Shell Structures for Architecture: Form Finding and Optimization

Shell Structures for Architecture

Shell Structures for Architecture

Edited by: Sigrid Adriaenssens, Philippe Block, Diederik Veenendaal and Chris Williams, with a foreword by Pritzker Prize Winner Shigeru Ban
Publisher: Routledge: Taylor and Francis, 2014

This book presents contemporary design methods for shell and gridshell structures, covering formfinding and structural optimization techniques. Edited by experts including Princeton Assistant Professor of Civil and Environmental Engineering Sigrid Adriaenssens, the book introduces architecture and engineering practitioners and students to structural shells and provides computational techniques to develop complex curved structural surfaces, in the form of mathematics, computer algorithms and design case studies.

Laser device may end pin pricks, improve health for diabetics

Diabetes sensor

Claire Gmachl, Kevin Bors and Sabbir Liakat test a laser-based glucose-sensor. (Photo by Frank Wojciechowski)

PRINCETON RESEARCHERS have developed a way to use a laser to measure people’s blood sugar, and, with more work to shrink the laser system to a portable size, the technique could allow diabetics to check their condition without pricking themselves to draw blood.

“We are working hard to turn engineering solutions into useful tools for people to use in their daily lives,” said Claire Gmachl, the Eugene Higgins Professor of Electrical Engineering and the project’s senior researcher. “With this work we hope to improve the lives of many diabetes sufferers who depend on frequent blood glucose monitoring.”

In an article published June 23, 2014, in the journal Biomedical Optics Express, the researchers describe how they measured blood sugar by shining their specialized laser — called a quantum cascade laser — at a person’s palm. The method exceeded the accuracy required for glucose monitors, said Sabbir Liakat, the paper’s lead author and a graduate student in electrical engineering. The team is now working on making the device smaller and portable.

Besides Liakat and Gmachl, researchers included Princeton undergraduate students in electrical engineering Laura Xu (Class of 2015), Callie Woods (Class of 2014) and Kevin Bors (Class of 2013); and Jessica Doyle, a teacher at Hunterdon Regional Central High School. Support for the research was provided in part by the Wendy and Eric Schmidt Foundation, the National Science Foundation, Daylight Solutions Inc., and Opto-Knowledge Systems.

–By John Sullivan

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

Inventions Bridge the Gap between lab and marketplace

Road trip

A road trip offered Mark Zondlo and his team the opportunity to test their new air quality sensors. (Photo by Lei Tao)

The college experience often involves at least one road trip, but most students do not bring along their faculty adviser. But last spring, two graduate students crammed into a rented Chevy Impala with Professor Mark Zondlo and a postdoctoral researcher to drive eight hours a day across California’s Central Valley, testing their new air-quality sensors, which were strapped to a rooftop ski rack.

The sensors are an example of technologies being developed at Princeton that have the potential to improve quality of life as commercial products or services. Although teaching and research are Princeton’s core missions, the campus is home to a vibrant entrepreneurial spirit, one that can be found among faculty members who are making discoveries that could lead to better medicines as well as students working to turn a dorm-room dream into the next big startup.

“Princeton has a number of initiatives aimed at supporting innovation and technology transfer,” said John Ritter, director of Princeton’s Office of Technology Licensing, which works with University researchers to file invention disclosures and patent applications, and with businesses and investment capitalists to find partners for commercialization. “Our goal is to accelerate the transfer and development of Princeton’s basic research so that society can benefit from these innovations,” he said.

Crossing the valley

One of the ways that Princeton supports this transfer is with programs that help bridge the gap between research and commercialization, a gap that some call the Valley of Death because many promising technologies never make it to the product stage. One such program is the Intellectual Property Accelerator Fund, which provides financial resources for building a prototype or conducting additional testing with the goal of attracting corporate interest or investor financing.

Zondlo, an assistant professor of civil and environmental engineering, is one of the researchers using the fund to cross the valley — in this case literally as well as figuratively. Earlier this year, Zondlo and his research team, which consisted of graduate students Kang Sun and David Miller and postdoctoral researcher Lei Tao, tested their air-quality sensor in California’s Central Valley, a major agricultural center that is home to some of the worst air pollution in the nation.

Their goal was to compare the new portable sensors to existing stationary sensors as well as to measurements taken by plane and satellite as part of a larger NASA-funded air-quality monitoring project, DISCOVER-AQ.

