MIT’s sustainability director describes how 2016 effort has inspired Boston and other cities.
MIT 3Q Solar Newman Web
Julie Newman, Ph.D., Director of the MIT Office of Sustainability. Image, Dominick Reuter.

In 2016, MIT announced that it would neutralize 17 percent of its carbon emissions through a unique collaboration with Boston Medical Center and Post Office Square Redevelopment Corporation: The three entitites formed an alliance to buy solar power, demonstrating a partnership model for climate-change mitigation and the advancement of large scale solar development.

Boston Mayor Martin Walsh recently announced that his city will undertake a similar but much larger effort to purchase solar energy in conjunction with cities across the U.S., including Chicago, Houston, Los Angeles, Orlando, and Portland, Oregon. At the time of this announcement, Walsh called upon more cities to join in this collective renewable energy initiative. In describing the agreement, Boston officials said the effort is modeled on MIT’s 2016 effort.

Julie Newman, the Institute’s director of sustainability, spoke with MIT News about the power of MIT’s pioneering model for purchasing solar energy.

Q: Can you describe MIT’s alliance with Boston Medical Center and Post Office Square Redevelopment Corporation to purchase solar energy?

A: Climate partnerships are not new to cities like Boston and Cambridge, where urban stakeholders work together to try to advance solutions for climate mitigation and resiliency. In Boston, MIT participates on the city’s Green Ribbon Commission, which is co-chaired by Mayor Walsh and includes leaders from Boston’s business, institutional, and civic sectors. In MIT’s host city of Cambridge, the Institute works collaboratively with the municipality on a range of initiatives related to solar energy, resiliency planning, building energy use, and other efforts focused on climate change.

In October 2016, MIT, Boston Medical Center, and Post Office Square Redevelopment Corporation formed an alliance to buy electricity from a large new solar power installation. The goal was to add carbon-free energy to the grid and, equally important, we wanted to demonstrate a partnership model for other organizations.

Our power purchase agreement, or PPA, enabled the construction of Summit Farms, a 650-acre, 60-megawatt solar farm in North Carolina. The facility is now operational and is one of the largest renewable-energy projects ever built in the U.S. through an alliance like this.

MIT committed to buying 73 percent of the power generated by Summit Farms’ 255,000 solar panels, with BMC purchasing 26 percent and POS purchasing the remainder. At the time, MIT’s purchase of 44 megawatts — equivalent to 40 percent of the Institute’s 2016 electricity use — was among the largest publicly announced purchases of solar energy by any American college or university.

Summit Farms would not have been built without the commitments from MIT and its partners. The emissions-free power it generates every year represents an annual abatement of carbon dioxide emissions equivalent to removing more than 25,000 cars from the road.

A unique provision in the agreement between MIT and Summit Farms will provide MIT researchers with access to a wealth of data on performance parameters at the North Carolina site. This research capability amplifies the project’s impact and contributes to making the MIT campus a true living laboratory for advances in technology, policy, and business models.

Q: What exactly has the City of Boston announced that it plans to do, and how is this modeled on MIT’s solar-power collaboration?

A: MIT, our collaborators, the city of Boston, and the numerous other cities joining Mayor Walsh all share an interest in reducing carbon emissions at the global scale. We want solutions that will transform the energy market, create clean-energy jobs, and sustain healthy, thriving communities. In collaboration, we can have a greater impact than we could if we tried to mitigate emissions on an institute-by-institute or city-by-city basis. By combining our purchasing power, we can escalate the demand for renewable energy more rapidly, triggering new development and installation of renewables through the energy sector in the U.S.

Our project used a convening force, the group A Better City, to invite disparate entities to combine efforts to increase demand for renewable energy. Similarly, Mayor Walsh has called upon leading members of the Climate Mayors Network, representing over 400 cities and 70 million people, to combine their collective purchasing and bargaining power to reduce energy costs and spark the creation of large-scale renewable energy projects across the country. This invitation has launched a coast-to-coast effort to increase the demand for renewable energy across the eight regional grids.

Q: Has the Institute fielded expressions of interest from other entities interested in trying this model? Is there evidence that it will spread further?

A: We are excited about this solution, and we’ve shared this model of solar-collaboration with peers across the country. We’ve hosted webinars, meetings, and presentations, and received immediate and passionate interest from statewide systems, large corporations, and multiuniversity partnerships that have since pursued collective renewable energy projects. We can now point to a dozen or more projects that have been inspired by this model and are pursuing renewable energy aggregation.

It is important to note that the success of an external collaboration is only as strong as our internal collaboration. The development of the MIT power purchase agreement relied on expertise from more than eight academic and administrative departments, including researchers from related fields, engineers in our utilities area, and staff with expertise in purchasing, finance, and legal areas. We are on the verge of tapping back into these partnerships as we look ahead to determine what is next.

We now have real-time data on energy, emissions avoidance, and financial performance and can evaluate the real world impacts of our project. These findings will influence our thinking going forward. We are considering such questions as how can MIT continue to amplify our efforts? How can we shape our energy impact in the world, and what is the best way to pursue our interest in collectively transforming the energy market? We are continuously broadening our clean energy knowledge base, from multidimensional carbon-accounting frameworks to the exploration of new technologies. Along the way, we have learned that the location of a new wind or solar project matters significantly to its carbon dioxide reduction impact. (The project has a greater benefit if it’s located in a dirtier power grid.) This will inform our work as we actively pursue new partnerships for future scenarios.

back to newsletter– Steve Bradt | MIT News Office
July 16, 2018

 

Friday, 17 November 2017 10:10

A new way to store thermal energy

MIT researchers create material for a chemical heat “battery” that could release its energy on demand.

