Researchers are always looking for the next big breakthrough in renewable energy technologies. An engineer at Duke University thinks he has one that could point the way toward a new hybrid solar-fuel cell system that produces energy much more efficiently than current technology.
Nico Hotz, assistant professor of mechanical engineering and material science, developed a system that uses sunlight to heat a combination of water and methanol in a maze of glass tubes on a rooftop. While the hybrid solar collector looks like a traditional solar collector from a distance, it is actually a series of copper tubes coated with a thin layer of aluminum and aluminum oxide, sealed in a vacuum and filled with a combination of water, methanol and catalytic nanoparticles.
According to Hotz, the design is capable of absorbing 95 percent of the sunlight that hits the collector – achieving temperatures of well over 200 degrees Celsius within the tubes. By comparison, a standard solar collector heats water to between 60 and 70 degrees Celsius. Next, tiny amounts of a catalyst are added to produce hydrogen. The hydrogen can then be directed to a fuel cell to provide electricity to a building during the day, or compressed and stored in a tank to provide power later.
Hotz and his fellow researchers compared the hybrid system to three other technologies: a standard photovoltaic (PV) cell that converts sunlight directly into electricity and then splits water into hydrogen and oxygen; a system in which PV cells turn sunlight into electricity, which is then stored in a lithium ion battery; and a similar, yet simpler “photocatalytic” system. The hybrid solar-methanol system was found to be the least expensive option of the three.
The paper describing the results of Hotz’s analysis was named top paper at the ASME Energy Sustainability Fuel Cell 2011 conference in Washington, D.C.