Nano solar radiation collectors were awarded two Nano50 Awards to the research team at Idaho National Laboratory and partners Microcontinuum, Inc. and the University of Missouri. The approach uses a novel manufacturing process to stamp square spirals of conducting metal onto plastic sheets. The spirals are 1/25th the diameter of human hair.
The spectacular aspect is the range of sunlight these tiny collectors can absorb. With sunlight ranging from frequencies of 0.3 to 400 THz these collectors are more properly described as solar antennas. Al Fin’s post sets out the potential more fully than the original news story that came from the Idaho National Laboratory. The team led by Steven Novak and Patrick Pinhero estimate that collecting solar energy based on the radiation energy by antenna can absorb up to 80% of the available energy and while the working area cools after sunset the antenna will continue to work as the surrounding materials release the absorbed infrared energy.
At the earth’s surface infrared radiation is a large part of the net solar spectrum. The atmosphere clears off a substantial part of the high frequency energy making the gathering of the near visible infrared a key to high efficiencies. This property of the nano solar antennae makes the working period much broader, including more collection during overcast days, and into the night as the infrared is re radiated back.
Antennas operate by resonance, a phenomenon one can see when the frequency of a high pitched note shatters a “glass antenna.” The antennas we see, like the cell phone, television, and WiFi are larger to match the length of those frequencies. Infrared, so much smaller, needs engineering to devise antenna sizes to work cheaply and in size that can grasp the energy available in shorter lengths. Novak says “It’s not that this concept is new, but the boom in nano technology is what has really made this possible.”
The team’s innovation has been developed to lay 10 million antennas on 15 cm (6 inch) circles of plastic sheeting. The goal is to produce the antenna-laden film like a foil or plastic wrap. Impressive, indeed.
An array of nanoantennas, printed in gold and imaged with a scanning electron microscope. The deposited wire is roughly a thousand atoms thick. A flexible panel of interconnected nanoantennas may one day replace heavy, expensive solar panels.
The next step is to tune the nano antennas and perfect the properties before mass printing. The team offers that it is easy to work out the physics of one antenna yet when antennas are combined in close proximity complex interactions occur such as high-energy electromagnetic fields from certain infrared frequencies that can also affect the materials. The research is now focused on computer modeling to find the ways tuning can take out the problematic electromagnetic fields and gain further efficiency. Novak offers that small tweaks in things like antenna shape and materials can make big differences.
Another issue is that the electrical potential comes from the antenna arrays in very high frequency alternating current, some ten thousand billion times a second. Compared to the 50 or 60 alternations per second we’re familiar with in commercial grid current that seems to be quite a problem. The team is exploring ways to slow that alternating rate down using such ideas as embedding conversion devices such as capacitors directly into the nano antenna array. Another candidate is a high-speed rectifier, a form of diode that could be placed at the center of each antenna and make a conversion to direct current. Dale Kotter, an INL engineer says, “we have very promising exploratory research underway.” The news report states that patent applications are pending on a variety of energy conversion methods.
While there are these early issues to be worked out, the prospect of collecting solar energy by grasping the energy of the radiation rather than the photons offers a very different and more complete solar efficiency. It will take some time to engineer the solutions to the issues, find and solve what other matters might arise and formulate low cost manufacturing. Quoting Al Fin “People will naturally move away from fossil fuels for the same reason they moved away from gas street lights and whale oil lamps. Because a better alternative came along.”
This is one of the best examples of innovation I’ve seen in some time. The connection of nano printing and material sciences, combined with the realization that gathering the energy in the frequency of solar radiation is a revolution in solar energy. We are much closer than one might think to choosing a product that will make a huge difference.