Solar-grade silicon at low cost

Apr 19, 2012
Edge of silicon ingot. Credit: BT Usdin on flickr

(Phys.org) -- A new process developed by scientists at the University of Cambridge has the potential to drive down the cost of manufacturing solar-grade silicon and could increase the use of photovoltaic devices for capturing the sun’s energy.

In less than the time it takes to read this paragraph, the will have provided as much energy to Earth as used by all of human civilization in one day. Yet, despite the huge opportunities solar power affords as a renewable source of energy, it still represents a small fraction of our current capacity to generate power.

One factor holding back the growth of the photovoltaic (PV) industry, which provides the modules that make up a solar panel, is the high cost of the solar-grade on which it currently depends. Now, scientists from the University of Cambridge are developing and up-scaling a new for making solar-grade silicon that they estimate will be 80% more efficient in terms of energy consumption and cost and generate 90% less CO2.

Based on a procedure known as the FFC Cambridge process developed by Professor Derek Fray and colleagues in Cambridge’s Department of Materials Science and Metallurgy, the new modification pioneered by Dr Antony Cox has extended FFC to silicon for the first time and is now in its final research and development stages.

Silicon is the most commonly used material in PV cells. Numerous attempts have tried to find a new process for producing solar-grade silicon but, as Cox explained: “All are energy intensive, with a myriad of complex stages, and none have become a commercial process.”

Moreover, the manufacturing methods commonly used to make crude silicon produce some 10 tons of CO2 for every ton of silicon produced, and the refinement stage (the Siemens process) produces a further 45 tons of CO2 as well as toxic gases.

“It’s somewhat ironic that such an environmentally destructive process supplies 95% of the silicon required by the PV industry to harness a clean and sustainable energy source,” said Cox. “In fact, a solar cell fabricated with the Siemens process would need to be operating for up to six years to match the same energy required to make it.”

For PV cells to work there must be no impurities in the silicon that could hamper the movement of electron charge carriers within the material. When photons of sunlight strike the PV cell, their energy is absorbed by the semiconducting silicon, exciting electrons into a higher energy state and creating an electric current.

The two-stage process Cox has been developing uses white sand and calcium chloride (a product used commonly in the food industry) as raw materials. First, tablets of compressed sand are immersed into the calcium chloride electrolyte and heated to 900°C. The silicon in sand is present as an oxide and, during the FFC process, the oxygen atoms are ionised, migrate to the anode and are discharged as oxygen, which is the only by-product of the reaction. Sand is not easy to reduce to silicon and Cox has spent the past four years solving this fundamental challenge and up-scaling the first stage of the process.

In the second stage, an electrorefining process within the same cell takes silicon from 99.99% purity to the Holy Grail of 99.9999% purity. “Preliminary investigations were very encouraging and we are now developing the second stage,” said Cox, whose research was funded by the Engineering and Physical Sciences Research Council.

“Crucially, this process requires minimal consumption, generates O2 rather than CO2 as a by-product, and is easily up-scalable because it involves fewer production stages,” he added. “Many attempted scale-ups for other processes have been thwarted due to the sheer difference in scale between a pilot plant and a commercial plant where unforeseen problems are often revealed. In this process we plan to use many independent smaller cells allowing more control, rather than one huge plant. This should facilitate the transition to a commercial ‘process’.” Based on the results of an independent economic survey, he believes that the process will drive down the cost of manufacturing solar-grade silicon from around the current $40–200/kg to a maximum of $8/kg, making solar power a more affordable option to generate power.

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User comments : 9

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dschlink
4.5 / 5 (2) Apr 19, 2012
Interesting, I wish them luck. What is really needed is innovation in the installation process.

FFC FrayFarthingChen
CapitalismPrevails
1.6 / 5 (5) Apr 19, 2012
Interesting, I wish them luck. What is really needed is innovation in the installation process.

