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      in Environment

      Megawatt electrical motor designed by MIT engineers could help electrify aviation

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      Aviation’s huge carbon footprint could shrink significantly with electrification. To date, however, only small all-electric planes have gotten off the ground. Their electric motors generate hundreds of kilowatts of power. To electrify larger, heavier jets, such as commercial airliners, megawatt-scale motors are required. These would be propelled by hybrid or turbo-electric propulsion systems where an electrical machine is coupled with a gas turbine aero-engine.

      To meet this need, a team of MIT engineers is now creating a 1-megawatt motor that could be a key stepping stone toward electrifying larger aircraft. The team has designed and tested the major components of the motor, and shown through detailed computations that the coupled components can work as a whole to generate one megawatt of power, at a weight and size competitive with current small aero-engines.

      For all-electric applications, the team envisions the motor could be paired with a source of electricity such as a battery or a fuel cell. The motor could then turn the electrical energy into mechanical work to power a plane’s propellers. The electrical machine could also be paired with a traditional turbofan jet engine to run as a hybrid propulsion system, providing electric propulsion during certain phases of a flight.

      “No matter what we use as an energy carrier — batteries, hydrogen, ammonia, or sustainable aviation fuel — independent of all that, megawatt-class motors will be a key enabler for greening aviation,” says Zoltan Spakovszky, the T. Wilson Professor in Aeronautics and the Director of the Gas Turbine Laboratory (GTL) at MIT, who leads the project.

      Spakovszky and members of his team, along with industry collaborators, will present their work at a special session of the American Institute of Aeronautics and Astronautics – Electric Aircraft Technologies Symposium (EATS) at the Aviation conference in June.

      The MIT team is composed of faculty, students, and research staff from GTL and the MIT Laboratory for Electromagnetic and Electronic Systems: Henry Andersen Yuankang Chen, Zachary Cordero, David Cuadrado,  Edward Greitzer, Charlotte Gump, James Kirtley, Jr., Jeffrey Lang, David Otten, David Perreault, and Mohammad Qasim,  along with Marc Amato of Innova-Logic LLC. The project is sponsored by Mitsubishi Heavy Industries (MHI).

      Heavy stuff

      To prevent the worst impacts from human-induced climate change, scientists have determined that global emissions of carbon dioxide must reach net zero by 2050. Meeting this target for aviation, Spakovszky says, will require “step-change achievements” in the design of unconventional aircraft, smart and flexible fuel systems, advanced materials, and safe and efficient electrified propulsion. Multiple aerospace companies are focused on electrified propulsion and the design of megawatt-scale electric machines that are powerful and light enough to propel passenger aircraft.

      “There is no silver bullet to make this happen, and the devil is in the details,” Spakovszky says. “This is hard engineering, in terms of co-optimizing individual components and making them compatible with each other while maximizing overall performance. To do this means we have to push the boundaries in materials, manufacturing, thermal management, structures and rotordynamics, and power electronics”

      Broadly speaking, an electric motor uses electromagnetic force to generate motion. Electric motors, such as those that power the fan in your laptop, use electrical energy — from a battery or power supply — to generate a magnetic field, typically through copper coils. In response, a magnet, set near the coils, then spins in the direction of the generated field and can then drive a fan or propeller.

      Electric machines have been around for over 150 years, with the understanding that, the bigger the appliance or vehicle, the larger the copper coils  and the magnetic rotor, making the machine heavier. The more power the electrical machine generates, the more heat it produces, which requires additional elements to keep the components cool — all of which can take up space and add significant weight to the system, making it challenging for airplane applications.

      “Heavy stuff doesn’t go on airplanes,” Spakovszky says. “So we had to come up with a compact, lightweight, and powerful architecture.”

      Good trajectory

      As designed, the MIT electric motor and power electronics are each about the size of a checked suitcase weighing less than an adult passenger.

      The motor’s main components are: a high-speed rotor, lined with an array of magnets with varying orientation of polarity; a compact low-loss stator that fits inside the rotor and contains an intricate array of copper windings; an advanced heat exchanger that keeps the components cool while transmitting the torque of the machine; and a distributed power electronics system, made from 30 custom-built circuit boards, that precisely change the currents running through each of the stator’s copper windings, at high frequency.

      “I believe this is the first truly co-optimized integrated design,” Spakovszky says. “Which means we did a very extensive design space exploration where all considerations from thermal management, to rotor dynamics, to power electronics and electrical machine architecture were assessed in an integrated way to find out what is the best possible combination to get the required specific power at one megawatt.”

      As a whole system, the motor is designed such that the distributed circuit boards are close coupled with the electrical machine to minimize transmission loss and to allow effective air cooling through the integrated heat exchanger.

      “This is a high-speed machine, and to keep it rotating while creating torque, the magnetic fields have to be traveling very quickly, which we can do through our circuit boards switching at high frequency,” Spakovszky says.

      To mitigate risk, the team has built and tested each of the major components individually, and shown that they can operate as designed and at conditions exceeding normal operational demands. The researchers plan to assemble the first fully working electric motor, and start testing it in the fall.

      “The electrification of aircraft has been on a steady rise,” says Phillip Ansell, director of the Center for Sustainable Aviation at the University of Illinois Urbana-Champaign, who was not involved in the project. “This group’s design uses a wonderful combination of conventional and cutting-edge methods for electric machine development, allowing it to offer both robustness and efficiency to meet the practical needs of aircraft of the future.”

      Once the MIT team can demonstrate the electric motor as a whole, they say the design could power regional aircraft and could also be a companion to conventional jet engines, to enable hybrid-electric propulsion systems. The team also envision that multiple one-megawatt motors could power multiple fans distributed along the wing on future aircraft configurations. Looking ahead, the foundations of the one-megawatt electrical machine design could potentially be scaled up to multi-megawatt motors, to power larger passenger planes.

      “I think we’re on a good trajectory,” says Spakovszky, whose group and research have focused on more than just gas turbines. “We are not electrical engineers by training, but addressing the 2050 climate grand challenge is of utmost importance; working with electrical engineering faculty, staff and students for this goal can draw on MIT’s breadth of technologies so the whole is greater than the sum of the parts. So we are reinventing ourselves in new areas. And MIT gives you the opportunity to do that.” More

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      in Energy

      Six ways MIT is taking action on climate

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      From reuse and recycling to new carbon markets, events during Earth Month at MIT spanned an astonishing range of ideas and approaches to tackling the climate crisis. The MIT Climate Nucleus offered funding to departments and student organizations to develop programming that would showcase the countless initiatives underway to make a better world.

      Here are six — just six of many — ways the MIT community is making a difference on climate right now.

      1. Exchanging knowledge with policymakers to meet local, regional, and global challenges

      Creating solutions begins with understanding the problem.

      Speaking during the annual Earth Day Colloquium of the MIT Energy Initiative (MITEI) about the practical challenges of implementing wind-power projects, for instance, Massachusetts State Senator Michael J. Barrett offered a sobering assessment.

