Approximately 30 percent of the Earth’s surface is covered in snow. UCLA’s Maher El-Kady sees the pileup not as a nuisance, but as a source for power.
El-Kady, along with Prof. Richard Kaner and fellow researchers, has designed a new device that creates electricity from falling snow. The nanogenerator – flexible like a sheet of plastic – offers new possibilities for self-powered wearables and improved solar panels.
“The device can work in remote areas because it provides its own power and does not need batteries,” said senior author Richard Kaner, who holds UCLA’s Dr. Myung Ki Hong Endowed Chair in Materials Innovation. “It’s a very clever device — a weather station that can tell you how much snow is falling, the direction the snow is falling, and the direction and speed of the wind.”
The snow-based triboelectric nanogenerator, or snow TENG, generates charge through static electricity and the exchange of electrons. Snow, by its very nature, is positively charged and readily gives up electrons.
“Snow is already charged, so we thought, why not bring another material with the opposite charge and extract the charge to create electricity?” said co-author Maher El-Kady, a UCLA assistant researcher of chemistry and biochemistry.
With 3D printers, El-Kady and the team developed a layer of silicone and an electrode to capture the charge.
The snow TENG’s silicone — a synthetic rubber-like material that is composed of silicon atoms and oxygen atoms, combined with carbon, hydrogen and other elements — is negatively charged. When falling snow contacts the silicone surface, a charge is produced and stored.
The device could be produced at low cost given “the ease of fabrication and the availability of silicone,” Kaner said.
So, what’s possible with this new kind of snow tech?
When snow falls, solar panels often fail to operate. The accumulation of snow reduces the amount of sunlight that reaches the solar array, limiting the panels’ power output and rendering them less effective. The new device could be integrated into solar panels to provide a continuous power supply when it snows, said El-Kady.
Additionally, the nanogenerator could lead to new kinds of fitness and athletic wearables — a monitor, for example, for winter sports, like skiing.
El-Kady spoke with Tech Briefsabout his invention and snow's hidden power.
Tech Briefs:How did this kind of novel idea —producing energy from snow — come about?
Dr. Maher El-Kady: We made this discovery while investigating a natural phenomenon known as snow-triboelectriciation. In this process, snow is charged upon friction with another material. This process has been known for decades but was never used for producing useful electricity. One of our collaborators, Dr. Abdelsalam Ahmed from the University of Toronto, suggested harvesting this charge using triboelectric effect, which is the electron transfer as a result of two objects coming into contact with each other and separating. So, we designed the first-of-its-kind, 3D-printed device that can produce electricity from falling snow. After trying a countless number of materials, we found that silicone produces more charge with snow than any other material.
Tech Briefs:What makes snow already charged, and how does your technology take advantage of this property?
Dr. Maher El-Kady: Snow becomes positively charged when it comes in contact with other materials as a result of temperature and concentration gradient. The mechanism of this process was developed back in the early 1960s, when a group of physicists from the Imperial College of London found that the increase in temperature during friction (with another snow particle) causes an increase in the concentration of H+ and OH-. Because of the much greater mobility of H+ ions, they diffuse more rapidly into the colder part of the snow, leading to a potential difference across the snow particle with the colder end being positive.
It was later discovered in the 1970s that these thermal effects play a direct role in the snow charge transfer process. Thus, the snow layer is charged positively at temperatures of ‑5 °C and -10 °C and negatively at -15 °C and -20 °C.
In the 1990s, researchers at the US Army CRREL (Cold Regions Research and Engineering Laboratory) in New Hampshire took the first chances at extracting this potential difference by growing a layer of ice onto the outside of a steel cylinder, and then by using metal or dielectric sliders, they were able to generate an electric field having potentials up to 1.6 kV. This is amazing but is not practical!
Now, we know snow is willing to give up electrons, so we thought: Why not bring another material with the opposite charge to extract these electrons to create electricity? If you ever gave yourself a shock by touching a doorknob after rubbing your feet across a carpet; well, we create electricity using a similar mechanism.
Tech Briefs:What does the nanogenerator look like?
Dr. Maher El-Kady: The device is made of a thin layer of silicone rubber, as the active material, supported onto another layer of conductive plastic to collect the charge after contact with snow particles. So, the device looks like a sheet of plastic that is lightweight, transparent, flexible, and stretchable.
We attached the device to a bicycle for scavenging unused friction energy, such as from rolling tires on the snow.
When attached to clothing, our device can be used not only as a wearable energy harvester for charging electronic devices but also as an active, self-powered multifunctional tracking platform.
Tech Briefs:How do you envision this technology being used? What applications is it ideal for? Where would you place it?
Dr. Maher El-Kady: The results of this work could be astounding since seasonal snow covers around 33% of the earth’s land every year. So, we have a great source of energy ready to be collected! And we can do that using materials that are already produced in mass quantities.
We envision these devices integrated into solar panels to ensure continuous power supply during snowy weather conditions.
Tech Briefs:What is most exciting to you about this nanogenerator?
Dr. Maher El-Kady: The applications of our device is multifaceted. On one hand, it can be used as an energy harvester for generating electricity from falling snow. It can also be used as a weather station! In our experiments, we noticed that the shape of the electric signal of our device depends on the angle of the falling snow, and if it is snowing on a windy day, it could tell you the wind speed and direction. So, technically we made a weather station but one that is self-powered. Unlike conventional weather stations that are bulky in size and often rely on batteries for power, our device can work indefinitely without the need for an external power source. They are also flat and lightweight and are inexpensive to make.
Furthermore, our devices are stretchable and conformable and may enable a new range of wearable applications for self-powered monitoring and lifesaving systems. This includes tracking athletes (skiers, snowboarders, ice-climbers, etc.) in winter sports without the need for energy source or resource-intensive image analysis.
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