FFC FrayFarthingChen


Yeah, i think the best way to cut the cost of solar panels is to have them installed up during the construction of a building. Good article.
Vendicar_Decarian
0.4 / 5 (41) Apr 19, 2012
You have to wonder about the stupidity of urban planners that do not now require home construction to include the orientation of homes so that the largest roof area is available for solar collection.

Absolutely stupid.
SteveL
not rated yet Apr 19, 2012
Lending institutions also need to consistantly encourage, or at least allow, energy producing technolgies and require energy saving technologies in home and business building loans. Presently not that many do. It can be something as unobtrusive as requiring greater insulation R-values, window glazing and insulated hot water piping.

I see no reason a properly designed and installed solar thermal water heating system or other proven technology shouldn't be able to be included in a building loan. There are still banks out there that won't cover such "additions".
ForFreeMinds
2.8 / 5 (13) Apr 19, 2012
"You have to wonder about the stupidity of urban planners that do not now require home construction to include the orientation of homes so that the largest roof area is available for solar collection."

What is stupid, is allowing government the power to decide how your home is built. First, solar doesn't save money, it costs money. So why orient a house so an uneconomical product could be installed more effectively? Second, there are other reasons to orient a home a specific way, and why ignore these?

People should be free to adopt technologies that help humanity, not forced by government at our expense. If you want to bankrupt the US, then force everyone to obtain electricity via solar power.
ormondotvos
2.6 / 5 (5) Apr 19, 2012
What's REALLY stupid is to allow selfish individuals to disregard the effects their behavior has on society, under the rubric of "freedom."

Real freedom would be for them to be put in a basket at birth to fend for themselves, as their lunatic philosophy demands.

They conveniently ignore all the ways society keeps them alive, shedding those debts as inconvenient restraints on their whims.
CapitalismPrevails
2.7 / 5 (7) Apr 19, 2012
"What's REALLY stupid is to allow selfish individuals to disregard the effects their behavior has on society, under the rubric of "freedom."

What's REEEAAAALLLLLY stupid.....is people like you completley negate history. The U.S. was build on on self-interest AKA "selfishness" and not charity. Evidently, self interest inadvertently leads to prosperity. Utopian statists like you delusionally believe you can micromanage individuals / destroy individual initiative and create prosperity. Never worked before and it never will.

They conveniently ignore all the ways society keeps them alive, shedding those debts as inconvenient restraints on their whims.

And by "society" you mean the private sector? The government can't survive without the private sector because tax revenue come from the private sector and not the public sector.
wwqq
not rated yet Apr 20, 2012
You have to wonder about the stupidity of urban planners[...]


I have great difficulty fathoming the kind of stupidity that leads people to believe that diffuse and unreliable solar is now, or ever going to be, a solution to global warming or sustainability, much less energy poverty or fossil fuel dependency.

The amount of materials involved are enormous. You dig this stuff out of the ground and it's inherently dirty and polluting work.

Firming up solar power leads to fossil fuel lock-in; particularly natural gas, the scarcest fossil fuel. Sure you could combine it with "biomass" energy, but that's a massive waste of net primary production and burning stuff is polluting.

If you try to overbuild, build massive amounts of batteries and massive amounts of long distance transmission, you again need to go rummaging beneath the earth to find enormous quantities of materials(e.g. all the lead EVER MINED isn't enough to make a lead battery for the US grid).
Nicodemas
2.5 / 5 (2) Apr 20, 2012
@wwqq,
I'm not sure what the meaning your comments were.

@CapitalismPrevails,
WWII drives to restrict sale of and collect aluminum, pig iron, etc... is one example I can cite against your argument that selfishness built America - where the gov't stepped in to control the flow of goods. You should refrain from making blanket statements like that.

@ForFreeMinds,
"Uneconomical" can only be applied to a particular time period since prices dictate whether something is "economical" or not. If prices change for labor or energy services, it could alter the attractiveness of solar.

@Vendicar_Decarian,
I see your point, but that is over the top, in my opinion. Plus, there are some places that could not get peak use of solar anyway, given gradation, climate, or other surroundings.

@dchlink,
I agree, but again that's a mechanic dictated by prices.

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