Photovoltaics, by definition, is the conversion of light into energy. (Don’t take our word for it: That’s what NASA says.) But researchers at MIT are reporting they’ve come up with a photovoltaic energy-conversion system that can generate electricity in the absence of sunlight, relying on heat and heat alone.

OK, truth be told, the basic concept that PV cells can work sans sun isn’t new. MIT notes that, “Half a century ago, researchers developed thermophotovoltaics (TPV), which couple a PV cell with any source of heat: A burning hydrocarbon, for example, heats up a material called the thermal emitter, which radiates heat and light onto the PV diode, generating electricity.” But even with fairly new PV materials that can absorb more infrared radiation than standard silicon PVs, the heat-to-light-to-electricity process saw too much of the heat wasted, making the technology inefficient.

photovoltaics without sunlight
image via MIT/Justin Knight

The breakthrough, MIT says, was in coming up with a thermal emitter with the very specific function of radiating “only the wavelengths that the PV diode can absorb and convert into electricity, while suppressing other wavelengths.”

photovoltaics without sunlight, MIT
image via MIT

Too pull that off, the researchers turned to nanotechnology – and tungsten. “The team used a slab of tungsten, engineering billions of tiny pits on its surface,” MIT says. “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.”

So what’s the applicability of this expansion of our conception of solar power? MIT cites Mike Waits, an electronics engineer at the Army Research Laboratory in Adelphi, Md., who suggests it could lead to miniature power supplies and lighter portable electronics, which is “critical for the soldier to lighten his load. It not only reduces his burden, but also reduces the logistics chain” to deliver those devices to the field.

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