Low pressure, high mileage

A hydrogen storage system developed by Texaco Ovonic Hydrogen Systems (TOHS) in the US will allow future vehicles to run with a similar range and refuelling experience to petrol cars, the company claims.

The system allows relatively large volumes of hydrogen to be stored at low pressure, providing better capacity per litre of tank space than alternative compressed gas or liquid hydrogen fuel designs, and making the system safer.

Hydrogen bonds to the crystalline structure of a solid metal hydride alloy in the tank, storing the gas in an inert state.

‘This allows us to store more hydride; up to three times more per litre of space than a pressurised system and two times more than in liquid form,’ said Jeff Harvey, vice-president of marketing at ECD Ovonics, the parent company of TOHS.

Compressed hydrogen must be storied at around 10,000psi to give the car sufficient range.

Liquid hydrogen can provide greater range, but needs a cryogenic system, requiring complicated maintenance.

A 60-litre TOHS vessel stores 3kg of hydrogen, providing a 130-mile range compared to just 50 for a similar-sized compression system.

The tank design can be used at the refuelling site and on the vehicle. Refuelling takes under 10 minutes at 1,500psi.

The hydride is connected to a heat exchange system, allowing the material to be heated to release the gas and cooled to store it. Once in the vehicle the pressure of the hydrogen falls to 300psi, so the unit operates at low pressure for most of its cycle.

As the hydride does not have to be a particular shape fuel storage can be tailored to fit the car’s interior. By designing a larger unit it can also be used for fuel delivery trucks and storage at fuel stations.