4 ms·

Tangential thought: is there a sane physical upper limit to power storage/generation in a given space (say, 1cc)? Sometimes helps to bracket the question to pre

Tangential thought: is there a sane physical upper limit to power storage/generation in a given space (say, 1cc)? Sometimes helps to bracket the question to predict what's possible & reasonable. (Comparable ex.: total maximum possible solar energy capture is 1367 watts/m^2; circumstances will limit that around 10%)

zyxley 12y ago
From what I understand, with assorted chemical energy storage technologies you can get a (for our purposes) arbitrarily high power density... as long as you're also willing to deal with arbitrarily high volatility. See stories about laptop batteries igniting for an example just with current batteries. Of course, if you're talking about scifi theoreticals, the thing to do would be to calculate the energy from mixing X/2 volume of matter with X/2 volume of antimatter (presumably with some amount of the total volume skimmed off the top for containment structure).
greggyb 12y ago
Since energy and mass are tied, the upper limit would be the point at which you are about to create a black hole, wouldn't it?
- deeviant 12y ago
  Black holes are almost the perfect battery. Small black holes decay very quickly, a black hole the mass of, let's say a small mountain, would decay almost immediately, releasing it's energy as hard gamma via hawking radiation, whose energy could be captured and used via multiple processes including some sort of sterling engine/photovoltaic mechanism. If some how you were able to create a small "artificial black hole" you could just feed it mass, any mass, and it would be converted directly in energy, as if it were a matter/anti-matter reaction. At least, that's what my two semesters of modern physics and latent desire to be eventually be a sci fi author tell me. I am reasonably sure nature has some sort of small print that kills my awesome idea, like requiring 100x to create said black hole than energy released, bleh nature. IANAP.
  - benjiweber 12y ago
    Black holes were one of the power sources in Star Trek http://en.memory-alpha.org/wiki/Artificial_quantum_singularity#Artificial_quantum_singularity http://en.memory-alpha.org/wiki/Artificial_quantum_singulari...
teraflop 12y ago
Well, based on the characteristics Wikipedia quotes for Pu-238 radioisotope thermal generators, they can store about 10^8 times as much energy (per unit volume) as lithium-ion batteries. So that's a lower bound.
- deeviant 12y ago
  Yes, but they actually provide a very small amount of current per weight, as it's just a decay pile creating heat which is then fed into a TEC, which have very low efficiency (like really low something well below 10%).
  - teraflop 12y ago
    Yup. It's all a matter of what you want to optimize for.
ethbro 12y ago
> is there a sane physical upper limit to power storage/generation in a given space (say, 1cc)? Start off with e=mc^2, revise downward with appropriate number of engineering constraints. I'd imagine in practice that gets limited mostly by battery chemistry. So something like total reaction energy of components * conversion efficiency - conversion machinery mass - packaging / safety mass. Which, afaict, is why "battery breakthroughs" all tend to be in the chemistry or conversion efficiency.
- deeviant 12y ago
  As I understand it, much of the "battery breakthroughs" are generally along the lines of attempting to create a balance between capacity, discharge-recharge rate, safety and cost. The conversion efficiency of most batters is pretty good, it's making a long lasting, high capacity, quickly discharging/recharging and safe battery that's also cheap that is difficult. While pretty much everything above is related to chemistry/conversion efficiency, I was just trying to define the efforts a bit more along the goals.
- ctdonath 12y ago
  Considering water is common and a typically heavy substance, that gives about 89,876,000 MJ/cc. Uranium is about 19x heavier, giving a hard practical upper limit (natural occurring) of 1,710,340,280 MJ/cc ... but is much harder to come by and maintain safely. Chemically, seems XeF2 has the upper bound on energy density, but I can't find the energy per volume (which, from molecular structure, looks astoundingly high). ...not that you want pure Fluorine as exhaust...
CapitalistCartr 12y ago
Batteries have much less energy density than gasoline, diesel, or kerosine, so I'd use those as a reference. Anyone who can accomplish densities comparable to those fuels will rock the World.
- maxerickson 12y ago
  Wikipedia has a decent article on this: http://en.wikipedia.org/wiki/Energy_density http://en.wikipedia.org/wiki/Energy_density By unit mass, lithium ion batteries have about 1/50th the energy of gasoline.
  - ctdonath 12y ago
    Interesting link. My interest being more about volume than mass, lithium ion batteries have about 1/12.3 the energy of gasoline per volume. Does make for a better showing. While volume isn't mentioned in the link, I'm surprised that supercapacitors fare so poorly per weight.
    - cromwellian 12y ago
      Other interesting comparisons would be usable power. ICE is about 20% efficient, but electric motors are 90% efficient. So a lithium ion gas tank needs about 4x less energy.
      - zurn 12y ago
        Good coal, diesel and gas plants reach ~50% in power generation (and marine propulsion in diesel case), rocket engines 60+% (thrust).

