4 ms·

https://en.wikipedia.org/wiki/Electrolysis_of_water#Efficiency https://en.wikipedia.org/wiki/Electrolysis_of_water#Efficien... "Efficiency of modern hydrogen ge

https://en.wikipedia.org/wiki/Electrolysis_of_water#Efficiency https://en.wikipedia.org/wiki/Electrolysis_of_water#Efficien... "Efficiency of modern hydrogen generators is measured by energy consumed per standard volume of hydrogen (MJ/m3), assuming standard temperature and pressure of the H2. The lower the energy used by a generator, the higher its efficiency would be; a 100%-efficient electrolyser would consume 39.4 kilowatt-hours per kilogram (142 MJ/kg) of hydrogen,[23] 12,749 joules per litre (12.75 MJ/m3). Practical electrolysis (using a rotating electrolyser at 15 bar pressure) may consume 50 kW⋅h/kg (180 MJ/kg), and a further 15 kW⋅h (54 MJ) if the hydrogen is compressed for use in hydrogen cars." What about your sources for 93% efficiency?

darksaints 7y ago
93% is what I got in my own experiments with an used cell I bought that was made in 2008. My cell is a slight materials variant of the NASA BSC cell which was also tested at 93% efficiency. https://ntrs.nasa.gov/search.jsp?R=20090013708 https://ntrs.nasa.gov/search.jsp?R=20090013708 Here is a commercially available cell stack that is getting 88% efficiency, despite being a reversible cell (ie not optimized for electrolysis). http://www.helmeth.eu/index.php/technologies/high-temperature-electrolysis-cell-soec http://www.helmeth.eu/index.php/technologies/high-temperatur... This research system has already demonstrated 75% efficiency round-trip. That is electricity-to-hydrogen-to-electricity. 97% efficient in electrolysis alone. https://www.nature.com/articles/s41560-019-0333-2 https://www.nature.com/articles/s41560-019-0333-2
- tigershark 7y ago
  Even with a 93% efficiency adding the energy needed to compress the hydrogen and the fuel cell efficiency you arrive at an efficiency of 48%, pretty much half as the batteries.
  - darksaints 7y ago
    I can dispute those numbers too but that is beside the point. Batteries are probably good enough in energy density for most car users, and they do have an efficiency advantage (not as great as you're trying to portray but still better). For 99% of car buyers, that's a better option. But fuel cells still have a place where energy density is a major concern. That's likely to be the case for commercial vehicles, where long recharge times and low ranges are unacceptable.

darksaints 7y ago

93% is what I got in my own experiments with an used cell I bought that was made in 2008. My cell is a slight materials variant of the NASA BSC cell which was also tested at 93% efficiency. https://ntrs.nasa.gov/search.jsp?R=20090013708 https://ntrs.nasa.gov/search.jsp?R=20090013708 Here is a commercially available cell stack that is getting 88% efficiency, despite being a reversible cell (ie not optimized for electrolysis). http://www.helmeth.eu/index.php/technologies/high-temperature-electrolysis-cell-soec http://www.helmeth.eu/index.php/technologies/high-temperatur... This research system has already demonstrated 75% efficiency round-trip. That is electricity-to-hydrogen-to-electricity. 97% efficient in electrolysis alone. https://www.nature.com/articles/s41560-019-0333-2 https://www.nature.com/articles/s41560-019-0333-2

tigershark 7y ago
Even with a 93% efficiency adding the energy needed to compress the hydrogen and the fuel cell efficiency you arrive at an efficiency of 48%, pretty much half as the batteries.
- darksaints 7y ago
  I can dispute those numbers too but that is beside the point. Batteries are probably good enough in energy density for most car users, and they do have an efficiency advantage (not as great as you're trying to portray but still better). For 99% of car buyers, that's a better option. But fuel cells still have a place where energy density is a major concern. That's likely to be the case for commercial vehicles, where long recharge times and low ranges are unacceptable.