Bright sparks find more zing in the sun’s glow
Richard Macey, May 15, 2007
Source: Sydney Morning Herald
http://www.smh.com.au/news/environment/bright-sparks-find-more-zing-in-the-suns-glow/2007/05/14/1178995079845.html
It is believed that no more than 30,000 Australian homes – a small fraction of 1 per cent – are generating electricity from rooftop solar panels. The problem is the cost. The University of NSW says home owners can spend up to $20,000 installing 10 square metres of panels – enough to generate about two kilowatts of energy – to power lights, a refrigerator and most small electrical appliances, but not the stove or the hot-water system.
Last week’s federal budget doubled to $8000 the maximum rebate available to people who install photovoltaic solar panels, but the technology remains expensive. Up to 45 per cent of the cost of manufacturing a solar cell is invested in its silicon, an element that absorbs the sun’s energy.
Conventional panel modules are made of “wafers” of silicon about 300 microns thick – about the width of three human hairs. That may not sound like much, says Supriya Pillai, from the university’s Australian Research Council Photovoltaics Centre of Excellence, but silicon, despite being the second most common element in the Earth’s crust, is not cheap.
“Silicon is commonly used in micro-electronics and integrated chips,” says Pillai. While a microchip uses only a tiny speck of silicon, “in solar modules you are talking in terms of square metres. Due to the high demand for solar-grade silicon, prices have gone up”.
The amount used in a solar panel could be reduced by employing far more efficient energy-absorbing materials, such as gallium arsenide.
“Gallium arsenide is very expensive and is mostly used in space applications,” says Pillai.
Although far less efficient, “silicon is readily available, non-toxic and it has been an established technology for a long time”.
In an attempt to bring down the cost of solar technology, researchers are now seeking to develop “thin-film” silicon just 1.5 to two microns thick.
Of course, there is a catch. The best wafer modules convert about 20 per cent of the sunlight falling on the panels into electricity. The thin film is only 8 per cent to 10 per cent efficient and would need to cover twice as much roof area to make up the difference.
The university team believes it can do better. “We might be able to produce 13 to 15 per cent efficiency,” says Pillai.
To achieve the improvement the team has found a way to boost the energy-trapping ability of the silicon by coating it with silver nanoparticles. “It’s not a uniform layer of silver but more like metal blobs, or ‘islands’, sitting on it,” says Pillai. Each “island”, just 100 nanometres across, “scatters light into the silicon”.
The University of NSW researchers have estimated that thin-film technology could trim $5000 off the price of rooftop solar electric panels.
After installing energy-efficient lights and appliances, Pillai says, home owners with photovoltaic systems can sell any surplus power generated by their system back to the grid, adding to their savings.