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The future of solar is looking much brighter

Solar power is taking off around the world.  Europe is planning to deploy various types of solar power to the Sahara to provide for the European Union's energy needs.  Meanwhile, here in the U.S., California is expanding its solar efforts as well.

However, amid the progressing adoption of solar technology, one perpetual criticism that persists is that solar power is inefficient and expensive.  To some extents this is true.  The current generation of photovoltaic solar panels -- the type of solar power perhaps most associated with the field -- is only around 20 percent efficient and thus costs remain relatively high, like many forms of alternative energy.

A new breakthrough from U.S. Department of Energy's National Renewable Energy Laboratory (NREL) is looking to solve those problems.  It pushes solar cells to uncharted technology with a record 40.8 percent efficiency.  The new work shatters all previous records for photovoltaic device efficiencies.

The researchers first used a special type of cell, an inverted metamorphic triple-junction solar cell.  The custom cell was designed, fabricated, and independently measured at NREL.  The next step was to expose the solar cell to concentrated light of 326 suns, yielding the record-breaking efficiency.  A sun is a common measure in the solar power industry which represents the amount of light that hits the Earth on average.

The new cell targets a variety of markets.  One potential market is the satellite solar panel business.  Satellites natural absorb more intense sunlight, thanks to no atmospheric interference.  Another possible application is deployment in commercial concentrated PV cells.  Concentrated PV is a burgeoning field, with several companies currently contracted worldwide to build the first utility grade plants.

The new record was welcome news, but little surprise at NREL -- they held the previous record as well.  In order to beat their old design, one key was to replace the germanium wafer at the bottom junction with a composite of gallium indium phosphide and gallium indium arsenide.  The mixture splits the spectrum into three parts, each of which gets absorbed by one of the junctions.  Both the middle and bottom junction become metamorphic in the new design.  This means their crystal lattices are misaligned, trapping light in the junction and absorbing more of it.  This yields an optimal efficiency.

One key advantage is the new solar cell can be conveniently processed by growth on a gallium arsenide wafer.  It is also both thin and light.  The NREL believes this cell will be cheaper than current commercial models, while delivering far more power.

Some of the credit for the work goes to NREL's Mark Wanlass, who invented the cell's predecessor.  The new cell was redesigned by a team led by John Geisz.

The NREL is operated by the DOE by Midwest Research Institute and Battelle.



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One thing I don't get...
By Oralen on 8/18/2008 7:36:02 AM , Rating: 3
That efficiency record was, as far as I understand, obtained by submitting the solar cell to light equivalent to 326 suns, right...

Does that record still hold when the light is just 1 sun ? Like... Mmm, simply putting it outdoor ?

Because if it doesn't... That thing will only be usefull in a lab.




RE: One thing I don't get...
By trajan on 8/18/2008 7:45:52 AM , Rating: 5
It does sound like they needed the 300+ suns of light to get it up to 40% efficiency but its still a nice feat. Aside from the usefulness in space, as pointed out, maybe these would be useful in combination with reflecting mirrors. Not necessarily one of those giant arrays they build out in deserts, but picture a satellite-dish sized reflector with a very small cell at the focal point. A 1 cm^2 cell would only need ~350 cm^2 worth reflector to hit the right efficiency. And instead of building a huge solar cell you can build a tiny one - cost savings.

Just brainstorming, I have no idea if the cell that built would actually be able to work that way, but just because you need all the extra light doesn't mean this isn't still good news. (If they got 40% efficiency using normal sunlight, with an easy to manufacture design, that would have been on the front page of most major newspapers, I'd wager).


RE: One thing I don't get...
By 67STANG on 8/18/2008 11:12:57 AM , Rating: 3
That's exactly the problem, these aren't easy to manufacture- nor are any multi-junction solar cell. (That's why they cost so much). These are typically only used in government or space appliactions as it's cheaper to run twice as many panels than it is to run twice as efficient panels.

Not really sure this is too terribly exciting news, the work that the Idaho National Laboratory did that could possibly yield 80% efficiency through a combination of light and heat absorption is much more promising...


RE: One thing I don't get...
By freaqie on 8/18/2008 2:43:24 PM , Rating: 2
A 1 cm^2 cell would only need ~350 cm^2 worth reflector to hit the right efficiency. And instead of building a huge solar cell you can build a tiny one - cost savings.

why not put a boiler down there instead and a turbine hooked up to a generator
and get 75+ percent efficiency
or a stirling engine... 80% efficient...

it is a nice idea but others are just better


RE: One thing I don't get...
By PKmjolnir on 8/18/2008 7:47:48 AM , Rating: 2
It will be useful outside the lab too, you just need to redirect 326m² of sunlights with mirrors per one m² of PV, the mirrors are cheaper than PV either way, with a slight cost increase induced by PV cooling systems.

The concept is not that new.

http://en.wikipedia.org/wiki/Concentrated_Photovol...


