Storage

Question 1

What are the different hydrogen storage methods?

Answer 1

Compressed gas, liquid, and solid state hydrides.

Potentially cryogenic also (BMW experimented with 50/50 liquid and compressed gas)

Question 2

What are the design features of a compressed gas system?

Answer 2

350 and 700 bar standard. Use impermeable linings to stop hydrogen reacting with tank. Pressure relief valve and vent.

Question 3

What are the pros of a compressed gas system?

Answer 3

Smaller cylinders for less stress. Quick refuelling.

Question 4

What are the cons of a compressed gas system?

Answer 4

Cylinders are inefficient for packaging. Tank lifetime 10 years before disposal for 2015 Toyota Mirai. Compression requires 10% energy of fuel.

Question 5

What are the pros of a liquid system?

Answer 5

Higher energy density.

Question 6

What are the cons of a liquid storage system?

Answer 6

Cooled to 20 K, which requires 40% of the energy of the fuel.
Thick tank walls still necessary, not for pressure, but to keep cool.
Bad long term storage.

Question 7

Where does the energy in solid state fuel cells come from?

Answer 7

Hydrogen is chemically stored in metal.

Question 8

What are the pros of a solid state system?

Answer 8

Very high volumetric efficiency.

Question 9

What are the cons of a solid state system?

Answer 9

Bad gravimetric efficiency.
Switches between exo and endothermic during charge and discharge so can’t suddenly increase RoR or temperatures change too much.
Degrade more quickly.