Imagine cooling your building with the same principle that kept Victorian-era icehouses stocked with lake-frozen blocks, but in modern form. That’s the idea behind ice batteries, a clever energy storage hack that’s been quietly slashing cooling costs across commercial buildings. The invention works by freezing water when energy is cheap, and using that stored cold later, they turn major power hogs (air conditioning, we’re looking at you) into more efficient, cost-effective systems.
Pioneers like Nostromo Energy and Ice Energy are refining the tech. Nostromo’s IceBrick modules pack 25 kWh of cooling capacity each, install on rooftops, and cost around $250 per kWh—about half the price of lithium-ion storage. Ice Energy’s Ice Bear 40 integrates with HVAC systems, shifting up to 95% of peak cooling demand to off-peak hours. And for homes, the Ice Bear 20 replaces traditional AC units while doubling as a thermal battery.
Unlike lithium-ion, ice batteries don’t degrade chemically – their water is endlessly reusable. Combining the technology with this hack, it’s even possible in environments where water is scarce. But the trade-off? They only store cooling energy. No frozen kilowatts for your lightbulbs, just an efficient way to handle the biggest energy drain in most buildings.
Could ice batteries help decentralize energy storage? They’re already proving their worth in high-demand areas like California and Texas. Read the full report here and let us know your thoughts in the comments.
Original photo by Kelly Sikkema on Unsplash
No it’s not. That’s about twice the cost of lithium ion battery cells.
https://about.bnef.com/blog/lithium-ion-battery-pack-prices-hit-record-low-of-139-kwh/
More to the point, since heat pumps move more heat than the input energy you supply, a kWh of batteries would run an AC for more than a kWh of cooling by a factor of 2-8 depending on circumstances, further dropping the cost for the same effect.
Of course the ice would be made by a heat pump in the first place, but for storage capacity a lithium battery would be both smaller, less expensive, and more readily retrofitted to existing systems, since all you need is a pass-through capable charger that throws the AC on to battery power when the grid prices go up. Basically a big UPS for your HVAC system.
At these prices, the difference in electricity cost between peak and low would need to be around 6 cents to break even. That’s easily exceeded with common time-of-use rates.
I installed such a system back in the ’90s in an office building. It was making ice during the night and cooling the building during the day, making use of the difference in both environment temperature and electricity pricing.
I also wonder what the charge rate is like. Ice doesn’t transmit heat well so the centre of a block of ice takes longer to form than the edges. Ice makers have a finger-like shape to increase surface area and reduce the maximum distance any bit of water can be from the cooling surface but this adds cost and volume overhead to an ice battery.
The ice battery should slow down significantly as it charges. Meanwhile lithium batteries will sustain 1C+ to high SoCs only tapering as they approach fully charged.
I remember a popular science article back in the day using slaked ice dumped into a tub.
It’s typically an insulated slush pool.
A lot of work has gone into getting ice to release from the cold plates.
Coatings, sound, temperature swings, water additives etc.
Not a ‘solved problem’.
I see that price/report for batteries published a lot – but it is relatively meaningless as a consumer can’t buy batteries at anything like that price…
“No it’s not.”
Yes it is.
A BEV pack is not the same as a home battery/solar battery with inverter at all. It lacks an inverter and it is much larger so economy of scale kicks in. The battery is the most expensive part of an EV, and with a lot of competition requires small margins.
Price of a home battery or solar battery is about $900 per kWh. Those are used for storing electrical energy. You can also convert the electricity to heating or cooling water to later cool or heat the building with. You won’t use a car battery for that.
It is indeed a nice application. I think its very similar to the concept of grid controlled load/heating, just done with heat pumps. I do not however like calling them ice “batteries” since the term is associated with using chemical reaction to generate electrical energy.
My father and I had been contemplating making a dimmer controller (RF and WiFi) for grid controlled load applications and selling them to electricity companies but it never materialised.
The pricing is rather sad – it is in the same ballpark as batteries already, but adding pumps and complexity. Limited to commercial nieches.
Why not just add the thermal battery directly? For example thick brick walls that cool down and keep the cold during the day. Better yet, have phase change material in the wall/floor, to keep temperature stable. Or add a “thermal battery” to the refrigerator.
NightHawkInLight did a lot on phase change materials. Is there a material for freezer/refrigerator temperatures? Add a thermal battery block and use cheap electricity to cool down, turn off when prices go high?
