Hydrogen Fuel Tanks
Since hydrogen-powered cars are still an emerging industry, so
too are hydrogen fuel tanks for cars, trucks and other vehicles.
Hydrogen fuel tanks come in two main variety including those that
contain compressed hydrogen gas and those that contain cryogenic
hydrogen (super-cooled liquid hydrogen).
Hydrogen Fuel Tanks
There is a third type that is uncommon which is a tank that holds
a hydrogen slurry (a hydrogen-rich hydrogen compound). At this
link you can read more about hydrogen
So, the most common hydrogen fuel tank for cars, trucks, buses
and other vehicles is that which holds compressed hydrogen gas
in a range of 3,600 psi - 10,000 psi. Most hydrogen fueling stations
now days dispense compressed hydrogen gas at 5,000 psi and 10,000
psi or at both pressures.
There are only a few hydrogen fueling stations which dispense
cryogenic liquid hydrogen. This is mainly because almost all of
the major carmakers have chosen to fuel their prototype cars with
compressed hydrogen gas. The one exception has been BMW as their
7 automobile uses cryogenic hydrogen and gasoline (it's a
dual fuel vehicle).
Cryogenic Tanks ...
BMW used to have a boil off problem with their cryogenic hydrogen
tanks which means that if you left the vehicle sit for a couple
of weeks, say at the airport, the liquid hydrogen would find its
way out of the tank and evaporate. BMW within the last couple
of years has claimed to have solved this problem.
But there are other problems with cryogenic liquid hydrogen.
To maintain liquidity, hydrogen has to be stored at a temperature
at or below negative 253 degrees Celsius. The only way to maintain
that temperature in a truck for transporting the liquid to fueling
stations is to have a technologically advanced freezer system
installed in the truck.
Liquid Hydrogen Tank
In addition to the expense of the truck
itself, the operating cost, especially the truck's own fuel,
would be large. Because liquid hydrogen is so cold, it is
capable of freezing the air around it. This quality could
cause the truck's equipment to stall or degrade.
In regard to compressed hydrogen fuel tanks, most of these now
days are made of some sort of carbon fiber composites or carbon
fiber and metal alloys and composites.
The U. S. Department of Energy says this about a hydrogen fuel
tank developed by Quantum Technologies, "Carbon fiber-reinforced
5000-psi and 10,000-psi compressed hydrogen gas tanks are under
development by Quantum Technologies and others. Such tanks are
already in use in prototype hydrogen-powered vehicles. The inner
liner of the tank is a high-molecular-weight polymer that serves
as a hydrogen gas permeation barrier.
"A carbon fiber-epoxy resin composite shell is placed over
the liner and constitutes the gas pressure load-bearing component
of the tank. Finally, an outer shell is placed on the tank for
impact and damage resistance. The pressure regulator for the 10,000-psi
tank is located in the interior of the tank. There is also an
in-tank gas temperature sensor to monitor the tank temperature
during the gas-filling process when tank heating occurs."
Now, what is inside the hydrogen fuel tank is also an area with
several options. For instance, some manufacturers compress the
H2 gas into open space. Other manufacturers are using metal hydride
technology where hydrogen is stored the porous metal hydride material
then the gas is released by adding a little heat to the tank.
The drawback with using metal hydrides in hydrogen fuel tanks
is that they are generally very heavy. This weight then cuts down
on the MPG's of the vehicle.
Nano Materials ...
Manufacturers are also experimenting with other nano materials
for storing hydrogen. Carbon nanotubes and various types of doped
metals such as aluminum hold promise in creating lightweight hydrogen
Another issue of course is cost. Creating a 20-gallon fuel tank
prototype from metal hydrides or carbon nanotubes can add up to
$30,000 to the price of a car. However, scientists at the 13th
Annual Green Chemistry and Engineering Conference in Delaware
believe they have found an alternative to these costly materials.
feather fibers may be able to keep hydrogen from leaking out
of a gas tank. This method would add only about $200 to the price
of a car. Of course, much of the hydrogen fuel tank technology
for cars is still experimental.
At one time Great Britain wanted to buy a number of Honda Clarities
for police work. The caveat was that the compressed hydrogen fuel
tanks had to be bullet proof. Honda succeeded in creating a handful
of such H2 custom built tanks at great expense.
If hydrogen cars are to succeed in the marketplace it's not only
the price of fuel cells that needs to come down (with economies
of scale of course). But hydrogen fuel tanks need to be lighter,
hold more volume and cost less than they presently do.
Scientists and researchers are now working on this issue and
as with many other technology driven challenges the future will
most likely hold a variety of workable solutions.
Check out more info about hydrogen
fuel tanks from our blog.