It isn’t a totally new concept, in CSP (concentrated solar power) plants, a molten salt is used to store the heat as well.
novelty is secondary to implementation
Giant 'sand battery' holds a week's heat for a whole town
11–20 of 181 posts
Re: Giant 'sand battery' holds a week's heat for a whole town
#12I'm curious about "why sand", is it better at holding heat than say water?
Can store a lot more heat by volume. Water has other bad properties. The higher the temperature the higher the pressure.
> [Sand] Can store a lot more heat by volume.
A quick caveat/clarification: It's only true if you're pushing the system over the 100°C mark. Otherwise a volume of liquid water--with its greater latent heat-capacity--will outclass the same volume of sand.
Water's heat-capacity is 4.186 J/g°C, while estimates for sand run towards ~0.830 J/g°C. If we also assume the sand is 1.6x denser, then our below-boiling water still comes out ahead at ~3.15x the joules per volume.
There are hints [0] this system tops out around 600°C.
Re: Giant 'sand battery' holds a week's heat for a whole town
#13There's some interesting companies in this space.
https://gofourth.com/ - focusing on grid storage, uses graphite (carbon) and liquid tin for heat transfer
https://antoraenergy.com/ - industrial heat and electricity
https://rondo.com/ - industrial heat
You can find interviews with their founders on the Volts podcast.
Re: Giant 'sand battery' holds a week's heat for a whole town
#14I'm curious about "why sand", is it better at holding heat than say water?
In addition to what others have said, isn't one of the weird properties of water that it tends to take in energy easily, but not give it back so easily? I've never really understood how that works, but I think I've leqrned that at some stage. Hence why it's used in cooling so much. Somebody jump in and tell me how wrong I am, or if I'm on a track that doesn't lead completely nowhere.
Re: Giant 'sand battery' holds a week's heat for a whole town
#15NREL's ENDURING sand battery, storing heat at 1200 C in quartz sand. Round trip efficiency using turbines is estimated at ~53%.
https://arpa-e.energy.gov/sites/default/files/2021-03/07%20D...
The IP has been licensed by Babcock and Wilcox, who are the source of the nifty compact fluidized bed heat exchanger.
Re: Giant 'sand battery' holds a week's heat for a whole town
#16I'm curious about "why sand", is it better at holding heat than say water?
Sand is cheap, and stays stable up to 1200 C or so. For conversion back to work the efficiency will be much higher than for lower temperature water.
Re: Giant 'sand battery' holds a week's heat for a whole town
#17I'm curious about "why sand", is it better at holding heat than say water?
In addition to what others have said, isn't one of the weird properties of water that it tends to take in energy easily, but not give it back so easily? I've never really understood how that works, but I think I've leqrned that at some stage. Hence why it's used in cooling so much. Somebody jump in and tell me how wrong I am, or if I'm on a track that doesn't lead completely nowhere.
Water vaporizes, and at that point blows up just about every container you can build around it. As will ice when it cools down. Sand is just sand, very little difference, very unreactive from way under freezing temps to about 1300 degrees.
And you might vent steam, but you should probably take into account that while water < 45 degrees or so is pretty innocent, steam will strip flesh from bone starting at 180 degrees or so, it won't "just" burn you.
Re: Giant 'sand battery' holds a week's heat for a whole town
#18Earlier quoted context omitted.
Can store a lot more heat by volume. Water has other bad properties. The higher the temperature the higher the pressure.
> [Sand] Can store a lot more heat by volume. A quick caveat/clarification: It's only true if you're pushing the system over the 100°C mark. Otherwise a volume of liquid water--with its greater latent heat-capacity--will outclass the same volume of sand. Water's heat-capacity is 4.186 J/g°C, while estimates for sand run towards ~0.830 J/g°C. If we also assume the sand is 1.6x denser, then our below-boiling water stil…
Yeah see that but i imagine the safety engineering is a fair bit easier due to not having to worry about the pressure of super heated water.
Re: Giant 'sand battery' holds a week's heat for a whole town
#19Earlier quoted context omitted.
> [Sand] Can store a lot more heat by volume. A quick caveat/clarification: It's only true if you're pushing the system over the 100°C mark. Otherwise a volume of liquid water--with its greater latent heat-capacity--will outclass the same volume of sand. Water's heat-capacity is 4.186 J/g°C, while estimates for sand run towards ~0.830 J/g°C. If we also assume the sand is 1.6x denser, then our below-boiling water stil…
Yeah see that but i imagine the safety engineering is a fair bit easier due to not having to worry about the pressure of super heated water.
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Re: Giant 'sand battery' holds a week's heat for a whole town
#20I'm curious about "why sand", is it better at holding heat than say water?
It's more effective volume wise. I did the math, some time ago here are the rough numbers.
Sand has way less heat capacity then water per kg (about half).
Water can be heated to 95C with standard unpressurized vessel. Sand in this application is heated to 600C.
Sand is denser then water (kg/m3).
For the same heat energy stored this comes out to about 2.5x more volume of water(95C) compared to sand(600C).
Water and Sand are both dirt-cheap.
Hot water can be managed with standard plumbing equipment.
Sand needs some high temperature piping (hot air to water heat-exchanger, resistive heat tho heat up the sand).
How well both contain the heat is primarily dependent on the isolation. Which favors the smaller footprint of sand, but needs to isolate a higher temperature difference...