Graphite “Sponge” Sops Up Sunlight, Blows Off Steam

By: | September 5th, 2014

If MIT’s latest simulation can be extrapolated to a larger scale, then solar generation just gained new steam. As we recently reported here on IndustryTap, researchers at MIT have developed a super-efficient, solar steam-generating graphite “sponge” structure. They contend that 85% of the solar input is converted to steam and that the heat loss is minimal. This discovery especially holds promise for such uses as hygienic sterilization and desalination.

The concept is fairly simple. It is difficult to heat a large mass of deep water, using only the sun’s energy, sufficiently enough to generate steam. But if you had a constant source of water that could be capillaried through a black porous material, the sun’s energy would focus on the black “sponge” and heat that water to the point of steam more easily. And if you add a layer of foam insulation under the black sponge, the sopped up water is separated from the cooler source water so that the sun is only heating the water that is absorbed. The researchers say that this concentrated solar steam generation maximizes collection efficiency by a factor of “10 times the intensity of a sunny day.”

The more complex version is that the MIT researchers came up with a method of creating a “super porous” graphite “sponge” by heating the material in a microwave, causing it to swell and flake, thus its ability to absorb more liquid to be heated at the surface. The black color of the graphite top layer is Solar Energy 101 (dark colors absorb, light colors reflect). The layer under the graphite disc is a carbon foam that provides buoyancy for the graphite disc and insulation from the larger volume of water under the two hydrophilic layers.  When the sunlight hits the black graphite top layer, it creates steam while creating a pressure differential that allows the evaporated water to be replaced by capillary action through the two porous discs.

There is a need for small scale solar steam generation in areas that have insufficient infrastructure. Current generation methods are a large scale, complex activity requiring massive equipment. They generally use mirrors to focus the sun’s energy onto a central tower that produces steam to turn into electricity. Aside from the huge material investment required, conventional steam generators suffer from inefficiency due to heat loss. This solar sponge method improves on efficiency when steam is all that is desired, not electricity.

This is an early stage discovery that requires much more testing of various sizes and materials to determine all the uses that it can offer. But we can already be hopeful that some current social and environmental problems can be diminished if not alleviated.

Imagine a compact and affordable option for sterilization of medical equipment and hygienic cleaning as we see super bugs emerge in hospitals and viruses with no cure. Imagine a larger scale possibility of desalination at coastal deserts, like California, whose drought has reached record levels. Potable water is a major issue of our times and of our future. The lower cost and greater accessibility of the graphite sponge may prove to be its most valuable features. This discovery holds promise of ongoing development on many levels and ameliorates pending disasters in a host of realms. We should keep a close watch on this one; it has great potential.

Carol Mosley is a social ecologist, freelance writer, human rights activist, mini-farmer, and educator.

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