Lean & green: Engineering sustainability

Like a modern-day Galileo, Ravi Subramanian's view of energy revolves around the sun.

"I ask this question at the beginning of my course about solar energy: When I say solar what comes to your mind?" says Subramanian, an associate professor of chemical and materials engineering. "And it's only to avoid a doomsday scenario. People conveniently rule out the fact that the whole Earth is a product of solar energy. I mean the coal that we get, if you go back to basics, it's wood that has been fossilized, which grew some eons ago as plants. It's stored solar energy. So I think solar has been a part and parcel of our life in one way or the other."

Artist rendering of a wind turbine and solar-powered building

Subramanian's research focuses on identifying sustainable materials, some of which are sourced from plants, that can be used for both energy conversion and energy storage. But Subramanian believes that the biggest obstacle to increasing use of solar energy isn't technological. It's cultural.

Making that cultural change will involve prioritizing sustainability over convenience, at least in the near term. For example, Subramanian envisions a network of solar-powered charging stations for electric vehicles using a technology that is able to charge the vehicle battery in minutes, a fraction of the current charging time of six to eight hours. With that technology, which Subramanian acknowledges is a ways away, electric vehicles become viable options for long-distance driving.

"We are not there yet, but that will really be a game changer because now as an end-user I have a choice," says Subramanian. "Do I want to go and put fossil fuel into my car - I'm spending 2 minutes to do that - or should I take the solar energy to charge my car in maybe 15 minutes, maybe half an hour, but by making that choice I'm being responsible for the future generation."

“It’s not enough to look at solar as just something for energy generation. It’s a cultural change. It’s a philosophical change.”
Ravi Subramanian

Subramanian believes educational institutions need to take an active role helping people make that choice, offering accessible technology and education to the community.

"I hope the educational institutions become something of an epicenter of not just technical education but also hands-on facilities that advocate sustainable practices and green technologies," says Subramanian. "If we can offer knowledge on demand and complement it with hands-on expertise, I think that is a very, very good thing to increase awareness."

Subramanian believes solar will continue its trajectory of growth over the next 10 years, thanks largely to advanced photovoltaic technology that is improving the efficiency of solar energy and policy that encourages its adoption.

"We are looking at a very small, miniscule percentage of overall power that solar energy is able to provide, but if you see solar energy's growth as a subset of itself, it has been by quantum leaps," says Subramanian. "The way it is going, I think it is going to be a sizable part of the renewable portfolio, perhaps the highest part of the renewable portfolio."

But for solar energy to capture a more significant market share, the energy grid will also need to get smarter.

A Smarter Grid

Our existing energy grid was designed to be very good at one thing: delivering reliable energy to consumers across the U.S. Ensuring there was always enough electricity available to handle the peak demand - think about a hot summer evening when a city's worth of workers returns home, fires up the air conditioning, and heats up dinner - incentivized developing centralized, bulk capacity.

Artist rendering of a smart grid, showing colored lines moving around a building

Today, society is asking far more from the energy grid. Improving battery technology enables more energy storage, helping with the integration of intermittent energy sources like solar and wind. Climate- and cost-conscious consumers are installing rooftop solar panels, generating their own electricity and sending some of it back to the grid. The rising prominence of electric cars portends large numbers of batteries drawing power from the grid.

All told, these demands add up to the need for a far more responsive energy grid, one that makes use of big data and advanced sensing technology to deliver environmentally friendly, reliable and cost-effective energy to consumers.

"Things have changed," explains Hanif Livani, assistant professor of electrical and biomedical engineering. "From a technical perspective we are going to see more energy storage being integrated. We are going to see more electric vehicles being integrated. When we have an active distribution level, then we need to invest more in monitoring and better control of that."

Already, sensors across the grid are helping researchers and utilities more finely monitor supply and demand. Smart meters, which have been installed in about 65 million homes and businesses around the U.S., are one example of this, providing high-resolution data to utility companies about consumer demand for energy. In the future, the amount of available data could grow by a factor of up to 1,000, Livani says.

Corralling that data into advanced monitoring and control algorithms that enable better coordination between distributed energy resources and centrally controlled bulk generators is one focus of Livani's research.

"There will be more advanced monitoring devices and sensors which may convey up to 1,000 times more information than we have today," says Livani. "We need to interpret those data in a meaningful way so that system operators can extract useful information, whether it is about the customer's behavior or technical difficulties from the grid."