      The senate chair of the Joint Committee on Telecommunications, Utilities, and Energy, Barrett reported that while the coast of Massachusetts provides a conducive site for offshore wind, economic forces have knocked a major offshore wind installation project off track. The combination of the pandemic and global geopolitical instability has led to such great supply chain disruptions and rising commodity costs that a project considered necessary for the state to meet its near-term climate goals now faces delays, he said.

      Like others at MIT, MITEI researchers keep their work grounded in the real-world constraints and possibilities for decarbonization, engaging with policymakers and industry to understand the on-the-ground challenges to technological and policy-based solutions and highlight the opportunities for greatest impact.

      2. Developing new ways to prevent, mitigate, and adapt to the effects of climate change

      An estimated 20 percent of MIT faculty work on some aspect of the climate crisis, an enormous research effort distributed throughout the departments, labs, centers, and institutes.

      About a dozen such projects were on display at a poster session coordinated by the Abdul Latif Jameel Water and Food Systems Lab (J-WAFS), Environmental Solutions Initiative (ESI), and MITEI.

      Students and postdocs presented innovations including:

      Graduate student Alexa Reese Canaan describes her research on household energy consumption to Massachusetts State Senator Michael J. Barrett, chair of the Joint Committee on Telecommunications, Utilities, and Energy.

      Photo: Caitlin Cunningham

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      3. Preparing students to meet the challenges of a climate-changed world

      Faculty and staff from more than 30 institutions of higher education convened at the MIT Symposium on Advancing Climate Education to exchange best practices and innovations in teaching and learning. Speakers and participants considered paths to structural change in higher education, the imperative to place equity and justice at the center of new educational approaches, and what it means to “educate the whole student” so that graduates are prepared to live and thrive in a world marked by global environmental and economic disruption.

      Later in April, MIT faculty voted to approve the creation of a new joint degree program in climate system science and engineering.

      4. Offering climate curricula to K-12 teachers

      At a daylong conference on climate education for K-12 schools, the attendees were not just science teachers. Close to 50 teachers of arts, literature, history, math, mental health, English language, world languages, and even carpentry were all hungry for materials and approaches to integrate into their curricula. They were joined by another 50 high school students, ready to test out the workshops and content developed by MIT Climate Action Through Education (CATE), which are already being piloted in at least a dozen schools.

      The CATE initiative is led by Christopher Knittel, the George P. Shultz Professor of Energy Economics at the MIT Sloan School of Management, deputy director for policy at MITEI, and faculty director of the MIT Center for Energy and Environmental Policy Research. The K-12 Climate Action and Education Conference was hosted as a collaboration with the Massachusetts Teachers Association Climate Action Network and Earth Day Boston.

      “We will be honest about the threats posed by climate change, but also give students a sense of agency that they can do something about this,” Knittel told MITEI Energy Futures earlier this spring. “And for the many teachers — especially non-science teachers — starved for knowledge and background material, CATE offers resources to give them confidence to implement our curriculum.”

      High school students and K-12 teachers participated in a workshop on “Exploring a Green City,” part of the Climate Action and Education Conference on April 1.

      Photo: Tony Rinaldo

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      5. Guiding our communities in making sense of the coming changes

      The arts and humanities, vital in their own right, are also central to the sharing of scientific knowledge and its integration into culture, behavior, and decision-making. A message well-delivered can reach new audiences and prompt reflection and reckoning on ethics and values, identity, and optimism.

      The Climate Machine, part of ESI’s Arts and Climate program, produced an evening art installation on campus featuring dynamic, large-scale projections onto the façade of MIT’s new music building and a musical performance by electronic duo Warung. Passers-by were invited to take a Climate Identity Quiz, with the responses reflected in the visuals. Another exhibit displayed the results of a workshop in which attendees had used an artificial intelligence art tool to imagine the future of their hometowns, while another highlighted native Massachusetts wildlife.

      The Climate Machine is an MIT research project undertaken in collaboration with record label Anjunabeats. The collaborative team imagines interactive experiences centered on sustainability that could be deployed at musical events and festivals to inspire climate action.

      Dillon Ames (left) and Aaron Hopkins, known as the duo Warung, perform a live set during the Climate Machine art installation.

      Photo: Caitlin Cunningham

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      6. Empowering students to seize this unique policy moment

      ESI’s TILclimate Podcast, which breaks down important climate topics for general listeners, held a live taping at the MIT Museum and offered an explainer on three recent, major pieces of federal legislation: the Inflation Reduction Act of 2022, the Bipartisan Infrastructure Bill of 2021, and the CHIPS and Science Act of 2022.

      The combination of funding and financial incentives for energy- and climate-related projects, along with reinvestment in industrial infrastructure, create “a real moment and an opportunity,” said special guest Elisabeth Reynolds, speaking with host Laur Hesse Fisher. Reynolds was a member of the National Economic Council from 2021 to 2022, serving as special assistant to the president for manufacturing and economic development; after leaving the White House, Reynolds returned to MIT, where she is a lecturer in MIT’s Department of Urban Studies and Planning.

      For students, the opportunities to engage have never been better, Reynolds urged: “There is so much need. … Find a way to contribute, and find a way to help us make this transformation.”

      “What we’re embarking on now, you just can’t overstate the significance of it,” she said.

      For more information on how MIT is advancing climate action across education; research and innovation; policy; economic, social, and environmental justice; public and global engagement; sustainable campus operations; and more, visit Fast Forward: MIT’s Climate Action Plan for the Decade. The actions described in the plan aim to accelerate the global transition to net-zero carbon emissions, and to “educate and empower the next generation.” More

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      Mike Barrett: Climate goals may take longer, but we’ll get there

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      The Covid-19 pandemic, inflation, and the war in Ukraine have combined to cause unavoidable delays in implementation of Massachusetts’s ambitious goals to tackle climate change, state Senator Mike Barrett said during his April 19 presentation at the MIT Energy Initiative (MITEI) Earth Day Colloquium. But, he added, he remains optimistic that the goals will be reached, with a lag of perhaps two years.

      Barrett, who is senate chair of the state’s Joint Committee on Telecommunications, Utilities, and Energy, spoke on the topic of “Decarbonizing Massachusetts” at MIT’s Wong Auditorium as part of the Institute’s celebration of Earth Week. The event was accompanied by a poster session highlighting some the work of MIT students and faculty aimed at tackling aspects of the climate issue.

      Martha Broad, MITEI’s executive director, introduced Barrett by pointing out that he was largely responsible for the passage of two major climate-related bills by the Massachusetts legislature: the Roadmap Act in 2021 and the Drive Act in 2022, which together helped to place the state as one of the nation’s leaders in the implementation of measures to ratchet down greenhouse gas emissions.

      The two key pieces of legislation, Barrett said, were complicated bills that included many components, but a major feature of the Roadmap Act was to reduce the time between reassessments of the state’s climate plans from 10 years to five, and to divide the targets for emissions reductions into six separate categories instead of just a single overall number.

      The six sectors the bill delineated are transportation; commercial, industrial, and institutional buildings; residential buildings; industrial processes; natural gas infrastructure; and electricity generation. Each of these faces different challenges, and needs to be evaluated separately, he said.

