Elements of the smart economy – 3rd generation solar


\"GratzelEarlier articles about the “smart economy” looked at nanobiotechnology and life sciences. This article examines ways in which advanced technology might provide more efficient ways of harnessing the sun’s energy.

One of the problems with using sunlight to generate electricity is the low efficiencies achieved by photovoltaic cells. Another is the high cost of cells based on silicon technology. So a great deal of research has been directed toward finding alternatives that improve these efficiencies and reduce the costs of cell production.

One of the more promising approaches is to emulate photosynthesis, the process by which plants convert sunlight into energy. Dye Sensitised Solar Cells (DSSCs) represent such an approach to third generation solar power generation. Invented by Michael Gratzel who received the prestigious 2010 Millennium Prize for his work, these devices are known as Gratzel cells.

A refinement of the idea which enables such devices to be printed was patented by Dr Mazhar Bari in 2008. This innovation dramatically reduces the cost of manufacturing such cells and Dr Bari’s Dublin based company is working with Fiat and scientists from British and Irish universities to demonstrate a fully flexible coating capable of converting sunlight into electricity and that can be incorporated into a vehicle sun roof in order to power on-board electronics. (Fiat and R&D consortium to develop next generation solar technology to cover the surface of electric vehicles, University College Dublin press release 2 July 2010)

Whilst such devices generate electricity directly from sunlight, another important strand of development seeks to use synthetic photosynthesis to produce fuels by converting water into its component elements, oxygen and hydrogen.

Although this has been done successfully on a laboratory scale, hitherto such attempts fall short of the efficiencies necessary for practical application according to a survey undertaken by Department of Chemistry and Biochemistry and Center for Bioenergy and Photosynthesis, Arizona State University, published in November 2009. (Devens Gust, Thomas A. Moore and Ana L. Moore, Solar Fuels via Artificial Photosynthesis; Department of Chemistry and Biochemistry and Center for Bioenergy and Photosynthesis, Arizona State University, Tempe, Arizona 85287Acc. Chem. Res., 2009, 42 (12), pp 1890–1898   doi: 10.1021/ar900209b, Publication Date (Web): November 10, 2009)s

Recently a team of researchers led by the Head of the School of Physics at Trinity College Dublin and Principal Investigator at the Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN), Professor John Donegan, has discovered a way of further increasing the efficiency of synthetic photosynthesis using quantum dots and purple bacteria.

The research, which involved international collaboration with a team of Spanish, French and Russian scientists, was published in September 2010 in the leading German based chemistry journal Angewandte Chemie International and can be viewed on line.  (Nabiev, I., Rakovich, A., Sukhanova, A., Lukashev, E., Zagidullin, V., Pachenko, V., Rakovich, Y. P., Donegan, J. F., Rubin, A. B. and Govorov, A. O., Fluorescent Quantum Dots as Artificial Antennas for Enhanced Light Harvesting and Energy Transfer to Photosynthetic Reaction Centers. Angewandte Chemie International Edition, 49: 7217–7221. doi: 10.1002/anie.201003067)

Quantum dots (aka nanocrystals) are nanoscale semiconductors that behave like molecules and are capable of being manufactured with tailor made properties. The materials that the researchers used were chosen because they give off light when exposed to solar radiation, remain stable in the long term, and can absorb a broad range of sunlight. This means they are much better suited to the task than the organic dye molecules previously utilised and which have the twin disadvantages of capturing too small a range of wavelengths from sunlight and being unstable under long term exposure to solar radiation.

The term “purple bacteria” relates to bacteria that contain bacteriochlorophyl making them capable of carrying out photosynthesis without oxygen. They occur in anaerobic aquatic environments and are the active constituents in anaerobic digestion, a process used in the conversion of biological wastes into fuel.