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Giant 'sand battery' holds a week's heat for a whole town

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Re: Giant 'sand battery' holds a week's heat for a whole town

#141

Post by fragmede »

captainbland wrote: post #140
onetimeuse92304 wrote: post #127

100MWh = 3.6 * 10^11 joules sand's heat capacity = 830 J/kg degree C sand battery size is "13m tall and 15m wide". Assuming most voluminous possible shape that's 13m * 15m * 15m = 2925 cubic meters of sand (100% fill, no account for insulation, etc.) Dry sand density is about 1600kg/m3 Total weight of sand would be 2925m3 * 1600kg/m3 = 4.7Mkg (4.7kt) 4.7Mkg of sand has a heat capacity of 830J/kg * 4.7Mkg = 3.9 * 10^9…

They might get quite a good deal on types of sand which are no good for construction but are highly abundant like sea sand or desert sand.

That’s the question, innit. Is there a sand-ologist around here?

Re: Giant 'sand battery' holds a week's heat for a whole town

#142

Post by Pigalowda »

onetimeuse92304 wrote: post #127

100MWh = 3.6 * 10^11 joules sand's heat capacity = 830 J/kg degree C sand battery size is "13m tall and 15m wide". Assuming most voluminous possible shape that's 13m * 15m * 15m = 2925 cubic meters of sand (100% fill, no account for insulation, etc.) Dry sand density is about 1600kg/m3 Total weight of sand would be 2925m3 * 1600kg/m3 = 4.7Mkg (4.7kt) 4.7Mkg of sand has a heat capacity of 830J/kg * 4.7Mkg = 3.9 * 10^9…

If it’s going to function as an energy source doesn’t it need to run a turbine so it can’t be water? The article said it’s going to just use heat directly so I guess they could use water.

But if ever the need arose it needs to be higher than 100C so it can generate steam for the turbine? Maybe I’m way off, I’m just a guy.

Re: Giant 'sand battery' holds a week's heat for a whole town

#143

Post by codewench »

ametrau wrote: post #133
onetimeuse92304 wrote: post #127

100MWh = 3.6 * 10^11 joules sand's heat capacity = 830 J/kg degree C sand battery size is "13m tall and 15m wide". Assuming most voluminous possible shape that's 13m * 15m * 15m = 2925 cubic meters of sand (100% fill, no account for insulation, etc.) Dry sand density is about 1600kg/m3 Total weight of sand would be 2925m3 * 1600kg/m3 = 4.7Mkg (4.7kt) 4.7Mkg of sand has a heat capacity of 830J/kg * 4.7Mkg = 3.9 * 10^9…

They heat the sand to 600c. But you could just use more water. I don’t get it also.

Another concern is losses. Water can evaporate, can leak, and tends to corrode fittings.

Sand? If some spills just grab a skid loader and stuff it back in.

Re: Giant 'sand battery' holds a week's heat for a whole town

#144

Post by rkangel »

Valgrim wrote: post #43
gorpy7 wrote: post #35

Ben_bai said it pretty well. water is good but it can cause rust, pressure, freeze, leak, etc. sand avoids most of this. the big thing is that sand can be heated much much hotter and this helps make up for its shortcomings relative to water. they likely charge and discharge with air blowing thru stainless steel network of pipes thru the sand. this would require special tuning. as someone else mentioned, the thing wit…

Some Youtube folks tried a much simpler approach: Take a large metal bucket or barrel. Put a heating element and a simple oven thermostat on the bottom. Fill with sand. Connect to a solar panel or other enrgy source. The air between the sand particles seem to actually provide a bit of convection and insulation. The thermostat turns the circuit off before getting too hot for the heating element. The heat accumulated d…

This is called a Storage heater (https://en.wikipedia.org/wiki/Storage_heater), usually referred to in the UK as a Night Storage Heater as it took advantage of cheap electricity at night to provide heat for a house.

Fitting Night Storage radiators was a much cheaper way of fitting central heating than the normal boiler and plumbing approach, and when electricity was cheaper it made more sense. Now, it makes no sense and if you buy a house with it the first thing you have to do is put in "proper" central heating. But maybe with excess renewables that will swing back.

Re: Giant 'sand battery' holds a week's heat for a whole town

#145

Post by dragontamer »

nimos wrote: post #136
dragontamer wrote: post #42

Earlier quoted context omitted.

1 cubic meters of water chilled 10C below ambient is 40MegaJoules of energy. Or in other words: 11kW-hrs of cooling, comparable to an entire Tesla Powerwall. We aren't talking about entire swimming pools here. Just a few cubic meters of water. Shift the temperature delta as you see fit but... It's actually very space efficient.

