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'Freeze-thaw battery' stores electricity long-term for seasonal release

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Re: 'Freeze-thaw battery' stores electricity long-term for seasonal release

#101

Post by pfdietz »

jessriedel wrote: post #100
pfdietz wrote: post #90

Earlier quoted context omitted.

Storing heat in rock is very natural. It's how geothermal works, after all. The basic idea is that the thermal time constant of a uniform sphere (or other shape of fixed aspect) is proportional to the square of its radius. So, for a sufficiently large sphere, the time constant can become very long, >> 1 year. Rock is a good choice because it's very cheap. The other thing one can do is store cold . This is useful not…

> The basic idea is that the thermal time constant of a uniform sphere (or other shape of fixed aspect) is proportional to the square of its radius. Shouldn't the thermal mass go like volume (radius cubed) while the power conducted away go like surface area (radius squared) so the time to cool should go like mass/power ~ volume/area, so linearly in radius?

The rate at which heat conducts out is also affected by the temperature gradient, which is inversely proportional to radius.

Re: 'Freeze-thaw battery' stores electricity long-term for seasonal release

#102

Post by t0mas88 »

PaulDavisThe1st wrote: post #69
t0mas88 wrote: post #65

Earlier quoted context omitted.

If you use solar power in a climate like Germany you will get that kind of math. Let's say you use 8000 kwh per year, and you have the solar capacity to create 8000 kwh per year. Assume you already have a normal home battery of ~14kwh so day/night is not an issue, the solar production during daytime charges the battery and all night time power comes from the battery. Now your big problem is that 70% of the 8000 kwh s…

> The other option is to buy much more solar panel capacity than you need, You need the space to install them also. I have a 6.6kW array, and would need 3x that capacity to heat my home using electrically-powered air source heat pumps during the winter months. Even with 0.75 acres / 0.30 hectares, that would be quite a lot of my property covered by panels, and way more than could ever feasibly fit on the roof (the cu…

Good roof space may become a sales argument for houses in the future. Mine happens to have a huge flat roof slightly sloped to the south. I have 8 kW solar and that’s less than half the roof covered.

Re: 'Freeze-thaw battery' stores electricity long-term for seasonal release

#103

Post by sacrosancty »

SECProto wrote: post #53
sacrosancty wrote: post #47

Earlier quoted context omitted.

Besides insulation, there's no hope of storing thermal energy as steam because the density is 1000 times lower than ice or water while the specific heat is similar, so the heat capacity per unit volume is about 1000 times lower.

Storing heat as steam is actually very good and efficient - as long as you're storing the heat for location shifting, not temporal shifting. It's regularly used in combined heat + power plants (Yeah, I know I'm being both pedantic and off topic, since the discussion here is specifically about seasonal storage)

Doesn't the word "storing" already mean temporal shifting?

Re: 'Freeze-thaw battery' stores electricity long-term for seasonal release

#104

Post by [deleted] »

pfdietz wrote: post #101
jessriedel wrote: post #100

Earlier quoted context omitted.

> The basic idea is that the thermal time constant of a uniform sphere (or other shape of fixed aspect) is proportional to the square of its radius. Shouldn't the thermal mass go like volume (radius cubed) while the power conducted away go like surface area (radius squared) so the time to cool should go like mass/power ~ volume/area, so linearly in radius?

The rate at which heat conducts out is also affected by the temperature gradient, which is inversely proportional to radius.

[deleted]

Re: 'Freeze-thaw battery' stores electricity long-term for seasonal release

#105

Post by jdmichal »

NickNameNick wrote: post #74
jdmichal wrote: post #63

Earlier quoted context omitted.

Do the tubes never cross a road? Why knock down a building instead of taking a vent to a street?

I think you're underestimating the size of vent needed. They'll turn the entire plot into a single giant chimney, and decorate the face to match the houses either side of it. like this: https://en.wikipedia.org/wiki/58_Joralemon_Street

Ah I was thinking of the subway vents you see along the street and sidewalks in New York. That is indeed a drastically different scale.
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