By Geoffrey Giller
Picture the future of energy.
Gleaming white turbine blades turn in a stiff wind. Solar panels cover rooftops. Battery-powered cars glide quietly down city streets. Buildings are heated and cooled with geothermal energy. Such utopic visions are, it seems, on the horizon. But this future will not arrive automatically. People must find the ideal places for wind turbines and then build them. The electric grid will need extensive modifications. And the storage capacity of modern batteries has started to plateau.
That’s where engineers come in. At Cornell Engineering, sustainable energy research is one of four strategic areas of significant research focus for the near future. “We’re not just interested in inventing gadgets,” says Jefferson Tester, a professor of sustainable energy systems, the director of the Energy Institute at Cornell and a fellow at the Atkinson Center for a Sustainable Future. Rather, engineers at the college want to help create a full, functioning system that integrates renewable energy supply from multiple sources with energy efficiency technologies so that the vision of a sustainable energy future can actually be realized.
Harness the Wind
Right now, wind power makes up about 5 percent of the total electricity generation in the United States. There are, of course, plenty of windy places in this country. But it’s not always easy to know where the best places are to put new turbines. Rebecca Barthelmie, a professor of mechanical and aerospace engineering, and her Ph.D. student Paula Doubrawa have overcome these obstacles for one of the windiest places in the country: the Great Lakes.
Measuring the wind resources over water is even more challenging than on land. Without site-specific measurements, there are three typical sources of data that can tell researchers how windy a particular spot is: satellite imagery, buoys and coastal stations. Satellites can measure year-round, but the temporal or spatial resolution may be insufficient; buoys provide real, on-the-water measurements, but they can’t stay out when the lakes freeze over; and coastal stations provide high-quality data but only from the shore, not from the spots where the turbines might eventually end up. “Each one has a different sampling period, different height of measurement, and so you can’t just easily combine all of them,” says Doubrawa. “We wanted to see how good of a result we could get if we just compiled all of the observational datasets.”
The result was a high-resolution “wind atlas” for the Great Lakes, showing the areas of highest and lowest wind speeds. Doubrawa notes that they didn’t take into consideration shipping lanes or bird migration routes; such constraints can now be overlaid on top of this existing map. And other researchers hoping to compile similar atlases for offshore areas can use the same methodology that Doubrawa and Barthelmie have developed.
Barthelmie also studies the vagaries of wind, from the minute to the global. “It’s a really hard problem,” she says. “We’re scaling from the really small scales of turbulence, the tiny structures of flow across the blades, all the way up to thinking about how does climate change impact wind resource.” And it’s not just the variety of scales that make this difficult: each component is endlessly complex. Famed physicist Richard Feynman called turbulence “the most important unsolved problem of classical physics,” and predicting climate change decades into the future—let alone how wind patterns will change along with the climate—depends on a huge number of variables.
One of Barthelmie’s most important tools in solving these problems is a set of four LiDAR instruments. Barthelmie deploys the instruments, which are packed with cutting-edge technology, to measure wind speed and direction with incredible precision and accuracy or look at turbine wakes at various cross-sections through the atmosphere. LiDAR (either a portmanteau of “light” and “radar” or an acronym for Light Detection And Ranging, depending on whom you ask) was developed specifically for wind energy research, which makes it invaluable to Barthelmie’s work. But, she notes, the instruments are “mind-bogglingly expensive.”
Once Barthelmie and her students return from the field, the work has only just begun. “We end up with gigabytes of data. Much of it may not be that useful, so we need some really finely-honed techniques” for extracting and analyzing the data, she says. The skill set required for this kind of work is expansive: expertise with getting instruments working in the field, running sophisticated statistical analyses, numerical modeling and managing data are all requisite.
Cornell Engineering has a rich and distinguished history in aeronautical, electrical and structural engineering. Barthelmie’s expertise in applying these disciplines to the technical challenges associated with wind energy has helped elevated Cornell as a leader in the field. “This type of work is really strongly rooted in engineering, but it also has a science basis,” Barthelmie says, noting the cross-disciplinary nature of the university. “That’s one of Cornell’s strengths.”
