4 ms·

Can you expand why separation from water is a net energy loss?

arbol 4y ago
Conversion from water to hydrogen via hydrolysis is only 60-80% efficient so it takes more energy to generate the hydrogen than the hydrogen will produce in future. Source: https://www.weforum.org/agenda/2021/08/hydrogen-carbon-intensive-energy-solution/ https://www.weforum.org/agenda/2021/08/hydrogen-carbon-inten...
bbojan 4y ago
Water electrolysis is around 60-80 percent efficient. Hydrogen fuel cells are around 40-60 percent efficient. Plus you spend additional energy to either compress or cool the hydrogen in order to be able to store it. Electricity storage in a lithium-ion battery is on the order of 98% efficient, and electric motors are around 90% efficient (if you take into account the whole drivetrain).
- wh33zle 4y ago
  Thanks! Although it seems like these numbers can be improved [0] and are not fundamentally linked to the technology. [0]: https://newatlas.com/energy/hysata-efficient-hydrogen-electrolysis/ https://newatlas.com/energy/hysata-efficient-hydrogen-electr...
  - ncmncm 4y ago
    Yes, hydrogen and ammonia handling efficiency will mostly go up, unless extra-cheap (to buy) electrolysers come out with unfortunately lower efficiency. What always matters most is cost. Inefficiency will get cheaper and cheaper as generation cost falls. Switching from gold & platinum catalyzing electrolysers to something not dependent on those and less efficient is still a win if you get a lot more electrolysers for your money.
ncmncm 4y ago
It is absolutely trivial that separating hydrogen from water uses energy. Then, when you burn it, you get water and energy back. That is the whole point.
- wh33zle 4y ago
  That is trivial yes and I was well aware of that :) What wasn't obvious to me from the parent comment was why it is apparently completely impractical. No energy conversion has an efficiency of 100% so the answer couldn't just have been "because thermodynamics" but as other comments have since revealed, it is because _current_ hydrolyzers only operate on an efficiency scale of 60-80%.
  - ncmncm 4y ago
    And, turbines and fuel cells are also at ~40-60%. So, round-trip is a fair bit lower than that, as little as 25%. But it doesn't matter much. Efficiency is improving, and will be much better before anything depends on it. What do you imagine is the raw efficiency of making hydrogen from. NG, vs the enthalpy of the input gas? BTW, "electrolysers". Hydrolysis is a thing plants do.

Conversion from water to hydrogen via hydrolysis is only 60-80% efficient so it takes more energy to generate the hydrogen than the hydrogen will produce in future. Source: https://www.weforum.org/agenda/2021/08/hydrogen-carbon-intensive-energy-solution/ https://www.weforum.org/agenda/2021/08/hydrogen-carbon-inten...

bbojan 4y ago

Water electrolysis is around 60-80 percent efficient. Hydrogen fuel cells are around 40-60 percent efficient. Plus you spend additional energy to either compress or cool the hydrogen in order to be able to store it. Electricity storage in a lithium-ion battery is on the order of 98% efficient, and electric motors are around 90% efficient (if you take into account the whole drivetrain).

wh33zle 4y ago
Thanks! Although it seems like these numbers can be improved [0] and are not fundamentally linked to the technology. [0]: https://newatlas.com/energy/hysata-efficient-hydrogen-electrolysis/ https://newatlas.com/energy/hysata-efficient-hydrogen-electr...
- ncmncm 4y ago
  Yes, hydrogen and ammonia handling efficiency will mostly go up, unless extra-cheap (to buy) electrolysers come out with unfortunately lower efficiency. What always matters most is cost. Inefficiency will get cheaper and cheaper as generation cost falls. Switching from gold & platinum catalyzing electrolysers to something not dependent on those and less efficient is still a win if you get a lot more electrolysers for your money.

ncmncm 4y ago

It is absolutely trivial that separating hydrogen from water uses energy. Then, when you burn it, you get water and energy back. That is the whole point.

wh33zle 4y ago
That is trivial yes and I was well aware of that :) What wasn't obvious to me from the parent comment was why it is apparently completely impractical. No energy conversion has an efficiency of 100% so the answer couldn't just have been "because thermodynamics" but as other comments have since revealed, it is because _current_ hydrolyzers only operate on an efficiency scale of 60-80%.
- ncmncm 4y ago
  And, turbines and fuel cells are also at ~40-60%. So, round-trip is a fair bit lower than that, as little as 25%. But it doesn't matter much. Efficiency is improving, and will be much better before anything depends on it. What do you imagine is the raw efficiency of making hydrogen from. NG, vs the enthalpy of the input gas? BTW, "electrolysers". Hydrolysis is a thing plants do.