Basic Research Needs for Solar Energy Utilization - Office of ...

coefficient. The thermal conductivity of most polymers is 0.2–0.4 W/m-K. A hundred- to
thousandfold increase in thermal conductivity is needed to make polymers competitive. New
composite materials hold the promise of high mechanical strength and high thermal conductivity.
Surface modifications are needed for photon and thermal management. High-efficiency solar
absorbers for water heaters can be formulated to exploit the concept of photonic crystals. Mirrors
and glass that repel dirt can significantly increase efficiency and reduce cleaning cost. Surface
engineering is also needed to prevent scale formation in solar thermal heat exchangers.
Fundamental research on particle-surface interactions and solid precipitation and deposition
processes can help solve these challenges.
Solar Thermochemical Fuel Production
Radiative Exchange in Chemically Reacting Flows. Fundamental research, both theoretical
and experimental, is needed in radiation heat transfer of multiphase chemical reacting flows. The
analysis of thermal radiative transport coupled to the reaction kinetics of heterogeneous chemical
systems, in which optical properties, species composition, and phases vary as the chemical
reaction progresses, is a complex and challenging problem to be tackled in the design of hightemperature
thermochemical reactors. Of special interest is the radiative exchange within
absorbing-emitting-scattering particle suspensions, applied in thermochemical processes such as
thermal cracking, gasification, reforming, decomposition, and reduction processes.
Directly Irradiated Solar Chemical Reactors. The direct absorption of concentrated solar
energy by directly irradiated reactants provides efficient radiation heat transfer to the reaction
site where the energy is needed, bypassing the limitations imposed by indirect heat transport via
heat exchangers. Spectrally selective windows can further augment radiation capture and
absorption. The use of nanoparticles in gas/solid reactions augments the reaction kinetics and
heat and mass transfer.
Materials for High-temperature Solar Chemical Reactors. Materials for construction of
solar chemical reactors require chemical and thermal stability at temperatures >1,500°C and
solar radiative fluxes >5,000 suns. Advanced ceramic materials and coatings are needed for
operating in high-temperature oxidizing atmospheres and for withstanding severe thermal shocks
occurring in directly irradiated solar reactors.
The ability to develop electrolysis processes at high temperatures depends on the development of
structural materials that are stable at T>800°C and other materials that can be used for various
components, such as absorbers, electrolytes, and electrodes of the solar reactor and electrolysis
units
The development of high-temperature materials for solar reactors is in a relatively early stage.
Progress in the above topics is crucial in assessing the technological viability of such processes
prior to estimates of their economical feasibility.
70