Sand batteries

[tacpot12]

It was interesting to hear Drake Landing Solar Community mentioned early in the video...

It's in a satellite community of Calgary, about 40km away. Yesterday it was in the national news because the community is considering moving to natural gas. Indeed some residents already have.

The context isn't that the technology doesn't work, because history shows it was successful.

Another factor is surely that Alberta has a ton of stranded gas so it's insanely cheap there, like <C$0.01 per kWh of gas.

Even if mercury was cheaper than tea, you wouldn't drink it.

[Mike4]

There, link sanitised for you.

The dude has misunderstandings about basic science concepts like "sand holds on to heat remarkably well" (it doesn't), contradicted just a few seconds later. The sand thing looks like a scam to me, he barely mentioned the insulation needed, and the stress on key parts from the high temperatures must surely demand higher maintenance than an equivalent capacity water system.

Not a convincing video for me (it's mainly there to sell the advertised product).

GS

I was thinking similarly. The idea is fine in theory but it relies wholly on near-perfect insulation and I'm not sure we have that yet. Not cheaply anyway. I think the idea will fall down on the practicalities.

The sheer weight of a suitably large volume of sand will be hard to both support AND superbly insulate sufficiently cheaply, particularly as to put it underground also means digging an expensive (in householder scale) big hole and making the thing long term waterproof, and above ground it will be a huge eyesore people won't accept taking up their limited garden space.

They may have found solutions to these issues but somehow I doubt it, or they'd have gone into it some detail in the video. I think the whole thing will prove too expensive to implement with small enough energy losses.

[DrFfybes]

Even if mercury was cheaper than tea, you wouldn't drink it.

Of course not - the milk would float.

[servodude]

For Pete's sake! It was meant to be a light-hearted dig at two posters who have a sense of humour.


Steve

For Pete's sake! It was meant to be a light-hearted dig ...

Who the f*** is Pete?

^--- that's a winkie, and us internet weans use it to indicate our tongues are in our cheeks...
... except Mike4!
Mike always forgets and we end up thinking he's a recidivist Poe's law transgressor.

[DrFfybes]

For Pete's sake! It was meant to be a light-hearted dig ...

Who the f*** is Pete?

Alice's husband.

[servodude]

Who the f*** is Pete?

Alice's husband.

Simultaneously literal and literay?
Must be some sort of record... chapeau!

[tjh290633]

There, link sanitised for you.

The dude has misunderstandings about basic science concepts like "sand holds on to heat remarkably well" (it doesn't), contradicted just a few seconds later. The sand thing looks like a scam to me, he barely mentioned the insulation needed, and the stress on key parts from the high temperatures must surely demand higher maintenance than an equivalent capacity water system.

Not a convincing video for me (it's mainly there to sell the advertised product).

GS

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

[Tedx]

The dude has misunderstandings about basic science concepts like "sand holds on to heat remarkably well" (it doesn't), contradicted just a few seconds later. The sand thing looks like a scam to me, he barely mentioned the insulation needed, and the stress on key parts from the high temperatures must surely demand higher maintenance than an equivalent capacity water system.

Not a convincing video for me (it's mainly there to sell the advertised product).

GS

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

Maybe we should just add more heat to the oceans ....?

Oh wait.

[Mike4]

The dude has misunderstandings about basic science concepts like "sand holds on to heat remarkably well" (it doesn't), contradicted just a few seconds later. The sand thing looks like a scam to me, he barely mentioned the insulation needed, and the stress on key parts from the high temperatures must surely demand higher maintenance than an equivalent capacity water system.

Not a convincing video for me (it's mainly there to sell the advertised product).

GS

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

[GoSeigen]

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.

Correct, and that's why the sand feels hot on a sunny day and the water does not!

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

Yes the higher temperature that sand can achieve may have certain advantages weighed against the reduced longevity and need for maintenance of a system working at high temperature. I also imagine that heat loss as a fourth power of temperature means even the higher volume of sand vs water doesn't entirely help. However I'm not very familiar with the maths and physics here so there may be important advantages to the much higher temperatures achievable with sand that I haven't appreciated -- certainly the heat exchange will be more efficient I guess.

GS

[odysseus2000]

The dude has misunderstandings about basic science concepts like "sand holds on to heat remarkably well" (it doesn't), contradicted just a few seconds later. The sand thing looks like a scam to me, he barely mentioned the insulation needed, and the stress on key parts from the high temperatures must surely demand higher maintenance than an equivalent capacity water system.

