Energy and environment center opens its doors

Andlinger Center for Energy and the Environment

Andlinger Center for Energy and the Environment PHOTO BY DENISE APPLEWHITE

WITH CONSTRUCTION ESSENTIALLY COMPLETE, researchers are moving into the new home of the Andlinger Center for Energy and the Environment, a 129,000-square-foot complex dedicated to research and teaching in areas involving energy efficiency, sustainable sources of energy, and environmental protection and remediation.

Located adjacent to the School of Engineering and Applied Science’s “EQuad,” the building is organized around multiple gardens and two large towers. The building holds a classroom and teaching laboratories, office space, a lecture hall, conference rooms, and research labs, including “cleanrooms” that have ultra-low dust levels and shared-use labs that house some of the world’s most sophisticated imaging and analytical equipment.

Emily Carter, the Gerhard R. Andlinger Professor in Energy and the Environment and founding director of the center, described it as a “living laboratory, both as it was being built and upon occupancy.”

The Andlinger Center translates fundamental knowledge into practical solutions that enable sustainable energy production and the protection of the environment and global climate from energyrelated anthropogenic change. The center was founded in July 2008 through a gift from international business leader Gerhard R. Andlinger, Class of 1952.

–By John Sullivan

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Focus on undergraduate research: Power grid solutions in Nigeria

Oladoyin Phillips

For her senior research thesis, Oladoyin Phillips, Class of 2014, explored solutions to the electricity shortage in her home country, Nigeria. (Photo by Christopher Kwadwo Ampofo Gordon)

GROWING UP IN LAGOS, NIGERIA, Oladoyin Phillips was accustomed to the power outages that struck just as she was about to use her computer or charge her cellphone. “I was frustrated on those afternoons,” she said, “but I would remind myself that I was lucky because many Nigerians have no access whatsoever to electricity.” When it came time to select an independent research project for her senior thesis, required of all Princeton undergraduates, Phillips chose to examine solutions to Nigeria’s power problems.

Although home to vast stores of oil and natural gas, Nigeria delivers just 2 percent of the electricity typically needed to serve a nation of 168 million inhabitants. Over the last few years, the Nigerian government has privatized the power industry with the goal of improving its efficiency. But Phillips noticed that while Nigeria’s plan called for new power plants, it failed to address bottlenecks in the electricity supply chain. “I saw the opportunity to look at the entire system, from generation to transmission, and to develop strategies for improving the power sector,” she said.

Using skills she acquired while majoring in operations research and financial engineering, Philips analyzed large systems by gathering data and creating computer models. She focused on the natural gas-fired power plants that produce 80 percent of the country’s electricity (the remaining 20 percent is from hydroelectric power).

Warren Powell, professor of operations research and financial engineering, was Phillips’ adviser. “She is the kind of person who, given a few years, could have a real impact,” he said.

Using daily reports compiled during 2013 by the Transmission Company of Nigeria, a publicly owned company appointed to run the power grid, Phillips built a model that simulated the flow of energy from the fuel source to electricity generation, through the national transmission grid, and to distribution points just prior to consumer delivery.

From her analysis emerged a large-scale picture of the bottlenecks at each stage of the chain. One of the surprising findings was that most plants did not operate at full capacity, either due to maintenance issues or a shortage of natural gas. Nigeria has the largest proven natural gas reserves in Africa and the ninth largest in the world, according to the U.S. Energy Information Administration, but there are not enough gas plants or pipes to bring the fuel to the plants.

Phillips also found that Nigeria’s transmission network was too limited to serve the existing power generated, let alone the planned expansion. The transmission lines were also organized as a radial system with few or no alternative routes for electricity to travel when blockages or backups occur.

Her conclusion: Fix existing bottlenecks before building new plants. “The first and most crucial goal while making investments in the power sector should not be to increase the available capacity in the country,” she concluded, “but rather to ensure firstly, that all of the capacity that is already available, is delivered to the end users.”

Phillips graduated with a Bachelor of Science in Engineering in 2014 and is working at an energy and transportation company based in India.

