System Integration and Modelling
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In view of the environmental benefits it is important that hydrogen fuel
is derived from renewable energy sources. Most of these sources, however,
display fluctuations in power production. As a loss of load cannot be
tolerated for the majority of transport applications, a certain share
of conventional (mainly fossil) grid backup will be required.
Obviously, the more fossil primary energy is used, the higher the level of emissions. Computer modelling is the key to evaluating the characteristics of hydrogen systems in these respects.
A minimum level of renewable energy will be necessary to achieve any environmental advantage relative to a standard (diesel) system. This level is determined by the “break even point“. At this point, diesel and fuel cell vehicle produce the same level of global emissions. For the case of CO2-equivalents and a fuel cell bus supplied by a EUHYFIS filling station, the break even point lies in the range of 65%. In other words, a minimum of two thirds of the energy consumed for generating the hydrogen need to come from renewable sources in order to surpass a conventional diesel supply in emission quality.
Minimisation of investment costs while obtaining a maximal environmental
benefit is a major issue of system integration and modelling. Studies
of this kind also yield vital information on the design of control and
safety management.
The figure below shows a typical dimensioning problem. When employing
fluctuating power (wind energy in this case), storage will improve the
share of “green“ hydrogen available. The relationship is non-linear. Main
parameters are the type of renewable energy source, meteorological site
characteristics, the daily load pattern etc.
