Jared Schwede
"You're talking about something that's competitive with virtually any engine ... but all in a really neat package."
Building a Power Plant on a Chip
Conversations about clean, renewable sources of energy tend to focus on sources of energy tend to focus on solar and wind power. But Jared Schwede ’03 has his eye on another option: thermionics, the conversion of heat into electricity by placing two different electrodes — one hot and one cold — on either end of a vacuum tube. The converter itself is not much bigger than a postage stamp.
“It’s basically the simplest heat engine you can possibly imagine,” says Schwede, who has a Ph.D. in physics but insists the science behind thermionics is accessible to all, if unfamiliar. The vacuum tube acts as an insulator, and the heat coming out of the hot side releases electrons that become a source of energy when they reach the cold side. It’s akin to heating water, which lets off steam just before it comes to a boil; in thermionics, the electrons are the steam. Schwede admits that the science is somewhat counterintuitive to most people — even he sounds awed by its capabilities: “You have something the size of a quarter, you dump heat on it, and it’s as efficient as an internal combustion engine, which is an amazing but complex piece of machinery.”
It’s inexpensive; it’s the same basic technology that’s at the heart of fluorescent lighting and cathode ray tube monitors, among other things; and if it sounds like something straight out of the 1960s, that’s because it is (though, as might be expected, it owes a debt to early work in electron evaporation by Thomas Edison). Thermionics originally gained traction as a tool in the space program, with researchers of the day achieving a 15 percent power conversion efficiency, but it fell out of favor as the Space Race ended and vacuum tube technology came to be viewed as outdated. Yet a handful of physicists continued working on it; by the time Schwede was publishing his thesis, “Photon-enhanced Thermionic Emission for Concentrated Solar Energy Harvesting,” in 2014, it was enjoying something of a low-key renaissance.
“We realized that by leveraging the things that worked well and adding new materials and new microfabrication techniques, we could take this technology with its 15 percent efficiency and increase its performance to 25 percent for the first generation and 35 percent for the second — if not higher,” says Schwede, who has since co-founded Spark Thermionics. “At that level, you’re talking about something that’s competitive with virtually any engine — a diesel generator or whatever you’d like — but all in a really neat package.”
It’s a package that might one day power homes, a use in which the U.S. Department of Energy is keenly interested and Spark is working toward, at least in part, Schwede says. Because the heating and cooling needs of a house in the United States are essentially balanced with its electricity needs, a thermionic generator that is heated by the combustion of natural gas or other fuels is able to meet all of those needs simultaneously.
“The miraculous thing is this is the cleanest way that you can generate electricity from natural gas, because you’re already using all the heat that would be wasted in a power plant to heat the water in your home,” Schwede says. “So it’s a very clean way to generate electricity, but it’s very complementary to highly distributive choices like wind or solar.” It’s also a uniquely attractive option for providing power to regions of the world that don’t have an electric grid already in place, since it allows for the creation of electricity right at the location where it will be used.
Schwede’s graduate work was initially focused on a blend of the photovoltaic effect — using the sun’s heat to create power — and thermionic emission. But the challenges that would be associated with retrofitting a lot of so-called power towers in the desert, coupled with the recognition that it would be burdensome to commercialize the technology when very few power plants would be built at any one time anywhere in the world, gave Schwede and his colleagues pause, and they turned back to the vacuum tube technology. “We realized it had gotten a bad rap,” he says. “Ultimately, using conventional thermionics would allow us to access different applications — we wouldn’t be limited to power towers out in the desert, and it could be a much better route to getting what we think could be a really transformative energy technology out into the world.”
At this point, the only real downside to the technology is that the existing prototypes are 30-plus years old (to get an idea how dated the science is, visit YouTube and watch GE’s “How a Thermionic Converter Works—A Model Demonstration,” one of the more “recent” video explanations from the 1950s). But the timing of Spark’s creation was fortuitous: Even as Schwede was wrapping up his Ph.D., the Lawrence Berkeley National Laboratory was establishing Cyclotron Road, a proto-startup incubator that provides tools, financing and experts to “hard energy” tech innovators. Spark Thermionics was invited to be a part of it. So rather than having to follow the stereotypical “a few guys in a garage” formula common to Silicon Valley startups, Schwede says, Spark has been able to leverage the knowledge and expertise of scientists who are leaders in their respective fields.
“Unlike the typical trajectory for an energy startup, where you raise money and hit the ground running before you even know what it is you’re trying to build, this gives us the flexibility to really understand our technology and tech development, while being able to work with — and lean on — the best scientists on the planet,” he says. For example, by sheer coincidence, a specialized spin-polarized, low-energy electron microscope (SPEEM) at Berkeley Lab that’s sensitive to structural and electrical properties of various surfaces turned out to be the perfect tool for examining thermionic electrodes. The collaboration at Cyclotron Road is working well: Spark has already received two government awards, including $3.8 million from the Department of Energy’s Advanced Research Projects Agency–Energy (ARPA-E). Spark has closed its first round of funding, and is hoping to have a functioning prototype within the next several months.
Schwede has been acknowledged for his work in thermionics with the Ross N. Tucker Award, which recognizes excellence in semiconductor and materials research, as well as with an award from Stanford’s Global Climate and Energy Project. A native of Washington State, he came to Exeter after earning a high score on what was then called the American High School Math Exam and receiving a subsequent invitation to apply to the Academy. For someone who is clearly accomplished in math and science, Schwede maintains a genuine sense of wonder in his chosen field.
“The principle is really simple,” he says of thermionics, “but it does seem like magic.”
-- Sarah Zobel
Editor's note: This article first appeared in the winter 2017 edition of The Exeter Bulletin.
Illustration credits: Sarah Hanson