How much would you need?
The “fridge load shifting device” could just be a sheet of phase change liquid, with the thermostat tuned to the temperature. How much you’d you need for a day? At 200kJ/kg, this gives about 55Wh for a kg block of PCM. I found numbers around 0.5 to 1kWh/day for a fridge, so you would need 10-20kg of PCM to put in your fridge. Likely even more, as the COP of the heat pump requires storing morethermal heat than electricity. Better to put 1kWh of batteries next to it.
Commercially not viable for the home, seems better to use batteries.
Thick brick walls would cost quite a lot in comparison. The internet says $15-30 per square foot, so I would assume that’s how much extra you’d pay for doubling up the walls. It adds up quite quickly once you count how many square feet of walls you have.
I imagine one would get other benefits beyond thermal.
Yes, but you still pay more for it.
Thick brick walls are a major upfront cost and only work for certain buildings anyway – you can’t build a tower block with 3ft thick walls like an old farm cottage, it would be physically impossible for it to stand up. Also very hard to retro-fit an extra couple of feet of brickwork to most buildings.
Thermal batteries are a great idea as they can be made from dirt cheap inert materials like sand or water and store & release heat/cool directly with minimal conversion, and can last for almost infinite cycles with zero degradation.
In addition to all the other reasons that this is marketing misinformation propaganda bull💩—
You still need power to generate the ice, and off-peak rates aren’t that massively different from on-peak rates. Typically < 20%.
We can’t just carriage the ice in from distant frozen lake beds, like Mr. Wu did for his meat locker?
It’s like we’re in a Rube Goldberg machine contest lol
we are getting 4 to 1 price difference nowadays (some parts of Aus) as there is more solar during the day than they know what to do with (getting to be effectively worthless).
So it’s now – if we could get batteries for reasonable prices in Aus (which we can’t) – worth it to charge during the day and use it during the night in a battery..
Not BS – potentially very good in fact; with renewables not always peaking at “useful” times this would allow cheap surplus to be used during those times thus reducing load during peak times and leaving more renewable energy for things that can’t be time-shifted.
A few years back I came across the German company Haase who tried to sell a water latent heat storage system. At least based on older heat pump tech, their product was not competitive.
Nothing about this is new, and it’s been possible for decades. The remaining qualifying aspect is whether or not a latent heat storage system pays for itself within its lifetime or not. More precisely this should be a geographical map showing years to amortisation based on local climate, PV generation and average price for installation, electricity, maintenance etc.
https://www.youtube.com/watch?v=fQtM-x4JVAo
“Please note that we have not been offering the ice storage system since the beginning of 2020. The market has turned out to be too small for the storage sizes we produce, and unfortunately it was not possible to offer a price that was acceptable for both the operator and us as the manufacturer.”
Generally when something uses technology as old and widely-available as this and you can’t find many instances of people using it 50 years ago, it’s because it doesn’t work well. There’s nothing here that couldn’t have been done at scale in the mid 20th century to save some money and yet it wasn’t
Except it is fairly common (making ice at night to cool during the day).
But only at scale and only in some environments and costs.
Capitalism has this covered.
Yeah money!
In some countries they dump ice in big silos or underground holes in the winter and use it to cool office buildings in the summer.
People in the comments don’t seem to get the “latent heat” storage idea – to be fair to them, the article does not talk about that either (and writing “it only stores cold” messes things up completely). I mean the general idea is very basic physics – we did that in high school, and looking at what the kids of friends and relatives do in elementary school, the basic idea is already discussed there with melting and cooking water (we probably did that as well, alas, it’s a couple of decades ago). Maybe it is not on the curriculum in all countries (I wonder…).
Working against the phase transistion does provide a lot of energy storage, and a heat pump can be designed to work at a specific temperature making it really efficient. It is more efficient than running the heat pump against ambient temperature.
If my memory is correct Honeywell cooled one of their buildings with a gigantic block of ice. They had a building and in the winter when it was well below freezing they made the inside of the building one very large ice cube and thawed it out in the summer. The freezing was done by mother nature.
Sorry can’t remember any details and I always wondered how big an ice cube would be needed to cool a building – but I always gave them credit for trying something different.
IIRC freedom units for AC capacity is Tons.
That’s equivalent tons of ice per week IIRC.
