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Friday, January 10, 2014

Fuel Cell Future Unlikely or Inevitable? Part 5 - Storage

To drive a hydrogen (H2) powered car, once the H2 is generated and distributed, it has to be stored in your car. To have a viable range in a fuel cell vehicles (FCV), you are going to need a large amount of H2. If you carried this gaseous H2 along uncompressed, you would need a hot air balloon sized storage.

Compression

Although methods of binding H2 in solid form or chilling it to liquid have in used in some applications, the method of choice for FCVs is compressing the H2 gas under high pressure, such as 5,000 to 10,000 psi.

To handle these high pressures, the tanks have to be very strong. For stationary applications, this can be done with thick metal walls. For mobile applications, like a car, however, these thick-walled tanks are too heavy and reduce the car's performance and range. This means, to meet the high strength and light weight requirements, mobile high pressure H2 tanks are made of advanced materials such as carbon fiber.

The act of compressing the H2 itself takes energy too. Depending on the level of compression that is used, from 2% to 5% of the energy content is lost to compression and cooling.

Permeation

Hydrogen is tricky to contain. It is a small molecule and it can pass through many solids via a process called permeation. Polymer lined tanks developed in the last decade have reduced this leakage to a near negligible amount.

Continue to Part 6: Fuel Cells