MIT generates photovoltaic power without sunlight

With heat, tungsten, and a silicon cell, MIT researchers have been developing a different way to get power from photovoltaics without sunlight.

Photovoltaic cells work best with light hitting them at certain wavelengths.

Ultra-violet and infrared waves, for instance, can be tough for semiconductors to absorb in order to generate electricity. But engineers at MIT have designed a system that converts heat into specific light wavelengths, custom fit for a solar cell. And possibly, custom fit for miniature electronics as well.

Such thermo-photovoltaic systems have been around for a while, but they haven’t performed as efficiently as the silicon chip “micro-reactors” described recently in the journal Physical Review A. Etching a pattern of nanoscopic pits and ridges into a bit of tungsten, the researchers created a thermal material that can partner up with a photovoltaic cell to absorb more light radiation.

The tungsten heats up and glows, with the design on its surface controlling the way light behaves. According to the study, the sculpted pits act resonators, emitting light with wavelengths best suited for uptake by the PV cell.

Need a recharge? Just add heat. This could come from the sun but doesn’t have to. For the study, the engineering team used the hydrocarbon butane. So in the future, butane might power more things in your pocket than your cigarette lighter.

They also developed a device that could draw heat from a decaying radioisotope. With such a heat source, years could pass between recharges. The researchers have long, dark space missions in mind.
Co-author Ivan Celanovic says in MITnews:

Being able to convert heat from various sources into electricity without moving parts would bring huge benefits, especially if we could do it efficiently, relatively inexpensively and on a small scale.

The silicon chip micro-reactors are shown above without PV cells attached to their sides. According to Celanovic, the devices are three times as efficient as lithium-ion batteries of similar size and weight. Yet the research team isn’t stopping there. They hope to one day triple even that