The Sand Battery

[Tuur]

Came across this article on the Popular Mechanics website. Someone's figured out how to use sand to store energy:

This Massive ‘Sand Battery’ Can Store Excess Solar and Wind Energy for Months

It can store 8 megawatt hours of thermal energy when full, and discharge about 200 kilowatts of power.

www.popularmechanics.com

Inefficient? Yet. But sand is cheap. The question is how well can it be scaled up.

 

[Kylie]

It can store the heat for months? How do they insulate it?

 

[FrumiousBandersnatch]

It can store the heat for months? How do they insulate it?

Surround it with sand?

 

[Kylie]

Surround it with sand?

Oh come on, you know what I mean, silly.

How do they stop the heat from the sand from dissipating out into the environment?

 

[FrumiousBandersnatch]

Oh come on, you know what I mean, silly.

How do they stop the heat from the sand from dissipating out into the environment?

They store it in an insulated silo with heat transfer pipes running through it.

 

[HARK!]

Surround it with sand?

I suspect that it might be SiO2 shaped up to simulate fiberglass insulation.

 

[loveofourlord]

I'm still witing for my diamond batteries.

 

[Tuur]

It can store the heat for months? How do they insulate it?

Don't know, but the trick could be as simple as increasing the size to decrease the surface area to volume ratio.

 

[Kylie]

Don't know, but the trick could be as simple as increasing the size to decrease the surface area to volume ratio.

That could do it, but the photo of it in the article doesn't look big enough...

 

[Ophiolite]

I am puzzled that no one has bothered checking the Polar Night Energy site for information on the insulation.

Their home site is here. Unfortunately it provide minimal details: "The heat storage is made of steel and insulated with standard, heat resistant insulating materials. The insulation is all around the heat storage between the outer steel layer and the inner one."
So, clearly nothing sophisticated.

 

[Diamond72]

They store it in an insulated silo with heat transfer pipes running through it.

If you go below the frost line the earth is 55 degrees. They do run pipes so if you pump water through them it will heat the water up to 55 degrees to help heat your house.

 

[Tuur]

If you go below the frost line the earth is 55 degrees. They do run pipes so if you pump water through them it will heat the water up to 55 degrees to help heat your house.

This gets into an interesting effect. These types of systems don't work well above a latitude that I've long ago forgotten. The problem is that the system takes out more heat that is restored in the summer, either by environmental heating or by putting heat back into the ground through air conditioning.

It suddenly strike me just how old this tech is. I learned of it at work nearly forty years ago.

 

[Diamond72]

It suddenly strike me just how old this tech is. I learned of it at work nearly forty years ago.

I think they use some sort of heat pump now.

 

[Tuur]

I think they use some sort of heat pump now.

It was a heat pump then, too, just it gets its heat or dumps heat in to the ground instead of the air. This is important because below a certain temperature, heat pumps can't get enough heat from the air and have to use heat strips, which is resistance heat. What that temperature is has likely improved from back in the day, as I noticed ours didn't have to go to heat strips during the cold snap. Even then, heat strips come on when the heat pump goes into a defrost cycle.

 

[Diamond72]

It was a heat pump then, too, just it gets its heat or dumps heat in to the ground instead of the air.

This would work out better in a place like Yellowstone where there are hot springs. So the temp you are working with is a lot higher.