Sheet of Tiny Antennae Harvest Sunlight and Heat

August 14, 2008

When you think of harvesting solar energy, most likely you think of solar cells, which convert sunlight into electricity.

But the sun is made up of a wide spectrum of light, and solar cells typically capitalize on only the visible light. Now researchers at the U.S. Department of Energy's Idaho National Laboratory have found a way to collect mid-infrared rays, which the planet radiates as heat. This kind of energy is not only produced constantly by the Earth after it absorbs sunlight during the day, but it's also generated by factories and coal-fired plants.

The researchers developed a thin plastic sheet containing billions of tiny nanoantennas that can harvest the mid-infrared rays. In addition to potentially harvesting energy radiating from the planet, the sheets could also work to absorb waste  heat and cool down buildings or electronic devices without air-conditioners and fans.

The nanoantennas are made from gold and set in a specially treated form of polyethylene, a material used in plastic bags. One square (at right) contains roughly 260 million antennae.

Modifying the antennae in size and shape allows them to pick up other wavelengths of light. This means that the sheets could be manufactured to have two sides -- each side harvesting energy from a different part of the sun's spectrum.

The plastic sheets could also be stamped with the gold antenna, the way newspapers are stamped with ink in a large printing press. That could make it cheap to manufacture large sheets that cover the roof of a building or form the skin of consumer gadget.

Photo courtesy Steven Novack, Idaho National Laboratory