–By Catherine Zandonella


Green roofs’ energy savings hinge on climate

Green roofs

Green roofs, such as these above the dormitory at Princeton’s Butler College, must be designed so that they take advantage of local climate conditions. (Photo by Brian Green)

Urban planners who want green roofs in their cities need to remember that the roofs may not work the same way in different climates. Green roofs, which are covered with a layer of a vegetation to keep the building cool, perform differently according to the amount of solar radiation and precipitation present, according to Elie Bou-Zeid, an assistant professor of civil and environmental engineering.

In a study published in the journal Building and Environment, Bou-Zeid and his team found that the green roofs on the campuses of Princeton and Tsinghua University in Beijing performed similarly when the researchers controlled for the radiation and precipitation levels in the two areas, indicating the levels’ importance in green roof function. With support from the U.S. Department of Energy through Pennsylvania State University’s Energy Efficiency Building Hub and the National Science Foundation of China, the researchers used surface temperature, heat convection from the Earth’s surface to the atmosphere, and the amount of incident energy conducted through the roof as performance measures.


Elie Bou-Zeid, an assistant professor in civil and environmental engineering, stands with a wireless sensing station that measures wind speed and direction, air temperature, relative humidity, surface temperature, and incoming and reflected solar radiation from black and white roofs. (Photo by Elle Starkman)

Bou-Zeid said he hopes his work will help city planners account for the specific climatic conditions in their cities when integrating rooftop gardens into their building decisions, and assess the potential benefits of irrigation that improves green roof performance in dry periods.

Highly effective green roofs are important in cities, which suffer from the “urban heat island” phenomenon: a sustained period of excessive heat in metropolitan areas caused by buildings that absorb heat and release it into the atmosphere, a lack of vegetation, and high human activity. Increasing the number of green spaces will trap rainwater, Bou-Zeid explained, thereby providing a “heat sink” in which evaporation of that water encourages heat loss and cools things down.

The New York City Office of the Mayor is taking the heat waves of the city particularly seriously, Bou-Zeid said. New York’s asphalt and concrete roads and buildings actively absorb heat, making the area sometimes up to seven degrees warmer than its neighbors. Bou-Zeid is working with representatives from the NYC Cool Roofs program, a citywide initiative to promote the use of reflective, white rooftop coating, to examine which areas of the city will suffer most during a heat wave. He later hopes to relate physical maps of area-specific heat stress in the city to physical health indicators.

“Heat waves are the deadliest natural disasters,” Bou-Zeid said. He noted that the 2003 European heat wave, which produced the Northern Hemisphere’s hottest-ever August, caused up to 70,000 deaths in the region. “They are silent killers.”

–By Tara Thean

The Princeton Plasma Physics Laboratory: Blazing a path to fusion energy

Ask researchers at the U.S. Department of Energy’s Princeton Plasma Physics Laboratory (PPPL) to name one of the greatest science and engineering challenges ever undertaken and the answer comes easily: harnessing fusion energy.

Fusion happens naturally in the sun and other stars. The tremendous gravity from these massive stellar objects crushes together the nuclei of hydrogen atoms and releases vast amounts of energy. Bringing this process down to Earth could provide a safe, clean and virtually limitless supply of power for generating electricity.

But harnessing fusion energy is a supremely difficult task. The positively charged nuclei — or ions — inside atoms resist being squeezed together, and there is no solar gravity in laboratories to force the stubborn particles to merge.

Enter PPPL’s National Spherical Torus Experiment (NSTX-U). This device, called a “tokamak,” is in the midst of a $94 million upgrade that will make it the most powerful fusion facility of its kind in the world when the work is completed in 2014. Such facilities heat hydrogen to astronomical temperatures and trap it in magnetic fields to produce the superhot, electrically charged plasma gas that fuels fusion reactions.

Scientists then study the gas to learn how to use it to create a “burning plasma,” or sustained fusion reaction — the goal of global fusion research. “It’s as if we’re trying to create a state of matter on Earth that hasn’t existed before,” said PPPL Director Stewart Prager. “And that’s a hard thing to do.”

PPPL is a leader in this worldwide quest and a key source of public information and classroom instruction about the physics involved. The laboratory, which is managed by Princeton University and is located about three miles from campus, collaborates in major fusion experiments in Europe, Asia and the United States, and conducts educational programs for participants ranging from the general public to graduate students (see box and map).

