51–60 of 190 posts
Helsinki did the same thing but storing the energy in water instead of sand: https://helsinkismart.fi/worlds-largest-cavern-thermal-energ...
90% roundtrip efficiency is pretty darn cool. I am not an engineer, but is it the high temperature difference that makes that possible?
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.
90% roundtrip efficiency is pretty darn cool. I am not an engineer, but is it the high temperature difference that makes that possible?
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
It'll just be cheaper to build it on the ground than to dig a big hole and then build it in the hole.
Earlier quoted context omitted.
I wonder if there are any chemical effects from heating the sand to 500 degrees Celsius. Finely roasted sand.
This is crushed soapstone, so it's mostly talc. Talc is apparently more or less stable up to about 800C, where it starts to break down into enstatite and silica: https://nvlpubs.nist.gov/nistpubs/jres/15/jresv15n5p551_A1b.... If it were pure silica sand, you could presumably get even hotter before anything changes chemically, but at the that point you start having materials issues with metal parts of the system: 500C…
Earlier quoted context omitted.
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...
Interestingly that's also about the pressure of gas in scuba tanks. Can't imagine how much energy to pressurize water to that
This is super cool but the ending is bizarre. > A comment on the YouTube video below complained, “Not a word about return on investment in the presentation. That means it’ll never pay off” MAGAlomaniacs are everywhere these days. Given the supposed 50+ year lifespan of such a battery, I find it hard to believe it doesn't turn a profit at some point. And I understand that debunking low-effort accusations is asymmetric…
If you made 30k a year for 50 years you'd return 1.5m from your 1m investment, but you're only making 3%, which is a low return especially given the future risk (you'd have to run for 33 years just to get your initial investment back)
Either way it's worthwhile, because the reason people expect 10% is because the externalities are borne by others. Majority of people and countries in the world do not deem ROI to be the sole or even primary driver for investment, and judging investments only on the immediate financial reward already biases the conversation
This is super cool but the ending is bizarre. > A comment on the YouTube video below complained, “Not a word about return on investment in the presentation. That means it’ll never pay off” MAGAlomaniacs are everywhere these days. Given the supposed 50+ year lifespan of such a battery, I find it hard to believe it doesn't turn a profit at some point. And I understand that debunking low-effort accusations is asymmetric…
Wonder if one could use staggered heatpumps here - in summer there's quite a bit of heat out there (some of which needs to be removed) so you could get 3-6x more bang for your buck.
The coefficient of performance for a heat pump from with cold/hot of 10C/40C is about 10 - this is ballpark where a domestic heating heat pump sits - this is why a heat pump house needs to be well-insulated to work - the heating loop isn't actually hot-hot like with a boiler). From 10C to 500C, it's 1.5. That's 9/0.5 = 18 times less advantage.
At any delta, you can eke out a bit of advantage as COP is always over one, but at some point overheads in the system start to overwhelm your theoretical advantage and you might as well keep it simple and use a cheap and reliable resistor to heat things for dead-cert COP of 1.
You could use a heat pump with a higher COP if you have a really gigantic tank that you only heat to about 40-50C, but obviously the thermal transfer from that is pretty bad and getting it where it needs to go while still being hot enough to be useful is a problem.