      The second bill, the Drive Act, set specific targets for implementation of carbon-free electricity generation. “We prioritize offshore wind,” he pointed out, because that’s one resource where Massachusetts has a real edge over other states and regions. Because of especially shallow offshore waters and strong, steady offshore winds that tend to be strongest during the peak demand hours of late afternoon and evening, the state’s coastal waters are an especially promising site for offshore wind farms, he said.

      Whereas the majority of offshore wind installations around the world are in deep water, which precludes fixed foundations and adds significantly to construction costs, Massachusetts’s shallow waters can allow relatively inexpensive construction. “So you can see why offshore wind became a linchpin, not only to our cleaning up the grid, but to feeding it into the building system, and for that matter into transportation, through our electric vehicles,” he said.

      Massachusetts’s needs in addressing climate change are quite different from global averages, or even U.S. averages, he pointed out. Worldwide, agriculture accounts for some 22 percent of greenhouse gas emissions, and 11 percent nationally. In Massachusetts the figure is less than one-half of 1 percent. The industrial sector is also much smaller than the national average. Meanwhile, buildings account for only about 6 percent of U.S. emissions, but 13 percent in the state. That means that overall, “buildings, transportation, and power generation become the whole ballgame” for this state, “requiring a real focus in terms of our thinking,” he said.

      Because of that, in those climate bills “we really insisted on reducing emissions in the energy generation sector, and our primary way to get there … lies with wind, and most of that is offshore.” The law calls for emissions from power generation to be cut by 53 percent by 2025, and 70 percent by 2030. Meeting that goal depends heavily on offshore wind. “Clean power is critical because the transmission and transportation and buildings depend on clean power, and offshore wind is critical to that clean power strategy,” he said.

      At the time the bills passed, plans for new offshore wind farm installations showed that the state was well on target to meet these goals, Barrett said. “There was plenty of reason for Massachusetts to feel very optimistic about offshore wind … Everyone was bullish.” While Massachusetts is a small state — 44th out of 50 — because of its unusually favorable offshore conditions, “we are second in the United States in terms of plans to deploy offshore wind,” after New York, he said.

      But then the real world got in the way.

      As Europe and the U.K. quickly tried to pivot away from natural gas and oil in the wake of Russia’s invasion of Ukraine, the picture changed quickly. “Offshore wind suddenly had a lot of competition for the expertise, the equipment, and the materials,” he said.

      As just one example, he said, the ships needed for installation became unavailable. “Suddenly worldwide, there weren’t enough installation vessels to hold these very heavy components that have to be brought out to sea,” he said. About 20 to 40 such vessels are needed to install a single wind farm. “There are a limited number of these vessels capable of carrying these huge pieces of infrastructure in the world. And in the wake of stepped-up demand from Europe, and other places, including China, there was an enormous shortage of appropriate vessels.”

      That wasn’t the only obstacle. Prices of some key commodities also shot up, partly due to supply chain issues associated with the pandemic, and the resulting worldwide inflation. “The ramifications of these kinds of disruptions obviously have been felt worldwide,“ he said. For example, the Hornsea Project off the coast of the United Kingdom is the largest proposed offshore wind farm in the world, and one the U.K. was strongly dependent on to meet climate targets. But the developer of the project, Ørsted, said it could no longer proceed without a major government bailout. At this point, the project remains in limbo.

      In Massachusetts, the company Avangrid had a contract to build 60 offshore wind turbines to deliver 1,200 megawatts of power. But last month, in a highly unusual move for a major company, “they informed Massachusetts that they were terminating a contract they had signed.” That contract was a big part of the state’s overall clean energy strategy, he said. A second developer, that had also signed a contract for a 1,200-MW offshore farm, signaled that it too could not meet its contract.

      “We technically haven’t failed yet” in meeting the goals that were set for emissions reduction, Barrett said. “In theory, we have two years to recover from the setbacks that I’m describing.” Realistically, though, he said “it is quite likely that we’re not going to hit our 2025 and 2030 benchmarks.”

      But despite all this, Barrett ended his remarks on an essentially optimistic note. “I hate to see us fall off-pace in any way,” he said. But, he added, “the truth is that a short delay — and I think we’re looking at just a couple of years delay — is a speed bump, it’s not a roadblock. It is not the end of climate policy.”

      Worldwide demand for offshore wind power remains “extraordinary,” said Barrett, mainly as a result of the need to get off of Russian fossil fuel. As a result, “eventually supply will come into balance with this demand … The balance will be restored.”

      To monitor the process, Barrett said he has submitted legislation to create a new independent Climate Policy Commission, to examine in detail the data on performance in meeting the state’s climate goals and to make recommendations. The measure would provide open access to information for the public, allowing everyone to see the progress being made from an unbiased source.

      “Setbacks are going to happen,” he said. “This is a tough, tough job. While the real world is going to surprise us, persistence is critical.”

      He concluded that “I think we’re going to wind up building every windmill that we need for our emissions reduction policy. Just not on the timeline that we had hoped for.”

      The poster session was co-hosted by the MIT Abdul Latif Jameel Water and Food Systems Lab and MIT Environmental Solutions Initiative. The full event was sponsored by the MIT Climate Nucleus. More

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      in Energy

      The answer may be blowing in the wind

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      Capturing energy from the winds gusting off the coasts of the United States could more than double the nation’s electricity generation. It’s no wonder the Biden administration views this immense, clean-energy resource as central to its ambitious climate goals of 100 percent carbon-emissions-free electricity by 2035 and a net-zero emissions economy by 2050. The White House is aiming for 30 gigawatts of offshore wind by 2030 — enough to power 10 million homes.

      At the MIT Energy Initiative’s Spring Symposium, academic experts, energy analysts, wind developers, government officials, and utility representatives explored the immense opportunities and formidable challenges of tapping this titanic resource, both in the United States and elsewhere in the world.

      “There’s a lot of work to do to figure out how to use this resource economically — and sooner rather than later,” said Robert C. Armstrong, MITEI director and the Chevron Professor of Chemical Engineering, in his introduction to the event. 

      In sessions devoted to technology, deployment and integration, policy, and regulation, participants framed the issues critical to the development of offshore wind, described threats to its rapid rollout, and offered potential paths for breaking through gridlock.

      R&D advances

      Moderating a panel on MIT research that is moving the industry forward, Robert Stoner, MITEI’s deputy director for science and technology, provided context for the audience about the industry.

      “We have a high degree of geographic coincidence between where that wind capacity is and where most of us are, and it’s complementary to solar,” he said. Turbines sited in deeper, offshore waters gain the advantage of higher-velocity winds. “You can make these machines huge, creating substantial economies of scale,” said Stoner. An onshore turbine generates approximately 3 megawatts; offshore structures can each produce 15 to 17 megawatts, with blades the length of a football field and heights greater than the Washington Monument.

      To harness the power of wind farms spread over hundreds of nautical miles in deep water, Stoner said, researchers must first address some serious issues, including building and maintaining these massive rigs in harsh environments, laying out wind farms to optimize generation, and creating reliable and socially acceptable connections to the onshore grid. MIT scientists described how they are tackling a number of these problems.

