Researchers from MIT built a device that boils water using solar energy to produce superheated steam
A team led by Gang Chen, the Carl Richard Soderberg Professor of Power Engineering at MIT, in 2014, reported the first demonstration of a simple solar-powered steam generator that was in the form of a graphite-covered carbon foam that floats on water. The structure can absorb and localize sunlight to the water’s surface. Earlier devices designed by the team floated directly on water, which caused the problem of contamination as the surfaces came in contact with salt and other impurities in water. In the current research, the team designed a device that is suspended above water and is structured to absorb short-wavelength solar energy. This helps to heat up the device and the device reradiates this heat to the water below in the form of longer-wavelength infrared radiation. The team also found that water more readily absorbs infrared wavelengths as compared to solar wavelengths.
The device’s top layer was made of a metal ceramic composite that is a highly efficient solar absorber. The bottom layer of the structure was coated with a material that easily and efficiently emits infrared heat. A layer of reticulated carbon foam was placed between these two materials. The foam is a sponge-like material covered with winding tunnels and pores, which helps to retain the sun’s incoming heat and can further heat up the steam that rises back up through the foam. A small outlet tube was also attached to one end of the foam that allowed the steam to exit and to be easily collected. The device was placed over a basin of water and the entire setup was surrounded with a polymer enclosure to prevent heat from escaping.
The team performed experiments in the lab to initially test the structure. The experiments included the use of a solar simulator that mimics the characteristics of natural sunlight at varying, controlled intensities. The team found that the structure was capable of heating a small basin of water to the boiling point to generate superheated steam at 122 degree Celsius. The team later increased the solar intensity by 1.7 times and found the device generated even hotter steam at 144 degree Celsius. The research was published in the journal Nature Communications on December 11, 2018.