Creating power from wasted heat

Today, about 90 percent of the world's electricity is created through an indirect and inefficient conversion of heat. It is estimated that two thirds of the heat used by thermoelectric converters are wasted and released. But now, researchers from the University of California at Berkeley have found a new way to convert this wasted heat into electricity by trapping organic molecules between metal nanoparticles. So far, this method of creating electricity creation is in its very early stage, but if it can scale up to mass production, it may lead to a new and inexpensive source of energy.

Today, about 90 percent of the world's electricity is created through an indirect and inefficient conversion of heat. It is estimated that two thirds of the heat used by thermoelectric converters are wasted and released. But now, researchers from the University of California at Berkeley have found a new way to convert this wasted heat into electricity by trapping organic molecules between metal nanoparticles. So far, this method of creating electricity creation is in its very early stage, but if it can scale up to mass production, it may lead to a new and inexpensive source of energy.

Let's start with a quote from Arunava Majumdar, , UC Berkeley professor of mechanical engineering.

"Generating 1 watt of power requires about 3 watts of heat input and involves dumping into the environment the equivalent of about 2 watts of power in the form of heat," said Arun Majumdar. "If even a fraction of the lost heat can be converted into electricity in a cost-effective manner, the impact it would have on energy can be enormous, amounting to massive savings of fuel and reductions in carbon dioxide emissions."

In the last 50 years, using this wasted heat was done with thermoelectric converters which are notoriously inefficient. So what did the UC Berkeley researchers do?

The researchers coated two gold electrodes with molecules of benzenedithiol, dibezenedithiol or tribenzenedithiol, then heated one side to create a temperature differential. For each degree Celsius of difference, the researchers measured 8.7 microvolts of electricity for benzenedithiol, 12.9 microvolts for dibezenedithiol, and 14.2 microvolts for tribenzenedithiol. The maximum temperature differential tested was 30 degrees Celsius (54 degrees Fahrenheit).

Below is a graphic showing a benzenedithiol molecule trapped between two gold surfaces. When one side is heated, a current is created. (Photo credit: Ben Utley). Here is a link to a larger version.

An organic molecule trapped between two gold surfaces

"The effect may seem quite small now, but this is a significant proof of concept, and the first step in organic molecular thermoelectricity," said Pramod Reddy, a postdoctoral researcher working with Rachel Segalman, a UC Berkeley professor of chemical engineering.] "We are going down the road of cheap thermoelectric materials."

So will this research lead to a new and inexpensive source of energy? In "Scientists Turns Heat into Electricity," Red Herring gives some additional comments (February 16, 2007).

Still, the technology is at the "science project stage," said nanotechnology consultant Scott Mize, explaining that it will likely take a while to bring the technology to market. But that's normal for the energy sector, he said. "A lot of the technology that we see today is information technology which tends to be developed very quickly, but when you’re talking about energy, it takes a lot longer to get that into the marketplace."
"What's important is that more and more companies are looking to UC Berkeley as a place where innovations happen and turn into market opportunities," said [Joel Makower, co-founder and principal of Clean Edge, a consulting firm helping companies understand the emerging clean-tech sector.]
Earlier this month, UC Berkeley received a large portion of a $500 million grant from British Petroleum (BP) for its Energy Biosciences Institute, focusing on development of biofuels and other alternative fuel sources.

Finally, this research work has been published by Science Express under the name "Thermoelectricity in Molecular Junctions" (February 15, 2007). Here is a link to the abstract.

Sources: University of California - Berkeley, February 15, 2007; and various other websites

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