Waste heat is the scurge of computing. In fact, much of the cost of powering a computer is from creating unwanted heat. That’s because the inefficiencies in electronic circuits, caused by resistance in the materials, generates that heat. The processors, without computing anything, are essentially converting expensively produced electrical energy into waste energy.
It’s a fundamental problem, and one that hasn’t been going away. But what if you could convert the unwanted heat back into electricity—recycle the heat back into its original energy form? The data center heat, instead of simply disgorging into the atmosphere to be gotten rid of with dubious eco-effects, could actually run more machines. Plus, your cooling costs would be taken care of—there’s nothing to cool because you’ve already grabbed the hot air.
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Scientists at Rice Univeristy are trying to make that a reality by developing heat scavenging and conversion solutions.
Currently, the most efficient way to convert heat into electricity is through the use of traditional turbines.
Turbines “can give you nearly 50% conversion efficiency,” says Chloe Doiron, a graduate student at Rice University and co-lead on the project, in a news article on the school’s website. Turbines convert the kinetic energy of moving fluids, like steam or combustion gases, into mechanical energy. The moving steam then shifts blades mounted on a shaft, which turns a generator, thus creating the power.
Not a bad solution. The problem, though, is “those systems are not easy to implement,” the researchers explain. The issue is that turbines are full of moving parts, and they’re big, noisy, and messy.
Thermal emitter better than turbines for converting heat to energy
A better option would be a solid-state, thermal device that could absorb heat at the source and simply convert it, perhaps straight into attached batteries.
The researchers say a thermal emitter could absorb heat, jam it into tight, easy-to-capture bandwidth and then emit it as light. Cunningly, they would then simply turn the light into electricity, as we see all the time now in solar systems.
“Thermal photons are just photons emitted from a hot body,” says Rice University professor Junichiro Kono in the article. “If you look at something hot with an infrared camera, you see it glow. The camera is capturing these thermally excited photons.” Indeed, all heated surfaces, to some extent, send out light as thermal radiation.
The Rice team wants to use a film of aligned carbon nanotubes to do the job. The test system will be structured as an actual solar panel. That’s because solar panels, too, lose energy through heat, so are a good environment in which to work. The concept applies to other inefficient technologies, too. “Anything else that loses energy through heat [would become] far more efficient,” the researchers say.
Around 20% of industrial energy consumption is unwanted heat, Doiron says. That's a lot of wasted energy.
Other heat conversion solutions
Other heat scavenging devices are making inroads, too. Now-commercially available thermoelectric technology can convert a temperature difference into power, also with no moving parts. They function by exposing a specially made material to heat. Electrons flow when one part is cold and one is hot. And the University of Utah is working on silicon for chips that generates electricity as one of two wafers heat up.