Solar solutions: Bio-inspired approach creates bespoke photovoltaics

ITHACA, N.Y. - There is more to photovoltaic panels than the materials that comprise them: The design itself can also drive – or potentially diminish – the widespread adoption of solar technology.

Put bluntly: Most solar panels are not much to look at. And their flat, nonflexible composition means they can only be affixed to similarly flat structures. But what if photovoltaic panels were instead a hinged, lightweight fabric that was aesthetically attractive and could wrap around complex shapes, even contorting its form to better absorb sunlight?

Thus was born the idea for HelioSkin, an interdisciplinary project led by Jenny Sabin, the Arthur L. and Isabel B. Weisenberger Professor in Architecture in the College of Architecture, Art and Planning at Cornell University, in collaboration with Itai Cohen, professor of physics in the College of Arts and Sciences, and Adrienne Roeder, professor in the Section of Plant Biology in the School of Integrative Plant Science, in the College of Agriculture and Life Sciences and at the Weill Institute for Cell and Molecular Biology.

“What we’re really passionate about is how the system could not only produce energy in a passive way, but create transformational environments in urban or urban-rural settings,” Sabin said. “Sustainability is about performance and function, but equally, it’s about beauty and getting people to get excited about it, so they want to participate. The grand goal is to inspire widespread adoption of solar for societal impact.”

Sabin, the inaugural chair of the new multicollege Department of Design Tech, has made a career of collaborating with diverse disciplines and taking cues not just from architecture, but also engineering. And physics. And mathematics. And, perhaps most importantly, biology. All of her projects are united by the same question: How might buildings and their integrated material systems behave more like organisms, responding and adapting to their local environments?

“Nature is not efficient,” Sabin said. “It’s resilient, and biology is in it for the long game, over much longer time scales. Additionally, it has been demonstrated that plants that track the sun exhibit a photosynthetic advantage. And we think that’s a pretty powerful way to think about sustainability and resiliency in architecture.”

Sabin’s design interests address a very real need. The primary convergent problem is that 40% of total greenhouse gas emissions in the United States comes from buildings, according to the International Energy Agency.

“By developing a new solar skin product that can scale, we aim to turn the needle by getting homeowners and businesses to adopt solar to reduce the 28% of CO2 that comes from the heating, lighting and cooling of buildings,” Sabin said.

HelioSkin originated in a partnership between Sabin and Mariana Bertoni, an energy engineer at Arizona State University, who is also a member of the HelioSkin team. Together they combined computational design, digital fabrication and 3D printing to create customized filters and photovoltaic panel assemblies – what Sabin calls “nonstandard angularity” – that could simultaneously boost light absorption and architectural beauty. The key to that effort was looking at the mechanics of heliotropism – how sunflowers track sunlight.

For HelioSkin, that research foundation expanded to include Roeder’s expertise in heliotropism and cellular morphogenesis – i.e., how plant cells grow to bend the plant toward the sun – and Cohen’s specialization in using geometric methods such as origami and kirigami to improve the mechanical performance of metamaterials, increasing their flexibility while expending very little energy.

The flowering Arabidopsis plant is an ideal model for HelioSkin because, as “the fruit fly of the plant world” according to Roeder, it’s easy to study at the cellular level. Those cells play a vital role in changing the curvature of the plant’s stem as it angles toward the sunlight, with the Arabidopsis’ hormones causing the cells on its sunless side to expand by 25%, bending the stem 90 degrees.

“We’ve already figured out how to translate our plant cells’ tracking mechanism into Jenny’s architectural software,” Roeder said. “Now we have to start figuring out how to make that transition in HelioSkin.”

‘The human-centered design process’

The ultimate goal is to generate a mechanically tracking solar-collection skin for retractable roofs, stadiums and skyscrapers, but to get there, the team is launching a three-year pilot project whereby they create small solar canopies for backyards, which can then be scaled up for urban parks.

Bringing that vision to market not only involves scientific innovation and smart design, but requires industry partnerships, capital and a marketing plan.

The project was launched through the National Science Foundation’s Convergence Accelerator program, which last year awarded the team $650,000 in phase I funding. The team has applied for the next phase of funding – $5 million over three years.

The industry partners include E Ink and Rainier Industries, which are helping integrate photovoltaics and ePaper onto lightweight, stretchable architectural fabric. SunFlex, a company that uses laser-welded back contact module technology for photovoltaics manufacturing, is onboard to help refine the HelioSkin prototypes in phase 2 – the sensing, the wiring, the arrangement of the panels, plus the geometry and substrate.

By the pilot project’s second year, the team plans to have a full-scale backyard canopy prototype that can potentially provide light and power outdoor appliances; by the third year, they aim to be in the early stages of commercialization.

As part of their commercialization plan, the team conducted extensive marketing analysis and interviews that showed HelioSkin’s gross cost, the cost-per-watt and system capacity were competitive with existing PV products.

“This was a really encouraging and exciting process to go through, to see how we compare to existing products and the potential that we have to then scale,” Sabin said. “The human-centered design process, including engaging people in many different industries, from end users to potential stakeholders to people that work for the energy grid and the state or the region – that’s been a big part of our process, and it’s been really helpful.”

The analysis revealed niche applications that the team hadn’t initially considered, such as “big box” commercial businesses that want to pursue solar to attain net-zero emissions but are also interested in display advertising or colorful pattern change for aesthetic applications. To that end, the team is working with E Ink to create a HelioSkin with electrically powered responsive display features, so solar skins can be placed on retail structures and stadiums and function as ever-changing billboards.

“This was something that came out of interviews,” Sabin said. “We had never thought about these types of applications.”

One of the virtues of working with E Ink is the company uses roll-to-roll printing to mass produce photovoltaic sheets – the same method that makes the low-cost manufacturing of perovskite photovoltaics feasible.

“The basic idea is to try to print things in 2D, which is cheap, and then morph it into 3D, allowing it to curve around structures,” Cohen said. “You can’t just take a normal sheet of paper and wrap something. It’s going to have all sorts of creases to it. Like if you try to wrap an orange, you get all these crinkles. One of the innovations that we came up with was to cut the paper into a pattern of panels and hinges that allows it to locally stretch around these round objects. A second strategy we came up with is to use fabric as a way to make the hinge. Fabric is floppy enough to give you that hinge-like behavior.”

In her experimental architecture practice, Sabin has spent more than 15 years developing large urban-scale canopies and architectural installations, experience that has served her well in launching a product.

“There’s a strong focus on commercialization and developing IP management plans. As a designer, I have a practice, and so I find this really interesting,” Sabin said. “But it’s also completely new for most of my collaborators. They don’t necessarily think about this level of application and spinning out a product. So the learning curve around that is pretty steep for all of us.”

The ability to collaborate across disciplines is what initially drew Sabin to Cornell in 2011. It’s a place where “everybody has their door open,” she said. The excitement, and the opportunities for impact, are palpable.

“Bottom line, we are in New York’s mecca for solar,” she said. “So there’s a lot going on, both in terms of innovative research, but also applied systems, in farming and agrivoltaics, solar farms, etc. So that dynamic community of people actively working on a common set of goals and questions and problems is super exciting for us, too.”