https://www.maltainc.com/our-solution

Some alternative methods and related companies:

https://www.greenbiz.com/article/big-money-flows-long-durati...

Seasonal storage and thermal batteries are pretty easy and cheap to construct. The materials tend to be cheap commodities. All you need is space to construct them and a way to produce the heat you use to charge them.

For example, I know of an experimental setup in the Netherlands called CESAR (https://materialdistrict.com/article/battery-natural-stone/) that uses basalt rock. The basalt is heated up using solar energy in the summer. It is stored in an a metal box insulated with wool that apparently retains heat for months/years. Long enough to last the winter. You 'discharge' by pumping cold water through it. Warm water comes out. Very simple. It has been running for a few years and it seems to be cheap and work as advertised. Relative to burning gas, this looks like a nice idea.

Converting heat to electricity is more tricky and the efficiencies tend to be not great. Of course if the storage is cheap enough that might not be that big of a deal. Efficiencies are also a challenge with geothermal energy. But it's a great solution for heating buildings. This particular solution seems to work around this using molten salt which allows for a relatively large temperature gradient. But without having to drill kilometers into the earth's crust.

Probably over time, cost will decide which solutions end up getting used where and how. A good insight here is that different storage solutions serve very different purposes. You don't use lithium ion for seasonal storage. It's way too expensive for that. But it's great for short term grid balancing needs and seems to be popular for that. Vice versa, thermal mass would be probably bad for balancing the grid it's great for storing lots of energy that you use up slowly during the winter.

It's a tradeoff between how much energy you need stored, how much space you have for storing it, and how quickly you want to charge/discharge. It's telling a lot that a relatively expensive solution like lithium ion batteries are actually cost competitive with things like gas peaker plants. We can do probably do better long term. There is no shortage of good & already validated ideas in this space. All we need is good old engineering and manufacturing to prove products in the market at scale.

It seems really difficult to make the economics for seasonal electricity storage work. The article mention a materials cost of 23$ per kWh for their battery. Let's say this battery lasts 23 years. Transferring 1 kWh from summer to winter would than cost 1$ per kWh. That is before the cost of constructing the battery, R&D, sales, insurance, etc. Cost for 1 kWh is now below $0.10. That would mean generating electricity in summer and transferring it to the winter would come at a 10-fold increase in cost of winter electricity. For any currently available method, it seems that it would be far cheaper to simply have overcapacity in electricity generation from renewables and discard the excess electricity generated in the summer.

the article is about an _electrical_ battery that is seasonally heated up for usage and cooled down for the long term storage of the charge contained in it...

i had only heard of molten salt batteries which need to stay hot long term, so they are heavily insulated

maybe this article is talking about a primary battery (i.e. electrically not rechargable), which would make more sense

Original article is a good read too:

https://www.cell.com/cell-reports-physical-science/pdf/S2666...

This is pretty sweet!

There isn't enough information about larger/heavier but greener battery technology that would be suitable for grid/home storage without the environmental costs associated with the rare earth stuff needed for transportation.

> The battery’s theoretical energy density is 260 watt-hours per kilogram

Makes me wonder how big a battery would need to be to handle all of the overwinter energy demands of some densely-populated US states.

Just to put some numbers around that...

Density of ice at 0 degC is 0.92 kg/L. So, 1 kg of ice =~ 1087 cubic centimeters of space, or a cube ~4.25 inches on a side.

Rounding that down to 4 inches for the moment, you get 27 of those per cubic foot, or (260 Wh * 27) = 7.02 kWh, and then round that down to give the extra quarter-inch back, you get ~6.5 kWh/ft3 theoretical capacity.

A typical household in the US uses 10,715 kWh/year[0], so (10715/6.5) = 1648.46 ft3 for a household's worth of freeze-thaw battery storage, or a cube 11.81 feet on a side.

Yes, of course it's more complicated than that, but the scale is pretty interesting.

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[0] https://www.eia.gov/tools/faqs/faq.php?id=97&t=3

Massive. But I don't think thats the point of this.

I imagine you'd pair this with an energy source(say solar), so that you are able to smooth out/absorb excess energy and release when its needed. You could use it as an energy supply of last resort.

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