Storing Renewable Energy Using Thermodynamics | Hacker News Reader

Storing Renewable Energy Using Thermodynamics

airthium.com

13 pointsmartind8120 comments

Similar tech, I expect:

https://arstechnica.com/information-technology/2017/04/start...

https://www.thenational.ae/uae/compressed-air-the-battery-of...

https://www.engadget.com/2013/09/16/sustainx-turns-on-first-...

Assuming about 300K ambient temperature (on site, above ground), 800K working temperature (store the heat at 500°C) and that the second law of thermodynamics still holds, the roundtrip efficiency can not be 70%. It must be below 40%, and not just a bit below.

I think you might be wrong but my thermal is very rusty. Where you are wrong is that you might be forgetting the over 100% efficiency in heat transfer when using a heat pump.

http://energystorage.org/energy-storage/technologies/pumped-...

https://www.economist.com/news/technology-quarterly/21603184...

http://wordpress.ei.columbia.edu/lenfest/files/2012/11/Abstr...

You are right, I stand corrected. If instead of the ambient temperature, we have a cryogenic storage tank, getting 60% round-trip may be feasible in large scale.

I don't follow. The second law of thermodynamics doesn't say anything about the specific efficiency limits of an energy conversion or storage system. Ideal reversible systems can maintain entropy if fully isolated (e.g. insulated). In real systems, perfect isolation is impractical, of course, but the resulting loss of energy is a function of the shortomings of the manufacturers of the system (e.g. use of low R factor insulation, high resistance electrical conductors, or poorly shaped pump impellers, etc), not some simple "2nd law limit".

https://en.wikipedia.org/wiki/Carnot%27s_theorem_(thermodyna...

Heat->mechanical energy can only be (1-Tc/Th) efficient. But mechanical energy->heat can be 1/(1-Tc/Th) efficient, so you can get close to unity round trip efficiency.

That's why people use heat pumps to heat buildings, because you get more heat out than energy in (the extra heat comes from the ground).

I need further explanation before this makes sense to me. How can M->H have greater than 100% efficiency?

You mentioned getting heat from the ground, but that only happens when the ground heat is greater than T_h, right? At which point it just sounds like geothermal but with extra steps.

A heat pump transfers heat from the cold side to the hot side, making the hot side hotter and the cold side colder. The thing you're heating is at Th and ground is at Tc. By putting 1 J of mechanical work in, you might draw 3 J from the cold side and pump 4 J into the hot side.

I am missing a profound description of the technology. Where is the innovation? The website containing only some key words is too sparse to arouse serious interest.

Same observation here ... seems to be a bit nebulous ...

They claim 0.05€ (~0.06USD) per KWh lifetime cost. Anybody know how that compares to current prices of grid-scale batteries? I can't find a up-to-date source.

Pumped hydro is about 3x as expensive, and batteries I think are still more expensive than pumped hydro, so it's absurdly cheap.

Pumped hydro and flywheels are at least demonstrated cost effective solutions. This? They don't even provide any details.

The issue with storing energy is that en investment of building infrastructure to transport the energy where it is deficit of energy is a more market safe solution.

Interesting concept. Wake me up when they demonstrate 10MWh.

forgive me if this is totally petty, but: "thermodynamic" is an adjective, not a noun.

"Storing Renewable Energy Using Thermodynamic" ... what, exactly?

First, not saying I believe that these guys are legit, but "thermodynamics" is a noun. Thermodynamic energy is a type of energy, like chemical energy is a type of energy. There is also nuclear, stored, potential, light, kinetic, and I'm sure I'm missing a few.

These are all basic physics concepts. These guys are claiming to be able to store the energy as thermal energy, and then get it back out at 70% efficiency without much degradation inside of 25 years.

All these ideas are plausible from a physics point of view, but I don't buy this simply because it requires an efficient way of converting heat to energy. If this existed, it would already be a holy grail for other reasons. Being able to turn the waste-heat from an engine back into more energy efficiently would be incredible. Right now, to get energy from heat, you typically need the heated material to be near something that's very cold, and you use the difference in temperature to get energy out of it. Or you boil water and spin turbines. It sounds like MAYBE that's what these guys are doing, if what they are claiming to be able to do is legitimate.

thermodynamics, yes.

"thermodynamic" is an adjective that denotes "having to do with thermodynamics".

this is utterly petty, i know, but it really jars.

Indeed. I fixed the title.

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