One of the new sensors measures nitrous oxide, the worst greenhouse gas after carbon dioxide and methane. Nitrous oxide escapes into the air when fertilizers are spread on farm fields. Currently, to measure this gas, workers must collect samples of air in bottles and then take them to a lab for analysis using equipment the size of refrigerators.

Zondlo’s sensor, which is bundled with two others that measure ammonia and carbon monoxide, is portable and can be held in one hand, or strapped to a car roof. “The portability allows measurements to be taken quickly and frequently, which could greatly expand the understanding of how nitrous oxide and other gases are released and how their release can be controlled,” Zondlo said.

The sensors involve firing a type of battery-powered laser, called a quantum cascade laser, through a sample of air, while a detector measures the light absorption to deduce the amount of gas in the air. The researchers replaced bulky calibration equipment, necessary to ensure accurate measurements in the field, with a finger-sized chamber of reference gas against which the sensor’s accuracy can be routinely tested.

The decision to commercialize the sensor arose from the desire to make the device available to air-quality regulators and researchers, Zondlo said. “Our sensor has precision and stability similar to the best sensors on the market today, but at a fraction of the size and power requirements,” said Zondlo, a member of the Mid-Infrared Technologies for Health and the Environment (MIRTHE) center, a multi-institution center funded by the National Science Foundation (NSF) and headquartered at Princeton. “We are already getting phone calls from people who want to buy it.”

Lighting up the brain — with help from a synthetic liver

Far from the dusty farm roads of California, Princeton faculty member John (Jay) Groves sits in his office in the glass-enclosed Frick Chemistry Laboratory, thinking about the potential uses for a new synthetic enzyme. Modeled on an enzyme isolated from the liver, the synthetic version can carry out reactions that human chemists find difficult to pull off.

One of these reactions involves attaching radioactive fluorine tags to drugs to make them visible using a brain-imaging method known as positron emission tomography (PET) scanning.

PET scans of the radiolabeled drugs could help investigators track experimental medicines in the brain, to see if they are reaching their targets, and could aid in the development of drugs to treat disorders such as Alzheimer’s disease and stroke, according to Groves, Princeton’s Hugh Stott Taylor Chair of Chemistry. The synthetic enzyme adds fluorine tags without the toxic and corrosive agents used with radioactive fluorine today.

Groves’ initial work was supported by the NSF, but to develop the technology for use in pharmaceutical research, the Groves team, which includes graduate students Wei Liu and Xiongyi Huang, is receiving funding from a Princeton program aimed at supporting concepts that are risky but have potential for broad impact. The Eric and Wendy Schmidt Transformative Technology Fund was created with a $25 million endowment from Google executive chairman Eric Schmidt, a 1976 alumnus and former trustee, and his wife, Wendy.

“The Schmidt funding is enabling us to explore ways to optimize the chemical reaction and create a prototype of an automated system,” Groves said. “This will allow us to create a rapid and noninvasive way to evaluate drug candidates and observe important metabolites within the human brain.”

Aiding the search for planets

Tyler Groff

Postdoctoral researcher Tyler Groff is creating an improved system for adjusting the blurry images seen through telescopes due to atmospheric turbulence, heat and vibrations. (Photo by Denise Applewhite)

Inspired by the search for planets outside our solar system, Princeton postdoctoral researcher Tyler Groff conceived of a technology that could enhance the quality of images from telescopes. Groff received Schmidt funding to develop a device for controlling the mirrors that telescopes use to correct blurring and distortion caused by atmospheric turbulence, heat and vibrations.

This technology, known as adaptive optics, involves measuring disturbances in the light coming into the telescope and making small deformations to the surface of a mirror in precise ways to correct the image. These deformations are made using an array of mechanical devices, known as actuators, each capable of moving a small area of the flexible reflective surface up or down. But existing actuators are limited in the amount of correction they can provide, and the spaces between the actuators create dimples in the mirror, producing a visible pattern in the resulting images that astronomers call “quilting.”

Groff envisioned replacing the array of rigidly attached actuators with flexible ones made from packets containing iron particles suspended in a liquid, or ferrofluid. Just as iron filings can be moved by waving a magnet over them, applying varying magnetic fields to the ferrofluid changes the shape of the fluid in ways that deform the mirror.

