Turning Sunlight into Steam
Steam is useful for a huge number of purposes ranging from running steam engines to sterilising medical instruments, but producing it uses a huge amount of energy. This is particularly a problem if you only want a small amount of steam, as most of the energy you use goes into heating the water before it becomes steam.
Naomi Halas and collegues at the Rice Quantum Institute, Rice University have been improving the efficiency of this process, using a principle first used by Stevenson in his Rocket steam engine. Stevenson did it by sending the gasses from his fire through small pipes, dramatically increasing the surface area of the heater. Publishing in the journal ACS Nano, Halas et al have done it by spreading metallic nano-particles, each about a 20,000th of a mm across, throughout the water. This creates an enormous surface area and can absorb light very effectively. If you then focus sunlight onto the water the energy is absorbed by the particles and transferred to the water very quickly.
Even without optimisation, about 24% of the energy goes directly into producing steam. This means that they can even produce steam directly from ice water.
The first place this could be used is for sterilising instruments in the third world, but it could be generalised to wherever there is plenty of sunlight and a requirement for steam.