A passive solar system engineered at MIT could improve capacity to purify potable water or sterilize medical equipment in remote regions. The equipment is simply left outside to absorb solar radiation and generate During tests at MIT, the suspended solar heating device generated steam at 146°C and converted seawater into clean drinking water. Source: MITsuperheated steam above 100° C for these and other applications.

A previously developed system that used a foamed graphite material to convert absorbed water into steam experienced component degradation due to impurities in the water. The revised design suspends the two-layer device above a container of water to prevent contact with the liquid and potential fouling by salts and other impurities.

Efficient solar heat absorption is effected by a top metal-ceramic composite layer, and heat is transmitted to the water receptacle below by the perforated, coated aluminum bottom layer. The steam produced is captured by porous graphite foam encased between the two layers, after which superheated steam is directed through a tube to be used directly or condensed into purified water.

Researchers tested the non-pressurized system outdoors with the addition of a curved mirror to concentrate incident radiation onto the top layer. The device produced steam at 146° C in less than four hours and was also demonstrated to resist degradation when used on a container of seawater.

The research is published in Nature Communications.