zyxley 12y ago

From what I understand, with assorted chemical energy storage technologies you can get a (for our purposes) arbitrarily high power density... as long as you're also willing to deal with arbitrarily high volatility. See stories about laptop batteries igniting for an example just with current batteries. Of course, if you're talking about scifi theoreticals, the thing to do would be to calculate the energy from mixing X/2 volume of matter with X/2 volume of antimatter (presumably with some amount of the total volume skimmed off the top for containment structure).

greggyb 12y ago

Since energy and mass are tied, the upper limit would be the point at which you are about to create a black hole, wouldn't it?

deeviant 12y ago
Black holes are almost the perfect battery. Small black holes decay very quickly, a black hole the mass of, let's say a small mountain, would decay almost immediately, releasing it's energy as hard gamma via hawking radiation, whose energy could be captured and used via multiple processes including some sort of sterling engine/photovoltaic mechanism. If some how you were able to create a small "artificial black hole" you could just feed it mass, any mass, and it would be converted directly in energy, as if it were a matter/anti-matter reaction. At least, that's what my two semesters of modern physics and latent desire to be eventually be a sci fi author tell me. I am reasonably sure nature has some sort of small print that kills my awesome idea, like requiring 100x to create said black hole than energy released, bleh nature. IANAP.
- benjiweber 12y ago
  Black holes were one of the power sources in Star Trek http://en.memory-alpha.org/wiki/Artificial_quantum_singularity#Artificial_quantum_singularity http://en.memory-alpha.org/wiki/Artificial_quantum_singulari...

teraflop 12y ago

Well, based on the characteristics Wikipedia quotes for Pu-238 radioisotope thermal generators, they can store about 10^8 times as much energy (per unit volume) as lithium-ion batteries. So that's a lower bound.

deeviant 12y ago
Yes, but they actually provide a very small amount of current per weight, as it's just a decay pile creating heat which is then fed into a TEC, which have very low efficiency (like really low something well below 10%).
- teraflop 12y ago
  Yup. It's all a matter of what you want to optimize for.

ethbro 12y ago

> is there a sane physical upper limit to power storage/generation in a given space (say, 1cc)? Start off with e=mc^2, revise downward with appropriate number of engineering constraints. I'd imagine in practice that gets limited mostly by battery chemistry. So something like total reaction energy of components * conversion efficiency - conversion machinery mass - packaging / safety mass. Which, afaict, is why "battery breakthroughs" all tend to be in the chemistry or conversion efficiency.

deeviant 12y ago
As I understand it, much of the "battery breakthroughs" are generally along the lines of attempting to create a balance between capacity, discharge-recharge rate, safety and cost. The conversion efficiency of most batters is pretty good, it's making a long lasting, high capacity, quickly discharging/recharging and safe battery that's also cheap that is difficult. While pretty much everything above is related to chemistry/conversion efficiency, I was just trying to define the efforts a bit more along the goals.
ctdonath 12y ago
Considering water is common and a typically heavy substance, that gives about 89,876,000 MJ/cc. Uranium is about 19x heavier, giving a hard practical upper limit (natural occurring) of 1,710,340,280 MJ/cc ... but is much harder to come by and maintain safely. Chemically, seems XeF2 has the upper bound on energy density, but I can't find the energy per volume (which, from molecular structure, looks astoundingly high). ...not that you want pure Fluorine as exhaust...

CapitalistCartr 12y ago

Batteries have much less energy density than gasoline, diesel, or kerosine, so I'd use those as a reference. Anyone who can accomplish densities comparable to those fuels will rock the World.

maxerickson 12y ago
Wikipedia has a decent article on this: http://en.wikipedia.org/wiki/Energy_density http://en.wikipedia.org/wiki/Energy_density By unit mass, lithium ion batteries have about 1/50th the energy of gasoline.
- ctdonath 12y ago
  Interesting link. My interest being more about volume than mass, lithium ion batteries have about 1/12.3 the energy of gasoline per volume. Does make for a better showing. While volume isn't mentioned in the link, I'm surprised that supercapacitors fare so poorly per weight.
  - cromwellian 12y ago
    Other interesting comparisons would be usable power. ICE is about 20% efficient, but electric motors are 90% efficient. So a lithium ion gas tank needs about 4x less energy.
    - zurn 12y ago
      Good coal, diesel and gas plants reach ~50% in power generation (and marine propulsion in diesel case), rocket engines 60+% (thrust).