In large parts of the developing world, people have abundant heat from the sun during the day, but most cooking takes place later in the evening when the sun is down, using fuel — such as wood, brush or dung — that is collected with significant time and effort.

Now, a new chemical composite developed by researchers at MIT could provide an alternative. It could be used to store heat from the sun or any other source during the day in a kind of thermal battery, and it could release the heat when needed, for example for cooking or heating after dark.

A common approach to thermal storage is to use what is known as a phase change material (PCM), where input heat melts the material and its phase change — from solid to liquid — stores energy. When the PCM is cooled back down below its melting point, it turns back into a solid, at which point the stored energy is released as heat. There are many examples of these materials, including waxes or fatty acids used for low-temperature applications, and molten salts used at high temperatures. But all current PCMs require a great deal of insulation, and they pass through that phase change temperature uncontrollably, losing their stored heat relatively rapidly.

Instead, the new system uses molecular switches that change shape in response to light; when integrated into the PCM, the phase-change temperature of the hybrid material can be adjusted with light, allowing the thermal energy of the phase change to be maintained even well below the melting point of the original material.

light activate

This blue LED lamp setup is used to trigger the heat discharge from large-scale films of phase-change materials. (Melanie Gonick/MIT)

The new findings, by MIT postdocs Grace Han and Huashan Li and Professor Jeffrey Grossman, are reported this week in the journal Nature Communications.

“The trouble with thermal energy is, it’s hard to hold onto it,” Grossman explains. So his team developed what are essentially add-ons for traditional phase change materials, or, “little molecules that undergo a structural change when light shines on them.” The trick was to find a way to integrate these molecules with conventional PCM materials to release the stored energy as heat, on demand. “There are so many applications where it would be useful to store thermal energy in a way lets you trigger it when needed,” he says.

The researchers accomplished this by combining the fatty acids with an organic compound that responds to a pulse of light. With this arrangement, the light-sensitive component alters the thermal properties of the other component, which stores and releases its energy. The hybrid material melts when heated, and after being exposed to ultraviolet light, it stays melted even when cooled back down. Next, when triggered by another pulse of light, the material resolidifies and gives back the thermal phase-change energy. 

“By integrating a light-activated molecule into the traditional picture of latent heat, we add a new kind of control knob for properties such as melting, solidification, and supercooling,” says Grossman, who is the Morton and Claire Goulder and Family Professor in Environmental Systems as well as professor of materials science and engineering.

The UV-activated thermal energy storage material shows the rapid crystallization and heat discharge upon visible light (blue LED) illumination. (Grossman Group at MIT)

The system could make use of any source of heat, not just solar, Han says. “The availability of waste heat is widespread, from industrial processes, to solar heat, and even the heat coming out of vehicles, and it’s usually just wasted.” Harnessing some of that waste could provide a way of recycling that heat for useful applications.

crystalization

“What we are doing technically,” Han explains, “is installing a new energy barrier, so the stored heat cannot be released immediately.” In its chemically stored form, the energy can remain for long periods until the optical trigger is activated. In their initial small-scale lab versions, they showed the stored heat can remain stable for at least 10 hours, whereas a device of similar size storing heat directly would dissipate it within a few minutes. And “there’s no fundamental reason why it can’t be tuned to go higher,” Han says.

In the initial proof-of-concept system “the temperature change or supercooling that we achieve for this thermal storage material can be up to 10 degrees C (18 F), and we hope we can go higher,” Grossman says.

Under a dark-field microscope, the microscale environment shows the rapid crystal growth can easily be monitored. (Grossman Group at MIT)

Already, in this version, “the energy density is quite significant, even though we’re using a conventional phase-change material,” Han says. The material can store about 200 joules per gram, which she says is “very good for any organic phase-change material.” And already, “people have shown interest in using this for cooking in rural India,” she says. Such systems could also be used for drying agricultural crops or for space heating.

“Our interest in this work was to show a proof of concept,” Grossman says, “but we believe there is a lot of potential for using light-activated materials to hijack the thermal storage properties of phase change materials.”

“This is highly creative research, where the key is that the scientists combine a thermally driven phase-change material with a photoswitching molecule, to build an energy barrier to stabilize the thermal energy storage,” says Junqiao Wu, a professor of materials science and engineering at the University of California at Berkeley, who was not involved in the research. “I think the work is significant, as it offers a practical way to store thermal energy, which has been challenging in the past.” 

dark field

The work was supported by the Tata Center for Technology and Design within MIT’s Energy Initiative.

David L. Chandler | MIT News Office
November 16, 2017

New material should be relatively easy to produce at an industrial scale, researchers say.
MIT Single Step Solar 01 Web
Illustration shows the apparatus used to create a thin layer of a transparent, electrically conductive material, to protect solar cells or other devices. The chemicals used to produce the layer, shown in tubes at left, are introduced into a vacuum chamber where they deposit a layer on a substrate material at top of the chamber. Illustration courtesy of the authors, edited by MIT News

MIT researchers have improved on a transparent, conductive coating material, producing a tenfold gain in its electrical conductivity. When incorporated into a type of high-efficiency solar cell, the material increased the cell’s efficiency and stability.

The new findings are reported today in the journal Science Advances, in a paper by MIT postdoc Meysam Heydari Gharahcheshmeh, professors Karen Gleason and Jing Kong, and three others.

