Alternative Energies on the Horizon
Imagine the perfect electric car: energy efficient, gasoline-free, and powered by a device that is no larger than a lighter.
How are these wonder cars feasible? In short, they’re not … At least not yet.
Weinberg researchers are actively pursuing interdisciplinary solutions that may soon make these dream automobiles and other energy-saving applications a reality. In conjunction with the Initiative for Sustainability and Energy at Northwestern University (ISEN), Weinberg physical and social scientists are coming together to find ways to address our growing energy needs and improve the efficiency of our current systems. Whether their research centers on developing thermoelectricity, streamlining the conversion of solar energy, or studying carbon taxation, the faculty share the same goal—to create a more sustainable environment for future generations and include Weinberg students in this path-breaking science.
At the forefront of Weinberg’s sustainability research is the reduction of carbon fuel emissions, an area of great interest to Mercouri Kanatzidis, Charles E. and Emma H. Morrison Professor of Chemistry. “Right now if you take any vehicle with an internal combustion engine, it burns fuel to get you from point A to point B. If you see how much of that energy is actually used it is only about 25 to 30 percent, which means 70 to 75 percent is wasted,” Kanatzidis explains.
Kanatzidis’s laboratory, which currently includes 14 graduate students, focuses on development of thermoelectric materials that convert heat energy into electrical energy more efficiently.
Today, commercial developers of thermoelectric generators are working with Kanatzidis and the Department of Energy to recover some of wasted heat energy from vehicles and convert it into electrical energy. By recycling the car’s hot exhaust, thermoelectric generators could put as much as 10 percent of the heat lost back into the car in the form of electricity, taking a car from 30 miles per gallon to 33 miles per gallon, Kanatzidis says.
How thermoelectric devices work
Thermoelectric devices rely on thermoelectric materials, also known as narrow band-gap semiconductors, for successful energy conversion. Through a process of high-temperature synthesis, combinations of heavy metals such as lead, tellurium, and selenium are essentially melted together to create an electrical conducting material. The resulting material is sandwiched between two metal surfaces that make up the thermoelectric device.
A temperature difference between the hot and cool metal surfaces generates an electrical current that can be easily conducted through the thermoelectric material. In automobiles, many of these thermoelectric devices could be grouped together to create a generator that absorbs the wasted heat normally lost as exhaust.
In a major development, Kanatzidis’s research group was able to create a material that scatters thermal energy while still effectively conducting the electrical energy, a step critical to synthesizing thermoelectric materials. The discovery was based on collaboration between Kanatzidis and a team of professors of materials science and engineering—David Seidman, Vinayak Dravid, and Chris Wolverton.
“It is difficult to create materials that have good electroconductivity with low thermoconductivity, because generally good electric conductors are also good thermal conductors,” Kanatzidis says.
“Kanatzidis’s approach has been highly cited in the literature, and has impacted research efforts in many groups around the world. It is clear that the Kanatzidis group’s efforts have, and will continue to have, strong impact on the future of the thermoelectrics industry,” says Tim Hogan, associate professor of electrical and computer engineering at Michigan State University.
While automotive applications for thermoelectric generators are closest to large-scale commercialization, possibilities for development in other industries are widespread. Use of thermoelectric devices could easily be applied in any setting that involves hot processes or heat loss—for example, a glass-making plant or coal refinery. By incorporating thermoelectric generators into their processes, these plants could become more energy independent, using electricity converted from the heat that they are losing, Kanatzidis says.
He also highlighted the possibilities for thermoelectric device usage in remote areas that are off the grid. For instance, gas pipelines coming from Alaska have sensors to monitor their status. Because they do not have access to electricity, engineers could potentially burn gas to create heat, and then use thermoelectric generators to power all of the sensor electronics.
NASA is also using thermoelectric devices and radioactive plutonium as heat sources to power spacecraft that venture into deep space, because there is not enough sun to support the solar cells, Kanatzidis said.
Another area of scientific strength at Northwestern is the study of solar energy conversion—turning sunlight into electrical energy.
Emily Weiss, assistant professor of physical chemistry, works to optimize semiconductors and nanostructures for efficient solar energy conversion. More specifically, her research focuses on chemically changing the surfaces of nanostructures to make them more efficient.
