An overview of solar thermochemical processes is provided by Steinfeld and Palumbo (2001).
Some topics addressed by recent studies are
- Evaluation of novel processes for fuel synthesis (Möller et al. 2002; Dahl et
al. 2004) and material production (Murray et al. 1995; Wieckert et al. 2004); - Development of novel solar reactors (Anikeev et al. 1998; Osinga et al. 2004);
and - Catalyst development for solar-driven high-temperature gas-gas reactions
(Berman and Epstein 1997).
The development of fuel production using solar energy is in a relatively early stage. Progress in
the above topics is crucial to assess the technological viability of such processes prior to
estimates of their economical feasibility.
Present long-term projections suggest that the solar fuel production processes described above
will probably be two to three times more expensive than present high-emission industrial
methods. However, they also predict that solar fuel production can be competitive if carbon
emission cost is considered (Steinfeld and Palumbo 2001).
Low-temperature Solar Thermal Systems
Low-temperature solar thermal systems have the potential to supply a significant number of U.S.
households and commercial buildings with heating, cooling, and refrigeration; refer to the Solar
Thermal Technology Assessment for further details. To overcome the current barrier of high
initial cost, there is a need for new materials in a number of roles. Durable polymeric materials
or films are sought that provide high transmittance in the visible spectrum and protection from
ultraviolet light, which is crucial in the successful development of polymer collectors (Davidson
et al. 2002). The viability of polymer heat exchangers and absorbers depends on the development
of extrusion-grade thermoplastic polymers with high strength to minimize the required thickness
of the polymer structure and resistance to hot chlorinated water.
Low-cost methods to improve the thermal conductivity of polymers are desirable. Some methods
are proposed by Danes et al. (2002) and Davidson et al. (2002), but further work is required. An
understanding of the mechanism leading to crystal growth on polymeric surfaces is required to
develop strategies to avoid such growth. Of key interest are chemical differences between
polymers, which influence their interaction with water; the mechanism of calcium carbonate
nucleation; and scale morphology and structural differences (e.g., surface roughness), which may
affect calcium carbonate nucleation and adhesion (Sherman 2001; Wang et al. 2005).
Other needs are found in the development of low-temperature solar thermal systems that can
supply both hot water and space heating. Cost-effective thermal storage is sought for seasonal or
annual rather than daily energy requirements. Chemical or phase-change materials may provide
performance superior to that of water-based storage options. Initiatives to develop systems that
are part of the building envelope should be supported for both existing and newly constructed
buildings. The solutions will be different. New buildings represent an opportunity for major