Energy researchers look to a bright future
Whether it is paint that converts sunlight to energy, or new ways of printing circuits onto plastic film, new research promises to make solar energy cheaper. Lou Reade reports
The need for sustainable energy – as a long-term replacement for fossil fuels – has been brought into sharp focus by the ever-rising cost of oil.
But while techniques exist to harness power from just about everything – wind, sun, tidal currents – this still accounts for a tiny proportion of energy needs, and is relatively expensive.
Solar energy is a case in point. It has traditionally relied on silicon technology to convert sunlight into electricity. But many researchers are looking into new, and potentially cheaper ways of harnessing the sun’s power.
The technique, dubbed Dye Sensitised Solar Cells (DSSCs) relies on a mixture of chemical ‘dyes’ – which are highly sensitive to light and will generate a current if exposed to it. Researchers as far apart as the UK, Netherlands, US and Australia are working to improve this technique – which could work out substantially cheaper than silicon-based technology.
One of the more intriguing suggestions is from researchers at Swansea University, who say they may be able to develop a ‘solar paint’ – which, when painted onto metal surfaces such as cladding, will be able to generate electricity.
“One of our doctorate students was researching how sunlight interacts with paint and degrades it – which led to us developing a new photovoltaic method of capturing solar energy,” says Dave Worsley, a reader in the Materials Research Centre in the University’s school of engineering.
The university has worked with the steel industry for decades, but its researches have focused on improving the material’s durability and corrosion resistance.
“We haven’t really paid much attention to how we can make the outside of the steel capable of doing something other than looking good,” he says.
Now, in conjunction with three other universities – Bangor, Bath and Imperial College – he will lead an effort to develop commercially viable photovoltaic materials that could be used by the steel industry. The project has attracted a £1.5m grant from Engineering and Physical Sciences Research Council.
When steel cladding is manufactured, it is passed through rollers in order to apply paint. If the project can develop a commercial way of applying the ‘solar paint’ to the cladding, it would give manufacturers – such as Corus Colours – an enormous ‘added value’.
Corus Colours produces around 100 million square metres of steel building cladding each year. If it were all treated with photovoltaic material – and had an energy conversion rate of just 5% – it would generate 4,500 gigawatts of electricity annually.
The materials being developed at Swansea claim to be more efficient at capturing low light radiation – so should be better suited to the British climate. The researchers will work closely with Corus to look at practical ways of applying the paint to the surfaces, at a rate of 30-40 square metres per minute.
Another key collaborator in the project is Australian technology company Dyesol, whose Dye Solar Cell (DSC) technology is at the heart of the technique. It has been working with Corus since 2006 on the ‘cladding’ project. Its expertise lies in the actual conversion of the sunlight to electricity, while Swansea’s is in marrying the coating with the steel substrate.
Dyesol describes its technique as ‘artificial photosynthesis’ – and claims it is far cheaper than conventional solar cells. According to Dyesol: “DSC thrives in variable light conditions. The low light performance of DSC is a very important attribute because – unlike conventional solar cells – it does not need direct solar radiation hitting its surface to produce electricity.”
By combining different dyes in the same cell, the Dyesol team – led by Hans Desilvestro and Ravi Harikisun – is able to capture a far broader spectrum of light.
This arrangement is also known as a Graetzel cell – and its originator, Michael Graetzel, is still working to perfect the technique. He leads a research group at the Swiss Federal Institute of Technology in Lausanne and has recently developed new sensitisers that should make this type of solar cell even more efficient.
The DSSC – or Graetzel cell – is based on a layer of titanium oxide particles covered with a sensitising dye. When sunlight shines onto the cell, electrons move from the dye and onto a ‘conducting band’, and are carried away by an external circuit. The trick is to prevent these electrons from recombining with the oxidised dye. This is achieved by holding it all in an electrolyte solution, whose negatively charged ions prevent the recombination.
Graetzel and his team have optimised the sensitiser – using a dye based on indoline – which allows the titanium dioxide layer to be thinner. This reduces the electron path length, boosting the efficiency to above 7%, which the team claims is a record for this type of device.
Meanwhile, researchers at the University of Washington have used molecular design to boost the efficiency of DSSCs. Using what it calls ‘popcorn ball design’, the team has developed a set of tiny ‘kernels’ that lead to a boost in efficiency – which was 2.4% using only small particles, but rose to 6.2% with the new ‘popcorn’ design.
The experiment was carried out using zinc oxide, and the researchers hope to transfer the concept to titanium dioxide – which gives far more efficient DSSCs.
And the breadth of interest in alternative solar cells continues. Earlier this year, US-based Konarka Technologies announced that it had produced plastics-based solar cells using inkjet printing.
“Demonstrating the use of inkjet printing as a fabrication tool for solar cells and sensors with small area requirements is a major milestone,” said Rick Hess, president and CEO of Konarka. The technology is based on its Power Plastic, which converts light into energy.
Back in Wales, work continues on developing a process that could coat all Corus cladding products in solar paint – and generate 4,500 gigawatts of electricity each year.
“That’s the equivalent output of roughly 50 wind farms,” says Dave Worsley.
It seems that solar energy researchers are not content with making cheaper solar cells – now they want to develop alternatives to alternative energy sources.
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