Solar Thermochemical Fuel Production
Solar concentrating systems currently provide the lowest-cost technology for solar electricity
production, and they offer the possibility of economically supplying high-temperature heat for
driving thermochemical processes for hydrogen generation. Solar fuel production via
thermochemical processes requires fundamental kinetic studies of the reactions involved and the
development of novel chemical reactor technology for effecting these high-temperature reactions
with high solar-to-fuel energy conversion efficiencies.
RESEARCH DIRECTION
Thermochemical Fuel Production
Research in thermochemical fuel production is aimed at the advancement of the thermochemical
and thermo-electrochemical sciences applied to the efficient thermochemical production of solar
fuels, with the focus on solar hydrogen production. Concentrated solar radiation is used as the
energy source of high-temperature process heat for the endothermic chemical transformations.
The research emphasis is on the following areas:
- The fundamental analysis of radiation heat exchange coupled to the kinetics of
heterogeneous thermochemical systems; - The design of advanced chemical reactor concepts based on the direct
irradiation of reactants for efficient energy absorption; - The development of high-temperature materials (T>1,500°C) for
thermochemical and thermo-electrochemical reactors; and - The production of hydrogen by water-splitting thermochemical cycles via
metal oxide redox reactions and by thermal decarbonization of fossil fuels via
gasification of carbonaceous materials.
Hydrogen Production by Solar Thermochemical Processes
Solar Water-Splitting Thermochemical Cycles. The single-step thermal dissociation of water
is known as water thermolysis. Although conceptually simple, the direct water-splitting has been
impeded by the need for a high-temperature heat source above 3,000K for achieving a reasonable
degree of dissociation and by the need for an effective technique for separating H 2 and O 2 to
avoid ending up with an explosive mixture. Water-splitting thermochemical cycles bypass the
H 2 /O 2 separation problem and also allow operating at relatively moderate upper temperatures.
Previous studies performed on H 2 O-splitting thermochemical cycles were mostly characterized
by the use of process heat at temperatures below about 1,200K, available from nuclear and other
thermal sources. These cycles required multiple steps (more than two) and suffered from inherent
inefficiencies associated with heat transfer and product separation at each step. Status reviews on
multistep cycles, with upper temperatures below 1,200K, are given by Funk (2001) and include
the leading candidates: General Atomics’ three-step cycle based on the thermal decomposition of