“The goal is to find a material that is electrically conductive as well as transparent,” Gleason explains, which would be “useful in a range of applications, including touch screens and solar cells.” The material most widely used today for such purposes is known as ITO, for indium titanium oxide, but that material is quite brittle and can crack after a period of use, she says.

Gleason and her co-researchers improved a flexible version of a transparent, conductive material two years ago and published their findings, but this material still fell well short of matching ITO’s combination of high optical transparency and electrical conductivity. The new, more ordered material, she says, is more than 10 times better than the previous version.

The combined transparency and conductivity is measured in units of Siemens per centimeter. ITO ranges from 6,000 to 10,000, and though nobody expected a new material to match those numbers, the goal of the research was to find a material that could reach at least a value of 35. The earlier publication exceeded that by demonstrating a value of 50, and the new material has leapfrogged that result, now clocking in at 3,000; the team is still working on fine-tuning the process to raise that further.

 The high-performing flexible material, an organic polymer known as PEDOT, is deposited in an ultrathin layer just a few nanometers thick, using a process called oxidative chemical vapor deposition (oCVD). This process results in a layer where the structure of the tiny crystals that form the polymer are all perfectly aligned horizontally, giving the material its high conductivity. Additionally, the oCVD method can decrease the stacking distance between polymer chains within the crystallites, which also enhances electrical conductivity.

To demonstrate the material’s potential usefulness, the team incorporated a layer of the highly aligned PEDOT into a perovskite-based solar cell. Such cells are considered a very promising alternative to silicon because of their high efficiency and ease of manufacture, but their lack of durability has been a major drawback. With the new oCVD aligned PEDOT, the perovskite’s efficiency improved and its stability doubled.

MIT Single Step Solar 02 Web
Postdoc Meysam Gharahcheshmeh (left) and Karen Gleason, the Alexander and I. Michael Kasser Professor of Chemical Engineering, are co-authors of the new paper. Image: Webb Chappell

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In the initial tests, the oCVD layer was applied to substrates that were 6 inches in diameter, but the process could be applied directly to a large-scale, roll-to-roll industrial scale manufacturing process, Heydari Gharahcheshmeh says. “It’s now easy to adapt for industrial scale-up,” he says. That’s facilitated by the fact that the coating can be processed at 140 degrees Celsius — a much lower temperature than alternative materials require.

The oCVD PEDOT is a mild, single-step process, enabling direct deposition onto plastic substrates, as desired for flexible solar cells and displays. In contrast, the aggressive growth conditions of many other transparent conductive materials require an initial deposition on a different, more robust substrate, followed by complex processes to lift off the layer and transfer it to plastic.

Because the material is made by a dry vapor deposition process, the thin layers produced can follow even the finest contours of a surface, coating them all evenly, which could be useful in some applications. For example, it could be coated onto fabric and cover each fiber but still allow the fabric to breathe.

The team still needs to demonstrate the system at larger scales and prove its stability over longer periods and under different conditions, so the research is ongoing. But “there’s no technical barrier to moving this forward. It’s really just a matter of who will invest to take it to market,” Gleason says.

The research team included MIT postdocs Mohammad Mahdi Tavakoli and Maxwell Robinson, and research affiliate Edward Gleason. The work was supported by Eni S.p.A. under the Eni-MIT Alliance Solar Frontiers Program.

back to newsletterDavid L. Chandler | MIT News Office
November 22, 2019

Materials scientist recognized for social, economic, and environmentally-sustaining inventions that impact millions of people around the world.
Cody Friesen is the winner of the 2019 Lemelson-MIT Prize for invention. Photo, Zero Mass Water.
Cody Friesen is the winner of the 2019 Lemelson-MIT Prize for invention. Photo, Zero Mass Water.

Cody Friesen PhD ’04, an associate professor of materials science at Arizona State University and founder of both Fluidic Energy and Zero Mass Water, was awarded the 2019 $500,000 Lemelson-MIT Prize for invention. Friesen has dedicated his career to inventing solutions that address two of the biggest challenges to social and economic advancement in the developing world: access to fresh water and reliable energy. His renewable water and energy technologies help fight climate change while providing valuable resources to underserved communities.

Friesen’s first company, Fluidic Energy, was formed to commercialize and deploy the world’s first, and only, rechargeable metal-air battery, which can withstand many thousands of discharges. The technology has provided backup power during approximately 1 million long-duration outages, while simultaneously offsetting thousands of tons of carbon dioxide emissions. The batteries are currently being used as a secondary energy source on four continents at thousands of critical load sites and in dozens of microgrids. Several million people have benefited from access to reliable energy as a result of the technology. Fluidic Energy has been renamed NantEnergy, with Patrick Soon-Shiong investing significantly in the continued global expansion of the technology.

Currently, Friesen’s efforts are focused on addressing the global water crisis through his company, Zero Mass Water. Friesen invented SOURCE Hydropanels, which are solar panels that make drinking water from sunlight and air. The invention is a true leapfrog technology and can make drinking water in dry conditions with as low as 5 percent relative humidity. SOURCE has been deployed in 33 countries spanning six continents. The hydropanels are providing clean drinking water in communities, refugee camps, government offices, hotels, hospitals, schools, restaurants, and homes around the world.

Carl V. Thompson and Cody Friesen.

2019 Lemelson-MIT Prize winner Cody Friesen, right, is shown here with his graduate advisor, Professor Carl V. Thompson. Photo, Michael J. Cima.

“As inventors, we have a responsibility to ensure our technology serves all of humanity, not simply the elite,” says Friesen. “At the end of the day, our work is about impact, and this recognition propels us forward as we deploy SOURCE Hydropanels to change the human relationship to water across the globe.”

