2 ms·

> [The GHG footprint of blue hydrogen is] more than 20% greater than burning natural gas or coal for heat and some 60% greater than burning diesel oil for heat

by elil17 5y ago

> [The GHG footprint of blue hydrogen is] more than 20% greater than burning natural gas or coal for heat and some 60% greater than burning diesel oil for heat Totally apples to oranges comparison - heating is and always will be way more energy efficient than electricity generation on a per-watt basis because you eliminate the inefficiencies inherent in the compressors and turbines. You have to compare hydrogen to what it’s being used to replace - internal combustion engines, which are wildly inefficient.

aardvarkr 5y ago
Thanks for pointing this out! That nuance seems to have been completely left out of the conversation
diarrhea 5y ago
> inefficiencies inherent in the compressors and turbines This is not why such thermal engines/plants perform (well below) 100% efficiency. You could have isentropic (i.e., ideal, working losslessly) components and will probably still land below 50% thermal efficiency, limited simply by the Carnot efficiency. That is to say, it's a fundamental physical limit, not an anthropological limit (e.g. component quality). I also don't understand the point you're making. If you burn these three fuels, they have certain carbon footprints. What's wrong with that comparison? You cannot "compare hydrogen to internal combustion engines" --- that's apples and oranges, comparing a fuel to an energy conversion machine. You can compare hydrogen and fuel cells to gasoline/Diesel and ICEs, which gets closer to the whole chain (but still ignores how the fuels were procured). Lastly, ICEs are not "wildly inefficient". Large-scale maritime Diesel engines are some of the most efficient machines we have in this sector. It's not about what's lacking to 100% --- 100% is physically unobtainable. It's about the delta to Carnot efficiency, which gets very small for these. It's important to regard energy qualities and types, since you are comparing apples and oranges otherwise. With energy, there's no free lunch, and a number like 90% efficiency might be entirely meaningless, e.g. for electric water kettles (doesn't stop advertisers).

by elil17 5y ago

aardvarkr 5y ago

Thanks for pointing this out! That nuance seems to have been completely left out of the conversation

diarrhea 5y ago

> inefficiencies inherent in the compressors and turbines This is not why such thermal engines/plants perform (well below) 100% efficiency. You could have isentropic (i.e., ideal, working losslessly) components and will probably still land below 50% thermal efficiency, limited simply by the Carnot efficiency. That is to say, it's a fundamental physical limit, not an anthropological limit (e.g. component quality). I also don't understand the point you're making. If you burn these three fuels, they have certain carbon footprints. What's wrong with that comparison? You cannot "compare hydrogen to internal combustion engines" --- that's apples and oranges, comparing a fuel to an energy conversion machine. You can compare hydrogen and fuel cells to gasoline/Diesel and ICEs, which gets closer to the whole chain (but still ignores how the fuels were procured). Lastly, ICEs are not "wildly inefficient". Large-scale maritime Diesel engines are some of the most efficient machines we have in this sector. It's not about what's lacking to 100% --- 100% is physically unobtainable. It's about the delta to Carnot efficiency, which gets very small for these. It's important to regard energy qualities and types, since you are comparing apples and oranges otherwise. With energy, there's no free lunch, and a number like 90% efficiency might be entirely meaningless, e.g. for electric water kettles (doesn't stop advertisers).