The ferrofluid mirror enables highquality images while being more resistant to vibrations and potentially more power efficient, which will be important for future satellite-based telescopes, said Groff, who works in the laboratory of Jeremy Kasdin, professor of mechanical and aerospace engineering. A ferrofluid mirror can also achieve something that a rigid actuator mirror cannot: it can assume a concave or bowl-like shape that aids the focusing of the telescope on objects in space. “A telescope that uses ferrofluid mirrors would be able to see dim objects better,” Groff said, “which would greatly enhance our ability to probe other solar systems.”

From drug discovery to space exploration, Princeton’s dedication to supporting technology transfer and potentially disruptive but high-risk research ideas is yielding tremendous benefits for the advancement of science and the improvement of people’s lives.

Box: From student project to startup

Carlee Joe-Wong (Photo by Steve Schultz)

Carlee Joe-Wong (Photo by Steve Schultz)

In 2009 when Princeton undergraduate Carlee Joe-Wong started working on the technology that would become the DataMi company, she didn’t even own a smartphone. Today, the startup company co-founded by Joe-Wong provides mobile traffic management solutions to wireless Internet providers, and also helps consumers manage their data usage through an app, DataWiz, that has been downloaded by more than 200,000 Apple and Android users.

Joe-Wong became involved in the study of mobile data usage in the spring of her junior year when Professor Mung Chiang challenged her to explore ways that wireless providers could reduce congestion by adjusting their prices based on the variations in network supply and demand. “I mostly just worked on the project in my dorm room,” Joe-Wong said. “I thought it would be cool if it was adopted but I didn’t think that I would be the one helping to make that happen.” After graduation, Joe-Wong became a graduate student working with Chiang on mathematical algorithms that predict the most effective methods for balancing network use across “peak” minutes and “valley” minutes.

“With companies charging $10 per gigabyte, mobile consumers today need to intelligently manage their data,” said Chiang, the Arthur LeGrand Doty Professor of Electrical Engineering. “What the DataWiz app does is tell you when, where and what app used how much of your quota.”

In May 2013 the team, under the engineering leadership of associate research scholar Sangtae Ha, opened an office for DataMi one block off campus. Needless to say, Joe-Wong now has a smartphone.

Taking it to the streets with help from Princeton’s eLab

ELab students

From left: Nathan Haley, Christine Odabashian, Luke Amber and Leif Amber. (Photo by Denise Applewhite)

A love of motorcycles brought them together: three Princeton undergraduates decided to explore building and marketing an electric motorcycle to provide a superior riding experience at significantly lower emissions than gasoline powered models.

The team was one of nine groups selected to participate in the 10-week eLab Summer Accelerator Program, an initiative of the Keller Center in the School of Engineering and Applied Science, which teaches entrepreneurship by offering resources, mentoring and working space.

Throughout the summer, the team members worked on ways to market the bike while simultaneously building a prototype. “We geared the product toward people who enjoy taking weekend trips,” said Nathan Haley, Class of 2014, an economics major.

Haley was joined by Luke Amber, Class of 2015, and Christine Odabashian, Class of 2014, both majors in mechanical and aerospace engineering. The team also included Luke’s older brother, Leif Amber, a graduate student in electrical engineering at Clarkson University.

-By Catherine Zandonella

Site-specific shades offer sun protection

Sun shade

Civil and environmental engineering graduate student Matthew Horner sits with Assistant Professor Sigrid Adriaenssens beneath a prototype of a pavilion designed to block harmful UV radiation by accounting for the sun’s path within its specific geographic location. (Photo by Denise Applewhite)

Children exposed to a lot of sunlight have a higher chance of developing skin cancer as adults, according to the Centers for Disease Control and Prevention. With this in mind, structural designer and assistant professor in the Department of Civil and Environmental Engineering Sigrid Adriaenssens is creating a sun shade designed to account for the sun’s path within a specific geographic location. This would allow the shade to work anywhere, protecting against the sun’s power and helping reduce skin cancer — the most common form of cancer in the United States.

Adriaenssens’ approach is to produce a dome shaped grid for the sun shade that works with surrounding climatic conditions and uses the least amount of building material possible. To do this, her team uses data from the National Oceanic and Atmospheric Administration and NASA coupled with their sun path algorithms to identify specific sunlight angles in the sun shade’s location and ensure that the grid shades for only those angles. This allows the structure to block damaging UV radiation, but lets through light that doesn’t affect the target shade area.

