Graphite popcorn could boost solar steam generation

By Laura Syrett
Published: Wednesday, 06 August 2014

A new system for creating solar steam developed by scientists at MIT could prove a cheaper and more efficient way of desalinating water and sterilising equipment, as well as providing a new end market for graphite.

A graphite-based heat concentration system could drastically improve energy generated from solar steam, scientists at the Massachusetts Institute of Technology ( MIT) have discovered.

Current solar steam generation systems rely on large fields of mirrors
to concentrate sunlight, but a new graphite-based method developed by
MIT could significantly cut costs and improve efficiency (source: Activ Solar). 

According to the research published in the journal Nature Communications, the new method involves heating graphite in a microwave to create a “popcorn” of exfoliated graphite flakes.

This is placed over a layer of porous graphite “foam”, which is floated on top of water that is then heated by sunlight to create steam that evaporates through the graphite.

The steam can be used for a variety of applications including desalination, hygiene systems and sterilisation.

The experiments to develop the new system were led by Hadi Ghasemi, a postdoctoral researcher in MIT’s department of mechanical engineering, along with the department’s head, professor Gang Chen.

Advantages of the graphite-based approach include the low cost of the graphite material, and, more importantly, its ability to convert 85% of incoming solar energy into steam – a marked improvement over existing solar steam generators.

Current systems for generating solar steam rely on large fields of mirrors or lenses to concentrate sunlight in order to heat large volumes of liquid. Such systems are costly and can be inefficient as significant amounts of heat may be lost during the process.

The MIT team’s findings show that by using graphite, which is both hydrophilic and thermally insulating, heat is concentrated into a hotspot to raise the temperature of the water and yield steam at a solar intensity of around 10 times that of an average sunny day.

“This is a huge advantage in cost reduction,” Ghasemi told MIT News, adding that this approach is likely to prove “especially useful in remote areas where the sun is the only source of energy.”

While graphite has proved a successful candidate for MIT’s initial published research in this area, Ghasemi believes that the system can be designed to be even more efficient by using different combinations of materials.

“There can be different combinations of materials that can be used in these two layers that can lead to higher efficiencies at lower concentrations,” he said. “There is still a lot of research that can be done on implementing this in larger systems.”

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