For engineers, the next set of challenges involves building out the communications infrastructure across the grid that can handle the volume of information a truly smart grid will produce.

"One of the main aspects of smart grid implementation is to integrate information and communication technologies into our existing grid in order to achieve these benefits," says Livani. "That is going to create two separate issues. One is how to handle big data when we are talking about more data, more precise measurement devices. The other one is cybersecurity. More devices are connected to the utility grid, so that makes it more vulnerable to cyberattacks. Making the system secure is one of the big challenges which really needs to be addressed."

Sustainable materials for clean energy

Sustainable pavement design with recycled materials

Research by engineers in the pavements engineering and science program is focused on developing sustainable approaches to pavement design. Annually, the U.S. produces 300 million used tires and 140 million pounds of waste from old asphalt. Research in the College’s Western Regional Superpave Center focuses on combining those old tires and asphalt into new engineering asphalt mix to be produced and constructed at significantly lower temperatures, reducing emissions and leading to a healthier environment.

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Security is an issue for the physical materials that power sustainable development as well. Nearly all of the most promising technologies for clean energy - from batteries to thin film photovoltaics to wind turbines - use materials designated by the Department of Energy as critical materials. Although not necessarily rare, these materials are often mined outside the U.S., putting their supply at risk of economic or political disruption.

"All our electronics depend on them, and all renewable energy materials depend on them, and we are not mining them right now," says Dev Chidambaram, Director of the Nevada Institute for Sustainability. "So we need a good plan to recycle them or to replace them with something that is cheaper and easily available. I think materials recycling will be a huge issue in the next 10 years."

The current economic landscape hasn't incentivized materials recycling - mining new materials is cheaper than investing in developing technology to recycle them - but Chidambaram sees that changing, especially when it comes to lithium ion batteries. Their increasing use, particularly in electric vehicles, will result in a large proliferation of old batteries.

"As our population grows, we are going to be mining more and more metals, at some point it's not going to be efficient to dump them," Chidambaram says. "It will be more efficient to reprocess them and get them back into the supply chain. A company like Tesla, which makes only one kind of battery, makes this viable to have a recycling plant for that particular kind of chemistry. They can do it at scale."

New materials for nuclear power plants

Scaling up battery technology is also a prerequisite for large-scale incorporation of renewable energy sources into the power mix, and at the moment, that technology is still in its early stages. So reducing our reliance on carbon-based fuels requires continuing to invest in nuclear power.

"We are not going to go away from nuclear for another 50 years or so, in my opinion," Chidambaram says. "If anything, in the world as a whole it's going to grow. I think molten salt-based reactors will become a reality. Presently, there's a lot of interest in the U.S. in building nuclear reactors based on molten salt. They are very efficient reactors."

But the laws of physics are clear: Building more efficient reactors requires operating them at higher temperatures.

"The only bottleneck, the Achilles Heel for that, is materials reliability, because things that work well at 300 degrees may not work as well at 650 degrees Celsius," says Chidambaram. "Colloquially speaking, metals and alloys start to become soft, sometimes they start to fail, so the materials challenges are a huge issue of all these reactors."

Chidambaram's lab is investigating potential materials and new alloys for these reactors. By first pinpointing the failure mechanisms in potential materials, Chidambaram's group is working to identify materials with the potential to survive the 60 years of ultra-high heat they will be subjected to inside a nuclear reactor.

Chidambaram is also collaborating with Argonne National Laboratory on a way to reprocess used nuclear fuel, which Chidambaram believes is among the most pressing issues related to material reuse and recycling.

"Long-term storage at Yucca Mountain will not solve our problem," says Chidambaram. "Its capacity is 77,000 tons, and we already have close to that amount and are generating more at the rate of about 2 tons per year."

But more than 95 percent of used nuclear fuel consists of uranium, which can be reprocessed, leaving behind a very small amount of material that needs to be stored and allowing engineers to extract 100 times more energy from the original uranium ore than currently obtained in commercial reactors.

"I am very happy to be collaborating with Argonne on addressing specific materials reliability and accountability issues," says Chidambaram. "These are all engineering problems. I think the outlook for engineers is very bright. If I can tell one thing to students, it is: Go into engineering and you will probably have the best guarantee of a future."