A rooftop antenna to funnel solar energy

MIT researchers create a carbon nanotube antenna to concentrate photons for photovoltaic cells. Could this be a future alternative to bulky solar panels?
Written by Melissa Mahony, Contributor

Instead of large photovoltaic solar panels adorning roofs, there might one day be an option for small antennas to help generate electricity from the sun's rays.

So hope scientists from MIT who have created a carbon-nanotube antenna, or "solar funnel," capable of capturing photons in large concentrations for use by a solar cell. Comprised of 30 million tiny, hollow tubes of carbon atoms, the fibrous rope of the antenna is just 10 micrometers long and 4 micrometers thick.

But a little goes a long way, apparently. Their research, published this week in the journal Nature Materials, suggests the antenna can concentrate solar energy 100 times more than a typical photovoltaic cell.

Enabling it to do so is the antenna's two layers of nanotubes, an outer and inner layer, each with varying electrical properties. When a photon strikes a material's surface, it excites an electron to a higher energy state, creating an exciton in the process. The outer nanotubes have higher band gaps. This encourages the excitons to move to a lower energy state within the antenna's inner layer. Shown in red in the image above are the regions of high energy density.

When surrounding a semi-conducting material core, the antenna would gather the light energy before converting it to electricity. Still, the scientists have yet to build such a photovoltaic device for their solar funnel. Further research will also focus on reducing energy loss as the excitons travel through the fiber. As of now the nanotubes lose around 13 percent of the energy they absorb.

The cost of carbon nanotubes will also figure in to the solar funnel's future, but Chemical Engineer Michael Strano, who is the lead author, isn't discouraged. He says in a statement:

At some point in the near future, carbon nanotubes will likely be sold for pennies per pound, as polymers are sold. With this cost, the addition to a solar cell might be negligible compared to the fabrication and raw material cost of the cell itself, just as coatings and polymer components are small parts of the cost of a photovoltaic cell.

Besides solar power, other applications being considered for the light-concentrating antennas are night-vision goggles and telescopes.

Image: Geraldine Paulus

This post was originally published on Smartplanet.com

Editorial standards