anyuser
26-07-2009, 08:53 AM
Solar energy in Israel It's a knockout (http://www.economist.com/sciencetechnology/displaystory.cfm?story_id=14082027)
Two novel approaches to making electricity from sunlight
ISRAEL is a country with plenty of sunshine, lots of sand and quite a few clever physicists and chemists. Put these together—having first extracted the oxygen from the sand, to leave pure silicon—and you have the ingredients for an innovative solar-power industry. Shining sunlight onto silicon is the most direct way of turning it into electricity (the light knocks electrons free from the silicon atoms), but it is also the most expensive. The scientists are what you need to make the process cheaper. And that is what two small companies based in Jerusalem are trying, in different ways, to do.
The physicists and chemists at GreenSun Energy, led by Renata Reisfeld, think the way is to use less silicon. Traditional solar cells are made of thin sheets of the element covered by glass plates. In GreenSun’s cells, though, only the outer edges of the glass plates are covered by silicon, in the form of thin strips. The trick is to get the light falling on the glass to diffuse sideways to the edges, so that the silicon can turn it into electricity. Dr Reisfeld’s team do this by coating the glass with a combination of dyes and sprinkling it with nanoparticles of a metal whose nature they are not yet willing to disclose.
Depth of field
The dyes are there to absorb the incident sunlight (a mixture is used in order to capture all parts of the spectrum). The role of the metal, though, is more subtle. The dyes in question are fluorescent—having absorbed the light, they re-radiate it. Normally, that would mean it was lost. But interaction with the nanoparticles turns it into a form of electromagnetic radiation called surface plasmons. These, as their name suggests, propagate over the surface of the glass until they are intercepted by the silicon at its edges.
Not only does all this make GreenSun’s cells cheaper than conventional ones, because they use so much less silicon; it also makes them better. In a conventional solar cell much of the energy is lost. The energy of light varies across the spectrum (blue light is more energetic than red) but only a certain amount of energy is needed to knock an electron free. If the incident light is more energetic than necessary, the surplus disappears as heat. Unlike the sun, which scatters its energy across the board, the dye/nanoparticle mix delivers plasmons of the right energy to knock electrons free without waste.
cont: Solar energy in Israel It's a knockout (http://www.economist.com/sciencetechnology/displaystory.cfm?story_id=14082027)
Two novel approaches to making electricity from sunlight
ISRAEL is a country with plenty of sunshine, lots of sand and quite a few clever physicists and chemists. Put these together—having first extracted the oxygen from the sand, to leave pure silicon—and you have the ingredients for an innovative solar-power industry. Shining sunlight onto silicon is the most direct way of turning it into electricity (the light knocks electrons free from the silicon atoms), but it is also the most expensive. The scientists are what you need to make the process cheaper. And that is what two small companies based in Jerusalem are trying, in different ways, to do.
The physicists and chemists at GreenSun Energy, led by Renata Reisfeld, think the way is to use less silicon. Traditional solar cells are made of thin sheets of the element covered by glass plates. In GreenSun’s cells, though, only the outer edges of the glass plates are covered by silicon, in the form of thin strips. The trick is to get the light falling on the glass to diffuse sideways to the edges, so that the silicon can turn it into electricity. Dr Reisfeld’s team do this by coating the glass with a combination of dyes and sprinkling it with nanoparticles of a metal whose nature they are not yet willing to disclose.
Depth of field
The dyes are there to absorb the incident sunlight (a mixture is used in order to capture all parts of the spectrum). The role of the metal, though, is more subtle. The dyes in question are fluorescent—having absorbed the light, they re-radiate it. Normally, that would mean it was lost. But interaction with the nanoparticles turns it into a form of electromagnetic radiation called surface plasmons. These, as their name suggests, propagate over the surface of the glass until they are intercepted by the silicon at its edges.
Not only does all this make GreenSun’s cells cheaper than conventional ones, because they use so much less silicon; it also makes them better. In a conventional solar cell much of the energy is lost. The energy of light varies across the spectrum (blue light is more energetic than red) but only a certain amount of energy is needed to knock an electron free. If the incident light is more energetic than necessary, the surplus disappears as heat. Unlike the sun, which scatters its energy across the board, the dye/nanoparticle mix delivers plasmons of the right energy to knock electrons free without waste.
cont: Solar energy in Israel It's a knockout (http://www.economist.com/sciencetechnology/displaystory.cfm?story_id=14082027)