Friesen joins a long lineage of inventors to receive the Lemelson-MIT Prize, the largest cash prize for invention in the United States for 25 years. He will be donating his prize to a project with Conservation International to provide clean drinking water via SOURCE Hydropanels to the Bahia Hondita community in Colombia.

“Cody’s inventive spirit, fueled by his strong desire to help improve the lives of people everywhere, is an inspiring role model for future generations,” says Michael Cima, faculty director for the Lemelson-MIT Program and associate dean of innovation for the MIT School of Engineering. “Water scarcity is a prominent global issue, which Cody is combating through technology and innovation. We are excited that the use of this award will further elevate his work.”

“Cody Friesen embodies what it means to be an impact inventor,” notes Carol Dahl, executive director at the Lemelson Foundation. “His inventions are truly improving lives, take into account environmental considerations, and have become the basis for companies that impact millions of people around the world each year. We are honored to recognize Dr. Friesen as this year’s LMIT Prize winner.”

Friesen spoke at EmTech MIT, the annual conference on emerging technologies hosted by MIT Technology Review at the MIT Media Lab on Sept. 18 at 5 p.m.

back to newsletterStephanie Martinovich, Lemelson-MIT Program | MIT News Office
September 18, 2019

Solar panel costs have dropped lately, but slimming down silicon wafers could lead to even lower costs and faster industry expansion.
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Currently, 90 percent of the world’s solar panels are made from crystalline silicon, and the industry continues to grow at a rate of about 30 percent per year.

Costs of solar panels have plummeted over the last several years, leading to rates of solar installations far greater than most analysts had expected. But with most of the potential areas for cost savings already pushed to the extreme, further cost reductions are becoming more challenging to find.

Now, researchers at MIT and at the National Renewable Energy Laboratory (NREL) have outlined a pathway to slashing costs further, this time by slimming down the silicon cells themselves.

Thinner silicon cells have been explored before, especially around a dozen years ago when the cost of silicon peaked because of supply shortages. But this approach suffered from some difficulties: The thin silicon wafers were too brittle and fragile, leading to unacceptable levels of losses during the manufacturing process, and they had lower efficiency. The researchers say there are now ways to begin addressing these challenges through the use of better handling equipment and some recent developments in solar cell architecture.

The new findings are detailed in a paper in the journal Energy and Environmental Science, co-authored by MIT postdoc Zhe Liu, professor of mechanical engineering Tonio Buonassisi, and five others at MIT and NREL.

The researchers describe their approach as “technoeconomic,” stressing that at this point economic considerations are as crucial as the technological ones in achieving further improvements in affordability of solar panels.

Currently, 90 percent of the world’s solar panels are made from crystalline silicon, and the industry continues to grow at a rate of about 30 percent per year, the researchers say. Today’s silicon photovoltaic cells, the heart of these solar panels, are made from wafers of silicon that are 160 micrometers thick, but with improved handling methods, the researchers propose this could be shaved down to 100 micrometers —  and eventually as little as 40 micrometers or less, which would only require one-fourth as much silicon for a given size of panel.

That could not only reduce the cost of the individual panels, they say, but even more importantly it could allow for rapid expansion of solar panel manufacturing capacity. That’s because the expansion can be constrained by limits on how fast new plants can be built to produce the silicon crystal ingots that are then sliced like salami to make the wafers. These plants, which are generally separate from the solar cell manufacturing plants themselves, tend to be capital-intensive and time-consuming to build, which could lead to a bottleneck in the rate of expansion of solar panel production. Reducing wafer thickness could potentially alleviate that problem, the researchers say.

The study looked at the efficiency levels of four variations of solar cell architecture, including PERC (passivated emitter and rear contact) cells and other advanced high-efficiency technologies, comparing their outputs at different thickness levels. The team found there was in fact little decline in performance down to thicknesses as low as 40 micrometers, using today’s improved manufacturing processes.

“We see that there’s this area (of the graphs of efficiency versus thickness) where the efficiency is flat,” Liu says, “and so that’s the region where you could potentially save some money.” Because of these advances in cell architecture, he says, “we really started to see that it was time to revisit the cost benefits.”

Changing over the huge panel-manufacturing plants to adapt to the thinner wafers will be a time-consuming and expensive process, but the analysis shows the benefits can far outweigh the costs, Liu says. It will take time to develop the necessary equipment and procedures to allow for the thinner material, but with existing technology, he says, “it should be relatively simple to go down to 100 micrometers,” which would already provide some significant savings. Further improvements in technology such as better detection of microcracks before they grow could help reduce thicknesses further.

In the future, the thickness could potentially be reduced to as little as 15 micrometers, he says. New technologies that grow thin wafers of silicon crystal directly rather than slicing them from a larger cylinder could help enable such further thinning, he says.

Development of thin silicon has received little attention in recent years because the price of silicon has declined from its earlier peak. But, because of cost reductions that have already taken place in solar cell efficiency and other parts of the solar panel manufacturing process and supply chain, the cost of the silicon is once again a factor that can make a difference, he says.

“Efficiency can only go up by a few percent. So if you want to get further improvements, thickness is the way to go,” Buonassisi says. But the conversion will require large capital investments for full-scale deployment.

The purpose of this study, he says, is to provide a roadmap for those who may be planning expansion in solar manufacturing technologies. By making the path “concrete and tangible,” he says, it may help companies incorporate this in their planning. “There is a path,” he says. “It’s not easy, but there is a path. And for the first movers, the advantage is significant.”