The NSTX-U upgrade will enhance all capabilities of the machine. The temperature inside the three-story-tall tokamak could rise above 60 million degrees Celsius during experiments and reach six times the temperature at the core of the sun. The electric current that powers the machine’s huge magnets will double, as will the strength of the magnetic fields.

The sharply increased forces will quadruple the stress on all the NSTX-U components that support the magnets. This has required PPPL engineers to redesign and reinforce such structures throughout the machine. “It took a tremendous amount of analysis time to do this,” said engineer Ron Strykowsky, project manager for the upgrade.

Research on the powerful NSTX-U, whose spherical shape resembles a cored apple as compared with the donut-like shape of conventional tokamaks, will be followed by fusion researchers around the world. Experiments will show whether the streamlined, spherical design of the PPPL machine can serve as a model for the next major step in U.S. fusion research, and will produce vital data for ITER, the huge international fusion facility under construction in France.

PPPL has charted a five-year plan of action for the NSTX-U. The spherical device set records for efficient plasma confinement when it operated from 1999 to 2011 prior to the upgrade. Researchers now want to see if the enhanced machine can confine far hotter and harder-to-corral plasmas just as efficiently.

Plans also call for testing a system that will line the inner walls of the tokamak to protect them from the scorching plasma that escapes the magnetic field. Researchers will coat the walls with a thin layer of lithium, a silvery metal that turns liquid when struck by stray particles, to absorb the hot gas. “It works the way sweat moistens and protects the skin,” said Masayuki Ono, project director for the NSTX-U department at PPPL.

The escaping heat poses further challenges. The plasma could easily slice through a metal plate called a “divertor,” which serves as an exhaust system in tokamaks, unless the heat can be spread before it reaches the plate. Researchers will test an awardwinning device called a “snowflake divertor,” which PPPL helped develop and employed prior to the upgrade, to see how well it can spread the NSTX-U heat flux.

Likewise high on the PPPL agenda will be testing new ways to create and sustain the electric current that runs through tokamak plasmas. This current now is generated by a coil called a “solenoid” that will be unable to operate in the continuous fashion that future facilities will require. While the NSTX-U will still use a solenoid, researchers also will inject current through a pair of electrodes installed in the tokamak as a possible replacement for the coil.

Scientists will address all these issues in experiments called “shots” that will heat the plasma and run the NSTX-U magnets for up to five seconds — five times longer than previously possible. Preliminary plans call for some three shots an hour, eight hours a day, for 120 experiments a week.

These shots will determine if a spherically shaped tokamak could be a strong contender for the next key device in the U.S. fusion program. That envisioned device, called a Fusion Nuclear Science Facility (FNSF), would assemble and test all the components needed for a fusion power plant. This would pave the way for a demonstration fusion facility that would generate electricity on the grid and lead in turn to construction of a commercial fusion plant around the middle of the century.

The FNSF “would propel fusion forward fantastically,” said Prager. And the NSTX-U “will give us the physics information so the world can make a yes-or-no judgment about whether the spherical tokamak is a good candidate for that next step.”

Bringing plasma to the people

Plasma is everywhere, from the gas in neon light bulbs to the fuel that lights the stars. PPPL’s mission includes highlighting the properties of this fourth state of matter for the general public and inspiring and educating the next generation of scientists. “We want the public to know what we do and why we do it,” said John DeLooper, head of the best practices and outreach programs at PPPL. “And we want to excite young people to go into the world of science.”

The Princeton Plasma Physics LaboratoryThe laboratory carries out this role through wide-ranging programs. PPPL has a variety of portable scientific demonstrations and experiments that staffers bring to public events and school classrooms. The laboratory also provides a 10-week summer internship in plasma physics for college undergraduates. Seventy-two percent of the physics and engineering students who have taken the course have entered doctoral programs in physics since 2000.

For students who go on with their studies, PPPL supports graduate education chiefly through the University’s Program in Plasma Physics in the Department of Astrophysical Sciences. The program has awarded more than 265 doctorate degrees, many to people who have become leaders in the field.

-By John Greenwald

The Edge of Energy

The Edge of EnergyOur thirst for energy comes at an environmental cost. Human beings have a profound effect on the planet, and the debate is no longer about whether we need to move away from carbon-based fuels, but when and how. Princeton researchers are looking for solutions at the edge of energy research.

