Basic Research Needs for Solar Energy Utilization

Spectral

Filter

hν> Eg

hν< Eg

Power

Bus

TPV Cells

Therma RadiatorCombustion

Thermal System

Management

Spectral

Filter

hhνν> E> Egg

hhνν< E< Egg

Power

Bus

TPV Cells

Therma RadiatorCombustion

Thermal System

Management

Figure 78 A typical thermophotovoltaic system

furnace TPV cogeneration system at 10 cents per kilowatt-hour. Such a system will reduce the
battery dependence of a pure solar system. For a GaSb-based TPV system, the estimated cell cost
accounts for 35% of the system cost.

The enablers for the cost and performance improvements are high-temperature selective emitters,
lost-cost filters, and efficient system design to recuperate waste heat below the emitter
temperature. Selective emitters that are durable for high-temperature operation and yet cost
effective, as well as cost-effective spectral filters are essential for system efficiency. Examples of
these structures are interference filters, photonic crystal emitters, and rare-earth-doped selective
emitters. Although the diodes themselves have impressive efficiency, there is room for further
improvements, for example, through band gap engineering, that are widely used in
semiconductor lasers and detectors. New concepts such as tunneling and surface-wave-based
TPVs (DiMatteo et al. 2001) and coherent thermal emission (Greffet et al. 2002) are worthy of
further exploration.

Solar PVs, TPVs, and thermoelectrics cover heat sources of different temperature range and
could work together to provide efficient power supplies for distributed systems. TPV diodes
evolved from tandem cells used for high-efficiency solar cells. Because thermoelectrics can
generate power at a lower temperature range, combined TPV and thermoelectric power
generation systems could lead to higher system efficiency.

REFERENCES

R. Almanza, G. Jiménez, A. Lentz, A. Valdés, and A. Soria, “DSG under Tow-phase and
Stratified Flow in a Steel Receiver of a Parabolic Trough Collector,” ASME J. Solar Energy Eng.
124 , 140–144 (2002).

V.I. Anikeev, A.S. Bobrin, J. Ortner, S. Schmidt, K.H. Funken, and N.A. Kuzin, “Catalytic
Thermochemical Reactor/Receiver for Solar Reforming of Natural Gas: Design and
Performance,” Solar Energy 63 , 97–104 (1998).