Solar panels light the way from carbon dioxide to fuel

July 1, 2014

Research to curb global warming caused by rising levels of atmospheric greenhouse gases, such as carbon dioxide, usually involves three areas: Developing alternative energy sources, capturing and storing greenhouse gases, and repurposing excess greenhouse gases. Drawing on two of these approaches, researchers in the laboratory of Andrew Bocarsly, a Princeton professor of chemistry, collaborated with start-up company Liquid Light Inc. of Monmouth Junction, N.J. to devise an efficient method for harnessing sunlight to convert carbon dioxide into a potential alternative fuel known as formic acid. The study was published June 13 in the Journal of CO2 Utilization.

The transformation from and water to was powered by a commercial solar panel generously provided by the energy company PSE&G that can be found atop electric poles across the state. The process takes place inside an electrochemical cell, which consists of metal plates the size of rectangular lunch-boxes that enclose liquid-carrying channels.

To maximize the efficiency of the system, the amount of power produced by the solar panel must match the amount of power the electrochemical cell can handle, said Bocarsly. This optimization process is called impedance matching. By stacking three electrochemical cells together, the research team was able to reach almost 2 percent energy efficiency, which is twice the efficiency of natural photosynthesis. It is also the best energy efficiency reported to date using a man-made device.

A number of energy companies are interested in storing solar energy as formic acid in fuel cells. Additionally, formate salt—readily made from formic acid—is the preferred de-icing agent on airplane runways because it is less corrosive to planes and safer for the environment than chloride salts. With increased availability, formate salts could supplant more harmful salts in widespread use.

Using waste carbon dioxide and easily obtained machined parts, this approach offers a promising route to a renewable fuel, Bocarsly said.

Explore further: Modified microbes turn carbon dioxide to liquid fuel

More information: White, J. L.; Herb, J. T.; Kaczur, J. J.; Majsztrik, P. W.; Bocarsly, A. B. "Photons to formate: Efficient electrochemical solar energy conversion via reduction of carbon dioxide." Journal of CO2 Utilization. Available online June 13, 2014.

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Eikka
not rated yet Jul 01, 2014
To maximize the efficiency of the system, the amount of power produced by the solar panel must match the amount of power the electrochemical cell can handle, said Bocarsly. This optimization process is called impedance matching.


Impedance matching means literally matching the impedance (resistive and reactive) of the devices. It has nothing to do with the amount of power the system can handle, because it's about maximizing transport efficiency of power.

As a simple example, suppose you have an amplifier with an output impedance of 8 Ohms and a loudspeaker with an input impedance of 80 Ohms. You can match the impedances with a 1:10 audio transformer to get the best transfer efficiency out of the system. The fact that the amplifier is rated at 100 Watts and the speaker at 50W, or vice versa, has absolutely no bearing on the matter.

For a solar panel, an MPPT controller does the impedance matching by decoupling the output voltage and current from the source.
11791
Jul 01, 2014
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