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ILP Institute Insider

November 8, 2012

Expending Energy to Save Energy

Doing exhaustive research on new solar and other energy technologies.

Steve Calechman

In 2009, Jeff Grossman was well-established at the University of California, Berkley, directing a nanoscience center and heading a research group on energy applications. He was also enjoying the Bay area weather, restaurants and overall lifestyle, and then he decided to leave it all to become an associate professor of power engineering at MIT.

Jeffrey Grossman
Associate Professor of Power Engineering
Department of Material Science and Engineering
Winters aside, the new academic environment fits his needs. “There are no barriers. There are no boundaries. There are just hard problems that we like to solve,” Grossman says. For the materials scientist, those solutions involve various means—partnering with industry, using computational science, designing prototypes in his lab—to achieve his ends of developing a range of sustainable and efficient energy technologies, from light harvesting to water desalination to rechargable solar fuel.

Trying to capture the sun

Grossman wants to build a three-dimensional solar cell. The increased height and surface area would harness more power than a traditional flat panel for the same base area, and the power can scale linearly with height, he says. Furthermore, Grossman has shown that 3D solar cells increase efficiency, as the amount of maximum power would begin at sunrise and remain at that level until sunset, without the need for tracking. Like with much of his work, Grossman first designed a model with computers, using a program to experiment with and evolve various shapes, and then built a prototype tower in his lab to test out his findings.

During the development process, one unforeseen aspect that Grossman didn’t include in the simulations was variable weather. He had to contend with a number of rainy days in the field. At first it was frustrating, he says, but his adopted Massachusetts climate ended up becoming a benefit. With a flat panel, cloudy days negatively impact harvesting, but the data gathered showed that three dimensions can take advantage of scattered light more efficiently, resulting in less of a hit, Grossman says.

The device is still in the research and testing phase, but Grossman already has discovered certain potentials. While the working models are funnel and flower shaped, he says that a design can be tailored to a specific environment, providing accessibility and flexibility. Grossman has also installed 3D panels on a scale model block of Cambridge buildings and is studying how much power can be collectively harnessed and generated. Grossman says that his lab is continuing to do what it can with the expertise and resources that they have, although this remains at a fundamental level of exploration. He’s now looking for an industry partner that wants to do large-scale prototyping and share resources and expertise, particularly in power electronics, to complete the project and determine the best setting for the towers and at what scale they would be most effective.

Harnessing solar fuel

Grossman is also working on developing a solar-thermal fuel. The on-going challenge with this technology is finding a material that can be continuously recharged by the sun without degrading and that provides energy that can be stored, transported, distributed and used in any location, regardless of where it was charged. The concept and motivation aren’t new, he says. They’ve been experimented with and tested before, but the sticking point has been finding an economically feasible material.

To tackle the problem, Grossman applied a materials design framework, taking molecules called photoswitches, which are well known to alternate between two states when a light is shined on them. “But they make terrible energy storage systems,” he says. Grossman’s team has addressed this by combining the switches with template materials, such as nanotubes and graphene. The result is a material that charges by sunlight, can cycle millions of times without degradation, and has energy densities comparable to the best lithion-ion batteries. “That’s been a very exciting development,” he says.

Again, the fuel systems were initially designed computationally, using quantum mechanical modeling. Now Grossman has added an experimental component to this research that’s been synthesizing and characterizing these fuels, he says. It’s ultimately this type of project that drives him. In energy, he says, materials are the dominant factor. Whatever the application—thermoelectronics, solar cells, solar fuels, hydrogen storage—it’s the development of new materials that will change the landscape. “That’s why I don’t sleep at night. That’s why I’m so happy with and excited about what I do,” Grossman says.

Letting the water run and leaving the salt behind

Another materials-related, nanotechnology project Grossman is pursuing involves using graphene in the process of desalination. As he says, the material can be an outstanding filter for saltwater, since it’s the ultimate membrane, one-atom thick that if tailored correctly would allow water but not salt to flow through. Focusing on graphene would be a different approach in the field since most of the research and work concentrates on the systems level. Grossman notes that an enormous factor in improvement would come from better membranes designed at the atomic scale. His team is starting to make and test new filters, and he says that while the impact on clean water is apparent, the technology could be applied to gas separation and various forms of water treatment and filtering.

Finding the best information exchange

While Grossman employs both computational modeling and practical design in his development of new technologies, ultimately he pursues whatever gives the greatest chance for success. And he doesn’t keep things exclusively in his lab, as he looks to partner with industry whenever appropriate, an attitude that’s endemic at MIT. “I haven’t seen that in the way it happens at MIT at any other institution,” Grossman says.

As he views it, that approach just makes for a better exchange of information. He can work on an issue in his lab and understand certain obstacles, but an industry partner voices obstacles from its perspective. “I see these kinds of close partnerships as absolutely essential to the kind of research I want to do,” he says. As an example, Grossman is working with a company on the next generation of quantum dot-based solar cell technology, devices that can covert the sun’s energy into electricity. Currently, efficiency in these devices for photovoltaics stands at 5 percent, a figure that he plans to more than double in the next few years, in close collaboration with his industry partner.

To that end, Grossman formed a team at MIT that includes his material science staff, along with faculty from electrical engineering and chemistry, which works with engineers from the company. Expertise and feedback is shared from both ends in a continual loop that influences the project’s direction all the way from the atomic scale to the device and manufacturing scales. Ultimately, the result is more usable, relevant technology. “It’s what I feel will allow us to make the most impact the most quickly,” Grossman says.