There have already been successful experiments involving solar powered boats, and there have already been people sailing them in the last ten years. Still, all of them have something in common: they use photovoltaic cells as an intermediate between the sunlight the mechanical work.
MIT’s Technology Review reports recent research carried out at the University of California, Berkeley, has revealed that solar power can also be used in other ways than that of photovoltaic cells.
Alex Zettl, professor of condensed-matter physics, and Jean M.J. Fréchet, professor of chemistry and chemical engineering, designed a special clear plastic mini-boat, having about a centimeter in length, and being directly propelled by sunlight, without any intermediate.
This boat has embedded strips of vertically aligned carbon nanotubes. These carbon nanotubes have the property that when the light from the sun or a laser is focused on the mini-boat, they absorb the heat and heat the water around them, causing a decrease in water surface tension located on one side of the boat, which propels the boat forward away from the low-tension part of the surface. Thus, the boat performs a linear motion of about eight centimeters/second.
The scientists have demonstrated another machine: a simple rotor with one nanotube strip on one side of each of its four fins. When exposed to direct sunlight, it spins at about 70 rotations per minute. Both machines have only been tested in containers in the lab.
In theory, these micromachines are interesting, but they need further testing in real-life conditions. Berkeley has already thought of scaling these experimental toys, and make a light focusing system that would directly propel the boat. “We think we’re on to something because surface tension is very powerful[…] This could be very efficient because nanotubes absorb light so well, but we have to see if this is a viable thermodynamic system,” says Zettl. You can watch a short video on these devices here.