U.S. researchers have developed a cheap way to produce plastic sheets containing billions of nanoantennas that collect solar energy. As said one Idaho National Laboratory (INL) scientist, 'these antennas are good at capturing energy, but they're not very good at converting it.' In fact, the team estimates these individual nanoantennas can absorb close to 80% of the available energy from the sun. So these sheets of 'nantennas,' as the team calls them, might first be used as cooling devices that draw waste heat from buildings or electronics without using electricity. According to the research team, nanoantennas have the potential to be a more efficient alternative to solar cells and we might be only a few years away of the next generation of solar energy collectors. But read more...
Let's start with a picture. You can see above an "array of nantennas, printed in gold and imaged with a scanning electron microscope. The deposited wire is roughly a thousand atoms thick. A flexible panel of interconnected nantennas may one day replace heavy, expensive solar panels." (Credit: INL)
The research team was led by INL physicist Steven Novack. The other scientists involved in this project are INL engineer Dale Kotter, W. Dennis Slafer of MicroContinuum, Inc. (Cambridge, Mass.) and Patrick Pinhero, now at the University of Missouri.
On the photo on the left, "INL researcher Steven Novack holds a plastic sheet of nanoantenna arrays, created by embossing the antenna structure and depositing a conductive metal in the pattern. Each square contains roughly 260 million antennas. Nanotechnology R&D usually occurs on the centimeter scale, but this INL-patented manufacturing process demonstrates nano-scale features can be produced on a larger scale." (Credit:INL) In a recent paper (see below), the researchers give additional details. "Processes have been developed to form nantennas onto polyethylene (PE) in a stamp and repeat process. Prototype nantenna electromagnetic collectors (NEC) structures have been fabricated onto flexible substrates. Using this semi-automated process, we have produced a number of 4-inch square coupons that were tiled together to form sheet of NEC structures."
So what are these nantennas made of? "The nanoantennas are tiny gold squares or spirals set in a specially treated form of polyethylene, a material used in plastic bags. While others have successfully invented antennas that collect energy from lower-frequency regions of the electromagnetic spectrum, such as microwaves, infrared rays have proven more elusive. Part of the reason is that materials' properties change drastically at high-frequency wavelengths, Kotter says."
And do they work? "The researchers studied the behavior of various materials -- including gold, manganese and copper -- under infrared rays and used the resulting data to build computer models of nanoantennas. They found that with the right materials, shape and size, the simulated nanoantennas could harvest up to 92 percent of the energy at infrared wavelengths. The team then created real-life prototypes to test their computer models. First, they used conventional production methods to etch a silicon wafer with the nanoantenna pattern. The silicon-based nanoantennas matched the computer simulations, absorbing more than 80 percent of the energy over the intended wavelength range."
Of course, there are still technical hurdles to solve before these solar energy collectors can become available. "If these technical hurdles can be overcome, nanoantennas have the potential to be a cheaper, more efficient alternative to solar cells. [...] Nanoantennas, on the other hand, can be tweaked to pick up specific wavelengths depending on their shape and size. This flexibility would make it possible to create double-sided nanoantenna sheets that harvest energy from different parts of the sun's spectrum."
The research team will report their findings on August 13 at the American Society of Mechanical Engineers's Energy Sustainability 2008 Conference (ES2008) held in Jacksonville, Florida. You can access the abstract of their presentation by viewing the technical program overview. You'll have to select the session #23 about 'Solar Photovoltaic and Hybrid Systems' and click on the "ES2008-54016" link. Here is a direct link to the full article, "Solar Nantenna Electromagnetic Collectors" (PDF format, 8 pages, 956 KB). The top image in this post has been extracted from this document.
This technology has been previously presented at the Nano Science and Technology Institute Nanotech 2008 meeting, held in Boston on June 1-5, 2008. In a short article by Robert F. Service published in Science, "Solar Cells Gear Up to Go Somewhere Under the Rainbow" (Volume 320, Issue 5883, Page 1585, June 20, 2008), the author noted that "researchers reported harvesting infrared photons with arrays of antennas akin to those on televisions and in cell phones, a first step toward solar cells that convert heat to electricity." Here are two links to the abstract and to the full article (PDF format, 1 page, 222 KB, several figures). And here is an additional link to the abstract of the paper presented at this conference, "Solar Nanoantenna Energy Collectors."
If you're interested in this technology, you also should read two additional papers.
Sources: DOE/Idaho National Laboratory, August 10, 2008; and various websites
You'll find related stories by following the links below.