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Solar Cells Improved By Graphite Nanoparticles

Mechanical engineers at Arizona State University hope to boost the efficiency and profitability of solar power plants using graphite nanoparticles, according to a new study published recently in the Journal of Renewable and Sustainable Energy (3, 2011).

Photovoltaic (PV) solar panels are popping up more and more on rooftops, but they're not necessarily the best solar power solution. "The big limitation of PV panels is that they can use only a fraction of the sunlight that hits them, and the rest just turns into heat, which actually hurts the performance of the panels," explains Robert Taylor, a graduate student in mechanical engineering at the university and one of the authors.

An alternative that can make use of all of the sunlight, including light PVs can't use, is the solar thermal collector. The purpose of these collectors -- which take the form of dishes, panels, evacuated tubes, towers, and more -- is to collect heat that can then be used to boil water to make steam, for example, which drives a turbine to create electricity.

To further increase the efficiency of solar collectors, Taylor and his colleagues have mixed nanoparticles -- particles a billionth of a meter in size -- into the heat-transfer oils normally used in solar thermal power plants. The researchers chose graphite nanoparticles that are 1000 times smaller than the width of a human hair, in part because they are black and therefore absorb light very well, making them efficient heat collectors.

In laboratory tests with small dish collectors, the researchers found that these nanoparticles increased heat-collection efficiency by up to 10 percent. This is actually much profitable: "We estimate that this could mean up to $3.5 million dollars per year more revenue for a 100 megawatt solar power plant," Taylor says. 

What's more, graphite nanoparticles "are cheap" -- less than $1 per gram -- but with 100 grams of nanoparticles providing the same heat-collecting surface area as an entire football field, Taylor adds. An additional positive aspect to this invention is environmental: "It might also be possible to filter out nanoparticles of soot, from coal power plants for use in solar systems," he says. "I think that idea is particularly attractive: using a pollutant to harvest clean, green solar energy."