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The Uncertain Future Of Hydrogen As
Transportation Energy
Brad
Templeton
Brad
Templeton Senior Contributor
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.
Brad Templeton
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