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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

#151

Post by onlyrealcuzzo »

merelysounds wrote: post #139
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…

> But sand is quite expensive so my question is, why sand and not water? The article says they will use a byproduct from a local industry, perhaps it's available for cheaper. "The sand itself will also be sustainably sourced – it’ll consist of crushed soapstone, which is a manufacturing byproduct of another local industry. This material can apparently conduct heat even better than regular old sand.".

> The article says they will use a byproduct from a local industry, perhaps it's available for cheaper.

Cheaper than water?!

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

#152

Post by tnjm »

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…

Another point, and I'd love to be corrected here, is that with a container of water you're going to get a ton of convection currents leading to a much sharper heat gradient at the edges, resulting in significant heat losses with the same amount of insulation.

At a guess, and I confess I'm not capable of running the numbers, this offsets the much higher temperature delta of sand.

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

#153

Post by onlyrealcuzzo »

prometheus76 wrote: post #146
Valgrim wrote: post #43

Earlier quoted context omitted.

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?

Why not just do solar heating?

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

#154

Post by seanc »

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…

Also, water is constantly trying to leak out of whatever you put it in.

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

#155

Post by lightedman »

onlyrealcuzzo wrote: post #151
merelysounds wrote: post #139

Earlier quoted context omitted.

> But sand is quite expensive so my question is, why sand and not water? The article says they will use a byproduct from a local industry, perhaps it's available for cheaper. "The sand itself will also be sustainably sourced – it’ll consist of crushed soapstone, which is a manufacturing byproduct of another local industry. This material can apparently conduct heat even better than regular old sand.".

> The article says they will use a byproduct from a local industry, perhaps it's available for cheaper. Cheaper than water?!

If that water has to come from underground, yes, it would be cheaper and easier to just grab surface stone and crush it for material to make a heat battery.

Also, water tends to make for a horrible heat battery as it is much more thermal-emissivity than rock particles. You need all sorts of additional insulation to retain the heat, whereas the sand will insulate itself.

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

#156

Post by mkesper »

AnthonyMouse wrote: post #111
mythhabit wrote: post #107

Earlier quoted context omitted.

It's a large enough volume of water, that adding insulation is feasible.

But then why put it in the house and not e.g. in the ground?

1. Not possible everywhere 2. Probably more expensive

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

#157

Post by giarc »

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…

Why not water - I wonder if it's because it's in Finland and 6 months a year you have to prevent the water from freezing.

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

#158

Post by ryukoposting »

giarc wrote: post #157
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…

Why not water - I wonder if it's because it's in Finland and 6 months a year you have to prevent the water from freezing.

You can heat sand above 100C without the sand turning into a gas.

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

#159

Post by tonyarkles »

pi-e-sigma wrote: post #110
tonyarkles wrote: post #63

Earlier quoted context omitted.

That’s the other bizarre thing about water/ice: most things expand as you heat them, but very few things expand as you cool them. Water has maximum density at 4C, so even before you freeze it it’s already starting to expand as you cool it.

You have it backwards. Density is mass/volume so with the same mass when density increases the volume decreses

You're right about how density works, but I don't have it backwards:

A given mass of water:

- At 20C is less dense/higher volume than water at 4C

- As you cool it the density increases and the water shrinks

- At 4C the water is now at maximum density and minimum volume

- As you continue cooling it from 4C, it starts expanding again

- At 3C the water is lower density than it was at 4C and is again expanding

- At 0C where the water starts to transition to a solid the volume expands significantly

I guess I wasn't clear that the expansion only starts again as you go from 4C -> 0C in the liquid phase.

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

#160

Post by dandy23 »

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…

I cannot explain the physics, but a big rock that has basked in the sun is really warm for a long time after sunset. A bucket of water loses its temperature faster.

The higher density of rock probably plays a big role.

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