Carbon Sponge Converts Solar Energy into Steam

Wednesday, August 13th, 2014
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A new material developed by engineers from MIT is capable of generating steam following exposure to sunlight with far greater efficiency than rival approaches.

The material is a thin, porous structure comprised of a layer of graphite flakes on top of a carbon foam base, which floats upon an underlying body of water.

The top layer is rendered highly porous by exfoliating the material in a microwave. This results in a nest of flakes which are capable of better absorbing and retaining solar energy.

The bottom layer of carbon foam contains pockets of air which keep the structure afloat and prevent heat from being ceded to the body of water beneath it. It is also riddled with tiny pores that permit water to rise through it by means of the capillary principle.

When solar radiation strikes the surface of the material, it generates heat in the top layer of graphite. This heat draws water up through the pores of the material, which is then emitted from its uppermost surface in the form of steam.

The new material marks a major advance upon other forms of sun-powered steam generation in terms of efficiency, and in laboratory tests has proved capable of converting 85 per cent of the solar energy it receives into steam. The method also produces steam at a solar intensity around 10 times that of a sunny day, which is the lowest optical concentration on record.

Hadi Ghasemi

Hadi Ghasemi

The high efficiency of the material should dispense with the need for elaborate and expensive systems for concentrating sunlight to raise the amount of solar radiation harvested.

“This is a huge advantage in cost-reduction,” said Hadi Ghasemi, a postdoc from MIT’s Department of Mechanical Engineering who led the research team that developed the material. “That’s exciting for us because we’ve come up with a new approach to solar steam generation.”

The material itself should also come at a relatively low cost, given that it can be manufactured from inexpensive and commonplace materials.

According to Ghasemi, the material should have a broad range of applications, particularly for remote, sun-parched areas.

“Steam is important for desalination, hygiene systems, and sterilisation,” he said. “Especially in remote areas where the sun is the only source of energy, if you can generate steam with solar energy, it would be very useful.”

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