Sand Batteries for Scalable Energy Storage on Moon / Mars?

[sanman]

Sand batteries are able to store heat, and are in the news these days, thanks to announcements from Finland:





Can this type of technology be used on the Moon or Mars? There seems to be plenty of sand over there, and this sounds like a technology that could be highly scalable. What are the drawbacks and limitations?

[edkyle99]

Looks like a thermal energy storage system, the term "battery" being a misnomer.  I  don't see why such a system could not be made to work on the Moon or Mars.  It works best as a means to store excess energy generated by wind or solar that can later be used for heating.  Sand is good for storing heat because you can cook it to very high temperatures.  The question is whether excess energy would ever be available on, say, a lunar base, and whether such a system would be more efficient then batteries as a means to store energy for the lunar night.  The cooked sand has to be stored in a very well insulated container.

 - Ed Kyle

[DanClemmensen]

Looks like a thermal energy storage system, the term "battery" being a misnomer.  I  don't see why such a system could not be made to work on the Moon or Mars.  It works best as a means to store excess energy generated by wind or solar that can later be used for heating.  Sand is good for storing heat because you can cook it to very high temperatures.  The question is whether excess energy would ever be available on, say, a lunar base, and whether such a system would be more efficient then batteries as a means to store energy for the lunar night.  The cooked sand has to be stored in a very well insulated container.

 - Ed Kyle

Heat storage systems are great if a good percentage of what you need is heat. For example, the demo sand system they installed in Finland serves a district heating system. If you mostly need electricity, they are not so good.

[JayWee]

... The cooked sand has to be stored in a very well insulated container.

Isn't that rather easy on the Moon (vacuum) or Mars (almost vacuum) ?

[sanman]

Looks like a thermal energy storage system, the term "battery" being a misnomer.  I  don't see why such a system could not be made to work on the Moon or Mars.  It works best as a means to store excess energy generated by wind or solar that can later be used for heating.  Sand is good for storing heat because you can cook it to very high temperatures.  The question is whether excess energy would ever be available on, say, a lunar base, and whether such a system would be more efficient then batteries as a means to store energy for the lunar night.  The cooked sand has to be stored in a very well insulated container.

 - Ed Kyle

Yeah, I was thinking mainly about storing thermal energy to last you through the lunar or martian night. Lunar day should allow plenty of excess energy collection from a good-sized solar farm, which you could then store up thermally inside this 'sand battery'.

I wonder if lunar regolith would work alright for this purpose?

Even with a local abundance of usable sand, the container would be the hard part. Could you just maybe get away with an open sandpile with an insulated floor/platform for the sand to sit upon, and forget about container walls? How much heat could be lost if there's no significant atmosphere on the Moon to conduct/convect it away? Or would there be significant radiative losses?

Could you use a large flexible sack to hold the sand, instead of a rigid container? Like a big sandbag? Or a sandpile surrounded by a tent?

Heat storage systems are great if a good percentage of what you need is heat. For example, the demo sand system they installed in Finland serves a district heating system. If you mostly need electricity, they are not so good.

Yes, for transferring just heat, then they're supposed to be quite efficient, but converting it into electricity drops the conversion efficiency by a factor of ~4.

But with an abundance of sand, you'd be able store plenty of energy to spare. However, it's the container which would limit the scalability.

Might there be some way to build a large insulated container on the Moon / Mars? Or are you stuck having to bring one with you? Could some kind of flexible sack be used instead of a rigid container?

Isn't that rather easy on the Moon (vacuum) or Mars (almost vacuum) ?

Yeah, that's what I was thinking. Could you maybe get away with just having an open sandpile sitting on an insulated floor/platform?

Unless you could somehow use insulated propellant tanks from a used rocket stage that you've somehow landed onto the surface. Either that or use a large sack and have that be insulated. Or maybe some combination of a sack and an insulated platform for it to sit on?

[Twark_Main]

the term "battery" being a misnomer.

Agreed. I don't see any artillery anywhere!!

The question is whether excess energy would ever be available on, say, a lunar base

... 14 days of sunlight?

whether such a system would be more efficient then [electrochemical] batteries

"Voltaic piles," please! "Batteries" is a misnomer after all.


Energy efficiency during operation isn't everything. There's also the cost of bringing heavy batteries vs using ISRU regolith.

Technically you don't even need a tank. Just a simple gravity pile of regolith with an insulating ISRU ceramic brick base and a high-temperature MLI cover blanket should do it.

