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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

#161

Post by btbuildem »

foofie wrote: post #86
m463 wrote: post #72

I get that sand is inexpensive and simple and I like the idea - especially since it scales to an entire town (!) But I can't help but think of one "technology" that could make a scheme like this MUCH more effective. a phase change. for example, it takes 1 calorie for water to go from 30 to 31 degrees F, but but it take 80 calories to go from solid at 32 to liquid at 32 F. A project I remember reading about that was r…

> But I can't help but think of one "technology" that could make a scheme like this MUCH more effective. I think this is one of those things that drive home the point that there are fundamental differences between physics and engineering. The article states that the thermal silos are heated with excess energy from the power grid. This alone tells you right from the start that efficiency is not the primary requirement…

Excess energy from the power grid -- in times when renewables produce excess energy.

Otherwise, the heat to be stored comes as a byproduct of local industry. Something that would otherwise be vented out and not used.

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

#162

Post by pi-e-sigma »

tonyarkles wrote: post #159
pi-e-sigma wrote: post #110

Earlier quoted context omitted.

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 wh…

ah OK, I get your point :) It doesn't really matter though because water when liquid doesn't cause any problem when expanding or contracting, its level in a vessel will just slightly change. It's only the ice that can fuck up pipes etc

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

#163

Post by Tade0 »

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 can think of several reasons I would choose sand:

-Order of magnitude smaller coefficient of thermal expansion.

-No real risk of phase change - freezing or boiling.

-No problems with corrosion/scale in high temperature. On one hand regular water contains minerals which can build up on the heat exchanger element, on the other demineralized water sucks in carbon dioxide and oxygen from the atmosphere, causing corrosion of steel parts. You would need an airtight container to alleviate this.

Sand is great because it's largely inert in a huge range of temperatures.

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

#164

Post by slow_typist »

adrianN wrote: post #125
slow_typist wrote: post #85

Earlier quoted context omitted.

The monetary case of PV does not account for the damage that is done to the environment over the entire lifecycle. Solar hot water panels are ecologically superior. Not only are they more efficient in W/sqm. Their production is not as energy intensive (plumbing included), the recycling process is less complex, poisonous materials can mostly be avoided. If heat is the desired product, they probably beat PV by an order…

You can run a heat pump with the electricity. That changed the calculation a bit.

Sure but a heat pump was not the scenario in the parent post.

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

#165

Post by slow_typist »

Retric wrote: post #138
slow_typist wrote: post #85

Earlier quoted context omitted.

The monetary case of PV does not account for the damage that is done to the environment over the entire lifecycle. Solar hot water panels are ecologically superior. Not only are they more efficient in W/sqm. Their production is not as energy intensive (plumbing included), the recycling process is less complex, poisonous materials can mostly be avoided. If heat is the desired product, they probably beat PV by an order…

PV’s falling prices have also been associated with falling environmental harm. When you’re talking multiple orders of magnitude you just cannot require as much in production. IE: You can’t burn 500 gallons of gas if the end product costs 500$. That applies not just to transportation but also how much material and thus mining the raw materials you need, including refining them, the amount of chemicals you can use per…

The argument is valid, if energy is not subsidised. However, burning pv for resistance heating is still wasteful and should be avoided. It is only acceptable for peak production that cannot be put to better use.

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

#166

Post by onetimeuse92304 »

Tade0 wrote: post #163
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 can think of several reasons I would choose sand: -Order of magnitude smaller coefficient of thermal expansion. -No real risk of phase change - freezing or boiling. -No problems with corrosion/scale in high temperature. On one hand regular water contains minerals which can build up on the heat exchanger element, on the other demineralized water sucks in carbon dioxide and oxygen from the atmosphere, causing corrosi…

> -Order of magnitude smaller coefficient of thermal expansion.

On the other hand the thermal expansion of water does not matter because water, you know, is a liquid -- it conforms to whatever vessel you put it in.

> -No real risk of phase change - freezing or boiling.

In a vessel that is meant to store thousands of tonnes of water that is hot and that is very well insulated to store energy for months, there is no real danger that the water will freeze. On the boiling side, water make it easy to monitor the temperature and you just stop adding energy if it starts boiling. Your kettle can do that reliably, we can do this for a huge battery.

> No problems with corrosion/scale in high temperature

It is hard to put 5 thousand tonnes of sand in a container and ensure it is dry. There is always going to be water that will be evaporating when you heat the sand in the middle and condensing on the sides that are cold.

There is no possibility of scale when you do not heat water to boiling.

> Sand is great because it's largely inert in a huge range of temperatures.

Crushed rock will release water when heated up.

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

#167

Post by darkerside »

nimos wrote: post #137
darkerside wrote: post #131

Earlier quoted context omitted.

Real estate is precious. You really want a massive heat battery taking up a lot of living space?

I'm not suggesting adding anything. Homes have lots of stuff in them. Everything in your house becomes a thermal battery - tables, chairs, beds, walls, counters, clothes and so on. Just allow a range of temperatures and when energy is very low cost drive the indoor temperature to the upper range. Ideally you have a brick/stone home with good exterior insulation.

Sure, I do that sometimes. The effect rounds to zero, but better than nothing?

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

#168

Post by onetimeuse92304 »

dandy23 wrote: post #160
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.

> I cannot explain the physics

Here, this is actually the problem.

Water can store many times the amount of energy per volume or mass, per degree Celcius, than rock.

What you see is that rock has much lower thermal conductivity. It can be hot inside but it is not as good at transferring that heat outside. It means when you have hot rock it will stay hot for longer than equivalent amount of water. That because water emits that energy faster.

But put that rock and water in a well insulated vessel and you will find that the properties of the insulation and the vessel will start dominating the process and what counts now is how much energy you can store in the material inside.

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

#169

Post by Tade0 »

onetimeuse92304 wrote: post #166
Tade0 wrote: post #163

Earlier quoted context omitted.

I can think of several reasons I would choose sand: -Order of magnitude smaller coefficient of thermal expansion. -No real risk of phase change - freezing or boiling. -No problems with corrosion/scale in high temperature. On one hand regular water contains minerals which can build up on the heat exchanger element, on the other demineralized water sucks in carbon dioxide and oxygen from the atmosphere, causing corrosi…

> -Order of magnitude smaller coefficient of thermal expansion. On the other hand the thermal expansion of water does not matter because water, you know, is a liquid -- it conforms to whatever vessel you put it in. > -No real risk of phase change - freezing or boiling. In a vessel that is meant to store thousands of tonnes of water that is hot and that is very well insulated to store energy for months, there is no re…

> Your kettle can do that reliably, we can do this for a huge battery.

Scale is important here, as you'd need an array of sensors immersed in the water so that there's no local pocket of close to boiling temperature.

> There is always going to be water that will be evaporating when you heat the sand in the middle and condensing on the sides that are cold.

That's a slow process, but even if - as long as the temperature is considerably above ambient the water will condense elsewhere.

> There is no possibility of scale when you do not heat water to boiling.

Actually it forms at temperatures as low as 28 °C.

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

#170

Post by samstave »

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?

Seems like according to everyone above - why not just use the water from your pool.
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