I'm just now creating my general chemistry lessons on electrochemistry and was looking for a discussion topic for my students to learn more about the chemistry and real world connections with climate, energy, hydrogen fuel cells, and batteries for transportation. This podcast just became an assignment for my students to generate class discussion.
Very cool. Aviation is one of the few applications that makes sense for hydrogen, and it was great to have that acknowledged in this discussion. I also like that they are making their own hydrogen, so it has good provenance and really is green and not beige, brown or any other wacky color.
Very interesting but you let Val get away with a misleading comparison: the specific energy of a hydrogen fuel cell system is dominated by the weight of the hydrogen storage system and fuel cell stack, not the weight of hydrogen itself. I’m sure Val has considered that in his analysis but it would be great to have more discussion of innovation in hydrogen storage. What’s happening with metal hydrides for example?
Hydrogen technology has been a thing for decades. More than fifty years ago I recall reading an article in Popular Science that promised hydrogen-powered cars would replace gas cars within a decade. Obviously that did not happen. It did not happen because of some pretty major obstacles. First of all, elemental hydrogen does not exist in nature. To acquire it you must separate the hydrogen from some compound. The easiest and most readily available hydrogen-containing compound is dihydrogen oxide, commonly known as water. To extract hydrogen from water you just run an electric current through it. Oxygen gathers at one electrode, hydrogen at the other. Simple, right?
Yes, but. Problem is, to get significant quantities of hydrogen requires enormous amounts of electrical energy, theoretically the same as you get back when you combust the hydrogen to get heat, hence motive energy. Your typical thermo-mechanical system, i.e. engine, is 30 to 40 percent efficient. So you spend a thousand watts of electricity to produce 30 or 40 watts of motive energy. Not a good deal.
Another problem is storage. Hydrogen atoms are the lightest of all elements, and have basically zero binding energy. To gather up a usable quantity of hydrogen requires compressing it to extraordinarily high pressures, at least 10,000 psi. To achieve this pressure requires enormous amounts of energy, and to contain it requires extremely robust, hence heavy, storage vessels. For reference, 10,000 psi is roughly the pressure exerted by the exploding gunpowder of a high-powered rifle bullet.
While it may be technically true that jet fuel and supercritical (liquid) hydrogen have roughly the same amount of potential energy, one can be stored in a lightweight inexpensive container of any shape you want, while the other requires a leak-proof, extremely strong, quite heavy container that may only be spherical or tubular. If the jet fuel tank should suffer a puncture, the fuel will just leak out, not blow a giant hole in your fuselage. Yeah, yeah, metal hydrides, but their energy density is quite low.
The aviation industry is nothing if not pragmatic. No way in hell is it going to trade piston and turbine engines, economical and ultra-reliable, hence safe, for hydrogen-electric or battery powered ANYTHING unless and until the latter technologies are superior to the former in all the ways that count. Emissions are way, way down the list of concerns, as they should be, when reliability and lives are on the line.
Your policy of zero tolerance for hydrocarbon fuels is a losing proposition. Electrified everything is a terrible idea and completely impractical. Everyone with sense knows this. It is for these reasons that Net Zero is collapsing.
Finally, CO2 is not the enemy. It's an absolutely critical trace gas that makes life on earth possible. The Earth is measurably greener thanks to the recent increase of it in the atmosphere. Yeah, it's probably contributed some to the recent warming, but that's a good thin when you consider that it delivered us from the ravages of the Little Ice Age, that period of anomalous cooling that made life miserable for pretty much everyone in the temperate zone for about 400 years.
Speaking of ice ages, we're in the middle of one right now, so the last thing we need to worry about is a little extra warmth.
Seriously, where is the carbon accounting? What is the (marginal) carbon footprint of the hydrogen? Remember, gotta count the carbon footprint of the solar cells: that “solar” power is not free in an economy based on TAC optimization.
I love engineering economics, in part because the practitioners are pretty much all good at math and so are easy to teach. Our problem now is to expand the basic engineering-economics curriculum to cover, to some extent, the general equilibrium, in a world with a critical shortage of terrestrial carbon.
That was fantastic! Thank you, David, Kyle & Val
Thanks for this, David!
