Workpackage 4:Techno-economical Evaluation

Workpackage leader George Kaplanis, TROPICAL

In today’s fuel cell driven prototype cars (e.g. Toyota FCHV, Ford Fusion, Chevrolet Volt, Daimler HYGENIUS) mostly compressed hydrogen gas storage (CHS) at pressures of up to 700 bar is employed (c.f. [1]) and investigations of the long term behaviour with regard to system performance, fatigue and safety are underway. Alternatively, also liquid hydrogen storage (LHS) has been demonstrated (BMW). Though the corresponding tank systems have reached a rather high degree of technical maturity, it is still unclear what will be the overall hydrogen supply system efficiency concerning e.g. energy consumption for the extremely high pressures or liquefying hydrogen resp. and necessary expenses on weight for cooling or heat exchanging systems.

In contrast to these storage techniques solid state storage operates at moderate gas pressures of up to 200 bars, which since long time has been the technical status. Due to the chemical bonding of hydrogen to the storage materials no sudden explosive release of hydrogen can take place. Therefore solid state storage materials are inherently safer than CHS or LHS techniques.

Prototype tank developed in the STORHY project at HZG. The tank is designed for 8 kg of NaAlH4 (≈ 400 g H2 / ≈ 4.5 m3 H2 at STP)

Currently, a test tank containing 8 kg of sodium alanate is set-up at GKSS (Figure to the right). Along with the development of novel materials (e.g. pure boro­hydrides or modified MgH₂) in the EU-Project NESSHY prototype tanks for these materials are developed, using the experience on tank design gained within STORHY and former projects.

The results achieved in the running EU projects on solid state hydrogen storage made clear, that with the materials developed so far the industrial targets for a storage tank cannot be achieved (e.g. [3] here): tank capacity 5 – 6 wt%, desorption pressure > 1 bar, hydrogen flow out of tank system at least 2 g/s hydrogen flow, which must be supplied also at low tank filling level, temperature of operation compatible with fuel cell to be supplied, ideally allowing for a heat balance between fuel cell and storage tank without the need for extra heating or cooling during continuous operation.

The techno-economical evaluation of the novel FLYHY materials will take place in the view of potential mobile and stationary applications and in the light of the above mentioned targets. Materials tank relevant properties (capacity, achievable flow rates at different operation temperatures), the potential up-scaling of the production of FLYHY materials (cost of raw materials and production process) and, their integration into tank designs (heat conductivity, effective capacity of powder materials, safety aspects) will be assessed, and a laboratory prototype tank will be tested together with a High Temperature PEM Fuel Cell. FLYHY will pay special attention to questions of safety in materials preparation handling and use. Setting up on the knowledge developed in former and co-existing projects, thus conclusions and recommendations for the industrial implementation of the FLYHY results will be drawn.