New Energy, New Grid
Widespread wind farms, a solar panel on every rooftop and an electric vehicle in every driveway may seem utopic. But Eilyan Bitar’s eyes see the underlying grid infrastructure—and the possibility for disaster. “The uncoordinated proliferation of distributed energy resources will wreak havoc at scale,” Bitar, an assistant professor of electrical and computer engineering, told the Cornell Chronicle last year. A sustainable energy future will require drastic changes in the way the grid is operated, he explains. Right now, everything is centralized. Power is generated primarily by large power plants and transmitted over long distances to buildings and homes at the edge of the grid. And the decisions of where, when and how much power to produce are determined centrally by independent system operators. But as more and more people generate electricity on their rooftops, that model is simply unsustainable.
Fortunately, Bitar is working on some solutions. One has to do with harnessing the inherent flexibility in consumers’ demand for electricity. In many cases, Bitar says, the energy required to meet a consumer’s needs is malleable—say, running a dishwasher or charging an electric vehicle—and can be deferred to a later time. For example, let’s say you show up to work in your electric car. You plug it in, with the expectation that it will be charged by the end of the workday. You’re indifferent to how your car is charged, as long as you receive enough charge by the time you leave. But as things stand now, your car would start charging immediately. “If a scheduling authority or utility was made aware of your flexibility—say your departure time,” says Bitar, “it could intelligently schedule the charging of your vehicle to attenuate peak demand or counteract fluctuations in renewables.”
Bitar and his colleagues have come up with an idea to encourage deferment: delay-differentiated pricing. If someone is willing to wait a few hours before their dishwasher runs or their car starts to charge, then they would pay less for that electricity. “The longer you’re willing to defer your consumption, the less you pay,” Bitar says. By preventing a sudden peak in electricity demand—caused by, say, droves of office workers showing up to work and plugging in their electric cars—the generation capacity required to meet the maximum demand for electricity is reduced.
Managing the consumption of all of these demand-side resources will require coordination. The traditional centralized approach to coordination, says Bitar, simply won’t work at a large scale, given the need to compute and communicate millions of control decisions every minute of every day. That’s why Bitar is also working on a new grid architecture, which he and his colleagues refer to as a “grid with an intelligent periphery,” or GrIP. “You de-emphasize the core, and you imbue the periphery of the power system with intelligence,” he says. “At a high level, you might view it as a federation of micro-grids.” Such a federation would enable the coordination of resources on the local scale, giving rise to largely self-sufficient micro-grids and diminishing the need for costly bulk generation and transmission.
A fundamental difference between fossil fuels and sustainable energy sources presents another challenge. Fossil fuels enable for "dispatchable generation resources,” or energy that is consistent and ready to produce at any moment. But renewables that depend on the sun shining or the wind blowing are instead variable, and thus less reliable in their ability to produce power. When faced with energy demand—people needing to run their refrigerators, turn on lights, or charge their electric cars—any shortfall in generating that energy means that someone, somewhere isn’t getting power. In the United States, for the most part, we think of electricity as something that’s simply there when you need it. But that belies the reality: power generation and consumption have to be balanced out on a second-to-second timescale. Generating extra power wastes fuel or costs money; generate too little power, and you get blackouts.
Besides generating flexibility through deferrable demand, Bitar envisions another tool to manage the variability of renewable energy resources: electric vehicles themselves. The batteries in electric cars require electricity, but they can also store energy that can be injected back into the grid at a later time. “Essentially, you can view a collection of electric vehicles as a dynamically evolving and reconfigurable network of energy storage devices—with the ability to both draw and supply energy to the grid,” Bitar says. He sees electric vehicles as being crucial to the widespread adoption of renewable energy resources, and vice versa. “Renewables and electric vehicles enable each other—the renewables providing clean energy to the electric vehicles, and the electric vehicles providing flexibility to balance the variability in renewables,” he says. “Neither one by itself will solve the climate change problem, but together, they might enable a future power system with little to no reliance on fossil fuels.”
Building Better Batteries
From wind turbines that generate electricity, through a smarter grid, electricity at last enters our homes. And chances are good that at this very moment, either your laptop or your smartphone is plugged in and charging. Maybe even your electric car, too. Our modern society depends heavily on batteries, and as we start driving more electric vehicles—or as they start driving us—this dependence will only increase. But it seems that no matter what, by the end of the day, we’re always scrambling to find an outlet to charge our phones just a little so that they’ll last until we get home.
