In the early twentieth century, when electric grids began to revolutionize everyday life, an unusual champion for renewable energy expressed his worries about the use of fossil fuels. In a 1910 interview for Elbert Hubbard's book, "Little Journeys to the Homes of the Great," Thomas Edison voiced concern about the use of combustion rather than renewable energy.
"This scheme of combustion to get power makes me sick to think of — it is so wasteful," remarked the engineer. "You see, we should harness natural forces to get all of our strength. The sun is a source of energy, as are the winds and tides. Do we utilize them? Oh, no! We burn wood and coal, and tenants burn the front fence for fuel."
More than a century later, fossil fuels continue to account for nearly 80% of worldwide energy use. As the environmental effect of climate change worsens, researchers and engineers feel compelled to produce scalable renewable energy alternatives.
"Even 100 years ago, Edison understood that we cannot replace combustion with a single alternative," says Reshma Rao PhD '19, a postdoc at MIT's Electrochemical Energy Lab who included Edison's words into her doctorate thesis. "We must look to different solutions that might vary temporally and geographically depending on resource availability."
Harvesting energy from waves
Waves outperform other renewable energy sources in two aspects. First, unlike solar, waves provide a steady energy supply regardless of the time of day. Second, because of the bigger mass of water, waves have a far higher energy density than wind.
Despite these benefits, wave energy collecting is still in its infancy. Unlike wind and solar, there is no agreement in the subject of wave hydrodynamics on how to effectively harvest and transform wave energy. Dick K.P. Yue, the Philip J. Solondz Professor of Engineering, hopes to alter that.
"My group has been looking at new paradigms," Yue says. "Rather than tinkering with small improvements, we want to develop a new way of thinking about the wave-energy problem."
One component of that paradigm is selecting the best shape for wave-energy converters (WECs). Emma Edwards, a graduate student, has been creating a systematic process for determining the form of WECs. "If we can optimize the shape of WECs for maximizing extractable power, wave energy could move significantly closer to becoming an economically viable source of renewable energy," Edwards said.
accelerating the discovery of photovoltaics
The quantity of solar energy that reaches the Earth's surface is an enticing potential in the search for renewable energy. Every hour, the sun delivers around 430 quintillion joules of energy to Earth. That is comparable to one year's worldwide energy use by humans.
Tonio Buonassisi, a mechanical engineering professor, has spent his whole career finding systems to collect and transform this energy into useable power. He does, however, emphasize the importance of time. "When you consider what we are up against in terms of climate change, it becomes increasingly clear we are running out of time," he said.
Buonassisi believes that in order for solar energy to make a significant influence, researchers must create solar cell materials that are efficient, scalable, cost-effective, and dependable. These four variables provide a challenge for engineers; rather than developing a material that meets just one of these criteria, they must produce one that checks all four boxes and can be brought to market as soon as feasible. "If it takes us 75 years to bring a solar cell that can do all of these things to market, it will not help us solve this problem." "We need to get it to market within the next five years," says Buonassisi.
To speed up the development and testing of novel materials, Buonassisi's team created a technique that combines machine learning with high-throughput experimentation, which allows a huge number of materials to be tested at the same time. The outcome is a tenfold boost in the pace of discovering and analyzing novel solar cell materials.
New materials that trap heat
While Buonassisi's team is focusing on solutions that convert solar energy directly into electricity, other researchers, like Gang Chen, Carl Richard Soderberg Professor of Power Engineering, are researching on systems that convert sunlight to heat. Thermal energy from the heat is then utilized to generate electricity.
"For the past 20 years, I've been working on materials that convert heat into electricity," Chen said. While most of this materials research is done at the nanoscale, Chen and his colleagues at the NanoEngineering Group are no strangers to large-scale experimental systems. They had previously created a to-scale receiver system that used concentrating solar thermal power (CSP).
CSP uses sunlight to heat a thermal fluid, such oil or molten salt. That fluid is then either utilized to create power via an engine, such as a steam turbine, or stored for later use.
Chen's team constructed a CSP receiver at MIT's Bates Research and Engineering Center in Middleton, Massachusetts, during a four-year effort supported by the United States Department of Energy. They created the Solar Thermal Aerogel Receiver, or STAR.