Millions of American homes are powered by solar panels, capturing light shining from above and converting it into electricity. Solar energy is a well-established energy resource with enormous potential and countless applications, perhaps limited only by our imagination. Fortunately, the imagination is an infinitely renewable resource for the Science and Technology (S&T) Branch.
The idea of clothing that can capture sunlight and turn it into electricity may sound like science fiction, but S&T is working to make it a reality. Photovoltaic (PV) energy harvesting fabric is not only possible, but also a practical solution to a persistent challenge. First responders need lightweight power sources for their sensors and other body-worn electronics. Energy harvesting fabric mitigates the risks associated with relying solely on wall outlets to charge equipment. For example, during a natural disaster and emergency response, power grids can be compromised. The fabric also eliminates the need to carry extra batteries.
“Smart textiles are the future,” said Kimberli Jones-Holt, S&T program manager. “This energy recovery fabric project is incredibly innovative. I was so impressed with the ingenuity of the research team and look forward to the day when first responders will wear and benefit from this product.
A point in time
The First Responder Resource Group initially identified this capability as a high priority need, and S&T listened. The solution in development now is to create a photovoltaic fiber that can be woven into electrical fabric and then integrated into first responder clothing, shelters and related equipment to provide reliable power to charge batteries to power electronics. The fabric’s power output will be enough to charge AA batteries in eight hours. This effort will provide the basic framework for the development of commercially viable, textile-integrated, energy-harvesting PV devices that can be tested for direct field application.
S&T awarded $199,260 to Boston-based company Protect the Force, LLC, in August 2018 to initiate this work as part of the Silicon Valley Innovation Program. The University of Massachusetts Lowell (UML) is also a partner in this important project through its world-class Fabric Discovery Center. Together, the team of industry, academic and S&T experts created a first fabric prototype with fibers containing an incredibly thin light-gathering coating on a smooth stainless steel wire core that measures just a few hundred nanometers. . This allowed the team to successfully demonstrate proof of concept on a small scale (100cm2 tissue sample) in July 2019 and then move on to the next phase of development.
Work in progress
“It’s real-time innovation,” said Francisco Martinez, vice president of chief technology officer at Protect the Force, LLC. “It’s a new technology, so the manufacturing equipment doesn’t exist yet. We are constantly adjusting and improving to deliver a product that works and can be scaled.
A key testament to the team’s ingenuity and real-time problem solving is how they were able to adapt and reconfigure their equipment. Their curing process is a prime example. They needed an ultraviolet lamp to harden the coating of the yarn, as uncured yarn is sticky and therefore difficult to work with. (Coating is the application of protective layers for insulation.) Working at the cutting edge of technology meant there was nothing commercially available for their needs. The team was able to identify the UV-curable coating material and the correct UV lamp to ensure even and uniform curing of the yarn, and subsequent quality and reliability of the woven fabric.
A bright future
Phase II includes initial production, testing of PV energy harvesting fabric samples, and demonstration of integration on a firefighter’s garment. While the initial application is intended for wildland firefighting, S&T is exploring exciting opportunities to take the technology to other agencies within the Department of Homeland Security and beyond.
“What we learn in this process can be used for many other things,” added Dr. Ramaswamy Nagarajan, professor of engineering at UML and co-director of the Harnessing Emerging Research Opportunities to Empower Soldiers (HEROES) program. from the Center for Advanced Materials. “We need to get this right to enable future applications.”
In the spring of 2022, UML successfully conducted weaving trials. The team embedded the photovoltaic nanofibers into hundreds of feet of Nomex® yarn, a flame retardant textile used in protective clothing, using a Thread Controller 2 digital loom.
Design optimization is currently in progress. Developers are working on weaving designs for textile fibers that maximize exposure to sunlight and thus create maximum energy output from the fabric. They experiment with various patterns including twill, satin, dobby and broken twill.
Flexibility and waterproofness are other very important factors, and both depend on a suitable coating. The developers will also test resistance to various stressors to ensure compliance with National Fire Protection Association standards and work to make the fabric breathable, which has proven to be a significant scientific challenge.
The project will wrap up later this year with the completion of Phase II. “The work that has been done so far will be used to help determine further interest from the first responder community in this type of technology,” Jones-Holt explained. “The task will culminate with the development of an energy harvesting fabric woven into a first responder garment.”
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