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The new solar cells from the University of California, Berkley use nanopillars to create cheap and efficient cells. An optimized cost could cut solar power costs to a third of current levels.  (Source: Ali Javey, UC Berkeley)
New technology may unlock some massive savings

One of the biggest factors in solar power remaining an expensive power source, despite constantly improving efficiencies, is the inherent cost of materials and processing for solar cells made of polysilicon.  Cutting these costs could make the solar power the preferred energy source for mankind, but thus-far there has been little high-performance designs made with cheaper processes or materials.

Now University of California, Berkeley researchers have created a new type of solar cells that may offer exactly that -- lots of solar energy with low processing and materials costs.  The new type of solar cells are composed of tiny nanopillars in a thin film layer atop aluminum foil.  The foil is enclosed in a protective layer of transparent, rubbery polymer.

The total materials costs are quite low, and the production costs, while not fully determined also look promising.  Ali Jarvey, an electrical-engineering and computer-sciences professor who led the work, cheers, "You won't know the cost until you do this using a roll-to-roll process, but if you can do it, the cost could be 10 times less than what's used to make [crystalline] silicon panels."

The cells use a nanofilm of cadmium telluride with uniform 500-nanometer-high pillars of cadmium sulfide laid on top of it.  Other thin-film solar cells with pillars have been made before, says Professor Jarvey, but they have relied on more expensive deposition techniques.  Further, the new cells have an efficiency of 6 percent in transforming sunlight into electricity, where past designs had efficiencies of less than 2 percent.

Silicon-based photovoltaics still have the cell beat in efficiency with 20 percent or more in commercially available designs; however, they are extremely pure, expensive crystalline silicon.  Impurities can cause electrons to get trapped in the semiconductor, so the expensive process of making this high quality crystal material is unavoidable for that design.  Purity is much less of a cost concern in the new design.

Creating an equivalent amount of power would require three times the area (panels) of photovoltaic cells, given their respective efficiencies.  This means that given the cost estimates, solar power costs could be cut to a third of the current levels.

Another key advantage of the new design over traditional photovoltaic panels is flexibility.  Traditional crystalline panels would break if flexed.  The thin film nanopillar cells, though, can be rolled and unrolled with ease.

The new design essentially divides silicon's responsibilities.  The thin film material absorbs light and generates electrons, while the pillars conduct the electrons to the circuit and help to trap light.  As electrons have a shorter distance to travel to reach the pillars they're less likely to get trapped by defects, and thus crystal quality is less of a concern.

Currently the cells are produced using a relatively cost-effective anodizing design to grow the pillars on a thin aluminum foil film, the bottom electrode.  The thin semiconductor film is then layered over the pillars and a top electrode of copper and gold is layered thinly to complete the circuit. 

Two key areas of improvement are the top film and the production process.  Adopting a roll-to-roll production system could speed up the assembly and make it cheaper.  Also, currently the gold only allows half the sunlight to enter the cell as its semi-opaque.  Replacing the gold with a transparent material like indium oxide could double the efficiency to 12 percent or more, while not significantly impacting the cost of materials.

States Professor Yang, "(The) architecture is most important--materials we can continue working on. The beauty of this paper is the demonstration of how well the architecture works."

The research appears in this month's edition of the journal Nature Materials.



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By on1wl on 7/7/2009 10:30:28 AM , Rating: 2
Most home solar systems in the forseeable future will not have batteries, rather, they will be grid tied. Size is irrelevant because the question is not how much you need, but how much you pay. When solar is cheaper than the grid price, we will install as much as we can and either sell the excess, or buy the shortage from the grid.




By SublimeSimplicity on 7/7/2009 10:50:18 AM , Rating: 4
I think your subject line is dead on. Look at the most extreme case of inefficient solar power... ethanol. At its roots (no pun intended, too corny for me... OK that one I meant) its solar power via photosynthesis in the plant. Photosynthesis is pretty inefficient, then add to that the processing is sometimes even more inefficient. Yet every time gas gets to around $4/gallon its considered.

Bottom line is that efficiency means almost nothing, when your materials (sunlight in this case) are free.


By WackyDan on 7/7/2009 10:51:06 AM , Rating: 2
The problem with most Residential solar or wind installs is the perception that YOU get paid by the local power company for the surplus you produce.

Fact is, in most states the utility does not pay you if you produce surplus. All that happens is that your surplus is banked on a monthly or yearly basis against times when you are not producing any surplus... ie; winter, periods of bad weather/overcast skies/no wind....

On top of that, you are still obliged to pay a monthly bill to your utility company that typically includes many of the same fees you pay today connected only to the grid. A connection/maintenance fee, State, Local, and federal taxes all for the luxury of having the power drop or burial connected to your dwelling.

Again, this varies by state, so do your research before you start calculating savings over time.


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