“We would like to gain a mechanistic understanding of energy conversion in nanoscopic materials, such that we can chemically design these materials to perform efficiently in photovoltaic and photocatalytic cells,” Weiss says.
Helping Weiss in the lab are undergraduate students who have a unique opportunity to work on cutting-edge research that some day could have far-reaching effects on sustainability. Andrew Ho ’13, an economics major with an interest in science, first encountered the myriad issues involved in a course called Climate Change and Sustainability, which examined the topic from the perspectives of philosophy, earth science, economics, and social science. “[The course] was so interesting because it was interdisciplinary—we studied all these facets wrapped under one topic.”
In January, Ho started researching aspects of quantum dots, which are nanoparticles of semiconductor material, with guidance from a graduate student. Also working in Weiss’s lab is Alyssa Love ’13. “I study the growth of semiconductor nanocrystals or ‘clusters,’ as they have come to be called,” says Love, a chemistry major who plans to pursue a graduate degree in chemistry. “These clusters are the building blocks that make up quantum dots. By varying different conditions in which these clusters are grown, I am attempting to understand the kinetics of how clusters form. In the distant future, understanding how clusters grow could allow clusters and quantum dots to be grown on a larger, perhaps industrial scale.
“There’s potential in the future to use materials like these for energy research that could help people down the line,” Love continues.
Photovoltaic cells—the cells found in solar panels—rely on the types of materials Weiss is developing. By refining the materials for use in solar panels, researchers could potentially create better applications for solar energy. “These devices could be scaled to provide personal power for laptops, cell phones, and possibly power home functions like electricity and water heating,” Weiss remarks.
Monica Prasad, associate professor of sociology and ISEN collaborator, studies how societies create and regulate markets. In recent work she has examined national and international renewable energy policies to understand and identify countries and states with the most effective legislation.
In particular Prasad looked at the issue of carbon taxation as a means of fiscal control in Scandinavian countries. Her research shows that not all carbon taxes work equally well and that Denmark’s present carbon emission tax is the most effective.
“One of the biggest problems with carbon tax is that people see it as a source of free revenue, but you are only getting the revenue if the pollution doesn’t go away. It is not really a case of double dividends,” Prasad says.
However, the Danish government actually uses the carbon tax-generated revenue to accomplish two goals: it provides incentive in the form of both punishment and reward, and it uses the revenue to help companies lower their carbon footprint.
Prasad’s research, which she presented at various national science conferences on policy and climate change, has led to a discussion about the possibility of scaling Denmark’s model in the United States. “One of the main responses is that we are not Denmark. There was pretty clear unwillingness to learn from Denmark,” she notes.
In looking at the U.S. data, Prasad said the carbon tax turned out to be the most successful, and she is not exactly sure why. “Increasing the amount of renewable energy does not reduce carbon emissions. It is not enough to just increase the use of renewable energy,” Prasad says.
Prasad and graduate student Steven Munch recently published an article entitled “State-level renewable electricity policies and reductions in carbon emissions” in the journal Energy Policy. They focused on states’ alternative energy policies because, unlike the frequently stalled, embattled national environmental policy, some states have moved beyond partisan wrangling and forged ahead with a range of renewable energy plans. The Prasad-Munch article examined in particular the effects from 1997 to 2008 of those policies on carbon emissions in 39 states with significant wind energy potential, and found the use of carbon taxes is associated with large and significant declines in carbon emissions.
Kanatzidis’s thermoelectric research shows long-term promise, but is still in early stages in terms of becoming commercially available. “We continue our research to be on the cutting edge and we hope in a few years we will be able to see some real products out of it,” he says. “For us the challenges are: How do we go from here and how do we raise the efficiency? What kinds of materials do we have to work with to increase the performance?”
Such questions highlight the challenges that Kanatzidis, Weiss, Prasad, and other Weinberg faculty face as they work toward applying their research to solve urgent environmental problems. Yet they remain confident that their efforts, which play important roles in the work of ISEN, will yield groundbreaking results. As Love explains, “We have to get the fundamental research done before we start looking at applications. But this work is satisfying because we know in the future it will serve a greater purpose.”
Christi Sodano is a graduate student in the Medill School of Journalism, Media and Integrated Marketing Communications.Back to top