RE: One thing I don't get...
By legoman666 on 8/18/2008 11:43:37 AM , Rating: 2
Indeed. A hemisphere of diameter 14.5cm would be enough to concentrate 330cm^2 of light (assuming the entire hemisphere receives light, which it won't.) onto a 1cm^2 panel. That's hardly huge.

Instead of a big satellite dish in the backyard, maybe we'll have a few solar dishes in the future...


RE: One thing I don't get...
By Solandri on 8/18/2008 6:58:51 PM , Rating: 2
Until the sun moves and the light is now missing your 1 cm^2 solar panel. The problem with reflectors as concentrators is that they need to track the movement of the sun, with all the problems that come with collimation, mechanical gearing, maintenance, and alignment to cancel out the earth's rotation and revolution.

That's why the article a couple weeks back on windows as solar collectors with the PV in the edges was so promising. Those didn't need to track the sun. You could just mount them and forget about them.


RE: One thing I don't get...
By MarkHark on 8/18/2008 7:24:25 PM , Rating: 2
I believe in this case parabolic would be a more efficient design than hemispheric.
But you got the general idea right.


RE: One thing I don't get...
By djc208 on 8/18/2008 7:50:25 AM , Rating: 2
Well the article discusses using reflectors to concentrate sunlight at these vice just put them in the sun. Of course that would increase the cost and area required vs a conventional solar pannel.


RE: One thing I don't get...
By PKmjolnir on 8/18/2008 8:10:20 AM , Rating: 2
You think 100m² of top grade super efficient photovoltaics really would come cheaper than 0,3m² of said PVs and 100m² of light gathering optics?


RE: One thing I don't get...
By masher2 (blog) on 8/18/2008 9:47:12 AM , Rating: 2
Normally it is more expensive, yes. A solar cell receiving 300+ suns of heat needs active cooling just to survive, and even still it's lifetime is shortened. It also needs a tracking mechanism as the optics tend to have a low angle of acceptance.

Furthermore, these ultra-efficient concentrating cells are made from multi-junction PVs, which are substantially more costly than your more typical cells.


RE: One thing I don't get...
By blaster5k on 8/18/2008 9:55:19 AM , Rating: 2
This is the comment I was waiting for -- the other side of the story. You know what they say about things that sound too good to be true.


RE: One thing I don't get...
By JasonMick (blog) on 8/18/2008 11:30:57 AM , Rating: 2
Not necessarily -- an Aussie company Sungri claims that it uses a nanotech material cooling mechanism to allow its cells to endure 3,000 F temperatures. They say their system will provide solar power at a cost of 5 cents per kilowatt hour within a year.

Source:
http://cleantechnica.com/2008/05/10/solar-power-go...

They may not achieve their ambitious goals, but they're either onto something or making a lot of big claims.

Also pared down models with lower concentrating factors, while sporting lower efficiencies should be able to survive their operational temperatures without elaborate cooling and offer more modest decreases in solar costs over traditional PV.

You're absolutely right that there's obstacles, but there's also a lot of progress in the field of concentrated PV, you must admit.


RE: One thing I don't get...
By kattanna on 8/18/2008 11:45:54 AM , Rating: 5
quote:
cells to endure 3,000 F temperatures.


if they are getting those temps, wouldnt it be more effective to be converting that heat into making steam to drive a turbine instead of trying to cool a small PV cell capturing the light?


RE: One thing I don't get...
By 306maxi on 8/18/2008 11:53:31 AM , Rating: 2
I was thinking that myself.


RE: One thing I don't get...
By masher2 (blog) on 8/18/2008 12:22:16 PM , Rating: 2
> "an Aussie company Sungri claims that it uses a nanotech material cooling mechanism..."

A) This is just a claim so far.
B) Cooling is still required; it's just (supposedly) done by a somewhat cheaper method.
C) Active tracking is still required.
D) Multi-junction cells are still required.
E) Concentrating PV doesn't work in cloudy conditions, whereas normal PVs produce at least a fraction of peak power.

So far, concentrated PV being feasible for commercial power generation is still just a pipe dream. It'll take much, much more than a 0.1% increase in efficiency to realize such a solution.


RE: One thing I don't get...
By haris on 8/18/2008 9:24:51 AM , Rating: 2
It's really hard to get sarcasm/bad jokes sometimes, so ignore this if you can read:
A sun is a common measure in the solar power industry which represents the amount of light that hits the Earth on average.


RE: One thing I don't get...
By Fracture on 8/19/2008 4:12:47 PM , Rating: 2
quote:
That efficiency record was, as far as I understand, obtained by submitting the solar cell to light equivalent to 326 suns, right... Does that record still hold when the light is just 1 sun ? Like... Mmm, simply putting it outdoor ? Because if it doesn't... That thing will only be usefull in a lab.


Most large scale solar power farms refract light off a number of mirrors instead of individual solar collectors. The light is redirected from each of these mirrors to a central point where all the solar energy is focused onto a container containing a salt solution. This energy is so great it turns it into molten salt, whose thermal energy can then be harnessed in a number of ways.

If you really want to break it down, 326 suns is just like having 325 mirrors (plus normal exposure) focus their light onto one point, a practice that is already in use today.


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