“The move toward a sustainable future requires truly innovative approaches with an emphasis on a range of fundamental investigations and applications,” said Emily Carter, the Gerhard R. Andlinger Professor in Energy and the Environment and founding director of the Andlinger Center for Energy and the Environment, which supports a vibrant program of research in energy development, conservation and environmental protection.

“With Princeton’s mix of engineers, scientists and social scientists, we are uniquely poised to solve these complex energy problems,” she said.

Innovations from Princeton could radically change how we produce and consume sustainable energy. For example, one group is developing a solar energy-driven charging station that could recharge your cellphone anywhere. Another group is tilting windmills on their sides to increase their efficiency, and another is attempting to mitigate the waste of combustion by turning carbon dioxide and water back into fuel.

Solar cell-ophane

If you own a smartphone, chances are you’ve resorted to poaching electricity by recharging your phone at an outlet in a public place such as an airport, lecture hall, library or museum.

A new technology developed in Princeton’s School of Engineering and Applied Science could make it possible to charge your phone just by placing it on a surface covered with a special plastic lining. The flexible plastic lining is embedded with solar cells and electronic circuits that convert sunlight into a wireless power signal strong enough to charge a phone or laptop.

With this cheap, tough and flexible plastic sheet, any surface could become a charging station. You could charge your phone on the table while out to lunch, or by placing it on your desk or on your beach blanket. Entire walls or roofs could be covered with these large-area sheets.

Solar charging station

Solar charging station: Plastic sheets embedded with solar cells and flexible electronics are under development in the laboratory of Assistant Professor Naveen Verma and colleagues in Princeton’s School of Engineering and Applied Science. The sheets could have a range of applications including solar charging stations for electronic appliances. On the left, electronic components are sandwiched between two solar cells. On the right, a closeup view shows the structures needed for wireless transmission. (Image courtesy of Naveen Verma)

“Our prototype integrates the energy-harvesting device with power electronics,”said Naveen Verma, an assistant professor of electrical engineering who developed the technology with James Sturm, the William and Edna Macaleer Professor of Engineering and Applied Science, and Sigurd Wagner, a professor of electrical engineering. The project is funded by the National Science Foundation (NSF) and the U.S. Department of Energy (DOE).

The flexible sheets of solar cells, or photovoltaic cells, are already commercially available. What is new is the incorporation of the electronic components for wireless transmission into the same technology, creating a path to a full charging system on one flexible sheet. Before now, flexible photovoltaic sheets needed to be wired to hard and inflexible integrated-circuit devices.

Creating flexible electronics was a challenge because the devices are made from amorphous silicon, which is not nearly as efficient as the rigid crystalline silicon used in conventional electronics. Because amorphous silicon is inefficient at transmitting electricity, large plastic sheets will be needed to charge even small devices.

Additionally, the engineers had to invent new circuit designs, said Verma, referring to the contributions of graduate students Liechao Huang, Yingzhe Hu, Warren Rieutort-Louis and Josue Sanz- Robinson. “We figured out how to build power inverters and amplifiers, and control circuits, all integrated with inductors and capacitors; these are all needed for wireless transmission,” Verma said.

Tilting windmills

The arms of giant wind turbines in today’s commercial wind farms rotate around a horizontal axis. But the efficiency of wind farms could be greatly improved, Princeton researchers suggest, by redesigning the wind turbines so that they rotate on a vertical axis (though the blades themselves are horizontal). In a vertical axis turbine, the blades can be supported in two locations rather than radiating from a single hub, so they can be built larger than current designs.

“The larger the area swept by the blades, the more energy you can capture from a single turbine,” said Alexander Smits, the Eugene Higgins Professor of Mechanical and Aerospace Engineering, who is working on the project with Luigi Martinelli, associate professor of mechanical and aerospace engineering.

Wind turbine

Wind turbines that rotate around a vertical axis, as shown in this experimental turbine built by Hopewell Wind Power Ltd. in Yangjiang, Guangdong Province, China, have the potential to be more efficient than conventional wind turbines, which rotate around a horizontal axis atop a fixed pole. (Image courtesy of Alexander Smits)

Support for the project has been provided by Princeton’s Seibel Energy Challenge funded by the Thomas and Stacey Siebel Foundation, and Hopewell Wind Power Ltd., a subsidiary of Hopewell Holdings Ltd., a Chinese firm headed by Princeton alumnus Sir Gordon Wu, Class of 1958.