Obviously not ‘stubby frog emperor’ tons.
It’s just plain tons. In regular freedom units, 1 ton of AC is equivalent to 12,000 btu/hr. So a 3 ton central AC system (house size) can move 36,000 btu of heat in 1 hour and could be replaced by melting 6,000 pounds of ice in the same period.
EDIT: it’s 1 ton of ice melted over the course of 24 hours. So 288,000 btu in a day or 12,000/hr. 3 tons, 6,000 pounds (750 gallons) of ice melting is equivalent to a 3 ton AC running continuously for 24 hours.
God, even the Freedom Gallon is screwed up and stunted. Everywhere else, a gallon of water is an honest ten pounds.
So, one module of 25 kWh at $250/kWh is $6,250.
But 25 kWh is just a quarter ton of cooling storage. That’s 3 hours of operation for my relatively small 2t/d (24,000 BTU/h, 7 kW) household air conditioner. To get through a peak day’s worth of cooling I’d need 2-3 units. Though one unit would work for all but a few days per year.
Doesn’t seem worth the expense, but perhaps it would let me undersize my main unit and save money there, though.
Also, as almost always, they are not factoring in how long it would take for this hare-brained scheme to offset its own manufacturing carbon cost (esp. all the concrete). I’d wager it would be long enough for people to get sick of their frozen swamp cooler and scrap it
You only really need to store the energy necessary to run the heat pump – not the resulting mass of ice.
The less of a temperature difference you want, the better the performance of a heat pump, so if you’re not making ice but simply cooling some air by a few degrees, the coefficient of performance of a heat pump can easily be 5-6, which means you actually only need to store 1/6th the energy for the same tonnage of cooling if you do it with an electric battery instead of an “ice battery”.
With battery prices already under half of $250/kWh we’re looking at <10% the cost to build a battery backed HVAC instead of making a big ice cube for equal cooling capacity.
So my “7 kW” heat pump draws a (real) 2.6 kW to provide a (real, measured, net) 5.0 kW of cooling. A local quote for a 13.5 kWh Powerwall is $14k, installed. (so, nothing like the magical “$125/kWh” figured touted). Coincidentally, I’d get 25 kWh of cooling out of that powerwall, the same amount out of the ice solution presented here that (claims to) cost about a half as much.
Not saying either solution is reasonable, but a real battery equivalent solution isn’t as cheap as it might appear on paper.
The people relying on air conditioners aren’t spending most of their energy on “a few degrees” of cooling. They’re using them for up to, for instance, 25C of difference in air temperature. The more common value could be perhaps 15C of difference. But of course it’s not sensible to expect there to be no temperature delta between the refrigerant and the heat exchangers on the hot and cold side, because everything has a thermal resistance, and it’s fairly high for air heatsinks. (It would take more power in fans and mass in heatsink material to reduce that resistance to a negligible amount than it’s worth.) That also ties in with how the air is circulated through the house since each room receives at most a certain flow rate, which is often not that high. Since air has a specific heat, if you need more watts of heating or cooling in at least one room then the only way to do it is to increase the temperature difference once you can’t increase the flow. Besides that, in cooling mode you always run the cold side down to a lower temperature than the desired setpoint because it dehumidifies at the same time. So for a long time the standard I’m aware of is 75F with a 55F dew point, which should be 50% relative humidity. I think some people go lower, maybe 72 and 50. (Note: A dehumidifier gadget is normally the same thing as an air conditioner except it exhausts the heat back into the room, so that’s not the solution.)
So let’s say the comparison is between a 10 Celsius ish cold side and a cold side that’s hopefully not much below 0, since it’s easier to exchange heat with water with a small delta. If the hot side is in the 50-60C range in both cases, a completely made up figure based on the assumption that it’s a fair amount hotter than the hottest outside air it’s meant to cope with, then the extra ten degrees doesn’t seem like as big of a deal as if things had been different. If we’re looking at places which feel pressured to reduce cooling energy usage, I could imagine they are the hotter places where that’s more reasonable. And in those places the daily temperature swing depends on humidity… In humid places there may not be that much less temperature at night, just less heat load. So maybe in those places you want to make a little ice using solar, because you know you’re going to be using a lot of cooling at all times, but I’m not sure how much excess capacity you’re likely to have for making ice in the heat of the day, regardless if the power is cheap. In dry places, the total temperature delta at night may be less while making ice than in the day making cold air. But you’ll be using non-solar to do it, of course, so that’s only ideal if it’s hydro or nuke or wind or whatever.