The cooked sand has to be stored in a very well insulated container.

That's the easy part. With no air you only need to block radiative heat loss, so MLI yields extremely high performance with extremely low mass.

[sanman]

Energy efficiency during operation isn't everything. There's also the cost of bringing heavy batteries vs using ISRU regolith.

Technically you don't even need a tank. Just a simple gravity pile of regolith with an insulating ISRU ceramic brick base and a high-temperature MLI cover blanket should do it.

The cooked sand has to be stored in a very well insulated container.

That's the easy part. With no air you only need to block radiative heat loss, so MLI yields extremely high performance with extremely low mass.

So with the reflective/insulating blanket on top, the main thermal losses would be via the base that the sandpile is sitting on.

And you say that base can be made from locally-manufactured ceramic bricks?

Has there been any formal research into this concept for possible Moon/Mars applications?
Any links would be appreciated.

Wait  - I found this:
Development of a Lunar Regolith Thermal Energy Storage Model for a Lunar Outpost

[Twark_Main]

And you say that base can be made from locally-manufactured ceramic bricks?

Sure, why not? You can make porous bricks.

The strength will depend on porosity, which will limit the maximum height/depth of the regolith on top. So there will be a whole-system optimization between maximum vertical dimension and brick porosity. You'll also trade on bricks vs no bricks.

Thickness of the brick "foundation" layer (if any) will be an optimization between construction cost and operational round-trip energy efficiency. You also have to account for cracking and/or heaving due to CTE, including subsoil.

You know, standard stuff.

Has there been any formal research into this concept for possible Moon/Mars applications?
Any links would be appreciated.

Wait  - I found this:
Development of a Lunar Regolith Thermal Energy Storage Model for a Lunar Outpost

Not any that I knew of, but thanks for digging that up.

[DanClemmensen]

And you say that base can be made from locally-manufactured ceramic bricks?

Sure, why not? You can make porous bricks.

The strength will depend on porosity, which will limit the maximum height/depth of the regolith on top. So there will be a whole-system optimization between maximum vertical dimension and brick porosity. You'll also trade on bricks vs no bricks.

I'm not sure why you need to store heat, but if you do, one of the considerations includes extracting and distributing it. Sure, store it in red-hot sand, but you use at least some of it at near human body temperature. This means heat escaping through the top layer of a multiplayer insulating floor is not all lost. The top of the floor can be hard ceramic but not a good insulator while lower layers can be ceramic "foam" but with some hard structural supports for the hard upper floor, and can include low-temperature extraction pipes. Walls and roof of the sand pile are more "foam" ceramic. Once the colony can manufacture it, add an outer MLI, but before then just use oversize sand piles.

[Lampyridae]

Regolith in vacuum is very, very insulating. So much so that the top 10–15cm of lunar regolith are over 100°C in the blazing noon and underneath is around -13°C (260°K, the average temperature of much of the lunar subsurface day or night).

A set0up with a simple non-tracking, concentrating lens refracting into a hollowed-out tub of sand (eg by placing a glass tube inside to pack the sand and let the light in) could be dotted around the landscape to provide emergency heat sources/power supplies during the lunar night,

[sanman]

Instead of using Photovoltaic solar panels to produce electric power that then gets converted into heat via resistive heating elements for storing thermal energy in our Sand Battery, can we instead just use some more direct solar heating method - perhaps using Fresnel lenses - for greater solar energy conversion efficiency?

The ability of the sand to remain stable at very high temperatures of over 1000 °C gives it relatively good thermal energy storage density for a locally sourced material. But regolith isn't uniform and will vary in its composition and properties. How do we avoid smelting the sand/regolith? Or does it even matter?

Could we just build our large mound of sand around some central pole or post, and have a fresnel lens heating the top of the post which would then conduct heat into the rest of the sand pile? Maybe our post could be helical or coil-shaped, for better contact with the sand pile. Or do you want to heat the base of the sand pile, expecting the heat to travel upwards to distribute itself throughout the sand mound?

[sanman]

Regolith in vacuum is very, very insulating. So much so that the top 10–15cm of lunar regolith are over 100°C in the blazing noon and underneath is around -13°C (260°K, the average temperature of much of the lunar subsurface day or night).