      “When you design a floating structure, you have to prepare for the worst possible conditions,” said Paul Sclavounos, a professor of mechanical engineering and naval architecture who is developing turbines that can withstand severe storms that batter turbine blades and towers with thousands of tons of wind force. Sclavounos described systems used in the oil industry for tethering giant, buoyant rigs to the ocean floor that could be adapted for wind platforms. Relatively inexpensive components such as polyester mooring lines and composite materials “can mitigate the impact of high waves and big, big wind loads.”

      To extract the maximum power from individual turbines, developers must take into account the aerodynamics among turbines in a single wind farm and between adjacent wind farms, according to Michael Howland, the Esther and Harold E. Edgerton Assistant Professor of Civil and Environmental Engineering. Howland’s work modeling turbulence in the atmosphere and wind speeds has demonstrated that angling turbines by just a small amount relative to each other can increase power production significantly for offshore installations, dramatically improving their efficiencies. Howland hopes his research will promote “changing the design of wind farms from the beginning of the process.”

      There’s a staggering complexity to integrating electricity from offshore wind into regional grids such as the one operated by ISO New England, whether converting voltages or monitoring utility load. Steven B. Leeb, a professor of electrical engineering and computer science and of mechanical engineering, is developing sensors that can indicate electronic failures in a micro grid connected to a wind farm. And Marija Ilić, a joint adjunct professor in the Department of Electrical Engineering and Computer Science and a senior research scientist at the Laboratory for Information and Decision Systems, is developing software that would enable real-time scheduling of controllable equipment to compensate for the variable power generated by wind and other variable renewable resources. She is also working on adaptive distributed automation of this equipment to ensure a stable electric power grid.

      “How do we get from here to there?”

      Symposium speakers provided snapshots of the emerging offshore industry, sharing their sense of urgency as well as some frustrations.

      Climate poses “an existential crisis” that calls for “a massive war-footing undertaking,” said Melissa Hoffer, who occupies the newly created cabinet position of climate chief for the Commonwealth of Massachusetts. She views wind power “as the backbone of electric sector decarbonization.” With the Vineyard Wind project, the state will be one of the first in the nation to add offshore wind to the grid. “We are actually going to see the first 400 megawatts … likely interconnected and coming online by the end of this year, which is a fantastic milestone for us,” said Hoffer.

      The journey to completing Vineyard Wind involved a plethora of painstaking environmental reviews, lawsuits over lease siting, negotiations over the price of the electricity it will produce, buy-in from towns where its underground cable comes ashore, and travels to an Eversource substation. It’s a familiar story to Alla Weinstein, founder and CEO of Trident Winds, Inc. On the West Coast, where deep waters (greater than 60 meters) begin closer to shore, Weinstein is trying to launch floating offshore wind projects. “I’ve been in marine renewables for 20 years, and when people ask why I do what I do, I tell them it’s because it matters,” she said. “Because if we don’t do it, we may not have a planet that’s suitable for humans.”

      Weinstein’s “picture of reality” describes a multiyear process during which Trident Winds must address the concerns of such stakeholders as tribal communities and the fishing industry and ensure compliance with, among other regulations, the Marine Mammal Protection Act and the Migratory Bird Species Act. Construction of these massive floating platforms, when it finally happens, will require as-yet unbuilt specialized port infrastructure and boats, and a large skilled labor force for assembly and transmission. “This is a once-in-a-lifetime opportunity to create a new industry,” she said, but “how do we get from here to there?”

      Danielle Jensen, technical manager for Shell’s Offshore Wind Americas, is working on a project off of Rhode Island. The blueprint calls for high-voltage, direct-current cable snaking to landfall in Massachusetts, where direct-current lines switch to alternating current to connect to the grid. “None of this exists, so we have to find a space, the lands, and the right types of cables, tie into the interconnection point, and work with interconnection operators to do that safely and reliably,” she said.

      Utilities are partnering with developers to begin clearing some of these obstacles. Julia Bovey, director of offshore wind for Eversource, described her firm’s redevelopment or improvement of five ports, and new transport vessels for offshore assembly of wind farm components in Atlantic waters. The utility is also digging under roads to lay cables for new power lines. Bovey notes that snags in supply chains and inflation have been driving up costs. This makes determining future electricity rates more complex, especially since utility contracts and markets work differently in each state.

      Just seven up

      Other nations hold a commanding lead in offshore wind: To date, the United States claims just seven operating turbines, while Denmark boasts 6,200 and the U.K. 2,600. Europe’s combined offshore power capacity stands at 30 gigawatts — which, as MITEI Research Scientist Tim Schittekatte notes, is the U.S. goal for 2030.

      The European Union wants 400 gigawatts of offshore wind by 2050, a target made all the more urgent by threats to Europe’s energy security from the war in Ukraine. “The idea is to connect all those windmills, creating a mesh offshore grid,” Schittekatte said, aided by E.U. regulations that establish “a harmonized process to build cross-border infrastructure.”

      Morten Pindstrup, the international chief engineer at Energinet, Denmark’s state-owned energy enterprise, described one component of this pan-European plan: a hybrid Danish-German offshore wind network. Energinet is also constructing energy islands in the North Sea and the Baltic to pool power from offshore wind farms and feed power to different countries.

      The European wind industry benefits from centralized planning, regulation, and markets, said Johannes P. Pfeifenberger, a principal of The Brattle Group. “The grid planning process in the U.S. is not suitable today to find cost-effective solutions to get us to a clean energy grid in time,” he said. Pfeifenberger recommended that the United States immediately pursue a series of moves including a multistate agreement for cooperating on offshore wind and establishment by grid operators of compatible transmission technologies.

      Symposium speakers expressed sharp concerns that complicated and prolonged approvals, as well as partisan politics, could hobble the nation’s nascent offshore industry. “You can develop whatever you want and agree on what you’re doing, and then the people in charge change, and everything falls apart,” said Weinstein. “We can’t slow down, and we actually need to accelerate.”

      Larry Susskind, the Ford Professor of Urban and Environmental Planning, had ideas for breaking through permitting and political gridlock. A negotiations expert, he suggested convening confidential meetings for stakeholders with competing interests for collaborative problem-solving sessions. He announced the creation of a Renewable Energy Facility Siting Clinic at MIT. “We get people to agree that there is a problem, and to accept that without a solution, the system won’t work in the future, and we have to start fixing it now.”

      Other symposium participants were more sanguine about the success of offshore wind. “Trust me, floating wind is not a pie-in-the-sky, exotic technology that is difficult to implement,” said Sclavounos. “There will be companies investing in this technology because it produces huge amounts of energy, and even though the process may not be streamlined, the economics will work itself out.” More

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      Moving perovskite advancements from the lab to the manufacturing floor

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      The following was issued as a joint announcement from MIT.nano and the MIT Research Laboratory for Electronics; CubicPV; Verde Technologies; Princeton University; and the University of California at San Diego.

      Tandem solar cells are made of stacked materials — such as silicon paired with perovskites — that together absorb more of the solar spectrum than single materials, resulting in a dramatic increase in efficiency. Their potential to generate significantly more power than conventional cells could make a meaningful difference in the race to combat climate change and the transition to a clean-energy future.