What may be required, he says, is for the different key players in the industry to get together and lay out a specific set of steps forward and agreed-upon standards, as the integrated circuit industry did early on to enable the explosive growth of that industry. “That would be truly transformative,” he says.

Andre Augusto, an associate research scientist at Arizona State University who was not connected with this research, says “refining silicon and wafer manufacturing is the most capital-expense (capex) demanding part of the process of manufacturing solar panels. So in a scenario of fast expansion, the wafer supply can become an issue. Going thin solves this problem in part as you can manufacture more wafers per machine without increasing significantly the capex.” He adds that “thinner wafers may deliver performance advantages in certain climates,” performing better in warmer conditions.

Renewable energy analyst Gregory Wilson of Gregory Wilson Consulting, who was not associated with this work, says “The impact of reducing the amount of silicon used in mainstream cells would be very significant, as the paper points out. The most obvious gain is in the total amount of capital required to scale the PV industry to the multi-terawatt scale required by the climate change problem. Another benefit is in the amount of energy required to produce silicon PV panels. This is because the polysilicon production and ingot growth processes that are required for the production of high efficiency cells are very energy intensive.”

Wilson adds “Major PV cell and module manufacturers need to hear from credible groups like Prof. Buonassisi’s at MIT, since they will make this shift when they can clearly see the economic benefits.”

The team also included Sarah Sofia, Hannu Lane, Sarah Wieghold and Marius Peters at MIT and Michael Woodhouse at NREL. The work was partly supported by the U.S. Department of Energy, the Singapore-MIT Alliance for Research and Technology (SMART), and by a Total Energy Fellowship through the MIT Energy Initiative.

back to newsletter David L. Chandler | MIT News Office
January 26, 2020

Assistant professor in EECS and DMSE is developing materials with novel structures and useful applications, including renewable energy and information storage.

 

Ceramics research Jennifer Rupp headshot MIT Webm
Jennifer Rupp's current ceramics research applications range from battery-based storage for renewable energy, to energy-harvesting systems, to devices used to store data during computation. Photo courtesy of Jennifer Rupp.

Ensuring that her research contributes to society’s well-being is a major driving force for Jennifer Rupp.

“Even if my work is fundamental, I want to think about how it can be useful for society,” says Rupp, the Thomas Lord Assistant Professor of Materials Science and Engineering and an assistant professor in the Department of Electrical Engineering and Computer Science (EECS) at MIT.

Since joining the Department of Materials Science and Engineering in February 2017, she has been focusing not only on the basics of ceramics processing techniques but also on how to further develop those techniques to design new practical devices as well as materials with novel structures. Her current research applications range from battery-based storage for renewable energy, to energy-harvesting systems, to devices used to store data during computation.

Rupp first became intrigued with ceramics during her doctoral studies at ETH Zurich.

“I got particularly interested in how they can influence structures to gain certain functionalities and properties,” she says. During this time, she also became fascinated with how ceramics can contribute to the conversion and storage of energy. The need to transition to a low-carbon energy future motivates much of her work at MIT. “Climate change is happening,” she says. “Even though not everybody may agree on that, it’s a fact.”

One way to tackle the climate change problem is by capitalizing on solar energy. Sunshine falling on the Earth delivers roughly 170,000 terawatts per year — about 10,000 times the energy consumed annually worldwide. “So we have a lot of solar energy,” says Rupp. “The question is, how do we profit the most from it?”

To help convert that solar energy into a renewable fuel, her team is designing a ceramic material that can be used in a solar reactor in which incoming sunlight is controlled to create a heat cycle. During the temperature shifts, the ceramic material incorporates and releases oxygen. At the higher temperature, it loses oxygen; at the lower temperature, it regains the oxygen. When carbon dioxide and water are flushed into the solar reactor during this oxidation process, a split reaction occurs, yielding a combination of carbon monoxide and hydrogen known as syngas, which can be converted catalytically into ethanol, methanol, or other liquid fuels.

While the challenges are many, Rupp says she feels bolstered by the humanitarian ethos at MIT. “At MIT, there are scientists and engineers who care about social issues and try to contribute with science and their problem-solving skills to do more,” she says. “I think this is quite important. MIT gives you strong support to try out even very risky things.”

In addition to continuing her work on new materials, Rupp looks forward to exploring new concepts with her students. During the fall of 2017, she taught two recitation sections of 3.091 (Introduction to Solid State Chemistry), a class that has given thousands of MIT undergraduates a foundation in chemistry from an engineering perspective. This spring, she will begin teaching a new elective for graduate students on ceramics processing and engineering that will delve into making ceramic materials not only on the conventional large-scale level but also as nanofabricated structures and small-system structures for devices that can store and convert energy, compute information, or sense carbon dioxide or various environmental pollutants.

To further engage with students, Rupp has proposed an extracurricular club for them to develop materials science comic strips. The first iteration is available on Instagram (@materialcomics) and it depicts three heroes who jump into various structures to investigate their composition and, naturally, to have adventures. Rupp sees the comics as an exciting avenue to engage the nonscientific community as a whole and to illustrate the structures and compositions of various everyday materials.

“I think it is important to create interest in the topic of materials science across various ages and simply to enjoy the fun in it,” she says.

Rupp says MIT is proving to be a stimulating environment. “Everybody is really committed and open to being creative,” she says. “I think a scientist is not only a teacher or a student; a scientist is someone of any age, of any rank, someone who simply enjoys unlocking creativity to design new materials and devices.”

This article appears in the Autumn 2017 issue of Energy Futures, the magazine of the MIT Energy Initiative.

