MIT's TPV reactors. Fuel is injected into one of the clear tubes on
each, the other is an exhaust. A PV cell would be attached to the
bigger sides of the reator to collect the photonic energy. (via MIT)
The concept is an old one. Thermophotovoltaic (TPV) is the direct conversion of heat to electricity via photons. A TPV consists of a thermal emitter connected to a Photovoltaic (PV) diode. Thermal emissions are the spontaneous emission of photons due to thermal motion of charges in a material. In other words, some materials emit photons when heated. Thermal radiation emits more infrared wavelengths than solar. In fact, some TPV materials invented decades ago absorb more infrared radiation than today's standard silicon PVs. However, much of the energy is still wasted in current TPV elements. MIT has just released a new TPV that exceeds all expectations.
Their method is a simple one. Research engineer Ivan Celanovic stated the ideal solution is to create a thermal emitter that only produces the wavelength that the PV diode can absorb while suppressing all other wavelengths. The team developed a photonic crystal filter that has nanoscale features on the surface, like craters, pits, or holes that allows light to propagate only at the chosen wavelengths. The researchers explained, "[We] used a slab of tungsten, engineering billions of tiny pits on its surface. When the slab heats up, it generates bright light with an altered emission spectrum because each pit acts as a resonator, capable of giving off radiation at only certain wavelengths.” The result - they created a button size generator that has 3 times the fuel to energy efficiency of a lithium ion battery of the same size.
The TPV reactor (via MIT)
Using butane as a fuel, the team ran the gas through the nanoscale pitted material where is was combusted. The heat energy then propagated through the material where the energy was channeled to the wavelength the PV diode would absorb. The Researchers tout the ability to recharge this energy source just by inserting another fuel cartridge. Celanovic said, At that point, our TPV generator could power your smartphone for a whole week without being recharged." Also, using the radioactive decay of a radioisotope could generate power for decades.
Efficient use of all energy sources is the only option in the world today. Although TPV systems do not scale effectively, MIT's solution may help push the research into a new infrastructure power source.