Not a convincing video for me (it's mainly there to sell the advertised product).

GS

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

The problems with water are that any small hole will lead to leaks & more importantly is that unless it is confined in a pressure vessel it will boil & escape as steam. Sand by comparison is easier to confine & does not boil so it can be heated to much higher temperatures without needing a pressure vessel.

Regards,

[GoSeigen]

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

The problems with water are that any small hole will lead to leaks & more importantly is that unless it is confined in a pressure vessel it will boil & escape as steam. Sand by comparison is easier to confine & does not boil so it can be heated to much higher temperatures without needing a pressure vessel.

Regards,

Okay, can you quantify how much use the higher temperature is and discuss the trade-off in terms of radiation/conduction losses?

GS

[odysseus2000]

The problems with water are that any small hole will lead to leaks & more importantly is that unless it is confined in a pressure vessel it will boil & escape as steam. Sand by comparison is easier to confine & does not boil so it can be heated to much higher temperatures without needing a pressure vessel.

Regards,

Okay, can you quantify how much use the higher temperature is and discuss the trade-off in terms of radiation/conduction losses?

GS

Higher temperatures make the transfer of heat easier. Heat pumps struggle when the reservoir is cool, as in air source heat pumps, and the room is warm, but when the reservoir is hot and the the final destination cool they work well.However, sand batteries can be used like the night storage radiators were, but instead of having to have many in a house the heat can be extracted from a single underground battery by a simple circulating water system. In this case the higher the reservoir temperature the better as you have to heat water that is already hot as needed for radiators in a warm house.

Radiation, conduction losses are all insulation dependent.

The standard equation for heat transfer q is q=Constant x (Temp of reservoir - temp of surround) x Area

This is dominated by the constant and modern insulators are good, especially if the insulation can be applied thickly which would be the case for underground storage and is not the case for example when trying to insulate house walls.

Regards,

[tjh290633]

Okay, can you quantify how much use the higher temperature is and discuss the trade-off in terms of radiation/conduction losses?

GS

Higher temperatures make the transfer of heat easier. Heat pumps struggle when the reservoir is cool, as in air source heat pumps, and the room is warm, but when the reservoir is hot and the the final destination cool they work well.However, sand batteries can be used like the night storage radiators were, but instead of having to have many in a house the heat can be extracted from a single underground battery by a simple circulating water system. In this case the higher the reservoir temperature the better as you have to heat water that is already hot as needed for radiators in a warm house.

Radiation, conduction losses are all insulation dependent.

The standard equation for heat transfer q is q=Constant x (Temp of reservoir - temp of surround) x Area

This is dominated by the constant and modern insulators are good, especially if the insulation can be applied thickly which would be the case for underground storage and is not the case for example when trying to insulate house walls.

Regards,

That's odd. My Chemical Engineering colleagues used to tell me that the effect of extra insulation fall off rapidly when you get beyond 4" thick. Have the rules of nature changed?

TJH

[odysseus2000]

Higher temperatures make the transfer of heat easier. Heat pumps struggle when the reservoir is cool, as in air source heat pumps, and the room is warm, but when the reservoir is hot and the the final destination cool they work well.However, sand batteries can be used like the night storage radiators were, but instead of having to have many in a house the heat can be extracted from a single underground battery by a simple circulating water system. In this case the higher the reservoir temperature the better as you have to heat water that is already hot as needed for radiators in a warm house.

Radiation, conduction losses are all insulation dependent.

The standard equation for heat transfer q is q=Constant x (Temp of reservoir - temp of surround) x Area

This is dominated by the constant and modern insulators are good, especially if the insulation can be applied thickly which would be the case for underground storage and is not the case for example when trying to insulate house walls.

Regards,

That's odd. My Chemical Engineering colleagues used to tell me that the effect of extra insulation fall off rapidly when you get beyond 4" thick. Have the rules of nature changed?

TJH

Heat can be thought of as a fluid and insulation as an absorber. Sure you get a huge improvement with a small amount of insulation over a naked heat source, but not complete absorption, some of the heat gets out & the thicker the insulation the less heat is lost.

If you consider the earth it has a molten core that would have long ago cooled except for the heating from radioactive decay & the shell of insulation above the magma that retains most of the heat, except for the leaks such as a thermal vent & the odd volcano so that the temperature is approximately constant.

