"What am I, chopped liver?" That's what the entire field of thermoelectrics (at least as it relates to waste heat recovery) wants to know. In a field of showy alternative energy candidates like biofuels, solar cells, fuel cells, and powerful wind turbines, the challenge of eking out bits of excess energy that would otherwise be wasted as heat to make incremental improvements in energy efficiency seems a bit, well, proletarian. One could almost envision the poor, lonely drudges doomed to try and recover snippets of wasted heat energy for all eternity in Dante's Ninth Circle of Hell, while Lucifer looks on and snickers.

In short, it's a thankless task. Small wonder Lon Bell (BSST LLC and NREL) jokingly calls his work in this area "the chopped liver of new technologies." But now that the great Global Energy Challenge has moved to the forefront of both national and international concerns, there's been a resurgence of interest in the Little Heat Engine That Could, particular when it comes to waste heat recovery. Bell and his colleagues are finally beginning to get a bit more respect from the general populace at large.

At the heart of Bell's scheme for recovering wasted heat from vehicle exhaust (thereby reducing CO2 emissions) -- as well as from residential, commercial and industrial fuel-fired heating systems, not to mention diesel-powered electric generators -- is a well-known (among physicists) phenomenon known as the Peltier-Seebeck Effect (a.k.a., the thermoelectric effect): the direct conversion of electrical voltage into temperature differences, and of temperature differences into electrical voltages.

Let us take a slight historical detour. There was a time a few hundred years ago when thermodynamics was all the rage, even if folks didn't know that's what it was called. Back in the 19th century, a little-known French physicist named Sadi Carnot became obsessed with building ore efficient steam engines. His motives were admittedly a bit odd. He was the son of a French aristocrat, and his father was one of the most powerful men in France prior to Napoleon's ignominious defeat. For some reason, the young Sadi seemed to think England's superior technology in this area had contributed to Napoleon's downfall and the loss of his family's prestige and fortune. But regardless of motive, his research proved revolutionary.

In 1824 he published Reflections on the Motive Power of Fire, which described a theoretical "heat engine" that produced an amount of work equal to the heat energy put into the system. Carnot was no fool: he knew from endless experimentation that in practice, his design would always lose a small amount of energy to things like friction, noise and vibration. His lasting contribution was to set out the physical boundaries so precisely that, after his untimely death from cholera at the age of 32, Rudolf Clausius and William Thomson (Lord Kelvin) would draw on his work to build the foundations of modern thermodynamics in the 1840s and 1850s. Carnot also invented the so-called "Carnot cycle," drawing energy from temperature differences -- the basis of modern-day refrigerators and air-conditioners. (The Carnot cycle also lies behind the popular Dunking Bird science toy.)

Ten years later, a retired French clock maker named John-Charles-Athanase Peltier made a similar "discovery." (Peltier retired at the age of 30 to devote himself to scientific investigation. Apparently he was a hugely successful clock maker. Either that, or he had a trust fund.) He joined a piece of copper wire with a second piece of bismuth wire, connected the bismuth end to a battery, ad then completed the circuit loop back to the copper wire. When he switched on the battery, one of the copper-bismuth junctions got hot, while the other one got cold. The Peltier Effect can be used to make a rudimentary refrigerator, just by sticking the cold junction into an insulated box -- inefficient and not very powerful, but reliable since it has no moving parts.

The Peltier Effect is very nice and all, but Bell's interest lies in its mirror image: the Seebeck Effect. Three years before Carnot published his seminal work, and 13 years before Peltier's observations, a German-Estonian scientist named Thomas Johann Seebeck was fiddling in his lab with a metal bar made out of two dissimilar metals (perhaps copper and bismuth), and discovered that if the junctions between them were at different temperatures, a compass magnet's needle would be deflected. Initially Seebeck thought this was due to magnetism induced by temperature difference, but he soon realized it was creating an electrical current. Furthermore, the voltage was directly proportional to the temperature difference: the greater the differential, the higher the voltage. This is called the Seebeck co-efficient, and it's crucial to Bell's work on waste heat recovery.

Thermoelectric (TE) devices are essentially reversible, solid-state heat engines, according to Bell. Apply a temperature difference across a thermoelectric array, and you'll get electric power; apply electric power, and a portion of the array will cool (create a "heat sink"), while another portion will heat up. They're rugged, and very low maintenance. Yet apart from select military and space applications, TE devices haven't played a major role in power generation because they're not all that efficient in terms of energy conversion (only one-fourth as efficient as an A/C system), plus the materials and systems cost more than other alternatives.

That's changing, however: Bell and Company have been hard at work in the lab, developing more efficient thermodynamic cycles and improving the overall design and the materials used in such systems. The technology has evolved to the point where lab-based systems are reaching efficiencies of more than 6%, with the possibility of attaining 20% conversion efficiency in the future.

That's too inefficient for the technology to be used for major stuff like auxiliary power generation, or general cooling and heating, but it's ideal for some smaller niche applications, says Bell. Things like a desktop heater/cooler, now being developed by a company called Herman Miller; beverage heater/coolers under development by Tellurex; infrared sensor coolers; and scavenging waste heat to both heat and cool car seats, as needed. (Ford, Nissan, and Hyundai are among the automotive companies using TE devices to capture and recycle heat in some car models.) Couple TE waste heat recovery with things like fuel cells and solar photovoltaics, and it could at least enhance the performance of larger power generation systems.

The transportation sector is proving to be the early adopter of this technology. NREL has a $16.2 million program to further develop thermoelectric waste heat recovery schemes for passenger cars to improve fuel efficiency, thereby reducing the use of fossil fuels and associated emissions -- perhaps incrementally, but incremental improvements can add up quickly if they're broadly applied. Simply recovering wasted heat from car, van, truck and bus exhaust could result in 5% to 10% reductions in CO2 emissions.

My shiny Prius features "regenerative braking," in which the at least some of the heat produced by friction when one brakes is captured and fed back into the car's battery. I thought it was ingenious when I heard about it, but it's nothing new to Bell and his colleagues. They've been toiling away quietly in the background, the wallflowers of the Great Energy Dance. It'd be nice if they got a chance to take a spin on the dance floor now and then.