      However, current methods to create stable and efficient perovskite layers require time-consuming, painstaking rounds of design iteration and testing, inhibiting their development for commercial use. Today, the U.S. Department of Energy Solar Energy Technologies Office (SETO) announced that MIT has been selected to receive an $11.25 million cost-shared award to establish a new research center to address this challenge by using a co-optimization framework guided by machine learning and automation.

      A collaborative effort with lead industry participant CubicPV, solar startup Verde Technologies, and academic partners Princeton University and the University of California San Diego (UC San Diego), the center will bring together teams of researchers to support the creation of perovskite-silicon tandem solar modules that are co-designed for both stability and performance, with goals to significantly accelerate R&D and the transfer of these achievements into commercial environments.

      “Urgent challenges demand rapid action. This center will accelerate the development of tandem solar modules by bringing academia and industry into closer partnership,” says MIT professor of mechanical engineering Tonio Buonassisi, who will direct the center. “We’re grateful to the Department of Energy for supporting this powerful new model and excited to get to work.”

      Adam Lorenz, CTO of solar energy technology company CubicPV, stresses the importance of thinking about scale, alongside quality and efficiency, to accelerate the perovskite effort into the commercial environment. “Instead of chasing record efficiencies with tiny pixel-sized devices and later attempting to stabilize them, we will simultaneously target stability, reproducibility, and efficiency,” he says. “It’s a module-centric approach that creates a direct channel for R&D advancements into industry.”

      The center will be named Accelerated Co-Design of Durable, Reproducible, and Efficient Perovskite Tandems, or ADDEPT. The grant will be administered through the MIT Research Laboratory for Electronics (RLE).

      David Fenning, associate professor of nanoengineering at UC San Diego, has worked with Buonassisi on the idea of merging materials, automation, and computation, specifically in this field of artificial intelligence and solar, since 2014. Now, a central thrust of the ADDEPT project will be to deploy machine learning and robotic screening to optimize processing of perovskite-based solar materials for efficiency and durability.

      “We have already seen early indications of successful technology transfer between our UC San Diego robot PASCAL and industry,” says Fenning. “With this new center, we will bring research labs and the emerging perovskite industry together to improve reproducibility and reduce time to market.”

      “Our generation has an obligation to work collaboratively in the fight against climate change,” says Skylar Bagdon, CEO of Verde Technologies, which received the American-Made Perovskite Startup Prize. “Throughout the course of this center, Verde will do everything in our power to help this brilliant team transition lab-scale breakthroughs into the world where they can have an impact.”

      Several of the academic partners echoed the importance of the joint effort between academia and industry. Barry Rand, professor of electrical and computer engineering at the Andlinger Center for Energy and the Environment at Princeton University, pointed to the intersection of scientific knowledge and market awareness. “Understanding how chemistry affects films and interfaces will empower us to co-design for stability and performance,” he says. “The center will accelerate this use-inspired science, with close guidance from our end customers, the industry partners.”

      A critical resource for the center will be MIT.nano, a 200,000-square-foot research facility set in the heart of the campus. MIT.nano Director Vladimir Bulović, the Fariborz Maseeh (1990) Professor of Emerging Technology, says he envisions MIT.nano as a hub for industry and academic partners, facilitating technology development and transfer through shared lab space, open-access equipment, and streamlined intellectual property frameworks.

      “MIT has a history of groundbreaking innovation using perovskite materials for solar applications,” says Bulović. “We’re thrilled to help build on that history by anchoring ADDEPT at MIT.nano and working to help the nation advance the future of these promising materials.”

      MIT was selected as a part of the SETO Fiscal Year 2022 Photovoltaics (PV) funding program, an effort to reduce costs and supply chain vulnerabilities, further develop durable and recyclable solar technologies, and advance perovskite PV technologies toward commercialization. ADDEPT is one project that will tackle perovskite durability, which will extend module life. The overarching goal of these projects is to lower the levelized cost of electricity generated by PV.

      Research groups involved with the ADDEPT project at MIT include Buonassisi’s Accelerated Materials Laboratory for Sustainability (AMLS), Bulović’s Organic and Nanostructured Electronics (ONE) Lab, and the Bawendi Group led by Lester Wolfe Professor in Chemistry Moungi Bawendi. Also working on the project is Jeremiah Mwaura, research scientist in the ONE Lab. More

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      MIT Energy Conference grapples with geopolitics

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      As Russia’s war in Ukraine rages on, this year’s MIT Energy Conference spotlighted the role of geopolitics in the world’s efforts to lower greenhouse gas emissions and mitigate the worst effects of climate change.

      Each year, the student-run conference, which its organizers say is the largest of its kind, brings together leaders from around the globe to discuss humanity’s most pressing energy and sustainability challenges.

      The event always involves perspectives from the investment, business, research, and startup communities. But this year, as more than 600 attendees gathered on April 11 and 12 for a whirlwind of keynote talks, fireside chats, and panel discussions, common themes also included the influence of Russia’s war, rising tensions between the U.S. and China, and international collaboration.

      As participants grappled with the evolving geopolitical landscape, some speakers encouraged moving past isolationist tendencies.

      “Some people push for self-sufficiency, others emphasize that we should not rely on trading partners that don’t share our values — I think both arguments are misguided,” said Juan Carlos Jobet, Chile’s former ministry of energy and mining. “No country has all that’s needed to create an energy system that’s affordable, clean, and secure. … A third of the world’s energy output is generated in nondemocratic countries. Can we really make our energy systems affordable and secure and curb climate change while excluding those countries from our collective effort? If we enter an area of protectionism and disintegration, we will all be worse off.”

      Another theme was optimism, such as that expressed by Volodymyr Kudrytskyi, CEO of Ukraine’s national power company, who spoke to the conference live from Kyiv. Kudrytskyi outlined Russia’s attacks on Ukraine’s power grids, which included more than 1,000 heavy missiles, making it the largest-ever campaign against a country’s power grid.

      Still, Kudrytskyi said he was confident he’d be able to attend the conference in person next year. As it happened, Kudrytskyi’s presentation marked the day Ukraine resumed its energy exports to other countries.

      “The good news is, after all of that, our system survived and continues operations,” he said.

      Energy security and the green transition

      Richard Duke, the U.S. Department of State’s deputy special envoy for climate, opened the conference with a keynote centered on the U.S.’ role in the global shift toward cleaner energy. Duke was among those advocating for a more integrated and diversified global energy system, noting that no country can address climate change on its own.

      “We need to do all of these things in parallel, in concert with other governments, and through the architecture of the Paris Climate agreement that wraps it together in ambitious net greenhouse gas abatement targets,” Duke said.

      Following his talk, Ditte Juul Jørgensen, the European Commission’s director general for energy, discussed the shift in the EU’s energy policies spurred by the Russian invasion of Ukraine.

      She admitted the EU had grown too dependent on Russian natural gas, but said the invasion forced European states to revise their energy strategy while keeping their long-term objective of net neutrality by 2050.

      “We see energy security and the green transition as interlinked. There is no energy security without the energy transition toward climate neutrality, and there’s no energy transition without energy security,” Jorgensen said.

      Jørgensen also outlined steps the EU has taken to improve its energy security over the last year, including rolling out additional renewable energy projects and replacing Russian fuel with fuel from the U.S., which has now become the continent’s main supplier of energy.