If you can store the heat without needing to change the delta, great. Means phase change or lots of regular thermal mass. I think there’s a case for ice but you have to do the numbers for each case.
“That’s 3 hours of operation”
It doesn’t matter how many hours it lasts. The goal is not seasonal storage or being able to cool an entire day with it. The goal is to save money. You will use this buffer in addition to regular AC.
You can store energy when there is a high supply and low demand for solar power. And then use it later when demand is high and supply is low. Instead of sending the power back to the grid for a low price. You will increase the rate at which you remove the heat too as the cooling effect of the ice is combined with the ACs.
Of course it matter how long it lasts. If I spend $6k for a device that can only supply a few minutes of cooling for a few minutes before it needs ‘recharging’, it’s a waste of money.
If $6k buys me a system that provides me a whole year of storage, so I can charge from zero-cost ambient temperatures instead of a heat pump, that might be OK. But since I spend less than $500/year on cooling, it’s still not a good deal.
$6k for a device than can only provide 3 hours of cooling has a pretty narrow use case, and not one that would work for me (and most people, I’d guess). It would never, ever, pay for itself.
“But the trade-off? They only store cooling energy”
Technically, if you have a cold reservoir in the presence of a higher ambient temperature you could rig up a thermoelectric generator unit (TEG) (like a peltier cooler but operating in get-energy-from-the-temperature-gradient mode) to get electrical energy out, the electrical energy can then power anything you desire… but it would be extremely inefficient.
A sterling cycle engine can convert such a temperature differential into useful work, and it could also function as the pump to cool the battery in the first place. In fact, you could pump heat out of one phase-change substance into another, and increase the total differential. Sterling cryocoolers (as the name implies) can achieve cryogenic temperatures.
It’s “Stirling”. And Carnot would like a word (“efficiency”) with you. You’re just not going to get much energy out of that small temperature differential.
Not quite analogous, but: The last Stirling cryocooler I worked with was best-in-class, and provided 0.5 watts of cooling at 10 K, for 6 kilowatts of input electrical power. That 6 kW of waste heat went into the building chilled water loop and, by the time it got dumped in the rooftop chillers, that 0.5 watts of cooling cost 50 kilowatts. And it ran 24×7. Thankfully I wasn’t paying the bill.
Stirling is not a sterling example of efficiency, even if it’s close to the best we’ve got.
This idea has been around since 1980 or earlier. Nuclear physicist Theodore B. Taylor was an early developer, as described in John McPhee’s “Ice Pond” (1981).
This is not “storage” of anything. This is an energy vacuum. Heat exchange. Your moving the heat out of the structure, but it’s just dumped into the atmosphere, and your counting on the atmosphere to have it’s own heat available when you need to reverse the exchange, but the atmosphere can be a little fickle about that, and the size of the energy vacuum you create is finite. This would be much more efficient if you had a fixed storage volume for the heat, but you would have to store a good bit more heat energy over that which the atmosphere can reliably provide, so that you have a reliable margin in either direction. Work done by a vacuum always has a bottom line, and you have to take time and energy to evacuate it again. So you build a building with a perfectly insulated heat core, and a perfectly insulated vacuum void, and you can spend minimal energy exchanging them, but the initial charge is expensive.
Before long, you’re looking for a source of energy that was already stored by nature to take advantage of, and suddenly we’re looking at nuclear not being that much more expensive.
Technically you are storing the energy everywhere else but the block of ice. In the entire universe minus the block of ice. So you are still storing the energy.
Another way to look at it is that you are lowering local entropy by creating a temperature difference. So you are storing “order”, which requires energy.
And from a practical point of view cooling requires energy and buffering cold effectively buffers the product of the energy for later use. So you are indirectly storing the energy.
Installing a box of ice on your roof, which will always be hotter than ground level (let alone in the ground) hardly seems like a good design choice. The only stength of the system seems to be using water, at least it won’t wear out from daily phase transitions (though the pumps and compressors…)
Don’t you need cooling exactly at that moment when solar cells produce the most energy – on hot, sunny days?
So I’d say it would make more sense to use a regular AC unit, and put up some solar cells to power it.
