Hydrogen Storage
To achieve a fully functioning hydrogen economy, hydrogen will need to be stored on a wide range of scales. Large, centralised storage would be required if hydrogen is produced in large plants for wider distribution; longer term or seasonal storage would be required in systems relying on large penetrations of renewable energy; comparatively small scale storage is required on board vehicles, possibly in homes, and for portable devices.
As well as compression and liquefaction, a wide range of potential hydrogen storage technologies are under research and development. Particular interests is being shown in solid-state hydrogen storage (see papers from H2NET Hydrogen Storage Materials meeting in December 2004).
The table indicates some broad classifications of hydrogen storage technologies and their potential advantages and disadvantages.
|
Hydrogen storage method |
Typical configuration |
Advantages |
Disadvantages |
|
Compressed
gas |
Steel
alloy cylinders at 200 bar (R&D devices now up to 700 bar) |
Simple Indefinite
storage time No purity
limits |
Hydrogen
embrittlement Danger of
autoignition if ruptured |
|
|
Composite
reinforced plastic tank, max. pressure 300 bar |
Simple Indefinite
storage time No purity
limits Good
burst behaviour (rips apart rather than disintegrating) |
Danger of
autoignition if ruptured |
|
Liquefaction
(LH2) |
BMW fuel
tank (double wall vacuum flask of Al/fibre glass) Purge
tank with nitrogen before filling Restrict
air from system during filling/fuelling operations or an explosive mixture
could form |
Widely
used for large volume storage Safer
than pressurised storage in the event of vessel rupture |
Liquefaction
process is energy intensive (40% of specific enthalpy or heating value) Cryogenic
temperatures |
|
Reversible
metal hydride |
M + H2
« M H2 |
Safe (low
pressure) Particularly
suitable for small quantities of hydrogen Useful
where weight is not a problem, but volume is |
Low
specific energy Long
filling times for vehicle applications High
purity hydrogen required to avoid damage to active material (not a problem
for renewable hydrogen) |
|
Alkali
metal hydrides |
CaH2
+ 2H2O ®
Ca(OH)2 + 2H2 "Powerballs"
are supplied in the form of polyethylene coated balls of sodium hydride
which are cut in half when required to produce hydrogen: NaH + H2O
® NaOH + H2 |
|
Disposal
of corrosive hydroxide water mix Large
volume of water Energy
required to manufacture the hydride is high |
|
Carbon
nanotubes |
|
Potentially
low weight systems |
Material
processing Initial
controversial claims for mass-storage effectiveness |
|
Methanol |
Fuel
reforming to yield hydrogen |
Safe,
simple, cheap to transport |
Toxic |
|
|
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