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back to article Brit boffins trap light in Lego-like lumps

It's long been known that texturing the surface of solar cells can help them retain light and get more efficient. Now, a group of researchers led by Imperial College, London, has found that nano-scale aluminium “studs” on a cell's surface can improve its light-gathering by as much as 22 percent. The team, which includes …

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Pax

What about an application of a type of reflective metallic tinting which lets the light through, and traps it on the inside?

This would keep much of the light trapped and able to be converted to electricity on the panels.

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I'm surprised that it's opaque materials in use. I would have thought the best answer would be a couple of layers of transparent material with appropriate refractive indices to allow light in but reflect any light that attempts to escape back into the cell.

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Who says gold, silver and aluminium are opaque? Vacuum deposited layers of any of these metals and many more are transparent - it is only when you have a thick layer that it becomes opaque.

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@Pax

What about an application of a type of reflective metallic tinting which lets the light through, and traps it on the inside?

That is exactly what they are doing.

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Good for you, boffins

The Reg often runs energy breakthrough stories about solar cells or battery technology, and there are frequent 'yah boo sux' comments, but I find it hopeful.

Each technique alone mass as a few percent in the real world, but adding them all together could really be impressive. Well done boffins, keep at it.

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Re: Good for you, boffins

"Each technique alone mass as a few percent in the real world, but adding them all together could really be impressive. Well done boffins, keep at it."

Agreed. Each new technique added to previous improvements can yield vast improvements, as well as new avenues previously never considered.

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Making them from Lego?

Well at least they'll be easy to stack!

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Anonymous Coward

Re: Making them from Lego?

... And have the added advantage of being an effective deterrant against barefoot cat burglars on your roof.

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Aluminium lots cheaper than gold or silver

So in principal a good idea.

Unless of course you can only put this layer on inside a hugely expensive (and small) UHV chamber of course.

It's V 0.1 tech but applied to ultra cheap thin film cells (the kind that really do come on a roll) or the ultra high performance triple junction cells (>43% already) this sounds like a winner.

If they can only get the commercialization right.. :( .

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Anonymous Coward

Re: Aluminium lots cheaper than gold or silver

According to the paper they used metal-organic vapour phase epitaxy (also known as MOCVD) for the deposition which is a well understood commercial process already used in HBLED and Power Device manufacture.

Although the paper isn't particularly clear on how the metal structures were formed, the mention of electron beam lithography would imply that a metal layer was deposited then etched back. The feature sizes are well within the capabilities of current production metal etch systems.

Basically then, all of this can already be done using current production technologies (although e-beam lithography is sloooooow....) so I would argue that this is more V0.9, and if it is really as good as the paper makes out there is little in the way to stop rapid commercialisation of this.

So more reason to be optimistic with this one! :)

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This is why the UK Governments PV subsidy is stupid

If they had put 1/4 or less of the money towards improving PV efficacy, then we'd have better PV arrays that might actually make sense commercially (even if not in Britain), rather than just pissing our money over rich people's roofing.

(And maybe not need to guarantee double market rate to Hinckley C as they wouldn't have already guaranteed the same for wind and quadruple for PV)

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Anonymous Coward

Re: This is why the UK Governments PV subsidy is stupid

then we'd have better PV arrays that might actually make sense commercially (even if not in Britain)

If they really worked they'd lower the government's energy income, which will result in higher energy taxation to keep revenue up. That is in general a very much underplayed side effect of efficiency.

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Re: This is why the UK Governments PV subsidy is stupid

Nuclear power is indeed much more appropriate for countries such as the UK.

If there really had been a need to promote PV technology, perhaps the government should have promoted its use in developing countries nearer to the equator. Despite recent history there are still allegiances within the Commonwealth.

With the sun passing closer to directly overhead and with less overall cloud cover there can be up to four times more available sunlight than in the UK. Rather than the 30 p/kWhr or so that is guaranteed in the UK, with more sunlight the cost of locally generated electricity would be on a par with or better than other technologies. In many areas electricity distribution remains prohibitively expensive, and there are situations such as in agriculture where the daily intermittency would not present much of a problem and where electricity would be a real boon.

