The Uncertain Future Of Hydrogen As Transportation Energy

Hydrogen is often touted as an important transportation “fuel” in the future, though it has never gotten significant traction. One reason is confusion over what it is – it’s not an energy source, though it is used like a fuel, but rather a form of energy storage. You take some other energy source (today it’s natural gas, in the future it’s renewable electricity) and you generate the hydrogen, which you can then turn back into useful energy through a fuel cell, or even by burning it.

Hyundai’s Mobility Innovator’s Forum closed a week of 3 different California mobility conferences I attended. There, I met folks from H2Pro, a company which claims a radical new electrolysis cell which converts electricity to hydrogen at a 95% efficiency. Unlike other methods of electrolysis, this one uses a consumable anode (which makes the oxygen, not the hydrogen) which can be restored by heating the system temporarily. With this, they hope (should they find a way to do it at scale) it will be over 90% efficient, compared to the 70-75% of existing systems. Even better, it can produce the gas at high pressure, saving the energy needed for compression.

That’s good – and as noted almost all the hydrogen generated today comes by cracking natural gas (methane) which is not renewable and causes emissions.

Hydrogen’s big advantage as an electricity source is you can pump it like a gaseous fuel. That means you can refill tanks quickly, though the tanks are expensive and large high-pressure tanks, not simple gasoline tanks. Its other big advantage is energy density per kilogram – 3-4 times better than jet fuel or gasoline, though there is less advantage due to the need for a large, strong tank.

To turn hydrogen back into electricity you use a fuel cell. Sadly, these are not currently very efficient, around 50%, and under 40% in hydrogen-electric cars. As such, even with a 90% efficient electrolysis, you’re only going to get well under half of your energy back with hydrogen, compared to around 85-90% for batteries. If you burn the hydrogen to move a car, you will only get about 1/3rd of the energy turned into motion. For heating homes, it’s better to use a fuel cell to run a heat pump. Heat pumps can be 300% “efficient” in turning electricity into indoor heat, and on top of that, the 50% waste heat of the fuel cell can be recovered for heating the building, too. However, better just to use the electricity directly – the only reason to turn it into hydrogen is to ship it, store it or carry it.

And I have not even discussed the issues withe costs costs and dangers of storing, transporting and using hydrogen – a highly flammable gas.

Hydrogen cars

People had hopes for hydrogen cars, and due to regulations, some have been produced such as the Toyota Mirai. They are not very good, and few have sold, and with filling stations being very rare, not convenient to use. Boosters of hydrogen didn’t predict the way that lithium battery prices would plummet, and it seems it’s time to declare batteries as the winner, at least for now, in electric cars. Hydrogen’s only advantage is the quick fill-up, and there’s lots of promise on having quick fill-up for batteries, and even the 45 minute fill-up of the Tesla supercharger turns out to be reasonable if you can time it with eating a meal.

Hydrogen Trucks

Hydrogen may still have promise as a truck and bus fuel. While these are also being built with batteries, the amount of batteries they need is very large, and the amount of power needed to charge them in a reasonable time is immense – several megawatts. The weight of such large battery packs is very high compared with both diesel and hydrogen, and trucks and buses can handle having large tanks on board. As such, this is where the action may be for hydrogen in ground transport.

Electric Aircraft

I think the real potential for hydrogen in transportation is in aircraft. Here, the fantastic energy per weight advantage of hydrogen comes into its own, as long as you can make lightweight tanks. As noted, it’s much better than jet fuel, and can be converted to spinning propellers at higher efficiency too. Batteries are just to heavy for anything but short range aircraft at present, and worse, no major breakthrough is sitting on the horizon to give great hope this will be solved. Batteries also have the annoying property of weighing the same full and empty – a fuel powered plane takes off very heavy and is inefficient, but as it travels, it gets lighter and lighter, gaining in efficiency. This would also apply to hydrogen.

Standing in the way of hydrogen-electric aircraft is the high cost of fuel cells per watt of output. Takeoff requires lots of power, especially in electric vertical takeoff (drone style.) Hundreds of kilowatts, even for small vehicles. Once up, you can fly with just a few kilowatts. One answer being explored is the combination of batteries and hydrogen fuel cells. Take off with a small battery pack that only has enough power for takeoff and an emergency landing. Fly (and recharge slowly) on the smaller fuel cell. This also solves an important reliability problem. Aircraft have to have backups in case any system fails. One powered on just a fuel cell would need two expensive fuel cells. Batteries can be split up into independent packs to provide reliability.

Grid storage

Hydrogen, and other forms of chemical storage, can make sense for grid storage. Grid storage is the big unsolved problem when it comes to creating an all renewable grid. Since we get no solar at night or on rainy days, and wind is also unreliable, the only way to have them generate most of our power is to be able to store extra power from sunny and windy days, and get it back over the course of a cloudy, rainy week or more. (The other big problem is the giant power demand peak that comes around 7pm, just after all the solar panels faded away.)

For batteries, if you want twice as much storage, you pay twice as much. For hydrogen, twice as much storage is mostly just twice as big a tank.

Off-grid storage

Efficient electrolysis may also offer an option for very remote renewable generation sources, such as offshore wind and wave power, or certain types of remote land renewables. One could imagine wave generators just floating out in the ocean, filling H2 tanks and serviced by robot tankers. (Though piracy could be an issue.) Due to the inefficiency of hydrogen, you would want these to be how you refilled your storage tanks and aircraft, not as a mainstream storage technology, but even the latter could make sense in certain cases.

So the future isn’t probably full of hydrogen as its boosters imagine, but there is hope yet.

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