Air conditioners have a COP of about 3 though. So really its more like 3.5kwh of storage. If you want to go lower temperature to store more then your COP drops.

The temperature delta is the hard part for me to estimate here.

I know that IceBear left the water around 45F, so take that for what you will.

Either way, we aren't talking about entire swimming pools here. Just a small, single digit number of cubic meters of water.

Re: Giant 'sand battery' holds a week's heat for a whole town

#146

Post by prometheus76 »

Valgrim wrote: post #43
gorpy7 wrote: post #35

Ben_bai said it pretty well. water is good but it can cause rust, pressure, freeze, leak, etc. sand avoids most of this. the big thing is that sand can be heated much much hotter and this helps make up for its shortcomings relative to water. they likely charge and discharge with air blowing thru stainless steel network of pipes thru the sand. this would require special tuning. as someone else mentioned, the thing wit…

Some Youtube folks tried a much simpler approach: Take a large metal bucket or barrel. Put a heating element and a simple oven thermostat on the bottom. Fill with sand. Connect to a solar panel or other enrgy source. The air between the sand particles seem to actually provide a bit of convection and insulation. The thermostat turns the circuit off before getting too hot for the heating element. The heat accumulated d…

I'm toying with the idea of building one of these to use as a pool heater. Has anyone here tried this?

Re: Giant 'sand battery' holds a week's heat for a whole town

#147

Post by squarefoot »

captainbland wrote: post #140
onetimeuse92304 wrote: post #127

100MWh = 3.6 * 10^11 joules sand's heat capacity = 830 J/kg degree C sand battery size is "13m tall and 15m wide". Assuming most voluminous possible shape that's 13m * 15m * 15m = 2925 cubic meters of sand (100% fill, no account for insulation, etc.) Dry sand density is about 1600kg/m3 Total weight of sand would be 2925m3 * 1600kg/m3 = 4.7Mkg (4.7kt) 4.7Mkg of sand has a heat capacity of 830J/kg * 4.7Mkg = 3.9 * 10^9…

They might get quite a good deal on types of sand which are no good for construction but are highly abundant like sea sand or desert sand.

I was about to write just that. Also, desertification is a problem, so they could possibly get free raw material from many places, paying only shipping, and doing something good at the same time.

Re: Giant 'sand battery' holds a week's heat for a whole town

#148

Post by ben_bai »

tjmc wrote: post #30
ben_bai wrote: post #20

Earlier quoted context omitted.

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 Sa…

One advantage of heating water over sand is that you can heat it up with high temperature heat pumps which currently have CoPs ranging between 2.4 to 5.8 [1]. So for every kW of electrical energy you put in you get at least 2.4kW of thermal energy out. So yes, the volume of 95C water would be much greater than that of 600C sand, but if volume wasn't an issue you could do it much more efficiently. Alternatively, you c…

In short: Sand for industry scale heat storage, water for private heating storage.

Using a heat pump will increase the yield. Usable temp range from 95C water all the way to 0C ice in theory (latent heat).

And a modern isolated home helps, but seasonal heat water storage is basically a big tank, with a house build around it.

https://www.energie-experten.ch/de/wissen/detail/waermespeic...

Re: Giant 'sand battery' holds a week's heat for a whole town

#149

Post by mrspuratic »

SuperNinKenDo wrote: post #14
photonbucket wrote: post #5

I'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.

maybe this? https://en.wikipedia.org/wiki/Mpemba_effect Or, more generally: "Heating and cooling are fundamentally asymmetric and evolve along distinct pathways" https://www.nature.com/articles/s41567-023-02269-z

Re: Giant 'sand battery' holds a week's heat for a whole town

#150

Post by mcv »

ametrau wrote: post #133
onetimeuse92304 wrote: post #127

100MWh = 3.6 * 10^11 joules sand's heat capacity = 830 J/kg degree C sand battery size is "13m tall and 15m wide". Assuming most voluminous possible shape that's 13m * 15m * 15m = 2925 cubic meters of sand (100% fill, no account for insulation, etc.) Dry sand density is about 1600kg/m3 Total weight of sand would be 2925m3 * 1600kg/m3 = 4.7Mkg (4.7kt) 4.7Mkg of sand has a heat capacity of 830J/kg * 4.7Mkg = 3.9 * 10^9…

They heat the sand to 600c. But you could just use more water. I don’t get it also.

More water takes more space, and perhaps the higher temperatures make it easier to reuse the heat? And you probably don't want your water to get above 100 degrees C, because then you need to deal with pressure.

Sand is also a really good insulator if I'm not mistaken. That could also be a factor somehow.

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