Having just been through a week of having my AC also run most of the night, and also having tens of kWh of “wasted” Solar capacity, being able to store that (beyond the 19kWh I can fit into my battery) would still be exceedingly useful.
Would it require that much changes to fridges so that they could run off grid for at peak hours and recharge themselves later ?
…Would you buy and use a fridge that had wildly variable temperatures depending on capricious factors outside your control, occasionally freezing solid things which weren’t meant to be frozen and spoiling things which were? For an incredibly minor energy savings that probably wouldn’t pan out once all factors were included
… would you charge a LIR2032 with a TIG welder and then complain about bad battery performance?
It doesn’t take much effort to make an off-peak fridge, but you have to do it youself, because the industry, the consumer and the electricity company are in a chicken-and-egg deadlock. Put some thermal packs in the fridge and scale the set point within the range acceptable for the contents, you can measure the mains frequency for peak detection.
My high school physics class built and tested a small version of a more passive system in the ’70s.
We used two tanks, an open air heat exchanger, and a pair of very small pumps with a couple of cross connect valves connecting one of the tanks to the heat exchanger in the “house” depending on season and the other to the outside exchanger.
Let one tank get colder all winter undisturbed, facilitated by circulating water through the external coil exposed to cold Minnesota air. Use the other tank for heat (ideally filled in the spring and warmed with the external exchanger until winter). We only proposed insulating the tank’s top surfaces, letting the dirt below serve as extra storage.
In the spring, revere the cross-feed to let the now very cold water into the house.
Swap again in late fall — repeat.
Kickstarting the system was the biggest problem in order to get the cycle self sufficient (one cold, one hot). Solved by burying the (BIG) tanks as construction started on the home.
If I remember correctly two 10,000 gallon tanks would handle a 1,200 square foot house – about $5,000 at the time.
We were afraid of letting the cold tank freeze, but the phase change energy would have really helped.
This is similar to the recent practice of burying a string of flexible tubing in the back yard in order to use the ground as a storage system. Some people use two wells to draw water from the ground , and then re-inject that water a distance away. (Heat pumps required)
My data center at work circulates water to the roof when the outside temperature is below 32 F. We rarely need our “real” chillers in the winter. (The Marketing Department wanted to brag about our efficiency .)
“They only store cooling energy.”
A) The energy removed from the water while freezing it has to go somewhere. It could easily be stored in another thermal reservoir.
Water’s heat capacity is ~4.2J/gK and its heat of formation is ~334J/g. If we start with 1kg of water at 25C, cooling it to 0.1C (the triple point) will move 105kJ. Turning the 0.1C water to 0.1C ice will move another 334kJ. Coolling the ice to -25C will move another 105kJ, for a total of 544kJ.
Aluminum has a heat capacity of ~0.9J/gK, as do sand, salt, and most other high temperature thermal mass materials. If we start with 1kg of aluminum at 25C and add 544kJ of heat, it ends up near 630C. If we let that cool to 45C, it will release enough energy to heat 6.2kg of water from 25C to 45C (typical water heating).
The theoretical limit for a heat pump operating between 25C and 630C (300K and 900K) is about 66%, so it would take extra energy to build a system like that.
B) Heat engines use thermal gradients. Storing the cold end works just as well as storing the hot end, and we can generate heat on demand with 100% efficiency.
C) Water expands about 9% when it freezes. Anything that expands and contracts can be turned into a piston: put a flexible barrier in a tank, fill one side with water and the other side with oil. Freezing the water will store energy as hydraulic pressure in the oil.
$250/KWh? The cost of LFP in China is $60/KWh.
That’s just the bare battery.
A LFP pack is not the same as a home battery/solar battery with inverter at all. It lacks an inverter.
Price of a home battery or solar battery is about $900 per kWh. Those are used for storing electrical energy. You can also convert the electricity to heating or cooling water to later cool or heat the building with. So you can compare the two solutions.
Is Ice required or would something like water and methanol which gets much colder and remains liquid work? A liquid would allow for more efficient heat transfer. Because it stays liquid and can get colder more heat is extracted from it?
You’d have to cool water more than 80 degrees C to equal the heat (‘coolth’) you store in the phase transition to ice. And since the refrigeration plant will get vastly less efficient the colder the cold end gets, you’re far more efficient to store the energy in the phase change.
This seems like something you could diy.
Are there any such projects?