Kelley Travers | MIT Energy Initiative
MIT News Office, February 9, 2018

Approach could bypass the time-consuming steps currently needed to test new photovoltaic materials.
MIT Assessing PVs Web
This experimental setup was used by the team to measure the electrical output of a sample of solar cell material, under controlled conditions of varying temperature and illumination. The data from those tests was then used as the basis for computer modeling using statistical methods to predict the overall performance of the material in real-world operating conditions. Image, Riley Brandt

The worldwide quest by researchers to find better, more efficient materials for tomorrow’s solar panels is usually slow and painstaking. Researchers typically must produce lab samples — which are often composed of multiple layers of different materials bonded together — for extensive testing.

Now, a team at MIT and other institutions has come up with a way to bypass such expensive and time-consuming fabrication and testing, allowing for a rapid screening of far more variations than would be practical through the traditional approach.

The new process could not only speed up the search for new formulations, but also do a more accurate job of predicting their performance, explains Rachel Kurchin, an MIT graduate student and co-author of a paper describing the new process that appears this week in the journal Joule. Traditional methods “often require you to make a specialized sample, but that differs from an actual cell and may not be fully representative” of a real solar cell’s performance, she says.

For example, typical testing methods show the behavior of the “majority carriers,” the predominant particles or vacancies whose movement produces an electric current through a material. But in the case of photovoltaic (PV) materials, Kurchin explains, it is actually the minority carriers — those that are far less abundant in the material — that are the limiting factor in a device’s overall efficiency, and those are much more difficult to measure. In addition, typical procedures only measure the flow of current in one set of directions — within the plane of a thin-film material — whereas it’s up-down flow that is actually harnessed in a working solar cell. In many materials, that flow can be “drastically different,” making it critical to understand in order to properly characterize the material, she says.

“Historically, the rate of new materials development is slow — typically 10 to 25 years,” says Tonio Buonassisi, an associate professor of mechanical engineering at MIT and senior author of the paper. “One of the things that makes the process slow is the long time it takes to troubleshoot early-stage prototype devices,” he says. “Performing characterization takes time — sometimes weeks or months — and the measurements do not always have the necessary sensitivity to determine the root cause of any problems.”

So, Buonassisi says, “the bottom line is, if we want to accelerate the pace of new materials development, it is imperative that we figure out faster and more accurate ways to troubleshoot our early-stage materials and prototype devices.” And that’s what the team has now accomplished. They have developed a set of tools that can be used to make accurate, rapid assessments of proposed materials, using a series of relatively simple lab tests combined with computer modeling of the physical properties of the material itself, as well as additional modeling based on a statistical method known as Bayesian inference.

The system involves making a simple test device, then measuring its current output under different levels of illumination and different voltages, to quantify exactly how the performance varies under these changing conditions. These values are then used to refine the statistical model.

“After we acquire many current-voltage measurements [of the sample] at different temperatures and illumination intensities, we need to figure out what combination of materials and interface variables make the best fit with our set of measurements,” Buonassisi explains. “Representing each parameter as a probability distribution allows us to account for experimental uncertainty, and it also allows us to suss out which parameters are covarying.”

The Bayesian inference process allows the estimates of each parameter to be updated based on each new measurement, gradually refining the estimates and homing in ever closer to the precise answer, he says.

In seeking a combination of materials for a particular kind of application, Kurchin says, “we put in all these materials properties and interface properties, and it will tell you what the output will look like.”

The system is simple enough that, even for materials that have been less well-characterized in the lab, “we’re still able to run this without tremendous computer overhead.” And, Kurchin says, making use of the computational tools to screen possible materials will be increasingly useful because “lab equipment has gotten more expensive, and computers have gotten cheaper. This method allows you to minimize your use of complicated lab equipment.”

The basic methodology, Buonassisi says, could be applied to a wide variety of different materials evaluations, not just solar cells — in fact, it may apply to any system that involves a computer model for the output of an experimental measurement. “For example, this approach excels in figuring out which material or interface property might be limiting performance, even for complex stacks of materials like batteries, thermoelectric devices, or composites used in tennis shoes or airplane wings.” And, he adds, “It is especially useful for early-stage research, where many things might be going wrong at once.”

Going forward, he says, “our vision is to link up this fast characterization method with the faster materials and device synthesis methods we’ve developed in our lab.” Ultimately, he says, “I’m very hopeful the combination of high-throughput computing, automation, and machine learning will help us accelerate the rate of novel materials development by more than a factor of five. This could be transformative, bringing the timelines for new materials-science discoveries down from 20 years to about three to five years.”

The research team also included Riley Brandt '11, SM '13, PhD '16; former postdoc Vera Steinmann; MIT graduate student Daniil Kitchaev and visiting professor Gerbrand Ceder, Chris Roat at Google Inc.; and Sergiu Levcenco and Thomas Unold at Hemholz Zentrum in Berlin. The work was supported by a Google Faculty Research Award, the U.S. Department of Energy, and a Total research grant.

David L. Chandler | MIT News Office
December 20, 2017

Monday, 21 May 2018 14:49

Powered by the sun

Flux, built by the MIT Solar Electric Vehicle Team, was recently unveiled at Johnson Rink in preparation for its participation in the American Solar Challenge.
MIT Solar Flux on road in Georgia Web
In January, Flux and the MIT Solar Electric Vehicle Team went on a road-testing trip in Georgia. Photo courtesy of the MIT Solar Electric Vehicle Team

On a recent April afternoon, MIT sophomore Francis Wang drove out of the Edgerton Center’s Area 51 garage, took a left on Massachusetts Avenue, a right onto Albany Street, and then a left through the wide doors into Johnson Rink.

