Flying with Hydrogen

Pipistrel is a European builder of light airplanes. They’ve been building electric airplanes (with an eye towards VTOL) for a while, but now they’ve proven hydrogen fuel cells:


I have no idea about the technical, logistic or economic details, but I’ve often wondered why the automobile industry abandoned (or so it seems) the hydrogen fuel-cell and gone all-in on batteries. There was a time (late 90’s early 2000’s) when hydrogen fuel-cells were all the rage. Maybe it’s a performance thing (e.g. available peak power), but it seems to me that the advantages of the fuel-cell would outweigh those of the battery.


Amory Lovins gave a talk at the Hackers’ Conference around 2000 on his “Hypercar” concept which envisioned a hybrid design with a hydrogen fuel cell and batteries. He said that at the time fuel cells were too expensive for cars, but he expected the price to fall into an affordable range within a few years. He noted that fuel cells are very picky about the purity of the reactants, and can be poisoned by contamination, so a supply chain for hydrogen will need maintain high quality.

The main problem with hydrogen as a fuel is producing it and developing the infrastructure to distribute and deliver it. Around 95% of hydrogen produced today is made by steam reforming of natural gas (methane), which releases 6 tonnes of CO₂ for every tonne of hydrogen produced. If you’re into “net zero”, that’s a spot of bother. Electrolysis of water yields only hydrogen and oxygen, but consumes around 50 kilowatt hours of electricity per kilogram of hydrogen—where’s that electricity going to come from?

Once generated as a gas, it takes around another 15 kWh to compress it for use in mobile applications or between 10 and 13 kWh to liquefy it. If you go with compressed gas, the vessels will be large and dangerous if punctured. Liquid hydrogen must be maintained at 20.8° K at atmospheric pressure, and this takes expensive insulation and refrigeration, especially due to the gotcha thanks to the spin isomers of hydrogen.

In the talk around 2000, Lovins saw hydrogen production migrating to well-head reforming of natural gas, with the CO₂ sequestered back in strata at the well. This would, of course, require a source of fresh water near the well, which may be a problem.

In short, hydrogen is messy, complicated, and difficult, and if the airline industry is bamboozled into adopting it, car makers would probably be wise to wait for them to solve the problems before jumping on the bandwagon.


Okay, now I understand the reasons why batteries are preferable. Thanks! :slight_smile: I didn’t realize that most of the hydrogen we currently produce is from natural gas (I had assumed it was from hydrolysis of water…don’t know where I got that idea). In the case of producing hydrogen by electrolysis, I had assumed that some combination of hydro, nuclear or solar power would address many of the environmental concerns (water vapor as a greenhouse gas might pose a problem, unless it could be condensed), but it seems that the logistical factors involved in production and distribution are just a bridge too far. As far as vehicle safety is concerned, I wonder which is more dangerous: puncturing a liquid hydrogen container or a battery. Both seem pretty bad to me. I guess the hydrogen would be more explosive. Based on what you’ve described, it sounds like the hydrogen solution might also be less energy efficient (power-plant to car).


For vehicular applications, other than the problems of compressed gas (if gaseous hydrogen is used), hydrogen is probably no more dangerous than gasoline. The advantage of hydrogen is that it is (very) light compared to air and quickly rises and dissipates into the atmosphere in case of a leak or spill. It is only explosive if mixed in a certain fraction with air, and when it does, it tends to disperse the rest of the hydrogen which has not yet mixed. Experience with explosions of hydrogen fuelled rocket stages indicates that the actual explosion is around 1/8 the power of what would be expected from an optimal mix of hydrogen and oxygen.

Gasoline, by comparison, leaks and spreads around the vehicle, with fire propagating along its surface and spreading outward. The fire does not dissipate the gasoline, which continues to burn until consumed or extinguished, which water does not do very well, since gasoline floats on top of it.


60 to 65 kwh without transportation or any other added energy needs or losses and 1kg of hydrogen has 33 kwh of usable energy.

Hydrogen via electrolysis is net energy negative.