Batteries are a distraction: the best way to store excess solar energy for nighttime use is using it to create "solar fuels" that rely on energy-dense chemistry, one research team has concluded. The prototype takes a cue from plants and uses a new type of solar cell that relies on the sun's energy to split water into hydrogen and oxygen. The latter is released, but the former can be stored and then later used for power, including potential in fuel-cell cars. Best of all, the system requires no external power source in order to work its hydrogen-generating magic.
That all takes place in a dye-sensitized photoelectrosynthesis cell (DSPEC), developed by a team led by Tom Meyer of the Energy Frontier Research Center at UNC-Chapel Hill. It's the product of many years development, however, since water is reluctant to be broken down.
Meyer's core design is a chromophore-catalyst assembly, which absorbs sunlight and uses the energy in it to trigger a catalyst that separates electrons from water. Meanwhile, a nanoparticle sheet - with thousands of chromophore-catalyst assemblies - is used to move the electrons away, leaving the process to make hydrogen fuel.
The tipping point was a nanoparticle coating of titanium dioxide, which accelerates the rate at which electrons can be carried away. Meanwhile, a protective coating to the chromophore-catalyst keeps it more effectively tethered to the nanoparticle, addressing issues with keeping the layers attached.
According to Meyer, while the technology may sound complex, it's actually based for the most part on existing technology, and is far more feasible than the idea of turning solar energy into electricity and then trying to stockpile that in huge battery arrays. As the project lead says, "the most energy dense way to store energy is in the chemical bonds of molecules."
Next up is a tweak to the system that will hopefully allow carbon dioxide to be converted in a similar manner to formate or methanol, which can also be used as fuels. That would simultaneously have the benefit of reducing the greenhouse gas and producing more oxygen.
Exactly when we might see production versions is unclear, though the team has to improve the efficiency of the system first. Right now, it generates the equivalent energy in hydrogen form as around 1-percent of the energy in the "raw" sunlight, though Meyer believes increasing that to 15-percent - around what the average solar panel achieves - is possible.