A set0up with a simple non-tracking, concentrating lens refracting into a hollowed-out tub of sand (eg by placing a glass tube inside to pack the sand and let the light in) could be dotted around the landscape to provide emergency heat sources/power supplies during the lunar night,

Alright, so we can use a solar concentrating lens to achieve the required high temperatures for better thermal energy density. (Actually parabolic mirrors would probably be better than Fresnel lens.) I'm not sure how the glass tube thing works - is that supposed to be some kind of light-pipe or waveguide, to send the light directly inside the sand pile? Is it not easier to simply rely on thermal conduction to distribute heat across the sand pile?


And why only use the sand batteries as emergency power supplies, strewn across the lunar landscape?

Why not use a sand battery as a main energy store for a lunar base/outpost, if it's so scalable and relatively easy to build?
Are there any reliability issues?

[Twark_Main]

And you say that base can be made from locally-manufactured ceramic bricks?

Sure, why not? You can make porous bricks.

The strength will depend on porosity, which will limit the maximum height/depth of the regolith on top. So there will be a whole-system optimization between maximum vertical dimension and brick porosity. You'll also trade on bricks vs no bricks.

I'm not sure why you need to store heat, but if you do, one of the considerations includes extracting and distributing it. Sure, store it in red-hot sand, but you use at least some of it at near human body temperature. This means heat escaping through the top layer of a multiplayer insulating floor is not all lost.

You seem to be picturing this as built under a habitat. That may be fine, but it's not what I was picturing.

The top of the floor can be hard ceramic but not a good insulator while lower layers can be ceramic "foam" but with some hard structural supports for the hard upper floor, and can include low-temperature extraction pipes.

A decent idea, but it's probably getting over-complicated. I'm not even sure it makes sense to use any bricks, vs. just using loose regolith as insulation.

Walls and roof of the sand pile are more "foam" ceramic.

No need for walls or a roof.

Once the colony can manufacture it, add an outer MLI, but before then just use oversize sand piles.

The great thing about MLI is that it's so lightweight that you don't have to manufacture it in-situ. It's cheap enough to bring it with you.

[Twark_Main]

Is it not easier to simply rely on thermal conduction to distribute heat across the sand pile?

As Lampyridae wrote:

Regolith in vacuum is very, very insulating[, so] much so that the top [10–15 cm] of lunar regolith are over [100 °C] in the blazing noon and underneath is around [-13 °C] ([260 K], the average temperature of much of the lunar subsurface day or night).

And why only use the sand batteries as emergency power supplies, strewn across the lunar landscape?

Indeed.

[DanClemmensen]

And you say that base can be made from locally-manufactured ceramic bricks?

Sure, why not? You can make porous bricks.

The strength will depend on porosity, which will limit the maximum height/depth of the regolith on top. So there will be a whole-system optimization between maximum vertical dimension and brick porosity. You'll also trade on bricks vs no bricks.

I'm not sure why you need to store heat, but if you do, one of the considerations includes extracting and distributing it. Sure, store it in red-hot sand, but you use at least some of it at near human body temperature. This means heat escaping through the top layer of a multiplayer insulating floor is not all lost.

You seem to be picturing this as built under a habitat. That's not what I was picturing.

The top of the floor can be hard ceramic but not a good insulator while lower layers can be ceramic "foam" but with some hard structural supports for the hard upper floor, and can include low-temperature extraction pipes.

No need for that. The porous layer is the limiting factor either way.

 

Walls and roof of the sand pile are more "foam" ceramic.

No need for walls or a roof either.

Once the colony can manufacture it, add an outer MLI, but before then just use oversize sand piles.

The great thing about MLI is that it's so lightweight that you don't have to manufacture it in-situ. It's cheap to bring it with you.

No, I was thinking of a pile of sand on top of an insulating floor, to minimize heat loss through the floor into the ground below. But if heat flow in the regiolith is low enough, then no actual structure is needed: just drill a hole and start adding heat.

[Lampyridae]

And why only use the sand batteries as emergency power supplies, strewn across the lunar landscape?

I didn't say "only", I just said "could". It's a possible application in addition to the obvious ones. The users could be a swarm of autonomous rovers on the Moon, extending their area of operations instead of trundling back to the habitat to recharge every few hours or days. For Mars, the short night is a non-issue. The base power is the most obvious application that's already being discussed.

Alright, so we can use a solar concentrating lens to achieve the required high temperatures for better thermal energy density. (Actually parabolic mirrors would probably be better than Fresnel lens.) I'm not sure how the glass tube thing works - is that supposed to be some kind of light-pipe or waveguide, to send the light directly inside the sand pile? Is it not easier to simply rely on thermal conduction to distribute heat across the sand pile?

