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Comment by BenoitEssiambre | Hacker News Reader

Do people talk about storing heat in houses in cold climate regions where there would be no efficiency losses? I always wondered if you could store solar panel energy in large cubes of firebricks that you could dissipate to heat your house. There seems to be some commercial systems (eg. by Steffes) but they are expensive, offer just an overnight amount of energy and seem to be usually used to smooth grid consumption. Why isn't there a version of this designed to store solar energy for longer periods in the winter when insolation is low?

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A quick back of the envelope calculation: A 6.5 feet by 6.5 feet cube (2mx2m) could store about 4500kWh at 1000C, this seems close to energy need for heating for more than a month ( Energy density of fireclay from here: https://www.engineeringtoolbox.com/sensible-heat-storage-d_1... ).

That's a very large amount of bricks and a potentially dangerously high temperature but still...

Pottery kiln manufacturers might be able to design this? Kilns go to higher temp than this and are used indoors.

Firebrick energy storage has been proposed! If one uses SiC bricks, which might act as their own resistive heaters, one could operate up to 1800 C.

That's cool if the bricks themselves can be resistive heaters. You might burn elements pretty quickly at those temps.

Right. The ordinary firebrick system with separate heaters would be limited to about 1000 C, although I've seen a concept using sand flowing through a heater that would reach 1200 C.

In cold climate regions solar power can't heat houses.

If talking about individual houses, not condos, most economic solution is a two-stage water heating powered by a wood pellet or gas burner, where the second stage has a 3-5 ton water tank as a heat storage, so that the burner doesn't need to run continiously. This is a proven, simple, maintainable and safe solution.

We're talking ~50-150kW thermal power here. Solar can not reach that. Several cubic meters of almost-boiling water is hazardous enough.

Keeping a highly corrosive liquid at 700C in your own home.. no, thanks.

Passive solar heating requires loads of storage, and often active systems to transfer heat.

But there’s a much easier, more economical way to use solar power for heating in cold climates: heat pumps! PV panels give you electricity and then you get 2-3X the power for heating. There are economies of scale in the supply chain, low CapEx, and not a lot of plumbing.

yeah, maybe solar plus geothermal heat pump would be the most advantageous system right now. Although you can't store and there isn't much solar in December and January here.

Geothermal heat pumps "store"...

They pump heat into the ground in the summer for air conditioning and pump it back out in the winter for heating.

You don't need to be "much", you need to ideally match the TCO of other fuels (or come close, if you care more about reducing fossil fuel use and CO2, which is arguably more important than TCO. People obsess about heating costs but then run out and buy $60,000 luxury cars to do an hour+ commute each day in.)

Not all cold climates lack sun. Here at 6-10,000' in northern New Mexico, we still get lots of sun in the winter, but also very cold (overnight) temperatures. Air source heat pumps make more sense in almost every way, and will operate down to -13F/-25C.

Our 6.6kW array can provide roughly 1/3 the electricity we need to heat all of our 1875 adobe home, which is poorly insulated at best. If this was closer to passivhaus standards, I imagine it could get close to 100%.

Air source heat pumps are pretty cheap and work well to low temps now. You might still need the grid, but can net-out over the year.

Yeah, as I just mentioned adjacent to this, our 6.6kW array produces 1/3 of what we need during the winter, but 3x what we need in the summer. Last year (the first full year), we generated 93% of our electricity use over the full year. We heat solely with air source heat pumps.

What is the benefit of storing the heat of wood pellet or gas? Can't you just use those on demand?

Also hot firebricks was my proposed solution. Water has comparatively low energy density and I wouldn't want the corrosive liquid either.

I understand that there isn't a ton of sun in winter months but maybe you could over provision your PV, store summer or fall solar energy and top up with whatever you can get from the sun in the winter?

> What is the benefit of storing the heat of wood pellet or gas? Can't you just use those on demand?

Burners scale badly to lower power. Also, automatic pellet feeders are prone to breaking down, which you absolutely do not want to happen when it's -15C on the outside.

Thus a thermal buffer is needed.

> Also hot firebricks was my proposed solution. Water has comparatively low energy density

Water actually has about four times more energy density than bricks.

> I understand that there isn't a ton of sun in winter months but maybe you could over provision your PV

Prohibitevily expensive in both money and area needed

> store summer or fall solar energy

Impossible. Where and how would you store enough?

Inter-seasonal heat storage is a thing, albeit rare.

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