Last few decades have seen unexpected rise in demands for fuel catering to the needs of ever expanding global industrialization. With limited known reserves and supply constraints, more controversial methods of energy such as fracking are being considered along with focus on clean renewable energy. Waste energy minimization is seen as an alternative to subdue the climatic impacts of increased energy consumption. Agency of Energy and environment report' 20081 suggests power plants lose over 60% of the total energy generated and heat loss along electrical carrier cables dissipates 20% of input energy. Similar energy pathway using heat engines/automotives reiterates the need for improving energy efficiency as only quarter of input energy is available for vehicle mobility and necessary power while the remaining is squandered in the form of waste heat in the exhaust, by cooling circuits, as friction and losses such as rolling resistance, aerodynamic drag.2
A promising way to extract the energy wasted during energy generation, is to use a Thermoelectric generator. A Thermoelectric Generator (TEG) works on the principles of the Seebeck Effect and essentially converts heat energy into electrical energy. The development of such generators has been supported since the mid-20th century and is consistently improving in quality and efficiency.
TEGs also finds applicability in long space programs where payload weight is absolutely critical and standard energy sources such as Fuel cells, supercapacitors, solar sails/panels become too heavy to be economical and feasible. NASA has been implementing Radioisotope Thermoelectric Generators (RTGs) where a decaying Plutonium-238 source is used as heat source for coupled TEG. Similar Low Power systems are still functional in space missions sent beyond the orbit of Jupiter for over 30 years such as Pioneer3. Development of new RTGs requires consideration of optimization of thermoelectric4 properties with operating conditions. Various other applications of TEGs will be seen in following sections.
With current thermoelectric (TE) technology and materials, the efficiency is about a fifth of the possible Carnot efficiency.
However, it must also be given due consideration that these TEGs have pronounced advantages over compressor/expander systems. The devices are scalable, prone to much lesser mechanical wear and tear compared to conventional systems, relatively cheap and easier to produce.
TE devices give improved energy efficiency when integrated with current energy systems. Chen et al7 have studied integration of TEGs in a Combined Heat and Production systems (CHP).
Such development in energy processing is required for energy conservation in this expanding global economy which still depends for about 85% of its energy requirement on coal reserves, with use of renewable energy to stabilise CO2 emissions.4 TEGs would have to be seen as an alternative energy extraction system, being mindful of our current reserves of Non-renewable sources at 39.375 exa-joules and ratio of annual production to current resources standing at 1:82 in 2018.
Refrences
1. Martin-Gonzalez, M.; Caballero-Calero, O.; Diaz-Chao, P., Nanoengineering thermoelectrics for 21st century: Energy harvesting and other trends in the field. Renew Sust Energ Rev 2013, 24, 288-305.
2. Yang, J.; Caillat, T., Thermoelectric Materials for Space and Automotive Power Generation. MRS Bulletin 2006, 31 (03), 224-229.
3. Rinehart, G. H., Design characteristics and fabrication of radioisotope heat sources for space missions. Prog Nucl Energ 2001, 39 (3-4), 305-319.
4. Jean-Baptiste, P.; Ducroux, R., Energy policy and climate change. Energ Policy 2003, 31 (2), 155-166.
5. DiSalvo, F. J., Thermoelectric cooling and power generation. Science 1999, 285 (5428), 703-706.
6. Vining, C. B., An inconvenient truth about thermoelectrics. Nat Mater 2009, 8 (2), 83-5.
7. Chen, M.; Lund, H.; Rosendahl, L. A.; Condra, T. J., Energy efficiency analysis and impact evaluation of the application of thermoelectric power cycle to today`s CHP systems. Appl Energ 2010, 87 (4), 1231-1238.
8. Andruleit, H.; Babies, H. G.; Meßner, J.; Rehder, S.; Schauer, M.; Schmidt, S. Annual Report : Reserves, Resources and availability of Energy Resources 2011 2010. http://www.bgr.bund.de/EN/Themen/Energie/Downloads/annual_report_2011_en.pdf?__blob=publicationFile&v=2.
