innovation by incorporating the solar systems into roof and wall. Combined solar thermal and
PV systems, both concentrating and nonconcentrating configurations, that produce electricity and
heat should be investigated, in particular for integration into the building envelope.
BASIC SCIENCE CHALLENGES, OPPORTUNITIES, AND RESEARCH NEEDS
Materials hold the key to the thermal utilization of solar energy. High-efficiency thermoelectric
and TPV converters coupled to solar concentrators have the potential to generate electricity at
converter efficiencies from 25 to 35%. Currently, terrestrial thermoelectric and TPV systems are
mostly based on combustion heat, and solar-based thermoelectric and TPV systems have not
been systematically investigated. However, concentrator-based thermoelectric and TPV systems
have advantages over combustion systems as the heat loss from combustion exhaust is
eliminated in solar concentrator systems. Solar concentrators and hot-water heaters call for new
low-cost polymer-based materials and composites. Significant progress has been made in these
areas over the last decade, particularly by exploiting nanoscience and nanotechnology. Further
fundamental research should target developing thermoelectric materials with ZT up to 4,
selective thermal emitters that can withstand >1,000°C and the development of polymer-based
materials for use in heat transfer and as structural materials.
Research in thermochemical fuel production is aimed at the advancement of the thermochemical
and thermoelectrochemical sciences applied in the efficient thermochemical production of solar
fuels, with focus on solar hydrogen production. Concentrated solar radiation is used as the
energy source of high-temperature process heat for endothermic chemical transformations.
Research emphasis should be placed on (1) the fundamental analysis of radiation heat exchange
coupled to the kinetics of heterogeneous thermochemical systems, (2) the design of advanced
chemical reactor concepts based on the direct irradiation of reactants for efficient energy
absorption, (3) the development of high-temperature materials (T>1,500°C) for thermochemical
and thermoelectrochemical reactors, and (4) 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.
Thermoelectric Materials
High-efficiency thermoelectric converters coupled to solar concentrators have the potential to
generate electricity at converter efficiencies from 25 to 35%. The primary challenge to achieve
these efficiencies is the development of new, high-efficiency thermoelectric materials with
thermoelectric figures of merit ZT>3. The approach is to develop new classes of materials by
using a combination of exploratory synthesis and transport properties characterization guided by
theoretical efforts.
Comprehensive Theoretical Guidance on Thermal and Electronic Transport in Complex
Structures. Over the past decade, progress has been made in the theory of thermoelectricity,
notably the quantum size effects on the electronic power factor (Hicks and Dresselhaus 1993),
interface effects on thermal conductivity (Chen 2001), and the use of density functional theory