Clearly at some practical point there is no benefit to more insulation, but that point is a lot more than 4 inches. Loft insulation originally started at around 4 inches, but now 12 inch or more is standard. For space craft advanced insulators are only a few mm thick, but are equivalent to much larger amounts of conventional insulation.

It all depends on what is the needed heat retainment & for how long & from there it is possible to calculate the needed insulation to satisfy these needs.

Regards,

[tjh290633]

That's odd. My Chemical Engineering colleagues used to tell me that the effect of extra insulation fall off rapidly when you get beyond 4" thick. Have the rules of nature changed?

TJH

Heat can be thought of as a fluid and insulation as an absorber. Sure you get a huge improvement with a small amount of insulation over a naked heat source, but not complete absorption, some of the heat gets out & the thicker the insulation the less heat is lost.

If you consider the earth it has a molten core that would have long ago cooled except for the heating from radioactive decay & the shell of insulation above the magma that retains most of the heat, except for the leaks such as a thermal vent & the odd volcano so that the temperature is approximately constant.

Clearly at some practical point there is no benefit to more insulation, but that point is a lot more than 4 inches. Loft insulation originally started at around 4 inches, but now 12 inch or more is standard. For space craft advanced insulators are only a few mm thick, but are equivalent to much larger amounts of conventional insulation.

It all depends on what is the needed heat retainment & for how long & from there it is possible to calculate the needed insulation to satisfy these needs.

Regards,

It's not that there is no benefit from more insulation, it's that the incremental benefit from each extra inch of insulation becomes almost vanishingly small. The first inch is the most effective, but after 4 inches the saving is not worth the cost. 12 inches of loft insulation is overkill.

TJH

[Bubblesofearth]

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

The thermal conductivity of sand is a lot lower than water. This means that as long as a large volume of sand is heated throughout it will retain that heat much longer than water will. On a hot day in the Med the sand on the beach can become too hot to walk on barefoot but dig down a bit and it's still relatively cool. The top layer will heat up and cool down much quicker than water (lower heat capacity) but this heat will not transfer very quickly.

So a sand 'battery' will retain it's heat much longer than a water-based one.

BoE

[9873210]

It's not that there is no benefit from more insulation, it's that the incremental benefit from each extra inch of insulation becomes almost vanishingly small. The first inch is the most effective, but after 4 inches the saving is not worth the cost. 12 inches of loft insulation is overkill.

TJH

That depends on the cost of energy, the cost of insulation, and a bunch of other things. Rules of thumb based on one set of conditions are almost certainly wrong in other conditions. These type of rules of thumb are not laws of nature, they aren't even laws of economics.

[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

The thermal conductivity of sand is a lot lower than water. This means that as long as a large volume of sand is heated throughout it will retain that heat much longer than water will. On a hot day in the Med the sand on the beach can become too hot to walk on barefoot but dig down a bit and it's still relatively cool. The top layer will heat up and cool down much quicker than water (lower heat capacity) but this heat will not transfer very quickly.

So a sand 'battery' will retain it's heat much longer than a water-based one.

BoE

Ah you nearly had me there, until I checked the date!

[Bubblesofearth]

The thermal conductivity of sand is a lot lower than water. This means that as long as a large volume of sand is heated throughout it will retain that heat much longer than water will. On a hot day in the Med the sand on the beach can become too hot to walk on barefoot but dig down a bit and it's still relatively cool. The top layer will heat up and cool down much quicker than water (lower heat capacity) but this heat will not transfer very quickly.

So a sand 'battery' will retain it's heat much longer than a water-based one.

BoE

Ah you nearly had me there, until I checked the date!

https://sciencing.com/substances-hold-h ... -7156.html

As a sedimentary material composed of the compound silicon dioxide, sand is found on beaches and in deserts all over the world. Sand has a low heat transfer coefficient of 0.06 watts per square meter degree Celsius. This means it can retain heat for very long periods of time and explains why the sand on the beach of a hot country remains warm hours after sunset. A 1-kilogram container of sand will cool from 104 degrees F to 68 degrees F in 5 hours, 30 minutes.


Water is a liquid and will experience convective cooling which sand obviously doesn't.

If you don't believe this then it's a relatively simple experiment to set up at home. Get a couple of containers of similar size, fill one with water and the other with sand, heat both thoroughly to the same temp and stick a thermometer into the middle of both to measure temp vs time.

BoE