4 ms·

> electrolysis has a ~45% efficiency That is not correct as far as i know. A modern PEM electrolyzer has an efficiency of around 80%. > All in all, methane wo

> electrolysis has a ~45% efficiency That is not correct as far as i know. A modern PEM electrolyzer has an efficiency of around 80%. > All in all, methane would be a saner, simpler target I kind of agree, but this actually the same thing. To synthesis methane, one uses the water and electricity to create hydrogen with an electrolyzer and then add CO2 through hydrogenation to create methane. Advantage of methane is of course the higher density and it's a bigger molecule that is easier to store.

wazoox 6y ago
OK, I probably misremembered the different numbers from conversion, compression, transport, etc, but the overall figure was that generation to wheel efficiency was in the realm of 20%, while generation to wheel with batteries is more in the 85% efficiency range.
timthorn 6y ago
Yeah, Powerhouse Energy has got a demonstration plant for this running now, taking poor quality plastic waste streams and generating H2 and syngas, as well as heat & electricity: https://www.powerhouseenergy.net/ https://www.powerhouseenergy.net/
darksaints 6y ago
There are research SOECs that have exceeded 99% efficiency, owing to the fact that the inefficiency at direct electrical conversion gets expended as heat which lowers the electrical energy levels required for water molecules to split. Basically start with an 80% efficient electrolyzed, but insulate the cell to capture all of the expended heat energy and use it to lower the need for electricity to split the cell. This is possible because of SOEC operating temperature ranges which wouldn't be possible with a PEM cell. I should also add that on the other end of the hydrogen energy cycle, production SOFCs are about 60% efficient at converting hydrogen to electricity, not 45%. And the temperatures of the waste heat are high enough to efficiently convert to electricity, bringing total electrical efficiency up to the 70-80% range. Oh, and they can use hydrocarbon fuels too.
- Hypx 6y ago
  While it's possible to exceeding 100% efficiency with an SOEC, you will need an external source of heat to drive the process.

wazoox 6y ago

OK, I probably misremembered the different numbers from conversion, compression, transport, etc, but the overall figure was that generation to wheel efficiency was in the realm of 20%, while generation to wheel with batteries is more in the 85% efficiency range.

timthorn 6y ago

Yeah, Powerhouse Energy has got a demonstration plant for this running now, taking poor quality plastic waste streams and generating H2 and syngas, as well as heat & electricity: https://www.powerhouseenergy.net/ https://www.powerhouseenergy.net/

darksaints 6y ago

There are research SOECs that have exceeded 99% efficiency, owing to the fact that the inefficiency at direct electrical conversion gets expended as heat which lowers the electrical energy levels required for water molecules to split. Basically start with an 80% efficient electrolyzed, but insulate the cell to capture all of the expended heat energy and use it to lower the need for electricity to split the cell. This is possible because of SOEC operating temperature ranges which wouldn't be possible with a PEM cell. I should also add that on the other end of the hydrogen energy cycle, production SOFCs are about 60% efficient at converting hydrogen to electricity, not 45%. And the temperatures of the waste heat are high enough to efficiently convert to electricity, bringing total electrical efficiency up to the 70-80% range. Oh, and they can use hydrocarbon fuels too.

Hypx 6y ago
While it's possible to exceeding 100% efficiency with an SOEC, you will need an external source of heat to drive the process.