His ride: Flux, the 14th solar car built mostly by hand, thanks to CNC machines and countless hours in the student shop.

The April 26 unveiling marked the official debut of Flux, an asymmetrical solar car that will race in the American Solar Challenge (ASC) in July.

For the team of 25 students on the MIT Solar Electric Vehicle Team (SEVT), the unveiling was as much a celebration of how far they’ve come and a send-off for how far they want to go. Seventeen hundred miles, to be exact, from Omaha, Nebraska to Bend, Oregon.

Professor J. Kim Vandiver, the Forbes Director of the Edgerton Center and dean for undergraduate research, spoke at the event, and referred to one of the first solar cars, Solectria 4, built by James Worden ’89 in 1988. In fact, about five years before the Edgerton Center was founded, Harold “Doc” Edgerton gave the team space in Building 20.

According to Worden, “unveilings” for solar cars were a little more off-the-cuff back then. Held at Worden’s house in Arlington, Mass., the team performed midnight test runs on Massachusetts Avenue from one end of Arlington to the other on a stretch of flat and straight, car-free road.

This unveiling was more sedate. Junior Veronica LaBelle, team captain, remarked on the power behind a large group of students engaged in intensive collaboration, and her gratitude for the team's commitment. Membership, she noted, has doubled in the past two years.

She also mentioned a road block in the summer of 2017. The team’s $10,000 entry fee for the Australian World Solar Challenge (WSC) had been paid, and Flux was ready to be shipped to Darwin, Australia, for the race. But more road testing was needed, and the timeline was too tight to ensure that Flux was in competition shape. After hours of agonizing discussion, the team decided to forfeit their entry fee and use their time to prepare Flux for the ASC.

Flux stands apart from previous iterations of the solar car with its asymmetrical body. The driver sits on the same right-hand side as the wheel base, which means there’s less drag as it’s racing down the road. The car’s body is made from honeycomb wrapped in carbon fiber.

The 5-kilowatt battery primarily stores energy converted from the solar array – 260 silicon solar cells on the canopy of the car. While cruising, the solar array powers the car without much help from the battery. Acceleration, however, requires more than solar power, and some battery power is required to meet the motor’s demand. During the ASC, the team will have a charging period and can start each day with a full battery.

Talking about the team’s Independent Activities Period road trip to Georgia this January, sophomore Harith Morgan was visibly excited at the memory. “It’s an endurance race, so we’re not only racing, it’s how the car performs and how we perform as a team. If we get a flat, how quickly do we respond to that? Who takes off the wheel, who gets the next wheel, who is tightening the wheel, getting the new wheel secured properly? And we do it in two minutes or less.”

Morgan joined the team in his first-year. “When I got to MIT I knew I was interested in mechanical engineering, and I was thinking of a way I could apply mechanical engineering to solving world problems, and I thought energy was a world problem and solar car was the perfect marriage of the two,” Morgan added.

The unveiling event gave the MIT community a chance to get up close and personal with Flux, and to learn first-hand what goes into designing, building, and racing a solar car. Some even took their Flux selfies.

After Flux had been sufficiently anointed with good solar car luck at the unveiling, Wang put her helmet on, got back in the car, and drove down Massachusetts Avenue to the Area 51 garage.

The team has a little more work ahead, including crush zone changes (bodywork that allows the car to absorb the impact of a crash) and new turning fairing. Plus some more hours of road training for the driver. And then, full sun-powered speed ahead, the ASC from Nebraska to Oregon.

back to newsletterCamilla Brinkman | Edgerton Center
MIT News Office, May 16, 2018

 

Monday, 23 July 2018 21:40

Pulling drinking water out of thin air

Powered only by solar energy, a new device developed at MIT could provide relief to regions where water is scare.

With droughts plaguing much of the western United States and millions of people across the globe living without access to safe water, the need for technologies that produce clean water is greater than ever. The key, according to Evelyn Wang, the Gail E. Kendall Professor and department head for MIT’s Department of Mechanical Engineering, is in the very air we breathe.

Video by: John Freidah

"Water vapor is all around us in the air, even in arid conditions,” explains Wang. She and her team in MIT’s Device Research Laboratory have developed a device that can tap into this abundant resource and literally pull water out of thin air.

The key to the process is a powder that desiccates the air, attracting vapor directly to the porous matrix at the base of the device’s main chamber like a sponge. The vapor is then condensed into liquid and can be collected as usable water – even in dry atmospheres with as low as 20 percent humidity.

The entire process of converting the water vapor found in air into potable water can be done using only the power of the sun. “The device is completely passive,” says Wang. “There is no need to use outside power supplies which can help keep the device low-cost and efficient.”

Keeping costs low and efficiency high is one of Wang’s central goals. “We hope to develop a device that provides relief to the millions of people living in communities that lack the infrastructure needed to provide access to clean drinking water or those living in regions plagued by drought,” adds Wang.

During a field test in Tempe, Arizona, earlier this year, a small proof-of-concept prototype of the device extracted a quarter-liter of water per day per kilogram of the absorbent powder. The researchers hope to increase this output by further tailoring the powder and optimizing the device.

