Passive solar heat device could be hygiene boon in remote regions

Hygiene is a persistent problem in remote regions of poorer countries. Medical facilities require sterilisation, and clean drinking water is often in short supply. A device developed by MIT engineers has the potential to provide both, using only the sun as a power source.

Led by mechanical engineer Thomas Cooper, the researchers report their results in Nature Communications. Their device is a development of previous research which resulted in a foamed graphite material that could turn water it absorbed into steam. Concerns over degradation of material caused by impurities in the water led Cooper to develop the system further, and he and his colleagues have now incorporated it into a device that can be suspended over a container of water, left in sunshine, and will generate superheated steam above 100°C. "It's a completely passive system - you just leave it outside to absorb sunlight," Cooper said.

The device is a flat tile about the size of a small tablet computer. It consists of three layers. The top layer is a metal-ceramic composite that is highly efficient at absorbing solar radiation. The bottom layer is perforated aluminium, painted with a coating that efficiently emits infrared energy. Sandwiched between these is a layer of reticulated carbon foam, a form of graphite riddled with a network of winding tunnels and pores. This is suspended above a container of water so that the lower layer is not in contact with the liquid.