      “The fight against climate change is our shared ambition, it’s our shared responsibility, and I think we’ve shown over these last few years that we can turn that ambition into action and bring results,” she said.

      A challenge and an opportunity

      Optimism also shone through in the way speakers framed the green energy transition as a business opportunity. In keeping with the idea, the conference included a showcase of more than 30 startups focused on clean energy and sustainability.

      “We’re all battling a huge problem that needs a collective effort,” said Malav Sukhadia of Sol Clarity, a conference exhibitor that uses electricity to clean solar panels as a way to replace water cleaning. “This is one of the best energy conferences in the world. We felt if you’re in climate tech, you have to be here.”

      Technological development was a pillar of the conference, and a big topic in those discussions was green hydrogen, a clean fuel source that could replace natural gas in a number of applications and be produced using renewable energy. In one panel discussion on the technology, Sunita Satyapal of the Department of Energy noted the agency has been funding hydrogen development since the 1970s. Other panel members also stressed the maturity of the technology.

      “A lot of the technology needed to advance the ecosystem exists now,” said Laura Parkan, vice president of hydrogen energy at Air Liquide Americas. “The challenge is to get things to a large enough scale so that the costs come down to make it more affordable and really advance the hydrogen ecosystem.”

      Still, panel members acknowledged more technological development is needed to leverage the full potential of hydrogen, such as better mechanisms for storage and transportation.

      Other advanced technologies mentioned in panel discussions included advanced geothermal energy and small modular nuclear reactors that could be built and deployed more quickly than conventional reactors.

      “Exploring these different technologies may actually get us to the net zero — or even a zero carbon future — that we’re hoping for in electricity generation,” said Emma Wong of the OECD Nuclear Energy Agency, noting there are more than 80 advanced reactor designs that have been explored around the world. “There are various challenges and enabling conditions to be addressed, but places like China and Russia are already building these things, so there’s not a technological barrier.”

      “Glass half full”

      Despite the tall tasks that lie ahead, some speakers took a moment to celebrate accomplishments thus far.

      “It’s incredible to think about the progress we’ve made in the last 10 years,” said Neil Brown of the KKR investment firm, whose company is working to build a large offshore wind project. “Solar and wind and electric vehicles have gone from impossibly expensive and hard to imagine penetrating the market to being very close to, if not already at, cost parity. We’ve really come an awful long way.”

      Other speakers mixed their positivity with a confession of envy for the opportunity ahead of the young people in the audience, many of them students from MIT.

      “I have a mix of excitement from the speakers we’ve heard so far and a little bit of envy as well for the open road the young students and professionals here have in front of them,” said Jobert. “Coming back to this place has made me reconnect with the sense of opportunity and responsibility that I felt as a student.”

      Jobert offered lessons learned from his country’s struggles with an energy crisis, populist policies, and severe droughts. His talk finished with questions that struck at the heart of the conference.

      “The evidence is clear: The Earth will change. How much is still to be decided,” Jobert said. “The energy sector has been a central part of the problem. We now must work to become an essential pierce of the solution. Where should we focus our efforts? What can we learn from each other?” More

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      Study: Shutting down nuclear power could increase air pollution

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      Nearly 20 percent of today’s electricity in the United States comes from nuclear power. The U.S. has the largest nuclear fleet in the world, with 92 reactors scattered around the country. Many of these power plants have run for more than half a century and are approaching the end of their expected lifetimes.

      Policymakers are debating whether to retire the aging reactors or reinforce their structures to continue producing nuclear energy, which many consider a low-carbon alternative to climate-warming coal, oil, and natural gas.

      Now, MIT researchers say there’s another factor to consider in weighing the future of nuclear power: air quality. In addition to being a low carbon-emitting source, nuclear power is relatively clean in terms of the air pollution it generates. Without nuclear power, how would the pattern of air pollution shift, and who would feel its effects?

      The MIT team took on these questions in a new study appearing today in Nature Energy. They lay out a scenario in which every nuclear power plant in the country has shut down, and consider how other sources such as coal, natural gas, and renewable energy would fill the resulting energy needs throughout an entire year.

      Their analysis reveals that indeed, air pollution would increase, as coal, gas, and oil sources ramp up to compensate for nuclear power’s absence. This in itself may not be surprising, but the team has put numbers to the prediction, estimating that the increase in air pollution would have serious health effects, resulting in an additional 5,200 pollution-related deaths over a single year.

      If, however, more renewable energy sources become available to supply the energy grid, as they are expected to by the year 2030, air pollution would be curtailed, though not entirely. The team found that even under this heartier renewable scenario, there is still a slight increase in air pollution in some parts of the country, resulting in a total of 260 pollution-related deaths over one year.

      When they looked at the populations directly affected by the increased pollution, they found that Black or African American communities — a disproportionate number of whom live near fossil-fuel plants — experienced the greatest exposure.

      “This adds one more layer to the environmental health and social impacts equation when you’re thinking about nuclear shutdowns, where the conversation often focuses on local risks due to accidents and mining or long-term climate impacts,” says lead author Lyssa Freese, a graduate student in MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS).

      “In the debate over keeping nuclear power plants open, air quality has not been a focus of that discussion,” adds study author Noelle Selin, a professor in MIT’s Institute for Data, Systems, and Society (IDSS) and EAPS. “What we found was that air pollution from fossil fuel plants is so damaging, that anything that increases it, such as a nuclear shutdown, is going to have substantial impacts, and for some people more than others.”

      The study’s MIT-affiliated co-authors also include Principal Research Scientist Sebastian Eastham and Guillaume Chossière SM ’17, PhD ’20, along with Alan Jenn of the University of California at Davis.

      Future phase-outs

      When nuclear power plants have closed in the past, fossil fuel use increased in response. In 1985, the closure of reactors in Tennessee Valley prompted a spike in coal use, while the 2012 shutdown of a plant in California led to an increase in natural gas. In Germany, where nuclear power has almost completely been phased out, coal-fired power increased initially to fill the gap.

      Noting these trends, the MIT team wondered how the U.S. energy grid would respond if nuclear power were completely phased out.

      “We wanted to think about what future changes were expected in the energy grid,” Freese says. “We knew that coal use was declining, and there was a lot of work already looking at the impact of what that would have on air quality. But no one had looked at air quality and nuclear power, which we also noticed was on the decline.”

      In the new study, the team used an energy grid dispatch model developed by Jenn to assess how the U.S. energy system would respond to a shutdown of nuclear power. The model simulates the production of every power plant in the country and runs continuously to estimate, hour by hour, the energy demands in 64 regions across the country.

      Much like the way the actual energy market operates, the model chooses to turn a plant’s production up or down based on cost: Plants producing the cheapest energy at any given time are given priority to supply the grid over more costly energy sources.

      The team fed the model available data on each plant’s changing emissions and energy costs throughout an entire year. They then ran the model under different scenarios, including: an energy grid with no nuclear power, a baseline grid similar to today’s that includes nuclear power, and a grid with no nuclear power that also incorporates the additional renewable sources that are expected to be added by 2030.

