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Comment by leobg | Hacker News Reader

What would interest me: Can I do this locally, at the site of the consumer? Take the unused PV output of my house in summer to fill my house’s tank with natural gas for use in winter? Is that something that would be technically feasible today?

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Why convert to gas for heating later when you can just store heat itself?*

There was an article/discussion here recently about heat batteries using sand to store heat for months, to use for heating in winter. This tech seems fairly simple to implement at scale.

https://www.abc.net.au/news/science/2022-07-19/sand-battery-...

https://news.ycombinator.com/item?id=32006791

*This is a rhetorical question, I'm sure everyone can easily think of many benefits. But there is elegance in simplicity.

In the residential context, the magic word here is "ground source heat pump". A really big coolant loop that stores heat underground. Depending on the jurisdiction and loop size, figure it will cost $15,000+

Storing heat for months requires really, really good insulation, and insulating many small stores is far more expensive than insulating one big store (essentially a square-cube thing).

So this kind of thing may only be viable for industrial processes.

Sounds great!

I wonder: Why is sand better than the dirt that’s already on site? Dirt, after all, contains water, which I believe should have an even higher thermal capacity, or not?

Also: How about combining this approach with a heat pump instead of resistive heating?

Hydrogen. This is my neighbor: https://hoermannsolar.de/wohnen-im-wasserstoffhaus/

I keep reading that H2 storage is difficult, lossy, and dangerous. H2 gas stations have blown up every now and then. Has that changed?

no.

Hydrogen can be stored underground (and is), just like natural gas. This is much cheaper per unit energy storage capacity than storing energy in batteries.

there is a short term battery based storage but the long term storage for the winter months is the h2 storage. I think the system is very expensive but a cool prove of concept and for sure a step in the right direction.

Do you have an idea of how much that system costs? I mean if you could pay 100k once and be free of all energy bills for the lifetime of the house/the system it could be quite a value proposition. May Putin, OPEC and the government do what they want - you just do your own power and heat, with no more middlemen.

AFAIK H2 is way more difficult to contain than natural gas, as the molecules are so tiny. Very hard to build a container that doesn't continuously leak the gas.

Hydrogen has been stored underground in multiple places. This is not some speculative technology, it actually exists. The problem you describe is not a blocker. Granted, underground storage is at a larger scale than for an individual. Storing hydrogen in your home is probably not a good idea. Storing thermal energy underground, on the other hand, could make sense for seasonal storage. Ground source heat pumps essentially do that.

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