31–40 of 190 posts
So this system could supply 12 houses? Shows the importance of proper insulation, which is still on our todo list.
Earlier quoted context omitted.
The article mentions that they heat the sand to 500°C, which is not possible with water (well, at least not without turning into steam along the way).
To be pedantic, yes you can but you'd need to pressurize it to uuhh... According to this calculator [0], you can get water to 370 degrees C if the pressure is 207 atmospheres, which is about the pressure of the ocean two kilometers deep. [0] https://www.engineeringtoolbox.com/water-vapor-saturation-pr...
I live in a desert where we have district cooling (and no shortage of sand or solar power), instead of district heating. Wonder if they can pull off the same trick.
Well you can't really do -600C sand (or anything), so the benefits of sand VS water largely diminished. "just" freezing water already gives you around 300C equivalent of sand (if my napkin is correct). Also the point of this plant is to exploit the counter-correlation of cheap electricity and cold. Usually there is a bigger correlation between cheap electricity and heat.
You can if you stagger AC/HP or even peltier elements.
For anyone interested in a breakdown of the basic logic, this recent blogpost that trended on HN is probably the best: https://austinvernon.site/blog/standardthermal.html Really interested in seeing how it fares in reality, almost sounds too good to be true.
There are significant trade-offs with this technology.
It's storing heat, so if you need electricity then you eat a lot of efficiency. I think Vernon said ~45% round trip efficiency. Batteries are 90%+.
The storage is at a high temperature (500-600C) which means that you can't use heat-pumps to produce the heat to be stored. This means that you miss out on ~400% energy gains possible from converting electricity to heat.
So the efficiency is pretty low.
That said, solar PV is really cheap and moving large amounts of earth into a pile is also a very much solved problem so in some cases, notably higher latitudes which have very long days and low heat/electricity demand in the summer and the opposite in the winter, it could still be a very good solution.
So why a surface sand silo instead of going down and using the soil/clay/bedrock/whatever is there? Ease of installation and maintenance?
presumably you need the insulation from the air, otherwise it would just sort of dissipate through the ground
A housing complex near mine got a massive tank like this installed thirty years ago, and I think they put it underground to be able to build a house on top.
Really like the idea, but my house alone has roughly 16 MWh/a heat consumption. Of which half gets consumed November through January. So this system could supply 12 houses? Shows the importance of proper insulation, which is still on our todo list.
It sounds to me like you're likely an outlier here, for curiosities sake, where do you live?
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The Wikipedia article says: "Rock, sand and concrete has a heat capacity about one third of water's. On the other hand, concrete can be heated to much higher temperatures (1200 °C) by for example electrical heating and therefore has a much higher overall volumetric capacity." and "Polar Night Energy installed a thermal battery in Finland that stores heat in a mass of sand. It was expected to reduce carbon emissions f…
I learnt some new concepts here, specific heat capacity vs overall volumetric, things I kind of understood intuitively, but now much clearer: If I add some fixed amount heat to some fixed volume of water, it might rise by 1℃, while the same volume of concrete rises by 3℃. And by the same logic, on release, that fixed volume of water dropping by 1℃ releases 3x as much heat as when that fixed volume of concrete drops b…
Also, looking at how hot water could theoretically get (decomposes between 2200-3300C), it looks like 1200C is an interesting limit. Above that and you get safety(practical) and cost issues with every material I could find (common salts, pure elements).
Sand just makes sense! Though, don't ever youtube sand battery.
Earlier quoted context omitted.
Well you can't really do -600C sand (or anything), so the benefits of sand VS water largely diminished. "just" freezing water already gives you around 300C equivalent of sand (if my napkin is correct). Also the point of this plant is to exploit the counter-correlation of cheap electricity and cold. Usually there is a bigger correlation between cheap electricity and heat.
> you can't really do -600C sand (or anything) You can if you stagger AC/HP or even peltier elements.
Earlier quoted context omitted.
The article mentions that they heat the sand to 500°C, which is not possible with water (well, at least not without turning into steam along the way).
To be pedantic, yes you can but you'd need to pressurize it to uuhh... According to this calculator [0], you can get water to 370 degrees C if the pressure is 207 atmospheres, which is about the pressure of the ocean two kilometers deep. [0] https://www.engineeringtoolbox.com/water-vapor-saturation-pr...