This battery-induced anxiety may not go away any time soon, but Lynden Archer and his students hope at least to lessen it. Archer, the director of the Robert Frederick Smith School of Chemical and Biomolecular Engineering, has been developing new battery technologies for the past several years. He is seeking to overcome a fundamental obstacle: the most powerful types of batteries are also somewhat dangerous. Early rechargeable batteries stored more energy per volume than today’s workhorse lithium-ion technology, but they had an unfortunate tendency to fail prematurely, causing them to explode. Charging of these early batteries produced rough deposits at their lithium-metal anode, which over time would grow into tree-like, dendritic structures that eventually short-circuited the cell. Modern lithium-ion batteries remedy this issue by using graphitic carbon to prevent or inhibit rough deposition and dendrite growth—which works well, Archer says, but also reduces the amount of energy stored in the batteries’ electrode by as much as a factor of 10. Even with this compromise, rechargeable lithium-ion batteries do still sometimes succumb to short-circuits, causing them to catch fire. Because of this, the FAA is currently considering banning bulk shipments of lithium ion batteries on airplanes.
To create batteries that are both energy dense and safe, Archer has created a hybrid, web-like membrane material that’s less likely to cause short-circuiting. At the center of each battery membrane is a spherical silica nanoparticle. The particles are held together by tiny hairs: organic molecules called polyethylene oxides, or PEOs, that are covalently bonded to the particles and to each other. PEO is an excellent conductor of lithium ions, allowing them to pass through—which is how the battery produces energy—but also preventing dangerous lithium dendrites from growing.
A description of these hairy nanoparticles recently appeared in the prominent journal Nature Communications. Snehashis Choudhury, the lead author, is a Ph.D. student in Archer’s lab. He’s been working on these networked particles for the past three years, starting as a master’s student. Choudhury uses theoretical models for dendrite growth to design new materials with specific structures predicted to inhibit that growth. This approach leads to an improved understanding of how nanotechnology might be used to engineer high-energy batteries not prone to failure.
Choudhury starts the process of creating a new battery in a fume hood, where he mixes ingredients together to create new electrolytes, a battery’s lifeblood. Next, he bombards the electrolyte with X-rays to check that he’s actually made what he was trying to make. The X-ray machine sits imposingly in a darkened corner of another room, surrounded by a curtain that hangs like a hospital privacy screen to keep out light and keep in X-rays.
Moving to a sealed box filled with nonreactive argon gas and accessible only through a pair of attached rubber gloves, Choudhury encloses the new concoction inside a small battery casing. These test batteries are unassuming; they resemble the small, nickel-sized batteries you might find in a watch. Finally comes the testing, to see how the battery performs under different conditions. “We apply different amounts of current to the battery and see after how much time it fails,” says Choudhury. They can then compare that data with the performance of commercial batteries. And then he repeats the process, taking into account what he’s learned.
Choudhury says that despite the publication of an influential paper on the hairy nanoparticles, “this is by no means the end. We have to keep improving.” And Archer thinks that soon, this new type of battery may indeed show up in our phones. Archer is a co-founder and board member of the Rochester, N.Y.-based NOHMs Technologies, which is developing commercial applications of the batteries. “Our experiences with NOHMs underscores the continuous thread of discovery required to bring new technologies to the public that overcome safety and performance barriers to current state-of-the art batteries. It is amazing to be able to take a novel idea from a tool for advancing fundamental understanding, to a concept, to an important application and ultimately to a product. It is a tremendous educational experience for both the faculty member and the students involved,” says Archer.
The Future of Energy
Ultimately, energy’s future “has to be sustainable from an environmental point of view, from an economic point of view, but it also should include pushing new high-performance technology to where it hasn’t been before,” says Tester. The wide range of research at Cornell, he adds, means that cross-disciplinary projects are the norm. Such collaborations aren’t always conventional, but the university’s scientists and engineers understand that sometimes one has to break the rules to push the limits of imagination.
Besides wind, grid, and battery research, Cornell engineering faculty and student teams are working on integrating geothermal and biomass energy sources for heating buildings, generating energy from underwater turbines in New York’s East River and even using marine algae to create sustainable biofuels. So when, in the not-too-distant-future, you look around and realize that many key aspects of the promised sustainable energy future have actually arrived, Cornell Engineering will have no doubt made a major contribution.