Another advantage is that vertical blades can turn regardless of wind direction. Conventional wind turbines are fixed and point primarily in one direction — the predominant wind direction — but they cannot reorient when the wind shifts. In contrast, wind coming from any direction can push the vertical axis blades. Because of their design, vertical axis turbines can be built taller than traditional designs and be more closely packed together.

Using computer simulations and experimental models, Smits and Martinelli are studying fundamental fluid-dynamics aspects of wind-power generation and are working to optimize the design of these vertical axis turbines. Smits is testing small-scale prototypes in a wind tunnel assisted by mechanical and aerospace engineering graduate student Tristen Hohman, while Martinelli and mechanical and aerospace engineering graduate student Mark Lohry are focused on the computational modeling of wind flow. Larger-scale testing will be conducted in Guangdong Province, China, using a prototype turbine with blades 26 meters long that was built by Hopewell Wind Power Ltd.

A number of challenges remain in the development of vertical axis turbines. First, winds travel more slowly near the ground versus high in the air, thereby pushing the blade unevenly. Smits and Hohman are working to replicate these conditions in their wind tunnel. In addition, the interaction of the wind flow around the support structure may interfere with the blades by creating vibrations that in the long term will weaken the structure of the blade. Finally, the blade can stall, resulting in uneven electricity generation. This last challenge may be overcome by optimizing the shape of the blade.

Reverse gear — running combustion backward

Although renewable resources such as solar power, wind energy and fusion are our future, society will continue to rely on the burning of fossil fuels for some time. But what if we could turn the resulting carbon dioxide back into fuel?

This reverse combustion is the goal of Professor of Chemistry Andrew Bocarsly. His team is exploring ways to use sunlight to convert carbon dioxide into fuels such as methanol, which can in turn be converted into gasoline. The technology is being commercialized by New Jersey-based Liquid Light, which was co-founded by Emily Cole, who earned her Ph.D. in 2009 in Bocarsly’s lab and now is exploring ways to scale up the technology.

Andrew Bocarsly and Emily Cole

Emily Cole (right), who earned her Ph.D. in 2009 in Andrew Bocarsly’s (left) lab, is director of chemistry at Liquid Light, a company she co-founded with Bocarsly to commercialize technology to convert carbon dioxide into fuels.

In the reverse combustion reaction, light drives the reaction of carbon dioxide and water in the presence of a catalyst and a semiconductor electrode to become methanol with the release of oxygen.

The project has received funding from the Air Force Office of Scientific Research (AFSOR), NSF and DOE. The collaboration between Liquid Light and the University was supported by the DOE Small Business Innovation Research program and the AFOSR Small Business Technology Transfer program.

One way to enhance the efficiency of this reaction is by improving the catalyst, but finding materials that efficiently drive the reaction is a challenge, said Princeton’s Emily Carter. She is carrying out theoretical calculations to identify new semiconductor electrodes that could improve the efficiency of reverse combustion. These electrodes are made from affordable elements such as iron and other metals that Carter, with funding from DOE and AFOSR, has already found have the potential to assist in the conversion of carbon dioxide to methanol.

“We aim to take the energy from sunlight, carbon dioxide and water and convert all three back into fuel,” Carter said. “It is really quite a trick to make that process run backwards.”

Further reading:

Cole, Emily B., Prasad S. Lakkaraju, David M. Rampulla, Amanda J. Morris, Esta Abelev and Andrew B. Bocarsly. 2010. “Using a One-electron Shuttle for the Multi-electron Reduction of CO2 to Methanol: Kinetic, Mechanistic, and Structural Insights.” J. Am. Chem. Soc., Vol. 132, no. 33: 11539-51.

Wagner, Sigurd, James C. Sturm and Naveen Verma. 2012. “Integrated All-silicon Thin-film Power Electronics on Flexible Sheets for Ubiquitous Wireless Charging Stations based on Solar-energy Harvesting.” Symposium on VLSI Technology, Paper C23-3.