Author Topic: Sand Batteries for Scalable Energy Storage on Moon / Mars? (Read 12160 times)

colbourne · « **Reply #20 on:** 10/01/2022 12:54 am »

A very cheap and efficient battery can be made with a very large flywheel with a motor/generator attached.
This could be made with locally sourced regolith. It is ideal for short term day/night storage from solar panels etc.
For use in vehicles a lightweight carbon fibre flywheel in a vacuum could be used but this raises other problems of gyroscopic forces.

Barley · « **Reply #21 on:** 10/01/2022 02:01 am »

Quote from: colbourne on 10/01/2022 12:54 am

A very cheap and efficient battery can be made with a very large flywheel with a motor/generator attached. This could be made with locally sourced regolith.

Could you go into more details?

As I understand it the energy that can be stored in a fly wheel depends on the tensile strength of the rotor, not the mass. Both the centripetal force and energy stored scale as mω².

If you have a light, strong flywheel, you can spin it very fast. If you add mass with buckets of sand, you can't spin it as fast before it flies apart and can't store any more energy.

If you want to use regolith, you'll want to use it in a form that is self-supporting. Perhaps solid stone disks or processed into fiberglass. This would be a lot harder than putting loose gravel in buckets.

colbourne · « **Reply #22 on:** 10/02/2022 01:47 pm »

I would assume they would use a section of the spaceship and fill it with regolith. If very heavy it does not need to spin very fast. The low atmospheric pressure on Mars will reduce friction losses.

lamontagne · « **Reply #23 on:** 10/07/2022 01:35 pm »

A well insulated installation on Mars or the Moon will probably overheat, making the whole question somewhat moot.
Anything protected with a meter of regolith will also almost certainly overheat. Any type of food production using plants will definitively overheat.

Getting rid of thermal energy is more to the point, I believe.

su27k · « **Reply #24 on:** 10/17/2022 02:35 am »

Related: https://twitter.com/DrPhiltill/status/1581302318263193603

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Interesting paper, downloadable from the link, that shows it takes only about half as much mass as batteries for the full lunar system to use sintered lunar soil for thermal energy storage to create electricity during the lunar night. https://upcommons.upc.edu/handle/2117/374285

lamontagne · « **Reply #25 on:** 10/17/2022 02:53 am »

Quote from: su27k on 10/17/2022 02:35 am

Related: https://twitter.com/DrPhiltill/status/1581302318263193603

Quote
Interesting paper, downloadable from the link, that shows it takes only about half as much mass as batteries for the full lunar system to use sintered lunar soil for thermal energy storage to create electricity during the lunar night. https://upcommons.upc.edu/handle/2117/374285

I have serious doubts about their mass budgets, but it's an interesting concept. The efficiency of electrical production may be optimistic and they don't seem to have actually studied that part, just put in 20%, 10% and 5% efficiencies as placeholders, At least these seem reasonably low. However it's really cold on the Moon at night so there may be a good temperature gradient, but my experience on Earth with geothermal systems, which this is, in a way, is that they are pretty labor intensive to set up.
You could probably get better efficiency be electrolysing some in situ water, and recombining it. But it would be worth another paper, at least. Wonder how hard it is to produce basaltic fibers on the moon from regolith? Then you could have in-situ tanks, with perhaps only the resin coming from Earth...