Friday, February 17, 2012

Idea could lead to cheap solar cells using plant waste

Grass clippings
Any waste vegetation can be used — even grass clippings
Flickr/Caro's Lines

Remote communities could eventually make their own solar cells using waste vegetation, thanks to a design developed by researchers in Switzerland and the United States.
The technology is inspired by photosynthesis. In plant cells, sunlight separates electrical charges with almost 100 per cent efficiency.
Electrical charges must also be separated to create currents in solar cells. For the past decade, researchers have attempted to make solar cells by extracting some of the molecules responsible for photosynthesis — known as photosystem-I (PS-I) — from plants to produce an electric current when exposed to light.
Earlier devices failed to generate much electricity. But a team led by Andreas Mershin at Massachusetts Institute of Technology, United States, now claims to have found a solution so simple it can be replicated in any lab.  
They have found a way of exposing more of the cell to the sun by creating a three-dimensional miniature 'forest' of zinc oxide nanowires and titanium dioxide sponges on a layer of glass, coated with PS-I, that absorbs any sunlight filtering down onto the surface from above and turns it into electricity. Previous versions of the cell, by other researchers, were flat.
The new experimental solar cell converts 0.1 per cent of incoming sunlight's energy to electricity. This is still short of the 1.0 per cent conversion rate it needs to be practical — but 10,000 times more than any previous cell of this sort.
Mershin hopes that, in a few years, rural communities would be able to mix waste vegetation — even grass clippings — into a bag containing the zinc and titanium, and paint the mixture onto their roofs to start generating electricity.
"All the major discoveries have now been made," he told SciDev.Net.
"We hope that other groups around the world can now replicate what we've done and optimise the techniques — and that is why we have published our findings in an open-access journal."
Devens Gust, director of the Arizona State University Center for Bio-Inspired Solar Fuel Production in the United States, said: "The advance here is devising a relatively simple method for preparing photovoltaic cells with significant light absorption for laboratory study using this material."
But Frederik Krebs of the Risø National Laboratory for Sustainable Energy in Denmark, who has experience of deploying organic solar cells in Africa, is more cautious.
"There is a very long way from a laboratory vision to a real live application to real live people having no knowledge of [the technology]," he said. He is also concerned that the sun could damage the organic material .
The research was published in Scientific Reports earlier this month (2 February).

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