Off-Grid Solar for Rural Development
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stand-alone woodstoves and also transform the huge amounts of waste energy from industrial furnaces and power plants.
The Future of Thermoelectric Materials
The future expansion of thermoelectric energy conversion technologies is tied primarily to enhanced materials performance along with better thermal management design. The best thermoelectric material should behave as a so-called phonon– glass–electron–crystal; that is, it should minimally scatter electrons, as in a crystalline material, whereas it should highly scatter phonons, as in an amorphous material. Materials researchers are now investigating several systems of materials including typical narrow-bandgap semiconductors (half-Heusler alloys), oxides, and cage-structure materials (skutterudites and clathrates).4 More exotic structures that exhibit reduced dimensionality and nanostructures have been the focus of much recent research, including superlattices, quantum dots, and nanodot bulk materials. Also, recent progress in nanocomposites, mixtures of nanomaterials in a bulk matrix, has generated much interest and hope for these materials.4 The emerging field of these thermoelectric nanocomposites appears to be one of the most promising recent research directions. Such nanocomposites could allow for higher ZT values by reducing thermal conductivity while maintaining favorable electronic properties. With new higher efficiency materials, the field of harvesting waste energy through thermoelectric devices will become more prevalent. The most stable, long-term, and readily available worldwide energy source is that of solar energy. The issue has always been
low-cost transformation and storage. Other alternative energy technologies such as fuel cells, wind energy, and thermoelectrics will provide some assistance in meeting our future energy needs. Many hybrid systems will be needed, and thermoelectrics is able to work in tandem with many of these other technologies, especially solar as it can use the heat source provided by solar radiation. Over the past decade, thermoelectric materials have been developed with ZT values that are a factor of 2 larger than those of previous materials. Another 50% increase in ZT (to ZT ≈ 3) with the appropriate material characteristics and costs will position thermoelectrics to be a significant contributor to our energy needs, especially in waste heat or solar energy conversion. The likelihood of achieving these goals appears to be within reach in the next several years. Furthermore, some contribution from many of these alternative energy technologies such as thermoelectrics will be needed in order to fulfill the world’s future energy needs.
References
1. T.J. Seebeck, Abh. K. Akad. Wiss. 265 (Berlin, 1823). 2. A.F. Ioffe, Semiconductor Thermoelements and Thermoelectric Cooling (Infosearch, London, 1957). 3. H.J. Goldsmid, R.W. Douglas, Br. J. Appl. Phys. 5, 386 (1954). 4. T.M. Tritt, M.A. Subramanian, MRS Bull. 31 (3), 188 (2006); six articles and all references therein. 5. J. Yang, T. Caillat, MRS Bull. 31 (3), 224 (2006). 6. S
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