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

SOLAR THERMAL AND THERMOELECTRICS
THERMAL SYSTEMS
Solar thermal systems use solar radiation as a source of heat; this heat can be used in several
ways. It can be used for climate control in buildings — heating and cooling. It can be
concentrated to produce temperatures high enough to generate electrical power, and it can also
be used in this concentrated mode to induce reactions to make chemical fuels. With focused solar
radiation, photovoltaic (PV) devices can function at a much higher efficiency.
Low-temperature solar thermal systems do not involve sunlight concentration; they may
occasionally employ low concentration at a factor of C ≤ 2. The optical concentration of direct
sunlight involved in power and fuel generation may range from about 20 to several thousand,
depending on the specific process and system involved. Solar PVs are found at the higher end of
this concentration range.
Innovations and new developments in solar thermal generally involve a significant reduction in
cost or the introduction of a previously unattainable mode of operation.
Low-temperature Solar Thermal Systems
Based on recent U.S. Department of Energy (DOE) Annual Energy Outlook reports, residential
and commercial buildings account for 36% of the total primary energy use in the United States,
and 30% of the total U.S. greenhouse gas emissions. About 65% of the energy consumed in the
residential and commercial sectors is for heating (46%), cooling (9%) and refrigeration (10%); in
principle this energy can be provided by non-concentrating solar thermal systems. Based on
population density and climate, 75% of U.S. households and commercial buildings are
appropriate candidates for non-concentrating, solar hot water systems.
Initial cost is considered a major barrier to the increased use and market growth of solar hot
water and heating systems. Improved performance and the use of low-cost materials are the best
means for cost reduction. Recent R&D efforts have focused on polymer-based systems, which
will be most cost effective when production capacity is scaled up. The progress of polymer
system hinges on material development with specific requirements for glazing and heat
exchangers — used to absorb incident sunlight and transfer solar energy to potable water.
Needed development areas include materials that are durable and compatible with potable water,
and design and manufacturing processes that take advantage of the cost savings potential of
replacing glass and metal with plastics.
Concentrated Solar Thermal Processes for Power Generation
A good fundamental review of solar thermal power plants in general and concentrating methods
used in solar thermal systems is provided by Winter et al. (1991). All power-generating solar
thermal systems can be hybridized with fuel to supplement solar power during low-insolation
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