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There's a lot to like about solar power: It's clean, it's getting less expensive, and it's probably the most sustainable form of energy available. But conventional solar cells have their drawbacks, and one is that up to 20 percent of the Sun's energy they capture is lost when the electrons move from the solar panel to its storage battery.
Now a team of researchers at Ohio State University (OSU) working under Yiying Wu, a professor of chemistry and biochemistry, has devised a hybrid solar battery that not only can capture solar energy but store virtually all the energy it collects.
At the heart of the solution is a solar panel in mesh form, which permits a free flow of air, and a new technique for transferring electrons from the solar panel to the battery's electrode. In the device, oxygen and light work to enable the multiple chemical reactions necessary to charge the battery.
"The state of the art is to use a solar panel to capture the light, and then use a cheap [lithium-ion] battery to store the energy," Wu said in an interview with the OSU Newsroom. "We've integrated both functions into one device. Any time you can do that, you reduce cost."
By how much? By one-fourth, Wu says.
The OSU technology, described in detail in the Oct. 3 issue of the journal Nature Communications, works this way: The solar panel allows sunlight captured by the solar cell to be converted into electrons inside the battery, a process that wastes virtually none of the electrons. These electrons are produced from sunlight that shines onto the mesh of the solar panel.
The built-in battery, meanwhile, contains lithium peroxide, which decomposes into lithium ions and oxygen. The oxygen is released into the air that flows through the mesh, while the lithium ions are transformed into lithium metal and stored safely in the battery.
The current design is based, at least in part, on a high-efficiency, air-powered battery developed previously by Wu and a doctoral student, Xiaodi Ren. That battery feeds power through a chemical reaction between oxygen and potassium.
"Basically, it's a breathing battery," Wu explained. "It breathes in air when it discharges, and breathes out when it charges."
That design was awarded the $100,000 clean energy prize from the U.S. Department of Energy in 2014, allowing Wu to form KAir Energy Systems LLC to develop the new technology. And that development was to combine the KAir battery with a solar panel.
Conventional solar cells, however, are made of solid panels, which keep air away from the battery. So another of Wu's doctoral students, Mingzhe Yu, developed the mesh for the hybrid, made from titanium gauze on which he managed to grow vertical rods of titanium dioxide as if they were blades of grass on a lawn. Air flows through the gauze while the rods capture the sunlight.