      They combined each simulation with an atmospheric chemistry model to simulate how each plant’s various emissions travel around the country and to overlay these tracks onto maps of population density. For populations in the path of pollution, they calculated the risk of premature death based on their degree of exposure.

      System response

      Play video

      Courtesy of the researchers, edited by MIT News

      Their analysis showed a clear pattern: Without nuclear power, air pollution worsened in general, mainly affecting regions in the East Coast, where nuclear power plants are mostly concentrated. Without those plants, the team observed an uptick in production from coal and gas plants, resulting in 5,200 pollution-related deaths across the country, compared to the baseline scenario.

      They also calculated that more people are also likely to die prematurely due to climate impacts from the increase in carbon dioxide emissions, as the grid compensates for nuclear power’s absence. The climate-related effects from this additional influx of carbon dioxide could lead to 160,000 additional deaths over the next century.

      “We need to be thoughtful about how we’re retiring nuclear power plants if we are trying to think about them as part of an energy system,” Freese says. “Shutting down something that doesn’t have direct emissions itself can still lead to increases in emissions, because the grid system will respond.”

      “This might mean that we need to deploy even more renewables, in order to fill the hole left by nuclear, which is essentially a zero-emissions energy source,” Selin adds. “Otherwise we will have a reduction in air quality that we weren’t necessarily counting on.”

      This study was supported, in part, by the U.S. Environmental Protection Agency. More

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      Flow batteries for grid-scale energy storage

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      In the coming decades, renewable energy sources such as solar and wind will increasingly dominate the conventional power grid. Because those sources only generate electricity when it’s sunny or windy, ensuring a reliable grid — one that can deliver power 24/7 — requires some means of storing electricity when supplies are abundant and delivering it later when they’re not. And because there can be hours and even days with no wind, for example, some energy storage devices must be able to store a large amount of electricity for a long time.

      A promising technology for performing that task is the flow battery, an electrochemical device that can store hundreds of megawatt-hours of energy — enough to keep thousands of homes running for many hours on a single charge. Flow batteries have the potential for long lifetimes and low costs in part due to their unusual design. In the everyday batteries used in phones and electric vehicles, the materials that store the electric charge are solid coatings on the electrodes. “A flow battery takes those solid-state charge-storage materials, dissolves them in electrolyte solutions, and then pumps the solutions through the electrodes,” says Fikile Brushett, an associate professor of chemical engineering at MIT. That design offers many benefits and poses a few challenges.

      Flow batteries: Design and operation

      A flow battery contains two substances that undergo electrochemical reactions in which electrons are transferred from one to the other. When the battery is being charged, the transfer of electrons forces the two substances into a state that’s “less energetically favorable” as it stores extra energy. (Think of a ball being pushed up to the top of a hill.) When the battery is being discharged, the transfer of electrons shifts the substances into a more energetically favorable state as the stored energy is released. (The ball is set free and allowed to roll down the hill.)

      At the core of a flow battery are two large tanks that hold liquid electrolytes, one positive and the other negative. Each electrolyte contains dissolved “active species” — atoms or molecules that will electrochemically react to release or store electrons. During charging, one species is “oxidized” (releases electrons), and the other is “reduced” (gains electrons); during discharging, they swap roles. Pumps are used to circulate the two electrolytes through separate electrodes, each made of a porous material that provides abundant surfaces on which the active species can react. A thin membrane between the adjacent electrodes keeps the two electrolytes from coming into direct contact and possibly reacting, which would release heat and waste energy that could otherwise be used on the grid.

      When the battery is being discharged, active species on the negative side oxidize, releasing electrons that flow through an external circuit to the positive side, causing the species there to be reduced. The flow of those electrons through the external circuit can power the grid. In addition to the movement of the electrons, “supporting” ions — other charged species in the electrolyte — pass through the membrane to help complete the reaction and keep the system electrically neutral.

      Once all the species have reacted and the battery is fully discharged, the system can be recharged. In that process, electricity from wind turbines, solar farms, and other generating sources drives the reverse reactions. The active species on the positive side oxidize to release electrons back through the wires to the negative side, where they rejoin their original active species. The battery is now reset and ready to send out more electricity when it’s needed. Brushett adds, “The battery can be cycled in this way over and over again for years on end.”

      Benefits and challenges

      A major advantage of this system design is that where the energy is stored (the tanks) is separated from where the electrochemical reactions occur (the so-called reactor, which includes the porous electrodes and membrane). As a result, the capacity of the battery — how much energy it can store — and its power — the rate at which it can be charged and discharged — can be adjusted separately. “If I want to have more capacity, I can just make the tanks bigger,” explains Kara Rodby PhD ’22, a former member of Brushett’s lab and now a technical analyst at Volta Energy Technologies. “And if I want to increase its power, I can increase the size of the reactor.” That flexibility makes it possible to design a flow battery to suit a particular application and to modify it if needs change in the future.

      However, the electrolyte in a flow battery can degrade with time and use. While all batteries experience electrolyte degradation, flow batteries in particular suffer from a relatively faster form of degradation called “crossover.” The membrane is designed to allow small supporting ions to pass through and block the larger active species, but in reality, it isn’t perfectly selective. Some of the active species in one tank can sneak through (or “cross over”) and mix with the electrolyte in the other tank. The two active species may then chemically react, effectively discharging the battery. Even if they don’t, some of the active species is no longer in the first tank where it belongs, so the overall capacity of the battery is lower.

      Recovering capacity lost to crossover requires some sort of remediation — for example, replacing the electrolyte in one or both tanks or finding a way to reestablish the “oxidation states” of the active species in the two tanks. (Oxidation state is a number assigned to an atom or compound to tell if it has more or fewer electrons than it has when it’s in its neutral state.) Such remediation is more easily — and therefore more cost-effectively — executed in a flow battery because all the components are more easily accessed than they are in a conventional battery.

      The state of the art: Vanadium

      A critical factor in designing flow batteries is the selected chemistry. The two electrolytes can contain different chemicals, but today the most widely used setup has vanadium in different oxidation states on the two sides. That arrangement addresses the two major challenges with flow batteries.

      First, vanadium doesn’t degrade. “If you put 100 grams of vanadium into your battery and you come back in 100 years, you should be able to recover 100 grams of that vanadium — as long as the battery doesn’t have some sort of a physical leak,” says Brushett.

      And second, if some of the vanadium in one tank flows through the membrane to the other side, there is no permanent cross-contamination of the electrolytes, only a shift in the oxidation states, which is easily remediated by re-balancing the electrolyte volumes and restoring the oxidation state via a minor charge step. Most of today’s commercial systems include a pipe connecting the two vanadium tanks that automatically transfers a certain amount of electrolyte from one tank to the other when the two get out of balance.

      However, as the grid becomes increasingly dominated by renewables, more and more flow batteries will be needed to provide long-duration storage. Demand for vanadium will grow, and that will be a problem. “Vanadium is found around the world but in dilute amounts, and extracting it is difficult,” says Rodby. “So there are limited places — mostly in Russia, China, and South Africa — where it’s produced, and the supply chain isn’t reliable.” As a result, vanadium prices are both high and extremely volatile — an impediment to the broad deployment of the vanadium flow battery.

