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UNC Breakthrough: Harnessing Solar Energy For Use At Night

By Rachel Nash Posted January 14, 2014 at 5:23 pm

CHAPEL HILL - UNC researchers have taken a cue from plants, finding a way to capture the sun’s energy during the day for use at night. It’s a system that converts the sun’s energy into hydrogen fuel, rather than electricity, so that it can be stored, allowing us to draw power long after the sun sets.

Tom Meyer, an Arey Distinguished Professor of Chemistry in UNC’s College of Arts and Sciences, led a team of researchers at the UNC Energy Frontier Research Center to develop the system which mimics natural photosynthesis.

“A lot of these energy systems with battery storage are fine, but if you are talking about making the sun a primary energy source—say it accounts for 50 percent of our energy needs—then you ask the question, ‘Where are you going to store the energy?’ It is staggering. There is no answer to that. Then the nighttime dilemma becomes really, really important,” Meyer said.

The process uses a device called a dye-sensitized photoelectrosynthesis cell (DSPEC).

The device, a dye-sensitized photoelectrosynthesis cell

The device, a dye-sensitized photoelectrosynthesis cell

The goal of the process is to produce solar fuel, which is high-energy molecules, like carbohydrates or hydrogen, with the energy of the sun stored in chemical bonds.

The hydrogen fuel product is generated by the DSPEC using the sun’s energy to split water into its component parts. After the split, hydrogen is sequestered and stored, while the by-product, oxygen, is released into the air, as explained here.

“The key to it is that it represents this most recent observation we made—a breakthrough. This plan where you combine molecules and semi-conductors, now you can see it is actually feasible. This was the last piece of a 40-year-old puzzle,” Meyer said.

Solar energy is one of the most popular methods of renewable energy.

The more commonly used photovoltaic cells are placed on rooftops and are used to generate electrical power by converting solar radiation into direct current electricity, but are dependent on the sun’s rays.

“What we have done is to develop a new way to do solar energy conversion, a really important problem. As time passes, with photovoltaic devices, we [will] see more and more solar panels, and they are great. The trouble is when the sun goes down, at night—you are stuck,” Meyer said.

This research breakthrough comes at a pivotal time for solar and other forms of renewable energy.

In 2013, the International Energy Agency (IEA) predicted that renewable power production, including solar, wind, and water, will top the production of gas and nuclear energy combined by 2016. Renewable energy is projected to deliver almost 25 percent of the world’s total energy by 2018.

“We want to find ways to use the sun and convert things that are readily accessible like water and carbon dioxide and turn them into fuels that people can use later.”

Meyer, courtesy UNC

Meyer, courtesy UNC

Meyer, who has been researching the sun energy to hydrogen fuel conversion possibility since the 1970s, said these are very early days in terms of where this research could go.

“Typically when a discovery like this is made, if it has the ability to make economic sense, it takes at least 10 or 15 years to get to the point where there is a technology that people are willing to use and put out into the field.”

The challenge at this point, Meyer explained, is that after the process is complete, the fraction of the solar energy that is harnessed is very small—less than 1 percent.

The research will now focus on adjusting and perfecting the process. Meyers said he hopes to one day be able to harness 10-15 percent of the energy captured. At that point, he said it could become economically viable.

In one hour, the sun puts out enough energy to power every vehicle, factory and device on the planet for an entire year, according to a news release on UNC’s website.

“So if it pays out and actually down the road does become economically viable, the University has a stake in the intellectual property through patents and stuff like that so it can also benefit financially if something actually came of it.”

This system was designed with help from Meyer’s colleagues at UNC and fellow researcher Greg Parsons and his team at North Carolina State University. The program began in 2009 with federal funding support.

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