UC Davis Institute of Transportation Studies

Many studies have already addressed the tradeoffs between the various hydrogen refueling stations, but few studies have worked on how a station should be managed on a day by day basis, in a market driven situation. No data are already available since the existing H2 stations are still in the permitting phase, and there are no big fleets refueling now. But parameters such as vehicle daily load profile, seasonality in demand, station electricity load, could have an influence on station design. Especially in the case where the hydrogen is produced locally at the station and stored as a gas, these problems could be a major hurdle if not considered prior to building the station: the combination of the storage, reformer compressor and dispenser must be sized for the most demanding day we can expect: but many station have a seasonality and a vehicle profile that will vary depending on the day of the week. There is also a tradeoff between the reformer size and the storage size: the bigger the reformer, the smaller the storage.

This is very different from a regular gasoline station, where the gasoline is brought by truck: there we simply meet the peaks of demand by bringing in more trucks. This could in fact make us reconsider the tradeoffs between the H2 pathways: a liquid storage has been said to be more expensive than a gaseous one, but a liquid storage should offer much more flexibility for demands with important variations. The transient response should be much better than with a reformer that usually needs to work at a steady state. The problems that arise with liquid H2 storage are much more understood since this technology is closer to what we know with gasoline (both are brought by trucks and stored liquid). For an onsite production and a gaseous storage, the problems and governing rules are completely different.

This study has evaluated various configurations and strategies for addressing the seasonality. It has also tackled the energy station, assessing how adding a fuel cell to a station might improve the results. This calls for a good understanding of the station electricity needs. The study also covers the station in a market buildup scenario and compared various technical solutions such as sizing the station to achieve a 100% capacity use in a future year and running it at lower loads; using a fuel cell to improve station use; following demand by adding capacity (i.e. reformer, compressor, storage) from time to time.