A critical assessment of present hydrogen production techniques: is solar cracking a viable alternative?

There has been extensive R&D on thermochemical production of hydrogen and synthesis gas via concentrated solar energy. A major objective of these efforts was to generate fuel for ground transportation, either as synthetic liquid fuel via Fischer-Tropsch or as pure hydrogen for fuel cell vehicles as compressed gas on board. In parallel, batteries for use in electric vehicles have made substantial progress primarily with respect to their energy density and charging time. This paper explores which sun-to-wheel route is more promising in terms of energy efficiency. The results show the surprisingly explicit conclusion that the solar-to-electricity route is superior indicating the need to improve solar conversion efficiencies of the current commercial photovoltaic and steam cycle technologies. One promising way to achieve this goal is via solar cracking of natural gas to produce hydrogen gas and solid carbon for use as fuels in hydrogen fuel cells and carbon fuel cells with a total potential efficiency that is significantly higher than photovoltaic and steam cycle based technologies.