Major automakers such as DaimlerChrysler want to extend the mileage of
fuel cell buses by increasing vehicle tank pressure. Instead of 200 bar
today (2860 psi) the future standard will be 350 bar (5000 psi). This
requires compressors that can consolidate hydrogen gas in the filling
station storage up to 550 bar (7860 psi).
In 2001 a detailed study of hydrogen fuel supply to
buses in public transport was completed at PLANET. The investigation followed
the rules for life cycle assessments as laid down in the series of standards
EN ISO 14040 – 14043. Seven scenarios were compared which rely on different
primary energy sources (e.g. coal, natural gas, wind and water power)
as well as various ways of energy conversion (electricity generation,
synthesis of methanol, liquefaction of hydrogen...).
The crucial question was, which of the scenarios would come off well
in comparison to diesel, the standard fuel for buses today. The consumption
of fossil resources and, closely linked to this, the emission of greenhouse
gases belonged to the prime criteria. In this context, the "ecological
rucksack" had to be considered, i.e. the effort of energy and materials
to build the necessary infrastructure like chemical production facilities,
wind turbines, pipelines for transportation etc.