# Workshop Opens Door to Energy Research

Materials research and nanoscience have the potential to help solve the world’s energy problems. More than 80 graduate students and postdocs attended the APS energy workshop held in New Orleans on Sunday March 9, before the March Meeting, to learn about opportunities for research. Presenters described a wide variety of areas where physics research can contribute to the energy problem, including photovoltaics, hydrogen, fuel cells, thermoelectrics, and solid state lighting.

Organized by APS and funded by the Department of Energy, the workshop was aimed at students who were not studying energy topics, but who showed enthusiasm about becoming involved with energy research.

While there is no discipline called “energy,” there is a lot of interdisciplinary work that needs to be done to solve our energy problems, said George Crabtree of Argonne National Laboratory in an overview of the workshop.

Clean energy is desperately needed. Right now only one percent of urban dwellers in China breathe air that is considered safe by European Union standards, Crabtree pointed out. Oil will eventually run out; while there are various estimates about when oil will peak, scientists generally agree that it will happen by the middle of the century, said Crabtree. Demand for energy is growing rapidly. The world now uses more than 10 terawatts of energy, and twice that amount will be needed by about 2050, according to projections, said Crabtree. “The truth is that no one knows where that energy is going to come from,” said Crabtree. “There is no single solution to this energy challenge.”

Solar energy can provide part of the solution. The amount of energy reaching Earth in just 1.5 days of sunlight is about the same as the amount of energy in three trillion barrels of oil, said Sara Kurtz of the National Renewable Energy Laboratory, who talked about “today’s photovoltaics.”

In recent years, photovoltaics have become commercially viable, and the industry is growing rapidly. “More silicon is used in solar cells than in the integrated circuit industry,” Kurtz said. We’re just getting into a range where solar energy is actually cheaper than conventional electricity, she said. There is plenty of room for improvement. For instance, nanomaterials could make better antireflective coatings for solar cells, or could be used to minimize gridlines that carry electricity away from the cells but block light coming in. Many different materials can potentially be used for solar cells. “If you can make a p-n junction out of it, chances are you can make a solar cell,” she said. Efficiency gains could also come from multi-junction cells, which use more than one p-n junction to capture light with a range of wavelengths, and from concentrators that focus sunlight onto the solar cell. NASA already uses very high efficiency (about 40%) multi-junction cells to power the Mars rovers, but those solar cells are extremely expensive. “We’re trying to bring that down to Earth,” Kurtz said.

Some gains could come from the “third generation” of solar cells, according to Arthur Nozik of the National Renewable Energy Laboratory. The first generation solar cells were made from single crystal or polycrystalline silicon. The second generation includes amorphous silicon, thin film silicon, organic semiconductors, and some other materials. The third generation, said Nozik, which could be based on quantum dots or other nanostructures, will have very high efficiency and low cost, but to reach that point, “we need some major breakthroughs,” said Nozik.

Hydrogen could be another significant element of the future energy mix. Mildred Dresselhaus of MIT pointed out that hydrogen is abundant, and combustion of hydrogen yields only water. Challenges remain in producing hydrogen in sufficient quantities, storing it, and utilizing it efficiently. For the next decade or so, hydrogen will primarily be produced using fossil fuels, but in the future hydrogen could be produced from renewable sources, Dresselhaus said. “New materials and nanoscience discoveries are necessary to get from where we are to where we have to go,” she said.

In some cases, centuries old technologies can be made dramatically better using nanoscience. Debra Rolison of the Naval Research Laboratory pointed out that batteries, first developed over two hundred years ago, haven’t changed much in their basic design. “There’s no Moore’s law for battery science,” she said. Nanotechnology could bring about new developments. For instance, some materials that aren’t useful in macroscopic form for energy-storage could be useful for batteries in nanostructured forms. “An old material that you would never have used as a battery is now a battery,” she said.  She also highlighted the potential advantages of disordered materials. “Order and periodicity are overrated,” she said. Progress is already being made, she said, giving an example of some new, high-capacity lithium ion batteries for plug-in electric and hybrid vehicles that have recently been developed using nanotechnology.

Solid state lighting is also making great strides. In the United States, 22% of electricity is used for lighting, yet standard incandescent lights are only 5% efficient, and fluorescents only about 20% efficient. Light emitting diodes (LEDs), on the other hand, are small and versatile, and have the potential for 50% efficiency. Solid state lighting is already a $40 billion industry worldwide. Single color LEDs are already in widespread use in applications such as automobile taillights and traffic signals. Replacing red traffic lights with LEDs saves$1000 per year per intersection, said Jerry Simmons of Sandia National Laboratory. Developing LEDs for general purpose lighting is somewhat more challenging–cost is still an issue, as is producing a white light that people find acceptable–but scientists and engineers are making rapid progress. Simmons pointed out several areas where research could contribute to improving solid state lighting.

GM staff research scientist Jihui Yang made a presentation on new thermoelectric technologies that would utilize the heat from a car’s exhaust pipe to power electric devices in the car. GM hopes to have a working prototype using this technology in just two years, which they claim will have a three to four percent fuel economy improvement. If every GM model car had such a device, that would save three to four million gallons of gas a year. In fact, GM engineers are shooting for 10% fuel economy improvement.

Thermoelectric energy faces challenges in terms of needing increased compactness, efficient and light-weight materials, and efficiency. GM is seeking to employ recently graduated engineers and physicists to work on these problems. Thermoelectric technology may be used in various other heat-waste systems such as power plants, aircrafts, trains, heavy-duty trucks, cars and buses, and fuel cells.

A panel discussion with representatives of funding agencies, industry, and national laboratories provided the students with some advice on how to find research opportunities in energy areas. While many postdoc positions seek someone with previous experience in energy research, Phil Price of Lawrence Berkeley National Laboratory said he had made a transition from atomic physics to energy and environmental research, and that a physics background can be useful.

One student at the workshop, Christina Hagemann of the University of New Mexico, studies dark energy detection, but says she would like to get involved with energy research after she graduates. She and other attendees Mark Wilson of Penn State and John Gregoire of Cornell appreciated the opportunity to find out more about the physics of energy research. “My experience with this stuff is pretty much the Discovery Channel,” says Hagemann, “It’s great to hear from the experts what the challenges are.” The graduate students agreed that the workshop was a chance to learn more about the primary questions being asked by researchers in the field of energy efficiency, and perhaps a way to relate their own research to the field of energy efficiency.

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Editor: Alan Chodos
Contributing Editor: Jennifer Ouellette
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