Sand batteries

[GoSeigen]

You are misunderstanding what heat is & the mechanisms of transfer within materials.

No sir, it is you who are misunderstanding. My mistake is answering your posts.


GS

[odysseus2000]

Check out the diagram 19s into the video in the OP. You want a balance between rate of heat release and heat storage. You don't want the reservoir to lose all its heat quickly but you want to be able to access the heat as quickly as is required. The design in the diagram shows how this is achieved.

BoE

If you insulate it the reservoir will not release (waste) heat. You cannot access heat as quickly as required if you use an insulating material. Imagine using polystyrene. How good a battery would that make? LOL

GS

You have this entirely wrong.

In a heat transfer system you have a high temperature reservoir & into this you put an extractor that will remove some of the heat. The main requirements are that the reservoir retains its heat & that the extraction system can take a little out.

Regards,

[odysseus2000]

You are misunderstanding what heat is & the mechanisms of transfer within materials.

No sir, it is you who are misunderstanding. My mistake is answering your posts.


GS

Well I have a PhD in physics and decades of experience as a professional physicist, worked as a project manager for an NASA project & including years of teaching undergraduates at Oxford.

Regards,

[tjh290633]

Except in this district scheme they are heating the sand to 600C.

How does water perform at that temperature?

https://www.bbc.com/future/article/2022 ... ean-energy

Given the specific heat of sand is only 1/5 that of water, I'd say the water performs five time better. The box containing it might need to be a bit stronger though.

You then have superheated steam, which means the latent heat of vaporization comes into play. From memory 840 kcal/kg. I think that trumps the sand argument.

TJH

[odysseus2000]

Given the specific heat of sand is only 1/5 that of water, I'd say the water performs five time better. The box containing it might need to be a bit stronger though.

You then have superheated steam, which means the latent heat of vaporization comes into play. From memory 840 kcal/kg. I think that trumps the sand argument.

TJH

Do you want a low cost efficient system or a very high cost system?

Most folk just want to be warm at the lowest cost possible.

Regards,

[tjh290633]

You then have superheated steam, which means the latent heat of vaporization comes into play. From memory 840 kcal/kg. I think that trumps the sand argument.

TJH

Do you want a low cost efficient system or a very high cost system?

Most folk just want to be warm at the lowest cost possible.

Regards,

This isn't most folk, though. It's the most efficient means of storing energy. Superheated steam may be the best way of releasing the stored energy.

TJH

[odysseus2000]

Do you want a low cost efficient system or a very high cost system?

Most folk just want to be warm at the lowest cost possible.

Regards,

This isn't most folk, though. It's the most efficient means of storing energy. Superheated steam may be the best way of releasing the stored energy.

TJH

It is often noted that perfection is the enemy of good.

Regards,

[tjh290633]

This isn't most folk, though. It's the most efficient means of storing energy. Superheated steam may be the best way of releasing the stored energy.

TJH

It is often noted that perfection is the enemy of good.

Regards,

This is not about perfection, it is about the best way of storing and releasing energy. There are time scales involved.

TJH

[odysseus2000]

It is often noted that perfection is the enemy of good.

Regards,

This is not about perfection, it is about the best way of storing and releasing energy. There are time scales involved.

TJH

Yes, but it is also about economics. If the best way is orders of magnitude more expensive than a good way, most will choose good.

Regards,

[Bubblesofearth]

If you insulate it the reservoir will not release (waste) heat. You cannot access heat as quickly as required if you use an insulating material.

GS

Depends how much heat you want and how quickly you want it. I have a microwaveable bag of wheat that I put on my feet at night that is very effective both in terms of speed and longevity

Clearly heat is released quickly enough by a sand battery for the purposes described in the video.

Polystyrene would be hopeless as it has such a low density. The density of dry sand is some 1.6x that of water which at least partly offsets the lower SHC when thinking in terms of volume required.

BoE

[9873210]

This is not about perfection, it is about the best way of storing and releasing energy. There are time scales involved.

TJH

Yes, but it is also about economics. If the best way is orders of magnitude more expensive than a good way, most will choose good.

Regards,

An alternative way to put odysseus's point is that if you end up choosing "good" over "best" it was "best" by the wrong metric.

In engineering almost any metric that does not include cost is the wrong metric. Even in emergency cost-be-damned projects cost still matters. If it costs more than the GDP of Earth (or some smaller area) it isn't going to work.

[9873210]

Given the specific heat of sand is only 1/5 that of water, I'd say the water performs five time better. The box containing it might need to be a bit stronger though.

You probably* want the capacity by volume rather than the capacity by mass. Since sand is 60% denser than water that helps a bit so water is only 3 times better by reasonable metrics.