I was mostly thinking of making it dead simple. Trough concentrators are fine but they are designed to focus light onto a pipe which carries a working fluid, whereas a setup with a Fresnel lens can focus onto a more specific spot. What I envision is a simple thermal battery system would need is for sunlight to fall on an exposed area of sand in some configuration. Dead simple, easily produced by ISRU to serve a large base, virtually maintenance free.

The glass tube (think of an empty jam jar thrust into a bucket of sand) just exposes more sand area to illuminate instead of just the top, spreading the energy input. The thermal conductivity is pretty poor so only the first few cm can heat up quickly. Or maybe the glass goes inside a sintered regolith block which conducts the heat better and is insulated by the sand. Doubtless there are many better ways to distribute the energy into a tonne or so of sand but it's just a first pass idea.


https://opg.optica.org/osac/fulltext.cfm?uri=osac-2-3-667&id=406932


One of the issues with sand batteries as shown by your paper is that they are very scale sensitive. Too small and they won't last long. Too big, and you may as well spend the downmass to bring in lithium batteries or fuel cells. The paper you linked showed that, and the cylinder was only designed to last 52 hours of night at Shackleton, not the 336 hours of a full lunar night.

So I think it's a good idea to incorporate scaled-up sintered regolith thermal blocks into a hab's radiation shielding as you've been discussing.

[john smith 19]

Yeah, I was thinking mainly about storing thermal energy to last you through the lunar or martian night. Lunar day should allow plenty of excess energy collection from a good-sized solar farm, which you could then store up thermally inside this 'sand battery'.

The joker in the pack is that regolith is a poor thermal conductor (like sand). It's a similar issue with ground source heat pumps and borehole heat exchangers. You can extract/dump near into the material close to the borehole, but the rest stays at the temperature of the ambient. You need to put a lot of pipes through it to head up the whole mass (or blow hot air through it and make it semi-fluidised, then shut of the gas (indeed evacuate the tank) to store the heat.

[DanClemmensen]

Yeah, I was thinking mainly about storing thermal energy to last you through the lunar or martian night. Lunar day should allow plenty of excess energy collection from a good-sized solar farm, which you could then store up thermally inside this 'sand battery'.

The joker in the pack is that regolith is a poor thermal conductor (like sand). It's a similar issue with ground source heat pumps and borehole heat exchangers. You can extract/dump near into the material close to the borehole, but the rest stays at the temperature of the ambient. You need to put a lot of pipes through it to head up the whole mass (or blow hot air through it and make it semi-fluidised, then shut of the gas (indeed evacuate the tank) to store the heat.

As long as you don't melt the sand or the pipes, it does not matter. There is no requirement for uniform temperature. Load it in through the central hole at the concentrated solar temperature, and unload it via pipes that are at the appropriate distances.

[stefan r]

We need an iron production capability.  I keep seeing people writing "we can not melt the sand".  Better to go the opposite.  Melt the Regolith. First separate iron rich regolith from the rest using a magnet. 

I think we usually call them "iron pigs" but you can call it a "charged hot sand battery" if you want to. 

Boston Metals has a process for iron production using electrolysis.  It produces oxygen from the ore.  They are selling the idea as a way around using fossil fuel.  On Luna that oxygen production has some potential value. 

A big slab of molten glass holds a lot of heat.  Fill a honeycomb of iron with glass.  Let it shatter between hot cold cycles.

A sulfur pool has some advantages.  You can use sulfur as cement in a type of concrete. 

[stefan r]

Sorry, double posting. 

On Mars you have a CO2 atmosphere.  We can compress the gas and it becomes hot.  Carbon dioxide has low viscosity and should easily flow into or through sand.  With outside pressure at less than 1% of atmospheric pressure we can easily recover the energy put into compressing the gas. 

In daytime (assumed surplus electricity) the sand drops the temperature of the compressed atmospheric gasses.  Liquid carbon dioxide condenses.  That leaves the argon, nitrogen, and smaller amounts of oxygen and carbon monoxide in the vapor phase.  The liquid carbon dioxide exchanges heat with incoming compressed atmosphere and the sand. 

The carbon dioxide is better thought of as the working fluid for the nuclear reactor.  A large reservoir allows the cold side of the Carnot cycle to be nighttime temperatures.  The day to night contrast can add energy to the Carnot cycle.  Gas distillation is plumbing that we need anyway. Argon and nitrogen for atmosphere and fertilizer.  Oxygen and carbon monoxide are either useful or can be burned off.