The new approach uses a special manufacturing process to stamp tiny loops of conducting metal as wide as 1/25 the diameter of a human hair onto a sheet of plastic. Because of their minute size, these nanoantennae absorb energy in the infrared part of the spectrum, just outside the range of what is visible to the eye. The sun radiates a lot of infrared energy, some of which is soaked up by the earth and later released as radiation for hours after sunset, whereby the nanoantennae can take in energy from both sunlight and the earth's heat, with higher efficiency than conventional solar cells. In contrast, traditional solar cells can only use visible light, rendering them idle after dark. Infrared radiation is an especially rich energy source because it also is generated by industrial processes such as coal-fired plants. The nanoantennae provide further added value as they have the potential to act as cooling devices that draw waste heat from buildings or electronics without using electricity.
Steven Novack is Advisory Scientist at INL and led the research team including INL engineer Dale Kotter, W. Dennis Slafer of MicroContinuum, and Patrick Pinhero, responsible for this exciting new technology. In this interview, we ask Steven to explain more about his solar nanoantenna electromagnetic collectors and his views on the current climate for R&D that pushes the boundaries of renewable energy technologies.
Interview date: November, 2009
Interviewer: Toby Price
Thanks for taking the time to answer my questions, Steven. First off, could you provide a brief description of how this technology works and what advantages it offers?
To put nanoantenna technology into perspective for the future, I like to compare it to current photovoltaic or solar cells. Simply put, traditional solar cells work by using the energy from light (photons) to release an electron from its atom to generate electricity. Only certain wavelengths of light are able to do this, which limits the amount of direct current (DC) electricity that can be produced. More sophisticated solar cells have been developed around this principle to increase the effeciencies by making different layers in a cell that capture different light wavelengths. These are known as multi-junction solar cells. However, these are expensive to make and still have an overall upper bound of 50% efficiency.
Nanoantenna technology works on a very different concept. It is this concept that shows potential for better future solar collection and energy harvesting, but also introduces some technical challenges. Light has both particle and wave characteristics. For this discussion I choose to use the wave characteristics of light to explain what occurs in our nanoantennas. Simply stated, light waves cause electrons in metal antennas to naturally move back and forth (oscillate). If you design the nanoantennas, which are really arrays of resonant circuits, correctly you can convert the light energy into electron movement with great efficiency.
We recently have had an industrial partner independently develop some small nanoantenna samples that have ~95% efficiencies in the low mid-infrared region they were designed for. The electrons then flow toward the feedpoint (typically the point of least resistance in an antenna structure), of the antenna where they can be collected for electricity. Because the electrons are oscillating, they generate alternating current as opposed to direct current. It is this oscillation that also presents us with some technical challenges.
The technical challenge lies in converting the alternating current to direct current at such high oscillations without losing electrical energy. Instead of using and creating exotic materials to induce a chemical reaction like in traditional solar cells, we develop simple antenna arrays with basic materials including plastics as a substrate. So the advantages are higher efficiencies without the limitations, cheaper, and more flexible future collection devices/arrays.
Have you patented the nanoantenna manufacturing process and are you in talks with any companies to start licensing it?
The answer to both questions is yes. We have patented the nanoantenna process, which includes the manufacturing, the modeling, and the concept/structures. We have had multiple companies with a wide variety of applications contact INL with interest in licensing this technology.
When do you believe your nanoantenna sheeting with become commercially available?
The ability for this technology to be commercially available depends on 2 factors — namely, how much funding we get to pursue this work and if we can overcome some of the technological hurdles. Given enough time, I have confidence the scientific community will solve these technical challenges. There are some very competent individuals who are working these issues and I believe they have a viable path forward that can be incorporated into a rectenna (antenna and rectifier) approach. I would estimate a 5-10 year time period to see this technology commercially available in some form.
Can this technology be taken further? I recently published an article on the use of nanotechnology in building structures (the Nano Vent-Skin concept) to generate renewable energy. Do you envisage your nanoantenna sheeting being fully integrated into building design to generate energy and provide cooling in the future?
One of the most exciting aspects of this technology is its ability to collect energy from a good portion of the energy spectrum since it is really based upon the size and dimensions of the antenna structures and its ability to be incorporated into multiple environments. The applications, including infrastructure, are wide open to the imagination. Of course, with each new application, we would need to develop some type of environmental protection layer for the sheets/skins that protects again deformation of the arrays and environmental conditions while being transparent to the frequencies of light we are interested in harvesting.
Are you involved in any other interesting renewable energy projects at present?
I am not currently involved in any other renewable energy projects. I have some ideas that I have discussed with colleagues that we are very excited about. It is a little premature to mention them yet. I am hopeful Idaho National Laboratory will fund some of the basic research needed to model these concepts in order to validate these innovative research opportunities.
The Idaho National Laboratory is benefiting from Recovery Act funding to further its work. How has the scientific community in the USA reacted to the US Government’s present willingness to invest in renewable energy R&D? Ironically, is the future looking brighter for scientists in the US since the recession precisely because it has strengthened the Government’s commitment to R&D and clean energies to lift the country out of recession?
What a great question! I can't answer for the entire scientific community, however I can say that as a member of the U.S. scientific community I am both excited at the prospect of using my knowledge and capabilities to solve some very challenging human problems in the quest for renewable energy solutions, and I feel an immense pride in the opportunity to do so.
I also feel that, until recently, the U.S. has not been performing the leadership role in renewable energy R&D to our fullest ability and that it should not have taken an economic crisis to shift our priorities.
In some ways the future is slightly brighter for scientists in the U.S. since we are spending more on R&D then in the past.
Obviously, you are in a privileged position to work for a prestigious, government-backed organisation such as the Idaho National Laboratory. What advice would you give to individual engineers, researchers and scientists who may have similar great concepts but do not have sufficient financial backing to develop them? For instance, where can they turn for financial support other than to venture capitalists?
Strangely enough, a good portion of the recovery funds thus far have been allocated to educational institutions and private industry. We have only seen one call in our area of expertise that allows the Federally Funded Research and Development Centers (FFRDCs) to lead a call financed by the recovery act. However, the national laboratories can participate in some of the other calls as a partner, which we have done.
Individual scientists, engineers and researchers who have wanted to further their ideas, but are not associated with an organization, have opportunities under Small Business Initiative Research (SBIR) grants to propose ideas and concepts. Recently I was asked to comment on such an individual in my state who had won a grant to further investigate the potential of a solar roadway. For concepts that require a more diverse background, I advise that individuals team with the likes of a university or national laboratory on such a grant that contains the required skills and equipment needed for the associated research.
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