I'm just now creating my general chemistry lessons on electrochemistry and was looking for a discussion topic for my students to learn more about the chemistry and real world connections with climate, energy, hydrogen fuel cells, and batteries for transportation. This podcast just became an assignment for my students to generate class discussion.
Very cool. Aviation is one of the few applications that makes sense for hydrogen, and it was great to have that acknowledged in this discussion. I also like that they are making their own hydrogen, so it has good provenance and really is green and not beige, brown or any other wacky color.
Very interesting but you let Val get away with a misleading comparison: the specific energy of a hydrogen fuel cell system is dominated by the weight of the hydrogen storage system and fuel cell stack, not the weight of hydrogen itself. I’m sure Val has considered that in his analysis but it would be great to have more discussion of innovation in hydrogen storage. What’s happening with metal hydrides for example?
Nothing was said about electric jet engines! Are they possible? Do they exist?
Hydrogen technology has been a thing for decades. More than fifty years ago I recall reading an article in Popular Science that promised hydrogen-powered cars would replace gas cars within a decade. Obviously that did not happen. It did not happen because of some pretty major obstacles. First of all, elemental hydrogen does not exist in nature. To acquire it you must separate the hydrogen from some compound. The easiest and most readily available hydrogen-containing compound is dihydrogen oxide, commonly known as water. To extract hydrogen from water you just run an electric current through it. Oxygen gathers at one electrode, hydrogen at the other. Simple, right?
Yes, but. Problem is, to get significant quantities of hydrogen requires enormous amounts of electrical energy, theoretically the same as you get back when you combust the hydrogen to get heat, hence motive energy. Your typical thermo-mechanical system, i.e. engine, is 30 to 40 percent efficient. So you spend a thousand watts of electricity to produce 30 or 40 watts of motive energy. Not a good deal.
Another problem is storage. Hydrogen atoms are the lightest of all elements, and have basically zero binding energy. To gather up a usable quantity of hydrogen requires compressing it to extraordinarily high pressures, at least 10,000 psi. To achieve this pressure requires enormous amounts of energy, and to contain it requires extremely robust, hence heavy, storage vessels. For reference, 10,000 psi is roughly the pressure exerted by the exploding gunpowder of a high-powered rifle bullet.
While it may be technically true that jet fuel and supercritical (liquid) hydrogen have roughly the same amount of potential energy, one can be stored in a lightweight inexpensive container of any shape you want, while the other requires a leak-proof, extremely strong, quite heavy container that may only be spherical or tubular. If the jet fuel tank should suffer a puncture, the fuel will just leak out, not blow a giant hole in your fuselage. Yeah, yeah, metal hydrides, but their energy density is quite low.
The aviation industry is nothing if not pragmatic. No way in hell is it going to trade piston and turbine engines, economical and ultra-reliable, hence safe, for hydrogen-electric or battery powered ANYTHING unless and until the latter technologies are superior to the former in all the ways that count. Emissions are way, way down the list of concerns, as they should be, when reliability and lives are on the line.
Your policy of zero tolerance for hydrocarbon fuels is a losing proposition. Electrified everything is a terrible idea and completely impractical. Everyone with sense knows this. It is for these reasons that Net Zero is collapsing.
Finally, CO2 is not the enemy. It's an absolutely critical trace gas that makes life on earth possible. The Earth is measurably greener thanks to the recent increase of it in the atmosphere. Yeah, it's probably contributed some to the recent warming, but that's a good thin when you consider that it delivered us from the ravages of the Little Ice Age, that period of anomalous cooling that made life miserable for pretty much everyone in the temperate zone for about 400 years.
Speaking of ice ages, we're in the middle of one right now, so the last thing we need to worry about is a little extra warmth.
Great conversation, super interesting--thank you David!
Gee whiz! I bet we get flying cars out of this!
Seriously, where is the carbon accounting? What is the (marginal) carbon footprint of the hydrogen? Remember, gotta count the carbon footprint of the solar cells: that “solar” power is not free in an economy based on TAC optimization.
I love engineering economics, in part because the practitioners are pretty much all good at math and so are easy to teach. Our problem now is to expand the basic engineering-economics curriculum to cover, to some extent, the general equilibrium, in a world with a critical shortage of terrestrial carbon.
Excellent discussion. My vision regarding the future of green aviation is a bit more positive thanks to the completeness of David's questioning.