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For fixed infrastructure, nothing beats power lines. For mobile applications, hydrogen has numerous problems. There are other options, like batteries, ammonia,
by u320 4y ago
For fixed infrastructure, nothing beats power lines. For mobile applications, hydrogen has numerous problems. There are other options, like batteries, ammonia, synthetic hydrocarbons etc that should be explored further.
Hydrogen doesn't even come close to deserving the title "the ultimate clean energy".
- ncmncm 4y agoThat wholly misses the point. We need hydrogen production in unlimited amounts for myriad processes. Want synthetic ammonia? Need hydrogen. Methane? Hydrogen. Kerosene? Hydrogen. Green steel production? Hydrogen. Furthermore, liquified hydrogen is the future of aviation. So a tech that produces hydrogen efficiently anywhere there is air is intrinsically important.
- eru 4y ago> Furthermore, liquified hydrogen is the future of aviation. What makes you think so? Why not eg methane? Or other synthetic carbohydrates?
- ncmncm 4y agoLH2's extreme mass-energy density will make other aircraft unable to compete, because the weight savings may be sold as additional paying cargo capacity. That presumes a joule of LH2 is the same price as of kerosene. But LH2 may end up much cheaper, increasing the gap.
- eru 4y agoOne would suppose mass energy density is even more important for rockets. In practice, only some rockets use LH2. Many rockets use souped up kerosene (RP1) or, more recently, methane. Compare https://en.wikipedia.org/wiki/Liquid_rocket_propellant#Hydrogen https://en.wikipedia.org/wiki/Liquid_rocket_propellant#Hydro... and https://en.wikipedia.org/wiki/Hydrogen-powered_aircraft https://en.wikipedia.org/wiki/Hydrogen-powered_aircraft Also: > With materials available in the 2020s, the mass of tanks strong enough to withstand this kind of high pressure will greatly outweigh the hydrogen fuel itself, largely negating the weight to energy advantage of hydrogen fuel over hydrocarbon fuels. Hydrogen has a severe volumetric disadvantage relative to hydrocarbon fuels, but future blended wing body aircraft designs might be able to accommodate this extra volume without greatly expanding the wetted area. From https://en.wikipedia.org/wiki/Aviation_fuel https://en.wikipedia.org/wiki/Aviation_fuel
- ncmncm 4y agoThe need for higher mass density exhaust to provide enough absolute thrust to get off the ground overwhelms H2's energetic efficiency. Thus, SLS, like STS before it, depends on solid-fuel rockets until well clear of the pad, and then jettisons them. Aircraft operation involves nothing analogous.
- semi-extrinsic 4y agoThe quote concerning mass of tanks is talking about compressed hydrogen storage, which people don't really consider feasible for large aircraft. Cryogenic liquid hydrogen storage is the way.
- coderenegade 4y agoPerformance-wise there's nothing close. You fly twice as high because hydrogen burns so lean, and you only need roughly 1/5th the equivalent mass of kerosene in fuel to get you the same distance. There are obvious barriers in the way (cost, certification, handling), but the potential benefits have been known for a long time.
- ncmncm 4y agoThe main problem with LH2 is that it won't fit in the wing tanks like kerosene. The tanks may be very light, because the pressure is low and the LH2 weighs nothing, but they will be big! Some bet LH2 aircraft will have a wholly new shape, more like a lifting body, with a lot more inboard room for the bigger tankage. But another possibility is long underwing nacelles, alongside the engines. Those might even be retrofitted to existing airframes. Some people dislike the idea of sharing the cabin with inboard hydrogen tankage, as a safety concern. Fuel tanks shearing off with the wings in a crash has saved lives. Probably the nacelles would be rigged to be dropped in an emergency, to leave behind detonation risk.
- coderenegade 4y agoYeah that's right, you need roughly twice the fuel volume, though that's easier to accommodate than needing to deal with a heavier fuel like ammonia, for example. Blended wing bodies and flying wings might make more sense with LH2. They haven't happened so far because they're harder to certify (essentially from scratch vs a standard design which uses evidence from previous designs to expedite certification), and they don't work too well with existing airport infrastructure. If you're going through the trouble of certifying LH2 anyway, that could provide justification for a new design, and working with airports to get the infrastructure going.
- ncmncm 4y agoI am betting compatibility with past practice wins over incremental efficiency. But I have no way to evaluate whether retrofitting existing airframes with underslung tankage will be practical.
- ZeroGravitas 4y agoAmmonia and synthetic hydrocarbons will be built from green hydrogen though.
- adrianN 4y agoHydrogen is pretty neat as a storage medium. It's easier to store a few terawatthours in gas than in batteries.
- usrusr 4y agoMost of all it's an intermediate for even neater chemical storage mediums. The entire range of non-biological regenerative fuels (or non-biological, period, if we include fossils in the biological group), including reduced Fe dust cycles, ammonia or plain old "e-fuel" hydrocarbons, they all start with hydrogen as the first stage. It's the natural short term storage medium that will be used as an input buffer for downstream processes so that they don't have to follow supply peaks as closely as they would have to without that buffer.