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# 10 Quadrillion BTU In Untapped Waste Energy Gets Supersonic Thermoelectric Treatment

If all goes according to plan, a new thermoelectric makeover for power plants will put the squeeze on fossil energy by converting waste heat to electricity.

According to the latest pre-COVID estimate, the US industrial sector churns out 13 quadrillion BTU in waste heat every year and only recaptures about 3 quadrillion of it. Just think of all that energy lying about with nothing to do. A lot of it could be reclaimed through the magic and science of thermoelectricity, if a new twist on something called supersonic cold-spray technology makes its way out of the lab and into the world.

Waste energy from power plants and other industrial facilities could be converted to electricity, someday (photo via Lawrence Livermore National Laboratory).

### Thermoelectric Waste Energy Recovery “Rather Immature” in 2015

For those of you new to the topic, thermoelectricity refers to the current that can be generated by leveraging the difference in temperature between two materials, which is something called the Seebeck effect.

Here, let’s have the Energy Department explain all this:

“Thermoelectric materials allow for direct electricity generation through the Seebeck effect where a temperature gradient applied to a circuit at the junction of two different conductors produces an electromotive force based on the relation Eemf=−𝑆∇𝑇where 𝑆 is the Seebeck coefficient (or 41thermopower).”

Got all that? Good! As recently as 2015, the Energy Department noted that “Seebeck generation products are rather immature,” meaning that there was scant interest in commercial applications.

That doesn’t mean no thermoelectricity. Run the system in the opposite direction and you get the Peltier effect, which refers to heating and cooling materials by apply an electrical current. Just ask your hot-n-cold seat about it.

### The Cold Spray Solution

The Peltier effect is typically deployed in small devices. To get the full bang for the buck out of a thermoelectric system, you need to scale up into power plants and other industrial applications.

Part of the challenge is how to achieve an “intimate contact” between your thermoelectric materials and surfaces like pipes and other equipment, which can be irregular, curved, and interrupted by joints and other hardware.

The solution sounds simple: just spray layers of thermoelectric material over the surface and there you have your seamless contact.

In fact, cold-spray technology is commonly used in industrial applications including repair work as well as corrosion resistance and other surface treatments. It involves introducing tiny metal particles into a supersonic gas and slamming them onto a metal surface, where the impact plasters them into a seamless coating.

Unfortunately, you can only do that with materials that are somewhat elastic or malleable. You can’t do that with semiconductor materials, which have a crystalline structure, which means they are brittle and they don’t tolerate the spray-on treatment very well.

### Supersonic Cold Spray Meets Waste Energy, Magic Happens

That explains why cold-spray has been slow to catch on for thermoelectric applications, but that could change thanks to new research from the Energy Department’s Lawrence Livermore National Laboratory in a partnership with the Virginia-based company TTEC Thermoelectric Technologies.

Here’s the short version of their findings:

“The team concluded that cold-spray deposition can fabricate bulk pieces of thermoelectric bismuth-telluride on a wide variety of substrates, without loss of structural integrity, demonstrating that cold-spray is a viable alternative to traditional manufacturing approaches for thermoelectric materials.”

The Journal of The Minerals, Metals & Materials Society, which published the findings, offers up more details:

“…The sprayed material has a randomly oriented microstructure largely free from pores (> 99.5% dense), and deposition is achieved without substantial compositional changes. The Seebeck coefficient and thermal conductivity are largely preserved through the spray process, but the defects introduced during deposition significantly increase electrical resistivity. Defects can be removed, and compressive strain relaxed by a post-deposition anneal, which leads to Bi2Te3 blocks with a typical ZT of 0.3 at 100°C.”

If you’re thinking there’s a connection between TTEC, thermoelectricity, and planetary exploration, run right out and buy yourself a cigar. Among other on-the-job experience, TTEC founder and owner Richard C. Thuss worked on just that very topic for NASA for almost 20 years.

### The Many Benefits Of Capturing Waste Energy With Thermoelectricity

Okay so they had to do some tinkering there at the end with that thing about defect removal, but still. The main point is that the spray-on method has the potential to produce economies of scale that would be difficult to achieve with other thermoelectric systems, in addition to overcoming curves, bumps and other geometrically complex surfaces.

For power plants, scaled-up thermoelectric systems would add yet another factor contributing to the falling demand for fossil fuels. That’s in addition to applications in many other industrial sectors. Let’s face it, nobody really likes fossil fuels any more.

The renewable energy angle can also come into play, for example by deploying thermoelectricity in a concentrating solar power system, as a complement to thermal energy storage.

Aside from its potential for capturing waste energy from large sources, thermoelectricity has also been pursued down at the other end of the scale for mobile applications including car exhaust systems, drones and of course, Abrams tanks.

Photo (cropped): Power plant via Lawrence Livermore National Laboratory.

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Written By

Tina specializes in military and corporate sustainability, advanced technology, emerging materials, biofuels, and water and wastewater issues. Views expressed are her own. Follow her on Twitter @TinaMCasey and Google+.

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