If the storage media is on or in the ground you won't care about the mass for reasonable materials. If it's in a tenth floor flat the mass may matter, but in that case hundreds of kg of near boiling water would have a different set of problems that sand might avoid. There's several reasons storage radiators don't use water, ceramic plates are, thermally, not that different from sand, but are less messy to install indoors.

[GoSeigen]

Check out the diagram 19s into the video in the OP. You want a balance between rate of heat release and heat storage. You don't want the reservoir to lose all its heat quickly but you want to be able to access the heat as quickly as is required. The design in the diagram shows how this is achieved.

That diagram shows effectively a sand-and-air system. As I noted in another post, I agree that is an interesting proposition. Heat is being extracted quickly because of the air being forced through the sand (mechanical transfer of heat) NOT because of the thermal conductivity of the sand itself, which is poor.

GS

[Bubblesofearth]

That diagram shows effectively a sand-and-air system. As I noted in another post, I agree that is an interesting proposition. Heat is being extracted quickly because of the air being forced through the sand (mechanical transfer of heat) NOT because of the thermal conductivity of the sand itself, which is poor.

GS

Yes and that's why its heat storage is so good.

BoE

[servodude]

Some batteries are...
... but sometimes I want a battery designed to hold energy/charge for a long time, and go months between charges.
It's always a tradeoff

IIUC you are discussing a different trade-off here. It's the problem that there is a correlation between the rate at which energy can be withdrawn and leakage/waste of that energy. If you don't require rapid withdrawal of the energy but you do need to minimise losses then of necessity you may have to reduce the energy withdrawal rate [or possibly the same could be forced by safety requirements].

Agreed.

But I don't think that equates to saying that batteries in general are best designed to release their energy slowly which is the implication if a highly insulating material is to be used for storing the energy. A slower release rate would be indicated by other factors.


GS
P.S. All interesting discussion for me as I am considering various upgrades to our commercial property.

I think my point could probably be distilled down to the fact that, in my world model, it's the storage property that makes a battery a battery.
Or more correctly it's storage that makes a cell a cell (whether you are storing charge, heat or counts from Monte Christo)
... having more than one cell makes it a battery.

How quickly you can get your "stuff" in and out of storage, how much you can store and how well it stores or retains it while it's there, are just all parameters you have to balance for the specific storage job at hand

[kempiejon]

or counts from Monte Christo)
... having more than one cell makes it a battery.

Thanks, that had been bothering me.

[GrahamPlatt]

If you are looking for heat capacity, surely water is the optimum medium. It has a higher specific heat than the alternatives however you measure it.

TJH

Yes. Remarkably having just looked it up, the specific heat of water is almost exactly five times that of sand.

The slight advantage sand has over water as the thermal store medium is that it doesn't boil away when heated far above 100 C (at atmospheric pressure).

https://en.wikipedia.org/wiki/Table_of_ ... capacities

They’re using water for this one: https://www.pv-magazine.com/2024/04/09/ ... ge-system/

“ Vantaa Energy plans to construct a 90 GWh thermal energy storage facility in underground caverns in Vantaa, near Helsinki. It says it will be the world’s largest seasonal energy storage site by all standards upon completion in 2028”

[Mike4]

Yes. Remarkably having just looked it up, the specific heat of water is almost exactly five times that of sand.

The slight advantage sand has over water as the thermal store medium is that it doesn't boil away when heated far above 100 C (at atmospheric pressure).

https://en.wikipedia.org/wiki/Table_of_ ... capacities

They’re using water for this one: https://www.pv-magazine.com/2024/04/09/ ... ge-system/

“ Vantaa Energy plans to construct a 90 GWh thermal energy storage facility in underground caverns in Vantaa, near Helsinki. It says it will be the world’s largest seasonal energy storage site by all standards upon completion in 2028”

Hmmm water-filled underground cavern, pressurised so they can heat the water to 140C!

[servodude]

They’re using water for this one: https://www.pv-magazine.com/2024/04/09/ ... ge-system/

“ Vantaa Energy plans to construct a 90 GWh thermal energy storage facility in underground caverns in Vantaa, near Helsinki. It says it will be the world’s largest seasonal energy storage site by all standards upon completion in 2028”

Hmmm water-filled underground cavern, pressurised so they can heat the water to 140C!

Sounds a bit dodgy geezer?

[Mike4]

Hmmm water-filled underground cavern, pressurised so they can heat the water to 140C!

Sounds a bit dodgy geezer?

Dunnit just!!!

Getting a cavern of 0.1 cubic kilometres in volume totally pressure-tight sounds like quite a project.

Out of interest, can you or anyone post up the calcs to work out the pressure required for the boiling point of water to reach 140C?