If the production capacity of the device can be increased, Wang’s research could have a tangible impact in places experiencing water scarcity — even in the driest of conditions.back to newsletter

Mary Beth O'Leary, Department of Mechanical Engineering
MIT News Office, July 23, 2018

Starting with higher-value niche markets and then expanding could help perovskite-based solar panels become competitive with silicon.
MIT Scaling Perovskite Web
Perovskites, a family of materials defined by a particular kind of molecular structure as illustrated here, have great potential for new kinds of solar cells. A new study from MIT shows how these materials could gain a foothold in the solar marketplace. Image: Christine Daniloff, MIT

Materials called perovskites show strong potential for a new generation of solar cells, but they’ve had trouble gaining traction in a market dominated by silicon-based solar cells. Now, a study by researchers at MIT and elsewhere outlines a roadmap for how this promising technology could move from the laboratory to a significant place in the global solar market.

The “technoeconomic” analysis shows that by starting with higher-value niche markets and gradually expanding, solar panel manufacturers could avoid the very steep initial capital costs that would be required to make perovskite-based panels directly competitive with silicon for large utility-scale installations at the outset. Rather than making a prohibitively expensive initial investment, of hundreds of millions or even billions of dollars, to build a plant for utility-scale production, the team found that starting with more specialized applications could be accomplished for more realistic initial capital investment on the order of $40 million.

The results are described in a paper in the journal Joule by MIT postdoc Ian Mathews, research scientist Marius Peters, professor of mechanical engineering Tonio Buonassisi, and five others at MIT, Wellesley College, and Swift Solar Inc.

Solar cells based on perovskites — a broad category of compounds characterized by a certain arrangement of their molecular structure — could provide dramatic improvements in solar installations. Their constituent materials are inexpensive, and they could be manufactured in a roll-to-roll process like printing a newspaper, and printed onto lightweight and flexible backing material. This could greatly reduce costs associated with transportation and installation, although they still require further work to improve their durability. Other promising new solar cell materials are also under development in labs around the world, but none has yet made inroads in the marketplace.

“There have been a lot of new solar cell materials and companies launched over the years,” says Mathews, “and yet, despite that, silicon remains the dominant material in the industry and has been for decades.”

Why is that the case? “People have always said that one of the things that holds new technologies back is that the expense of constructing large factories to actually produce these systems at scale is just too much,” he says. “It’s difficult for a startup to cross what’s called ‘the valley of death,’ to raise the tens of millions of dollars required to get to the scale where this technology might be profitable in the wider solar energy industry.”

But there are a variety of more specialized solar cell applications where the special qualities of perovskite-based solar cells, such as their light weight, flexibility, and potential for transparency, would provide a significant advantage, Mathews says. By focusing on these markets initially, a startup solar company could build up to scale gradually, leveraging the profits from the premium products to expand its production capabilities over time.

Describing the literature on perovskite-based solar cells being developed in various labs, he says, “They’re claiming very low costs. But they’re claiming it once your factory reaches a certain scale. And I thought, we’ve seen this before — people claim a new photovoltaic material is going to be cheaper than all the rest and better than all the rest. That’s great, except we need to have a plan as to how we actually get the material and the technology to scale.”

As a starting point, he says, “We took the approach that I haven’t really seen anyone else take: Let’s actually model the cost to manufacture these modules as a function of scale. So if you just have 10 people in a small factory, how much do you need to sell your solar panels at in order to be profitable? And once you reach scale, how cheap will your product become?”

The analysis confirmed that trying to leap directly into the marketplace for rooftop solar or utility-scale solar installations would require very large upfront capital investment, he says. But “we looked at the prices people might get in the internet of things, or the market in building-integrated photovoltaics. People usually pay a higher price in these markets because they’re more of a specialized product. They’ll pay a little more if your product is flexible or if the module fits into a building envelope.” Other potential niche markets include self-powered microelectronics devices.

Such applications would make the entry into the market feasible without needing massive capital investments. “If you do that, the amount you need to invest in your company is much, much less, on the order of a few million dollars instead of tens or hundreds of millions of dollars, and that allows you to more quickly develop a profitable company,” he says.

“It’s a way for them to prove their technology, both technically and by actually building and selling a product and making sure it survives in the field,” Mathews says, “and also, just to prove that you can manufacture at a certain price point.”

Already, there are a handful of startup companies working to try to bring perovskite solar cells to market, he points out, although none of them yet has an actual product for sale. The companies have taken different approaches, and some seem to be embarking on the kind of step-by-step growth approach outlined by this research, he says. “Probably the company that’s raised the most money is a company called Oxford PV, and they’re looking at tandem cells,” which incorporate both silicon and perovskite cells to improve overall efficiency. Another company is one started by Joel Jean PhD ’17 (who is also a co-author of this paper) and others, called Swift Solar, which is working on flexible perovskites. And there’s a company called Saule Technologies, working on printable perovskites.

Mathews says the kind of technoeconomic analysis the team used in its study could be applied to a wide variety of other new energy-related technologies, including rechargeable batteries and other storage systems, or other types of new solar cell materials.

“There are many scientific papers and academic studies that look at how much it will cost to manufacture a technology once it’s at scale,” he says. “But very few people actually look at how much does it cost at very small scale, and what are the factors affecting economies of scale? And I think that can be done for many technologies, and it would help us accelerate how we get innovations from lab to market.”

The research team also included MIT alumni Sarah Sofia PhD ’19 and Sin Cheng Siah PhD ’15, Wellesley College student Erica Ma, and former MIT postdoc Hannu Laine. The work was supported by the European Union’s Horizon 2020 research and innovation program, the Martin Family Society for Fellows of Sustainability, the U.S. Department of Energy, Shell, through the MIT Energy Initiative, and the Singapore-MIT Alliance for Research and Technology.

back to newsletter David L. Chandler | MIT News Office
February 6, 2020

 

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