Instead of feed-in tariffs taxing the poor to help the rich it would have been possible to generate the same return on capital though increased productivity from truly appropriate technology. Rather than causing higher prices for ordinary folk this could have helped farmers increase production efficiency, improving their income and living standards, and, through trade of some of their increased food production to cover costs, reduced the UK's food bills.

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Re: This is why the UK Governments PV subsidy is stupid

It's quite possible to transmit electricity 1500 miles, with modern UHV DC technology. That's the distance from the UK to the Sahara desert.

It's also less bad than that 1500 mile figure suggests, because in practice you'd tend to displace Spanish electricity to France and French electricity to the UK.

The biggest problem is the (in)stability of North African states. Huge solar farms in the Sahara would be a massive capital investment, and we just don't have confidence that the natives wouldn't hold us to ransom or just scrag it. Morocco is probably the best bet, but also probably not good enough. Especially not South of the Atlas mountains.

However, I am surprised there aren't more Spanish olive farmers grubbing up their trees and planting solar panels. Not enough grid capacity? Hello EU, where are you when we need you?

Could we cede the Olive business to the Moroccans or is it too dry there?

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bep

Re: This is why the UK Governments PV subsidy is stupid

Perhaps it would be better to use land that isn't being used for growing food at the moment.

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Re: This is why the UK Governments PV subsidy is stupid

"If there really had been a need to promote PV technology, perhaps the government should have promoted its use in developing countries nearer to the equator."

Nations near the equator are far better served with thermal collectors, as those are far, far, far more efficient and the solar input is more than sufficient in a rather small footprint.

It's farther north that one ends up with PV, as one cannot as easily collect enough sunlight to generate enough heat for prime power generation.

That said, PV sucks at prime power generation at its current state of the art, compared to nearly every other form of electrical power generation. However, there are new technologies for PV that are promising.

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Wait, you tried Gold and Silver first?

What is it with scientists always trying out rare earths and precious metals before the simple stuff from thier can of fizzy pop...

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Re: Wait, you tried Gold and Silver first?

In fairness gold is shiny and silver is very white, good for reflectiveness...

Nah, it's about the bling factor, they want the iP5s

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Anonymous Coward

Re: Wait, you tried Gold and Silver first?

More likely because its a lot easier to deposit decent films of gold and silver than Al...

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This is basically the difference between normal florescent lights, and ones with all the reflective slats that burn our retinas daily.

Im really surprised this sort of idea wasnt implemented from the start, then again i bet they were just happy to finally receive decent electrical energy from sunlight to bother to refine the design much.

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says

My first thought on reading the article is "rather like the cones and rods in the eyeball, then".

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Collected energy is normally proportional with collecting surface, not converter surface; I find ideas such as the inflatable metallic "balloons" (with one transparent face) that form a focusing mirror on their inner surface - needing only a small converter, like a satellite dish - a lot more interesting than various schemes trying to improve the still bloody-expensive-and-inefficient-in-1-on-1-coverage traditional type collectors. It's not like either solution would be "cleaning-free" (assuming these rods even survive cleaning)...

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Headmaster

"...trap individual rays of light..."

WTF is an "individual ray of light" in this context? Did you mean "photon", perhaps?

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The only logical name for this effect...

... is the Chippendale Effect.

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Holmes

Some Background

These features are much smaller than the wavelength of light. Therefore they do not reflect it so much as scatter it. When they do their job correctly, they scatter the light forward into the solar cell beneath them. The Earth's atmosphere scatters light, some wavelengths more than others; that's why the sky looks blue. Nanoparticles from something like smoke can scatter more red light and make spectacular sunsets

A normal silicon solar cell will look shiny. If you look at something like this it will not be shiny. For years high performance infrared sensors/detectors have been coated with nanomaterials such as "gold black" that reflect so little they look black to the naked eye. In that case the coating can absorb the IR and it is detected as heat. In the case of solar cells, they do not want the layer to absorb, simply to reduce reflections.

Gold and silver were probably used initially because they are relatively inert to many chemical processes, making process development less restrictive and more flexible. Once proof of concept has been demonstrated, one can try to use a cheaper material.

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