      Beyond vanadium

      The question then becomes: If not vanadium, then what? Researchers worldwide are trying to answer that question, and many are focusing on promising chemistries using materials that are more abundant and less expensive than vanadium. But it’s not that easy, notes Rodby. While other chemistries may offer lower initial capital costs, they may be more expensive to operate over time. They may require periodic servicing to rejuvenate one or both of their electrolytes. “You may even need to replace them, so you’re essentially incurring that initial (low) capital cost again and again,” says Rodby.

      Indeed, comparing the economics of different options is difficult because “there are so many dependent variables,” says Brushett. “A flow battery is an electrochemical system, which means that there are multiple components working together in order for the device to function. Because of that, if you are trying to improve a system — performance, cost, whatever — it’s very difficult because when you touch one thing, five other things change.”

      So how can we compare these new and emerging chemistries — in a meaningful way — with today’s vanadium systems? And how do we compare them with one another, so we know which ones are more promising and what the potential pitfalls are with each one? “Addressing those questions can help us decide where to focus our research and where to invest our research and development dollars now,” says Brushett.

      Techno-economic modeling as a guide

      A good way to understand and assess the economic viability of new and emerging energy technologies is using techno-economic modeling. With certain models, one can account for the capital cost of a defined system and — based on the system’s projected performance — the operating costs over time, generating a total cost discounted over the system’s lifetime. That result allows a potential purchaser to compare options on a “levelized cost of storage” basis.

      Using that approach, Rodby developed a framework for estimating the levelized cost for flow batteries. The framework includes a dynamic physical model of the battery that tracks its performance over time, including any changes in storage capacity. The calculated operating costs therefore cover all services required over decades of operation, including the remediation steps taken in response to species degradation and crossover.

      Analyzing all possible chemistries would be impossible, so the researchers focused on certain classes. First, they narrowed the options down to those in which the active species are dissolved in water. “Aqueous systems are furthest along and are most likely to be successful commercially,” says Rodby. Next, they limited their analyses to “asymmetric” chemistries; that is, setups that use different materials in the two tanks. (As Brushett explains, vanadium is unusual in that using the same “parent” material in both tanks is rarely feasible.) Finally, they divided the possibilities into two classes: species that have a finite lifetime and species that have an infinite lifetime; that is, ones that degrade over time and ones that don’t.

      Results from their analyses aren’t clear-cut; there isn’t a particular chemistry that leads the pack. But they do provide general guidelines for choosing and pursuing the different options.

      Finite-lifetime materials

      While vanadium is a single element, the finite-lifetime materials are typically organic molecules made up of multiple elements, among them carbon. One advantage of organic molecules is that they can be synthesized in a lab and at an industrial scale, and the structure can be altered to suit a specific function. For example, the molecule can be made more soluble, so more will be present in the electrolyte and the energy density of the system will be greater; or it can be made bigger so it won’t fit through the membrane and cross to the other side. Finally, organic molecules can be made from simple, abundant, low-cost elements, potentially even waste streams from other industries.

      Despite those attractive features, there are two concerns. First, organic molecules would probably need to be made in a chemical plant, and upgrading the low-cost precursors as needed may prove to be more expensive than desired. Second, these molecules are large chemical structures that aren’t always very stable, so they’re prone to degradation. “So along with crossover, you now have a new degradation mechanism that occurs over time,” says Rodby. “Moreover, you may figure out the degradation process and how to reverse it in one type of organic molecule, but the process may be totally different in the next molecule you work on, making the discovery and development of each new chemistry require significant effort.”

      Research is ongoing, but at present, Rodby and Brushett find it challenging to make the case for the finite-lifetime chemistries, mostly based on their capital costs. Citing studies that have estimated the manufacturing costs of these materials, Rodby believes that current options cannot be made at low enough costs to be economically viable. “They’re cheaper than vanadium, but not cheap enough,” says Rodby.

      The results send an important message to researchers designing new chemistries using organic molecules: Be sure to consider operating challenges early on. Rodby and Brushett note that it’s often not until way down the “innovation pipeline” that researchers start to address practical questions concerning the long-term operation of a promising-looking system. The MIT team recommends that understanding the potential decay mechanisms and how they might be cost-effectively reversed or remediated should be an upfront design criterion.

      Infinite-lifetime species

      The infinite-lifetime species include materials that — like vanadium — are not going to decay. The most likely candidates are other metals; for example, iron or manganese. “These are commodity-scale chemicals that will certainly be low cost,” says Rodby.

      Here, the researchers found that there’s a wider “design space” of feasible options that could compete with vanadium. But there are still challenges to be addressed. While these species don’t degrade, they may trigger side reactions when used in a battery. For example, many metals catalyze the formation of hydrogen, which reduces efficiency and adds another form of capacity loss. While there are ways to deal with the hydrogen-evolution problem, a sufficiently low-cost and effective solution for high rates of this side reaction is still needed.

      In addition, crossover is a still a problem requiring remediation steps. The researchers evaluated two methods of dealing with crossover in systems combining two types of infinite-lifetime species.

      The first is the “spectator strategy.” Here, both of the tanks contain both active species. Explains Brushett, “You have the same electrolyte mixture on both sides of the battery, but only one of the species is ever working and the other is a spectator.” As a result, crossover can be remediated in similar ways to those used in the vanadium flow battery. The drawback is that half of the active material in each tank is unavailable for storing charge, so it’s wasted. “You’ve essentially doubled your electrolyte cost on a per-unit energy basis,” says Rodby.

      The second method calls for making a membrane that is perfectly selective: It must let through only the supporting ion needed to maintain the electrical balance between the two sides. However, that approach increases cell resistance, hurting system efficiency. In addition, the membrane would need to be made of a special material — say, a ceramic composite — that would be extremely expensive based on current production methods and scales. Rodby notes that work on such membranes is under way, but the cost and performance metrics are “far off from where they’d need to be to make sense.”

      Time is of the essence

      The researchers stress the urgency of the climate change threat and the need to have grid-scale, long-duration storage systems at the ready. “There are many chemistries now being looked at,” says Rodby, “but we need to hone in on some solutions that will actually be able to compete with vanadium and can be deployed soon and operated over the long term.”

      The techno-economic framework is intended to help guide that process. It can calculate the levelized cost of storage for specific designs for comparison with vanadium systems and with one another. It can identify critical gaps in knowledge related to long-term operation or remediation, thereby identifying technology development or experimental investigations that should be prioritized. And it can help determine whether the trade-off between lower upfront costs and greater operating costs makes sense in these next-generation chemistries.

      The good news, notes Rodby, is that advances achieved in research on one type of flow battery chemistry can often be applied to others. “A lot of the principles learned with vanadium can be translated to other systems,” she says. She believes that the field has advanced not only in understanding but also in the ability to design experiments that address problems common to all flow batteries, thereby helping to prepare the technology for its important role of grid-scale storage in the future.

      This research was supported by the MIT Energy Initiative. Kara Rodby PhD ’22 was supported by an ExxonMobil-MIT Energy Fellowship in 2021-22.

      This article appears in the Winter 2023 issue of Energy Futures, the magazine of the MIT Energy Initiative. More