The inspiration for the shade’s design came in part from existing commercial sun shades, which are typically “one design fits all” and thus ineffective at actually shading their target areas. Individuals sitting under a patio set with a sun shade, for example, can find that the perimeter of the table around which they are sitting is not shaded at all, Adriaenssens explained.

Adriaenssens uses a “dialectic” strategy in her work, which is a reference to the dialectic form of discourse that looks for a solution to a problem by using various arguments, or design drivers in this case. For Adriaenssens, the drivers include engineering considerations such as structure and material as well as questions of environmental performance.

“I think sometimes you can design, in a very economic way, very elegant systems,” she said, noting that she encourages the dialectic approach among her students. Adriaenssens’ colleagues, including Assistant Professor of Civil and Environmental Engineering Mark Zondlo, Postdoctoral Research Associate Landolf Rhode- Barbarigos, and graduate students Matthew Horner and Dan Reynolds, recently erected a prototype sun shade near the Princeton University Stadium.

Other sun-related projects that adapt to different environmental conditions are on Adriaenssens’ radar. One of her models takes its cue from plants such as the waterwheel plant (Aldrovanda vesiculosa), which uses two lobes that rapidly snap shut to catch prey. The mechanics of this motion serve as the basis for shading structures that open and close based on the amount of sunlight present at a given time, ensuring lower manufacturing costs and energy consumption.

Adriaenssens hopes that the high efficiency of her creations will ensure a low-resource path to useful designs, especially in cities. With 70 percent of the world population predicted to live in urban environments by 2050, carbon emissions from existing and additional buildings — and the construction materials for creating them — required to support their needs will only increase, she explained.

“We must find more efficient ways to provide people with a good quality of life using fewer resources,” she said. “My research is all about how we can develop an engineering design framework for a future-oriented urban environment.”

–By Tara Thean

Storm of the century may become storm of the decade

Storm surge

Projected increases in sea level and storm intensity brought on by climate change could make devastating storm surges more frequent. Using the New York City area as a model, the researchers found that floods experienced every century could instead occur every one or two decades. The worst simulated flood was a 15.5-foot (4.7-meter) storm surge at Manhattan’s Battery (black star) that stemmed from a high-intensity storm (black line) moving northeast and very close to the city. The colored contours represent the maximum surge height, from 0 (blue) to 5 (violet) meters. (Image courtesy of Ning Lin)

As the Earth’s climate changes, the worst inundations from hurricanes and tropical storms could become far more common in low-lying coastal areas, a study from Princeton and the Massachusetts Institute of Technology (MIT) suggests. The study found that regions such as the New York City metropolitan area that currently experience a disastrous flood every century could instead become submerged every one or two decades.

The researchers reported in the journal Nature Climate Change in February 2012 that projected increases in sea level and storm intensity brought on by climate change would make devastating storm surges — the deadly and destructive mass of water pushed inland by large storms — more frequent. Using various global climate models, the team developed a simulation tool that can predict the severity of future flooding an area can expect.

The researchers used New York City as a test case and found that with fiercer storms and a 3-foot rise in sea level due to climate change, “100-year floods” — a depth of roughly 5.7 feet above tide level that occurs roughly once a century — could more likely occur every three to 20 years. What today are New York City’s “500-year floods” — or waters that reach more than 9 feet deep — could, with climate change, occur every 25 to 240 years, the researchers wrote.

The research is not only the first to examine the future intensity of storm surges, but also the first to offer a tool for estimating an area’s vulnerability to future flooding, said co-author Michael Oppenheimer, the Albert G. Milbank Professor of Geosciences and International Affairs at Princeton.

“As the world warms, risks will increase across a variety of fronts, and the threat to coastal infrastructure in the face of an already-rising sea level and potentially stronger hurricanes could be one of the most costly unless we are able to anticipate and reduce vulnerability,” Oppenheimer said.

Lead author Ning Lin, an assistant professor of civil and environmental engineering, said that knowing the frequency of storm surges may help urban and coastal planners design seawalls and other protective structures. Lin, who received her Ph.D. from Princeton in 2010, began the project at Princeton then continued it as a postdoctoral fellow at MIT; the current report is based on her work at MIT. The study was funded by the National Oceanic and Atmospheric Administration and the Princeton Environmental Institute.



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.