Researchers seek inexpensive, efficient ways to capture sun's energy (9/11/2007)

Sunkara believes tree-like networks of nanowires could lead to improved solar technologies.

Every minute, the Earth receives more energy from the sun than people burn up in fossil fuels in a full year. Virtually all of that free light and heat energy is unused, wasted.

Mahendra Sunkara envisions technologies that could change that.

A professor of chemical engineering in the University of Louisville's J.B. Speed School of Engineering, Sunkara directs UofL's new federally funded Institute for Advanced Materials and Renewable Energy.

Researchers at the institute include faculty and students from Speed School, the College of Arts and Sciences and the University of Kentucky. They study new materials and processes that could cheaply and efficiently convert solar and other energy into usable power.

The institute has three ambitious goals: to find ways to convert sunlight into energy; to use light to convert water to hydrogen; and to convert heat into electricity.

The eventual result could be houses covered in solar-power-converting sheets, color coordinated to blend in with a home's exterior look; hydrogen-powered cars their drivers fill with hydrogen made from water via solar technology; or hot equipment inside power plants covered in sheets of special materials that absorb heat and convert it into additional electricity.

Those scenarios may be a long way off, but Sunkara said he and colleagues already have developed promising nanomaterials (constructed on scales as small as individual atoms and molecules) that could help ease what some see as a looming power crisis.

Most people are familiar with a watt of power, which in its most basic terms is the amount of energy expended by a single candle. A household incandescent light bulb might use 60 watts - even 100.

"The entire world energy requirement right now is between 10 and 20 terawatts a year, (a terawatt is 1 trillion watts)" he said. "Those are staggering numbers, but they're not even close to what the sun produces. And world energy needs are expected to triple in 20 years or so."

Despite its promise as a clean, non-carbon energy source, solar power will remain a fringe alternative unless the inefficiency of current solar-conversion technology can be overcome, he said.

The Search for Materials

Sunkara's search for the most stable and efficient energy-converting materials is not unlike Thomas Edison's hunt for the right filament for the light bulb.

Take the challenge of using light energy to convert water into hydrogen as an example. So far, materials placed in water to perform energy conversion haven't fared well.

"Most of the materials we know of corrode in water; they can't absorb light and still be stable during photolysis of water," Sunkara explained. "So what we want is a material that is stable, can absorb visible light and can allow this water splitting to happen. By stability, we mean something that holds up for at least a few days to start off with, and eventually something that can last a few years."

It is possible, he continued, to create new alloys to do the job by modifying the composition of nanoscale-materials.

Another challenge is to create thin sheets of densely packed solar-converting devices that can cover large areas. Sunkara believes his years of research growing vast, tree-like networks of nanowires on thin films could lead to such improved solar technologies.

"What's great about this interdisciplinary group of scientists is that it consists of experts who have already developed some new materials or new processes," Sunkara said, "and they're taking us into some new directions where we can actually develop new materials. That's the point of this effort."

Note: This story has been adapted from a news release issued by the University of Louisville

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