3 ms·

Nit: we take 20w of chemical energy not electrical one like computers, way worse efficiency compared to solar panels Id say

im3w1l 2y ago
Our current society converts chemical energy to electrical, not the other way round. So its the electrical energy user that needs a lossy conversion step.
- tlb 2y ago
  Fossil fuel plants are chemical -> heat -> mechanical -> electrical. The heat -> mechanical step is the inefficient one, sadly limited to ~40% efficiency even with very fancy machinery. Most other conversions can be above 90% efficient.
  - pfdietz 2y ago
    The efficiency of gas-fired combined cycle power plants can exceed 60% (lower heating value). And their capex is just over $1/W. Combustion turbines are amazing. With a SOFC topping cycle they might approach 70-80% efficiency. SOFC with just a combustion turbine (no steam bottoming) could exceed 60%. Granted, SOFCs are direct chemical->electrical conversion, but their waste heat is very usefully hot. I don't think it's entirely a coincidence that nuclear power plants in the US stopped being built about the same time combustion turbines (by themselves, without the steam bottoming cycle) reached efficiency parity with high temperature steam turbines. (SOFC = solid oxide fuel cell, which operate around 1000 C.) ("Lower heating value" is based on energy that could be obtained burning natural gas to CO2 and water vapor. An additional 10% could be obtained by condensing the water vapor to liquid, this is "higher heating value".)
raverbashing 2y ago
That's why the most efficient use of Superman would be to turn a giant crank generating energy
- pfdietz 2y ago
  https://www.smbc-comics.com/index.php?db=comics&id=2305 https://www.smbc-comics.com/index.php?db=comics&id=2305
hwillis 2y ago
Actually, no! Producing ATP is ~30% efficient, which is much better than premium consumer solar panels. And while that heat is technically waste, even if it was more efficient we would still generate heat other ways just to keep warm. What's even more shocking is that conversion of food to energy period is ~90% efficient, which is crazy to me. The fact that you can burn food and measure the energy given off, and that's very close to how much energy you get from eating it- that's insane. The efficiency of the human body is all over the place. Muscles are only ~30% efficient, and the rest is waste heat... but humans walk using orders of magnitude less power than any walking robot. As far as I know we have never made a powered walking machine that is 10% as efficient as a person. The only way we can beat it is with a carefully balanced, specially-lubricated pair of legs that is leaned downhill on a treadmill and powered by gravity.
- fragmede 2y ago
  I'd wait until walking robots are commonplace before discounting our ability to make an efficient one. I don't think I've seen one in person yet.
  - hwillis 2y ago
    I wouldn't. We have been trying[1]; humans are genuinely shocking in this way. Mechanical systems should have so many advantages over humans; springs are 10x better than tendons, motors are 3x better than muscles. It's possible humans evolved walking as a predatory tactic. Even if we develop a super-efficient walking robot, humans are efficient at several speeds, and keep that efficiency while varying their stride and foot placement, and with one of the largest most complex brains of any animal. And the ratio of leg/torso length is pretty variable among humans! Not to mention the flexible spine and swinging hips should be a huge energy sap, but they just kind of... aren't. Beating human locomotion in the general case is pretty far off. It's a combination of body plan, extreme optimization of joints and energy storage, and really good algorithms. One killer feature of the human body is synovial fluid. It's very thin, non-newtonian, self-replenishing and contained in particularly low-friction bearing surfaces. It's certainly better than 99.9% of mechanical joints, because these surfaces filter, heal and re-lubricate themselves. Mechanical joints have sticky grease so they stay lubricated without maintenance, and work in the presence of water and grit. It's doubtful that any joint that doesn't heal itself can compete, long-term. [1]: https://spectrum.ieee.org/durus-sri-ultra-efficient-humanoid-robot https://spectrum.ieee.org/durus-sri-ultra-efficient-humanoid...

im3w1l 2y ago

Our current society converts chemical energy to electrical, not the other way round. So its the electrical energy user that needs a lossy conversion step.

tlb 2y ago
Fossil fuel plants are chemical -> heat -> mechanical -> electrical. The heat -> mechanical step is the inefficient one, sadly limited to ~40% efficiency even with very fancy machinery. Most other conversions can be above 90% efficient.
- pfdietz 2y ago
  The efficiency of gas-fired combined cycle power plants can exceed 60% (lower heating value). And their capex is just over $1/W. Combustion turbines are amazing. With a SOFC topping cycle they might approach 70-80% efficiency. SOFC with just a combustion turbine (no steam bottoming) could exceed 60%. Granted, SOFCs are direct chemical->electrical conversion, but their waste heat is very usefully hot. I don't think it's entirely a coincidence that nuclear power plants in the US stopped being built about the same time combustion turbines (by themselves, without the steam bottoming cycle) reached efficiency parity with high temperature steam turbines. (SOFC = solid oxide fuel cell, which operate around 1000 C.) ("Lower heating value" is based on energy that could be obtained burning natural gas to CO2 and water vapor. An additional 10% could be obtained by condensing the water vapor to liquid, this is "higher heating value".)

raverbashing 2y ago

That's why the most efficient use of Superman would be to turn a giant crank generating energy

pfdietz 2y ago
https://www.smbc-comics.com/index.php?db=comics&id=2305 https://www.smbc-comics.com/index.php?db=comics&id=2305

hwillis 2y ago

Actually, no! Producing ATP is ~30% efficient, which is much better than premium consumer solar panels. And while that heat is technically waste, even if it was more efficient we would still generate heat other ways just to keep warm. What's even more shocking is that conversion of food to energy period is ~90% efficient, which is crazy to me. The fact that you can burn food and measure the energy given off, and that's very close to how much energy you get from eating it- that's insane. The efficiency of the human body is all over the place. Muscles are only ~30% efficient, and the rest is waste heat... but humans walk using orders of magnitude less power than any walking robot. As far as I know we have never made a powered walking machine that is 10% as efficient as a person. The only way we can beat it is with a carefully balanced, specially-lubricated pair of legs that is leaned downhill on a treadmill and powered by gravity.

fragmede 2y ago
I'd wait until walking robots are commonplace before discounting our ability to make an efficient one. I don't think I've seen one in person yet.
- hwillis 2y ago
  I wouldn't. We have been trying[1]; humans are genuinely shocking in this way. Mechanical systems should have so many advantages over humans; springs are 10x better than tendons, motors are 3x better than muscles. It's possible humans evolved walking as a predatory tactic. Even if we develop a super-efficient walking robot, humans are efficient at several speeds, and keep that efficiency while varying their stride and foot placement, and with one of the largest most complex brains of any animal. And the ratio of leg/torso length is pretty variable among humans! Not to mention the flexible spine and swinging hips should be a huge energy sap, but they just kind of... aren't. Beating human locomotion in the general case is pretty far off. It's a combination of body plan, extreme optimization of joints and energy storage, and really good algorithms. One killer feature of the human body is synovial fluid. It's very thin, non-newtonian, self-replenishing and contained in particularly low-friction bearing surfaces. It's certainly better than 99.9% of mechanical joints, because these surfaces filter, heal and re-lubricate themselves. Mechanical joints have sticky grease so they stay lubricated without maintenance, and work in the presence of water and grit. It's doubtful that any joint that doesn't heal itself can compete, long-term. [1]: https://spectrum.ieee.org/durus-sri-ultra-efficient-humanoid-robot https://spectrum.ieee.org/durus-sri-ultra-efficient-humanoid...